Method and device for thermally stable operation of AOD

Abstract

The system comprises a first acousto-optic deflector (AOD) for diffracting an incident laser energy beam to generate and output a first laser energy beam and a second laser light beam therefrom; a second AOD positioned to receive the first laser energy beam and diffracting the received first laser energy beam to generate and output a third laser energy beam and a fourth laser energy beam therefrom; at least one first beam trap positioned and configured to absorb the second laser energy beam output from the first AOD; at least one second beam trap positioned and configured to absorb the fourth laser energy beam output from the second AOD; and a controller communicably connected to the first AOD and the second AOD, wherein the controller is configured to operate the first AOD without operating the second AOD.

Description

Technology Field

[0001] Embodiments of the present invention generally relate to an acousto-optic deflector, a laser processing device including the same, and a technique for operating the same. Background Technology

[0002] Referring to FIG. 1, a laser processing device (100) operated to process a workpiece (102) often includes, among other components, a laser source (104), a positioner (106), and a scan lens (108). The device will also typically include a controller (110) operated to control the operation of the laser source (104) and the positioner (106). The positioner (106) operates to reflect, refract, and / or diffract the laser energy beam to deflect the beam path (112) along which the laser energy of the laser energy beam travels as the laser energy beam propagates from the laser source (104) to the scan lens (108). The laser energy deflected to the scan lens (108) is focused and transmitted by the scan lens (108) and propagates along the beam axis to be delivered to the workpiece (102).

[0003] To rapidly deflect a beam path (112) in two dimensions with respect to a workpiece (102) (e.g., along the X-axis and Y-axis orthogonal to the illustrated X-axis and Z-axis), the positioner (106) may include a galvanometer mirror scanning system and an acousto-optic deflector (AOD) scanning system optically positioned "upstream" of the galvanometer mirror scanning system. The galvanometer mirror scanning system typically includes a pair of galvanometer mirrors optically positioned in series with each other (e.g., so that one galvanometer mirror operates to deflect the beam path (112) along the X-axis and the other galvanometer mirror operates to deflect the beam path (112) along the Y-axis). The AOD scanning system typically includes a pair of acousto-optic deflectors (AOD) optically positioned in series with each other. For example, and with reference to FIG. 2, the AOD scanning system may include a first AOD (200) positioned and configured to deflect a beam path (112) along the X-axis and a second AOD (202) positioned and configured to deflect a beam path (112) along the Y-axis.

[0004] As recognized by those skilled in the art, an AOD diffracts an incident optical wave (i.e., a laser energy beam in relation to the present application) simultaneously propagating through an AO cell by utilizing the diffraction effect caused by one or more acoustic waves propagating through the AO cell. When the AOD is driven to diffract an incident beam of laser energy, a diffraction pattern is generated that typically includes zero-order and first-order diffraction peaks and may also include other higher-order diffraction peaks (e.g., second, third, etc.). Generally, the amount of optical power diffracted to the first-order diffraction peak (e.g., compared to the zero-order diffraction peak) is determined by the manner in which the AOD is driven to diffract an incident beam of laser energy. As is known in the art, a portion of the laser energy diffracted beam at the zero-order diffraction peak is referred to as the "zero-order" beam, and a portion of the laser energy diffracted beam at the first-order diffraction peak is referred to as the "first-order" beam. Generally, the zero-order beam and other diffraction order beams (e.g., the first-order beam, etc.) propagate along different beam paths when exiting the AO cell (e.g., through the optical output side of the AO cell). For example, the zero-order beam propagates along the zero-order beam path, and the first-order beam propagates along the first-order beam path.

[0005] In FIG. 2, the zero-order beam path of the first AOD (200) is shown as 204, and the zero-order beam path of the second AOD (202) is shown as 206. Likewise, the first-order beam paths of the first AOD (200) and the second AOD (202) are each shown as 112. Additionally, the positioner (106) shown in FIG. 2 also includes one or more optical elements (e.g., one or more mirrors, lenses, etc., collectively shown as 208) arranged and configured to relay the zero-order beam path (204) and the first-order beam path (112) of the first AOD (200) to the second AOD (202). The positioner (106) shown in FIG. 2 includes a beam trap (210) positioned and configured to block (e.g., block or absorb) laser energy propagating along the zero-order beam path (206) without blocking laser energy propagating along the first-order beam path (112).

[0006] The AO cell of the AOD will absorb a portion of the laser energy beam propagating through it. If the power of the laser energy beam is sufficiently high, the absorbed energy may locally heat the material forming the AO cell and cause a thermal lensing phenomenon within the AO cell. Thermal lensing can focus, defocus, or distort the wavefront of the laser energy beam propagating along the beam path (112). Thermal lensing within the AO cell is not necessarily undesirable in itself. If the thermal gradient within the AO cell is relatively constant and fixed (e.g., while processing the workpiece (102)), wavefront distortion effects (e.g., focusing effects, defocusing effects, or other wavefront distortions as mentioned above) can generally be considered to ensure that the workpiece (102) is processed satisfactorily. However, if the thermal gradient within the AO cell is not relatively constant or fixed, it becomes very difficult to adequately compensate for changes in wavefront distortion effects.

[0007] In relation to the positioner (106) shown in FIG. 2, the optical element(s) (208) ensure that the optical power incident on the AO cell of the second AOD (202) is substantially constant, but the position where the zero-order beam path (204) is incident on the AO cell of the second AOD (202) may change slightly over time. Consequently, the thermal gradient within the AO cell of the second AOD (202) is found not to be appropriately constant or fixed, and as a result, an asymmetric energy distribution of the laser energy ultimately delivered to the workpiece (102) (with respect to the optical axis of the laser energy beam) occurs, and the ability of the second AOD (202) to accurately deflect the beam path (112) is also reduced.

[0008] One embodiment of the present invention may be characterized as a system comprising: a first acousto-optic deflector (AOD) for diffracting an incident laser energy beam to generate and output a first laser energy beam and a second laser light beam therefrom; a second AOD arranged to receive the first laser energy beam and diffracting the received first laser energy beam to generate and output a third laser energy beam and a fourth laser energy beam therefrom; at least one first beam trap arranged and configured to absorb the second laser energy beam output from the first AOD; at least one second beam trap arranged and configured to absorb the fourth laser energy beam output from the second AOD; and a controller communicably connected to the first AOD and the second AOD, wherein the controller is configured to operate the first AOD without operating the second AOD.

[0009] Another embodiment of the present invention may be characterized as a system comprising: a first AOD that operates to diffract an incident laser light beam to generate and output a first laser light beam and a second laser light beam therefrom; a second AOD that is positioned to receive the first laser light beam and operates to diffract the received first laser light beam to generate and output a third laser light beam therefrom; at least one first beam trap that is positioned and configured to absorb the second laser light beam output from the first AOD; at least one training beam trap that is positioned and configured to absorb the third laser light beam output from the second AOD; and a controller that is communicably connected to the first AOD and the second AOD. The controller is configured to command a first RF driver to apply a first driving signal to a transducer of the first AOD and to command a second RF driver to apply a second driving signal to a transducer of the second AOD. The controller operates the first AOD to diffract an incident laser light beam along a training beam path to the second AOD. The second AOD is configured to diffract a laser light beam from the first AOD along the training beam path to a training beam trap. The driving signal is modulated through a certain range of RF frequencies to control the temperature gradient within the first AOD and the second AOD. Brief explanation of the drawing

[0010] FIG. 1 schematically illustrates a laser processing apparatus of the relevant technology in which a positioning device according to an embodiment of the present invention may be included and operated according to an embodiment of the present invention. FIG. 2 schematically illustrates a positioner according to the relevant technology. FIG. 3 schematically illustrates a positioner according to one embodiment of the present invention. FIG. 4 illustrates a timing diagram for executing pulse slicing operation according to one embodiment of the present invention. FIG. 5 illustrates a timing diagram for executing an optical training operation according to one embodiment of the present invention. FIGS. 6 and 7 illustrate timing diagrams for executing pulse slicing and optical training operations according to embodiments of the present invention. FIG. 8 illustrates a laser energy monitoring system according to some embodiments of the present invention. FIGS. 9 and 10 illustrate aspects of a pulse shape analysis process using the laser energy monitoring system shown in FIG. 8 among other components, according to one embodiment of the present invention. Figure 11 illustrates a timing diagram for performing pulse slicing for non-uniform incident power for an AOD scanning system. FIG. 12 illustrates a timing diagram for executing RF training operation according to an embodiment of the present invention. FIG. 13 schematically illustrates a positioner according to another embodiment of the present invention. FIG. 14 illustrates a timing diagram for executing pulse slicing and RF training operations according to an embodiment of the present invention. Specific details for implementing the invention

[0011] Exemplary embodiments are described herein with reference to the drawings attached thereto. Unless otherwise explicitly stated, the sizes, positions, etc., and distances between components, features, elements, etc., in the drawings are not necessarily in a constant proportion and are exaggerated for clarity.

[0012] The terms used in this specification are merely for describing specific exemplary embodiments and are not intended to be limiting. As used in this specification, singular expressions are intended to include plural expressions unless the context clearly indicates otherwise. It should be recognized that when used in this specification, the terms “comprising” and / or “comprising” specify the presence of the mentioned feature, integer, step, operation, element and / or component, but do not exclude the presence or addition of one or more other feature, integer, step, operation, element, component and / or group thereof. Unless otherwise specified, the range of values ​​mentioned includes the upper and lower limits of the range, as well as partial ranges in between. Unless otherwise indicated, terms such as “first,” “second,” etc., are used only to distinguish one element from another. For example, one node may be named “first node,” and similarly, another node may be named “second node,” and vice versa. Section titles used in this specification are for organizational purposes only and should not be interpreted as limiting the subject matter described.

[0013] Unless otherwise indicated, terms such as “approximately,” “nearby,” and “substantially” mean that quantities, sizes, formulations, parameters, other quantities, and characteristics are not precise and do not need to be precise, but may be approximate and / or larger or smaller as desired, taking into account tolerances, conversion factors, rounding, measurement errors, and other factors known to those skilled in the art.

[0014] Spatially relative terms such as “bottom,” “below,” “lower side,” “top,” and “upper side” may be used herein for ease of description to explain the relationship between one element or feature and another element or feature as illustrated in the drawings. It should be recognized that spatially relative terms are intended to include orientations other than those shown in the drawings. For example, if an object in the drawings is flipped, an element described as being “bottom” or “below” another element or feature will be oriented “upper” of that other element or feature. Accordingly, the exemplary term “bottom” may include both upward and downward orientations. Objects may be oriented differently (e.g., rotated 90 degrees or oriented differently), and spatially relative descriptors used herein may be interpreted accordingly.

[0015] Similar numbers refer to similar elements throughout. Therefore, identical or similar numbers may be described by referring to other drawings, even if they are not mentioned or described in the corresponding drawings. Additionally, elements not indicated by reference numbers may also be described by referring to other drawings.

[0016] It will be understood that many other forms and embodiments are possible without departing from the spirit and teachings of the present disclosure, and therefore the present disclosure should not be interpreted as being limited to the exemplary embodiments described herein. Rather, these examples and embodiments are provided to ensure that the present disclosure is thorough and complete and conveys the scope of the present disclosure to those skilled in the art.

[0017] I. General Discussion on Positioners

[0018] According to an embodiment of the present invention, the AOD scanning system of the positioner (106) described above in relation to FIG. 1 may be provided as exemplarily shown in FIG. 3 (i.e., as an AOD scanning system (300)). Referring to FIG. 3, the AOD scanning system (300) includes a first AOD (302) positioned and configured to deflect a beam path (112) along a first axis and a second AOD (304) positioned and configured to deflect a beam path (112) along a second axis (e.g., perpendicular to the first axis). In FIG. 3, the zero-order beam path of the first AOD (302) is shown as 306, and the zero-order beam path of the second AOD (304) is shown as 308. Likewise, the primary beam path of the first AOD (302) is denoted as 112' and the second AOD (304) is denoted as 112". As is understood, the primary beam path (112') and the primary beam path (112'') each represent specific examples of beam paths through which a laser energy beam can propagate (e.g., to a scan lens (108)), and thus the beam path (112') and the beam path (112") each may also be collectively referred to as "beam path (112)" in this specification, so that the first AOD (302) is positioned and configured to deflect the primary beam path (112') along the first axis of the AOD scanning system (300), and the second AOD (303) is positioned and configured to deflect the primary beam path (112") along the second axis of the AOD scanning system (300).

[0019] Additionally, the AOD scanning system (300) shown in FIG. 3 includes a first beam trap (310) arranged and configured to block laser energy propagating along a zero-order beam path (306) (also laser energy propagating along a second-order or higher beam path) without blocking laser energy propagating along a first-order beam path (112'). Likewise, the AOD scanning system (300) includes a second beam trap (312) positioned and configured to block laser energy propagating along the zero-order beam path (308) (also laser energy propagating along the second-order or higher beam paths) without blocking laser energy propagating along the first-order beam path (112). Although not illustrated, the AOD scanning system (300) may further include a galvanometer mirror scanning system positioned optically downstream of the second AOD (304) in the beam path (112) (e.g., composed of a pair of galvanometer mirrors positioned and configured to deflect a laser energy beam along two axes as is known in the art).

[0020] Generally, the AO cells of the first AOD (302) and the second AOD (304) are formed of a material sensitive to thermal lenting (e.g., as described above) when there is a laser energy beam having sufficiently high optical power propagating along the beam path (112). For example, the AO cells of the first AOD (302) and the second AOD (304) may be formed of crystalline germanium. In this example, the laser energy beam propagating along the beam path (112) will have a wavelength in the range of 2 μm (or near there) to 20 μm (or near there) and will have an average power sufficiently high (e.g., 150 W or more or near there) to induce thermal lenting within the AO cells of the first AOD (302) and the second AOD (304). In this case, the laser energy beam may be generated by a laser source (e.g., laser source (104)) provided, for example, as a suitable high-power carbon dioxide or carbon monoxide gas laser. Typically, the high-power carbon dioxide or carbon monoxide gas laser is configured to generate a continuous wave (CW) or quasi-CW (QCW) beam of laser energy or to generate a laser energy beam consisting of individual pulses (typically having a duration of tens of microseconds or more).

[0021] Although not illustrated, the first AOD (302) and the second AOD (304) each include at least one transducer attached to its AO cell. Generally, this transducer is a piezoelectric transducer that operates to vibrate in response to an externally applied RF signal (i.e., a driving signal). The transducer is attached to the AO cell of the AOD so that the vibrating transducer generates a corresponding acoustic wave that propagates within the AO cell. As understood by those skilled in the art, the amplitude, frequency, and duration of the acoustic wave correspond to the amplitude, frequency, and duration of the RF power of the applied driving signal.

[0022] A driving signal may be applied to the input of a converter by an associated RF driver. Accordingly, the AOD scanning system (300) may include, for example, a first RF driver (314) electrically connected to each converter of the first AOD (302) and a second RF driver (316) electrically connected to each converter of the second AOD (304). Generally, each of the RF driver (314) and the second RF driver (316) may include an RF synthesizer, an amplifier coupled to the output of the RF synthesizer, and an impedance matching circuit coupled to the output of the amplifier. The RF synthesizer (e.g., a DDS synthesizer) generates and outputs a preliminary signal of a desired frequency, the amplifier amplifies the preliminary signal to a desired amplitude to convert the preliminary signal into a driving signal, and the driving signal is applied to the input of the converter through the impedance matching circuit.

[0023] The operation of the first RF driver (314) and the second RF driver (316) can be controlled in response to a command signal output by a controller (e.g., controller (318)) to generate a driving signal of different frequency and amplitude, and the driving signal can be rapidly applied to each converter of each AOD (e.g., at a speed of at least 1 MHz). Thus, the controller (318) will replace the controller (110) shown in FIG. 1 and can additionally control the operation of the laser source (104) in addition to the operation of the AOD scanning system (300) and other scanning systems of the positioner (106) (e.g., galvanometer mirror scanning system). For ease of initiation, the act of applying a driving signal to the converter of the AOD is referred to in this specification as "driving" the AOD. Accordingly, when the first AOD (302) is driven by a driving signal applied from the first RF driver (314), a portion of the laser energy incident on the AO cell of the first AOD (302) is diffracted and propagated along its first beam path (112') to the AO cell of the second AOD (304), and another portion of the incident laser energy propagates along the zero beam path (306). When no driving signal is applied from the first RF driver (314), the laser energy incident on the AO cell of the first AOD (302) simply propagates along the zero beam path (306). Likewise, when the second AOD (304) is driven by a driving signal applied from the second RF driver (316), a portion of the laser energy incident on the AO cell of the second AOD (304) (i.e. propagating along the primary beam path (112')) is diffracted and propagated along its primary beam path (112'') (ultimately going onto the scan lens (108)), and another portion of the incident laser energy propagates along the zero beam path (308).If the driving signal is not applied from the second RF driver (316), the laser energy incident on the AO cell of the second AOD (304) simply propagates along the zero-order beam path (308).

[0024] Generally, when the AOD is driven in response to an applied driving signal, the ratio of optical power diffracted into the first beam path (112) to optical power diffracted into the zero beam path is determined by the amplitude of the RF power of the applied driving signal and, in some cases, the frequency of the RF power of the applied driving signal. Additionally, the amount of optical power diffracted into the first beam path (112) will increase as the RF power increases until it reaches a maximum at some saturation level of the RF power. The act of setting or modulating the amplitude of the RF power of the driving signal applied to the AOD is referred to in this specification as "amplitude modulation control." The act of setting or controlling the amount of optical power diffracted into the first beam path (112) may be considered as setting or controlling the "transmission" of the AOD.

[0025] When the AOD includes multiple converters, the transmission of the AOD may be controlled by applying a driving signal to each converter, and the RF frequency of each applied driving signal is the same, but the phases are slightly different. As a result, the acoustic waves generated within the AO cell of the AOD interfere in at least a somewhat destructive manner. These destructive interference acoustic waves have the effect of reducing the transmission of the AOD, and thus, the degree to which the AOD transmission is reduced corresponds to the degree to which the acoustic waves within the AO cell destructively interfere with each other. The act of selecting or modulating the phase relationship of the driving signals applied to different converters of the common AOD is referred to as "phase modulation control" in the present invention. However, it should be noted that phase modulation control cannot be used to completely prevent optical power from being diffracted into the primary beam path (112).

[0026] By driving the first AOD (302) and the second AOD (304) in succession using driving signals of different frequencies, the AOD scanning system (300) can be operated to rapidly deflect the primary beam path (112'') to different locations within the two-dimensional scan field at different angles. Furthermore, to ensure that the amount of optical power propagated along the primary beam path (112'') is at least substantially constant regardless of the frequency of the driving signal applied to the first AOD (302) and the second AOD (304), the amplitude of the RF power of each driving signal applied in succession to the first AOD (302) and / or the second AOD (304) can be changed as a function of the frequency of the driving signal (if necessary).

[0027] According to the embodiments discussed herein, a laser energy beam propagated along the beam path (112) to the AOD scanning system (300) is generated by a suitably high-power laser (e.g., a carbon dioxide or carbon monoxide gas laser as described above), and a controller (318) is configured to operate the first RF driver (314) and the second RF driver (316) to drive the first AOD (302) and the second AOD (304), respectively, to generate laser energy pulses that are time-sliced ​​from the incident beam. Thus, these time-sliced ​​laser energy pulses are output from the AOD scanning system (300) along the beam path (112'') and propagated to the scan lens (108).

[0028] For example, and referring to FIG. 4, the laser source (104) is operated to generate a laser energy beam containing a laser pulse (402) (e.g., in response to an initial transition from a low state to a high state of a laser trigger command signal (400) output to the laser source (104) by the controller (318). As illustrated by example, the initial transition of the laser trigger command signal (400) to a high state begins at time t1 and ends at time t6. The optical power of the laser pulse (402) initially rises at time t2 before reaching approximately a constant level (e.g., from time t3 to time t6). At time t6 (i.e., when the laser trigger command signal (400) transitions back from a high state to a low state), the optical power of the laser pulse (402) begins to decrease. For example, at time t7, the optical power of the laser pulse (402) is reduced to 0 or some other negligible value. The portion of the laser pulse (402) between times t2 and t3 is referred to herein as the “head portion” of the laser pulse (402), and the portion of the laser pulse (402) between times t6 and t7 is referred to herein as the “tail portion” of the laser pulse (402). The portion of the laser pulse (402) between times t3 and t6 (i.e., the portion of the laser pulse (402) between the head portion and the tail portion) is referred to herein as the “main portion” of the laser pulse (402).

[0029] FIG. 4 illustrates a laser trigger command signal that remains in a constant "ON" state during the duration of the command, but it will be understood that the laser trigger command signal can be modulated as desired (e.g., pulse width modulation) (e.g., to prevent the laser source (104) from overheating, to regulate the optical power generated by the laser source, to change the pulse duration of the laser pulse generated by the laser source (104), or to perform any combination thereof). Also, FIG. 4 illustrates only a single laser pulse (402) of a laser energy beam generated by the laser source (104) in response to the laser trigger command signal (400), but it will be understood that a series of laser trigger command signals such as the laser trigger command signal (400) can be output to the laser source (104), and the laser source (104) will generate a laser energy beam composed of a series of laser pulses such as the laser pulse (402).

[0030] Now, referring to FIGS. 3 and 4. To generate a pulse (404) that is time-sliced ​​from the main portion of a laser pulse (402), the first AOD (302) and the second AOD (304) are driven (in response to a driving signal applied by the first RF driver (314) and the second RF driver (316), respectively), so as to have at least one common period (406) (in this specification, "slice During the period also called the “period”, laser energy incident on the AO cells of the first AOD (302) and the second AOD (304) is diffracted and propagates along their respective primary beam paths (112’ and 112”). Laser energy that is not diffracted into the primary beam path (112' or 112") by the first AOD (302) and the second AOD (304) (e.g., laser energy propagating along the zero-order beam path (306 and 308)) is blocked by the first beam trap (310) and the second beam trap (312). In the exemplary timing diagram shown in FIG. 4, the first AOD (302) and the second AOD (304) diffract incident laser energy into their respective primary beam paths (112) during two slice periods (406) (a first slice period between times t3 and t4 and a second slice period between times t5 and t6) to generate two pulses (404), each pulse having a pulse duration at least approximately equal to the duration of its associated slice period (406). The first AOD (302) and the second AOD (304) It should be understood that it can be driven for more or fewer than two slice periods (406), each slice period (406) can have any duration, and different slice periods (406) can have the same or different durations.

[0031] In FIG. 4, the temporal transmission profile of the first AOD (302) obtained by applying a driving signal from the first RF driver (314) to the first AOD (302) (i.e., transmission of the first AOD (302) as a function of time) is shown as line (408). Likewise, the temporal transmission profile of the second AOD (304) obtained by applying a driving signal from the second RF driver (316) to the second AOD (304) (i.e., transmission of the second AOD (304) as a function of time) is shown as line (410). Accordingly, FIG. 4 illustrates an example in which two separate driving signals are applied to each of the first AOD (302) and the second AOD (304), wherein the two separate driving signals are applied to the first AOD (302) to generate acoustic waves during the aforementioned first slice period (406) and also to generate acoustic waves during the aforementioned second slice period (406), and the two separate driving signals are applied to the second AOD (304) to generate acoustic waves during the aforementioned first slice period (406) and also to generate acoustic waves during the aforementioned second slice period (406).

[0032] For ease of discussion in this specification, it is assumed that the driving signal applied to the first AOD (302) generating the temporal transmission profile indicated by 408 has the same frequency, and that the driving signal applied to the second AOD (304) generating the temporal transmission profile indicated by 410 also has the same frequency. However, alternatively, the frequency of the driving signal applied to the first AOD (302) generating the temporal transmission profile indicated by 408 during the first slice period (406) may be different from the frequency of the driving signal applied to the first AOD (302) generating the temporal transmission profile indicated by 408 during the second slice period (406). Likewise, the frequency of the driving signal applied to the second AOD (304) that generates the temporal transmission profile indicated by 410 during the first slice period (406) may be different from the frequency of the driving signal applied to the second AOD (304) that generates the acoustic wave indicated by 410 during the second slice period (406). In these alternative cases, the amplitude and / or phase of the driving signal applied to the first AOD (302) and / or the second AOD (304) and generating the time transmission profiles indicated by 408 and 410 during the first and second slice periods (406) (in an embodiment where the first AOD (302) and / or the second AOD (304) comprises a plurality of transducers) may be set to ensure that the average optical power of the laser pulse (404) generated during the first slice period (406) is at least substantially the same as the average optical power of the laser pulse generated during the second slice period (406) (e.g., as discussed above).

[0033] As shown in FIG. 4, there is a minimum time delay between consecutive slice periods (406) (i.e., between times t4 and t5). This minimum time delay (also referred to herein as “slice delay”) is selected to be sufficiently long to allow the transient acoustic wave in the AO cell of the first AOD (302) at the end of the previous slice period (406) to be dissipated before the first AOD (302) is driven to diffract when the next slice period (406) begins (e.g., about 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs or more, or between these values, depending on one or more factors such as the amplitude and speed of the acoustic wave propagating in the AO cell and the size of the optical aperture of the AOD). Taking into account the duration of the main part of the laser pulse (402), the number of slice periods (406) that exist during the main part of the laser pulse (402), and the slice delay between consecutive slice periods (406), the slice period (406) generated from the common laser pulse (402) may have a duration of 0.1 μs or more or near thereto (e.g., 0.1 μs, 0.25 μs, 0.5 μs, 1 μs, 1.5 μs, 2 μs, 2.5 μs, 5 μs, 10 μs or more, etc. or any of these values).

[0034] As described above, the first beam trap (310) of the AOD scanning system (300) prevents the zero-order beam path (306) from reaching the AO cell of the second AOD (304), thereby avoiding the problem discussed above in relation to FIG. 2 (the problem regarding an improperly constant or fixed thermal gradient within the AO cell of the second AOD (304). However, as is evident from FIG. 3, the AO cell of the first AOD (302) is always exposed to laser energy propagating along the beam path (112), whereas the AO cell of the second AOD (304) will be exposed only to laser energy propagating along the first-order beam path (112') from the first AOD (302). That is, the AO cell of the second AOD (304) will be exposed to laser energy only when the first AOD (302) is driven by the first RF driver (314) to generate a primary beam that propagates along the primary beam path (112').

[0035] II. Discussion on Optical Training

[0036] Since the AO cell of the second AOD (304) is formed of a material sensitive to thermal lenticating when there is laser energy propagating from the first AOD (302) along the primary beam path (112'), the AO cell of the second AOD (304) may or may not give the laser energy beam (and ultimately the scan lens (108)) propagating along the primary beam path (112'') the aforementioned wavefront distortion effect, depending on how the first AOD (302) was previously driven. For example, prior to time t1 in FIG. 4, if the laser source (104) generates a laser energy beam consisting of a series of laser pulses propagating along the beam path (112), but the first AOD (302) and the second AOD (304) are not driven during the slice period as discussed above to generate a sliced ​​pulse such as pulse (404), then a thermal gradient capable of inducing a thermal lenting effect within the AO cell of the second AOD (304) will not be present within the AO cell of the second AOD (302) immediately before the start of the first slice period (i.e., at time t3). However, a thermal gradient capable of inducing thermal lenting may occur or advance within the AO cell of the second AOD (304) during the first slice period (assuming the first slice period has a sufficiently long duration) or during the slice period following the first slice period (assuming the consecutive slice periods have a sufficiently long duration and are sufficiently close to each other in time). Therefore, the thermal gradient within the AO cell of the second AOD (304) will not be relatively constant, and as a result, undesirable changes in the wavefront distortion effect will occur in the laser energy beam propagating from the second AOD (304) along the primary beam path (112) (and ultimately to the scan lens (108)).

[0037] In order to prevent or advantageously reduce the undesirable progression of the thermal gradient within the AO cell of the second AOD (304), the first AOD (302) is driven during one or more periods occurring outside the slice period (each referred to herein as an “optical training period”) (in response to one or more driving signals applied by the first RF driver (314) as commanded by the controller (318)). However, the second AOD (304) is not driven during the optical training period. Thus, during the optical training period, laser energy incident on the AO cell of the first AOD (302) is diffracted and propagated along its respective primary beam path (112’) (e.g., as discussed above). Then, the AO cell of the second AOD (304) absorbs a portion of the laser energy propagating along the primary beam path (112') of the first AOD (302), and as a result, local heating of the AO cell of the second AOD (304) and thermal lenting within it occur. Heating the second AOD (304) in this manner may be described herein as optically "training" the second AOD (304).

[0038] Generally, the timing and duration of the optical training period are selected to ensure that the thermal gradient within the AO cell of the second AOD (304) remains relatively constant over time, so that changes in wavefront distortion effects are negligible or sufficiently reduced to ensure that a workpiece, such as the workpiece (102), can be satisfactorily processed. For example, before time t1 in FIG. 4, the controller (318) may control the operation of the laser source (104) to generate a laser energy beam containing one or more laser pulses (402) propagating along the beam path (112), but may not control the AOD scanning system (300) to generate a sliced ​​pulse, such as the pulse (404), from the laser pulse (402) (or to drive the first AOD (302). In this example, a thermal gradient capable of inducing thermal renzing within the AO cell of the second AOD (304) will not be present within the AO cell of the second AOD (304) at the start of the first slice period described above in relation to FIG. 4 (i.e., at time t3 in FIG. 4). However, a thermal gradient capable of inducing thermal renzing may be present during the first slice period described above in relation to FIG. 4 (assuming the first slice period has a sufficiently long duration) or the first slice Is During the slice period following the period (assuming consecutive slice periods have a sufficiently long duration and are also sufficiently close to each other in time), it may occur or progress within the AO cell of the second AOD (304).

[0039] In order to prevent or advantageously reduce the undesirable progression of the thermal gradient within the AO cell of the second AOD (304) during a slice period or over a continuous slice period, the controller (318) may control the operation of the first RF driver (314) to drive the first AOD (302) (during the optical training period (500)) so as to diffract the incident laser energy of each laser pulse (402) generated before the aforementioned time t1 into the primary beam path (112') and propagate the primary beam from the first AOD (302) to the AO cell of the second AOD (304), thereby allowing the optical training operation to be performed, for example, as shown in FIG. 5. This driving of the first AOD (302) is exemplarily shown in FIG. 5, but for simplicity, only a single laser pulse (402) is shown. As shown in FIG. 5. The controller (318) does not control the operation of the second RF driver (316) to drive the second AOD (304) during the optical training period (500), so that all laser energy incident on the AO cell of the second AOD (304) is blocked by the second beam trap (312).

[0040] FIG. 5 illustrates that the optical training period (500) lasts for the entire duration of the laser pulse (402) (including the entire head portion and tail portion of the laser pulse (402)), but it will be understood that the optical training period (500) may be shorter than the entire duration of the laser pulse (402) or that the first AOD (302) may be driven during a continuous optical training period over the duration of the pulse (402). In this case, the first AOD (302) may not be driven during the entire or partial duration of the head portion of the laser pulse (402), during the entire or partial duration of the tail portion of the laser pulse (402), during the entire or partial duration of the laser pulse (402) between the head portion and the tail portion, or during any combination of these.

[0041] As mentioned above, FIG. 4 illustrates only a single laser pulse (402) of a laser energy beam generated by a laser source (104), but a series of laser trigger command signals (400) will generally be output to the laser source (104), so that, for example as shown in FIG. 6, the laser source (104) will generally generate a laser energy beam consisting of a series of laser pulses (402). If the duration between consecutively generated laser pulses (402) is sufficiently long, the thermal gradient within the AO cell of the second AOD (304) during the previous slice period (406) (e.g., the slice period (406') as shown in FIG. 6) associated with the previous laser pulse (402) (e.g., the laser pulse (402') as shown in FIG. 6) may be undesirably extinguished or reduced before a slice pulse such as the pulse (404) is generated during the next slice period (406) (e.g., the slice period (406") as shown in FIG. 6) associated with the next laser pulse (402) (e.g., the laser pulse (402") as shown in FIG. 6). Consequently, the wavefront distortion effect imparted to the pulse (404) by the AO cell of the second AOD (304) during the previous slice period (406') may differ from the wavefront distortion effect imparted to the pulse (404) by the AO cell of the second AOD (304) during the next slice period (406"). As understood, each of the laser pulses (402' and 402") represents a specific example of a laser pulse and may therefore be collectively referred to as a laser pulse (402) in this specification.

[0042] In order to prevent or advantageously reduce the undesirable extinction or reduction of the thermal gradient within the AO cell of the second AOD (304) between slice periods associated with the continuously generated laser pulses (402) (e.g., between slice periods (406', 406") associated with the laser pulses (402', 402"), the controller (318) may control the operation of the first RF driver (314) to drive the first AOD (302) to diffract the incident laser energy from the tail portion of the laser pulse (402') into the primary beam path (112') (and / or diffract the incident laser energy from the head portion of the laser pulse (402") and propagate the primary beam from the first AOD (302) to the AO cell of the second AOD (304), thereby allowing one or more optical training operations to be performed, for example as shown in FIG. 6. Thus, to diffract the incident laser energy from the tail portion of the laser pulse (402'). The period(s) during which the first AOD (302) is driven (and / or to diffract incident laser energy at the head portion of the laser pulse (402'')) is an example of the previously mentioned "optical training period".

[0043] As shown in FIG. 6, the controller (318) does not control the operation of the second RF driver (316) to drive the second AOD (304) during any optical training period, so that all laser energy incident on the AO cell of the second AOD (304) during the optical training period is blocked by the second beam trap (312). Also, as shown in FIG. 6, the controller (318) can control the operation of the first RF driver (314) to drive the first AOD (302) to diffract the incident laser energy from the head portion of the laser pulse (402') into its primary beam path (112') (and / or diffract the incident laser energy from the tail portion of the laser pulse (402)) and propagate the primary beam from the first AOD (302) to the AO cell of the second AOD (304) as needed or desired.

[0044] Additionally, as shown in FIG. 6, the controller (318) controls the operation of the first RF driver (314) so ​​that there is a time delay between the optical training period and the next consecutive slice period (or vice versa). If there is a time delay between the optical training period (500) and the next consecutive slice period (406) (e.g., between the optical training period (500) and the slice period (406) associated with the laser pulse (402)), the duration of the time delay must be sufficiently long to allow the transient acoustic waves in the AO cell of the first AOD (302) to be dissipated at the end of the optical training period (500) before the first AOD (302) is driven to diffract at the start of the next consecutive slice period (406) (e.g., about 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs, etc., or between these values, depending on one or more factors such as the amplitude and speed of the acoustic waves propagating in the AO cell and the size of the optical aperture of the AOD). If there is a time delay between the slice period (406) and the next consecutive optical training period (500) (e.g., between the slice period (406') and the optical training period (500) associated with the laser pulse (402'), the duration of the time delay may be smaller, equal to, or larger than the first time delay.

[0045] FIG. 6 illustrates only one optical training period (500) occurring during the head or tail portion of the laser pulse (402), but it will be understood that multiple intermittent optical training periods (500) may occur during any head or tail portion of the laser pulse (402). Additionally, FIG. 6 illustrates that the optical training period (500) associated with any laser pulse (402) lasts for a shorter time than the total duration of the head or tail portion of the laser pulse (402), but it will be understood that the optical training period (500) associated with any laser pulse (402) may last for the total duration of the head or tail portion of the laser pulse (402).

[0046] FIGS. 4 and FIGS. 6 illustrate an embodiment in which a pulse slicing operation is performed such that the slice period (406) occupies the entire duration of the laser pulse (402) between the head portion and the tail portion, excluding the slice delay mentioned above. However, in other embodiments, the controller (318) may cause one or more pulse slicing operations to be performed such that at least one period having a duration greater than twice the duration of the slice delay (or its vicinity) and outside the slice period is between the head portion and the tail portion of the laser pulse (402). Hereinafter, such a period is referred to as a "non-slice period." If a first time delay exists between an incidental optical training period (500) and any subsequent slice period (e.g., as described above), the controller (318) may cause an optical training operation to be performed during the non-slice period (e.g., as described above). For example, the non-slice period is exemplarily illustrated as 700 in FIG. 7, and an optical training operation is performed during the optical training period (500) within the non-slice period (700). As shown in FIG. 7, there is a first time delay between the optical training period (500) occurring during the non-slice period (700) and the next slice period (406'''), and there is also a time delay between the optical training period (500) occurring during the non-slice period (700) and the previous slice period (406). Also, as shown in FIG. 7, the optical training operation may also be performed at the head portion and / or tail portion of the laser pulse (402) (e.g., in the manner exemplarily described above in relation to FIG. 6).

[0047] From the embodiments discussed above, it will be understood that the controller (318) is configured to perform one or more optical training operations (e.g., as described above) during any entire non-slice period, during any entire head portion of the laser pulse, during any entire tail portion of the laser pulse, or during any combination thereof. In other embodiments, the controller (318) causes the optical training operation to be performed only during a portion of the non-slice period, only during a portion of the head portion of the laser pulse, only during a portion of the tail portion of the laser pulse, or during any combination thereof. In an embodiment where the controller (318) causes the optical training operation to be performed only during a portion of the non-slice period (in contrast to the entire non-slice period), only during a portion of the head portion of the laser pulse (in contrast to the entire head portion of the laser pulse), and / or only during a portion of the tail portion of the laser pulse (in contrast to the entire tail portion of the laser pulse), the optical training period (500) may be referred to as a "custom optical training period" (500).

[0048] According to an embodiment of the present invention, the duration of the customized optical training period (500) during which the optical training operation is performed may correspond to the optical power of the laser pulse (e.g., laser pulse (402)) during the customized optical training period (500). For example, less laser energy will be diffracted into the AO cell of the second AOD (304) during the customized optical training period (500) that occurs near the end of the head portion (or near the beginning of the tail portion) of the laser pulse (402) compared to the customized optical training period (500) that occurs near the beginning of the head portion (or near the end of the tail portion). Accordingly, the controller (318) may be configured to perform the optical training operation during a relatively long customized optical training period (500) that occurs near the beginning of the head portion of the laser pulse (402) or during a relatively short customized optical training period (500) that occurs near the end of the head portion of the laser pulse (402). Likewise, the controller (318) may be configured to perform an optical training operation during a relatively short customized optical training period (500) occurring near the beginning of the tail portion of the laser pulse (402) or during a relatively long customized optical training period (500) occurring near the end of the tail portion of the laser pulse (402).

[0049] According to another embodiment of the present invention, the duration of any customized optical training period (500) in which the optical training operation is performed may also correspond to the actual or estimated thermal gradient within the AO cell of the second AOD (304) immediately prior to the customized optical training period (500). To facilitate the performance of the optical training operation during the customized optical training period, the controller (318) may be provided with pulse shape information describing the amount of energy within the laser pulse (402) in various temporal "slices" of the laser pulse (402) or the temporal optical power profile of the laser pulse (402) (i.e., from the beginning of the head portion to the end of the tail portion) (or access to the pulse shape information may be made, for example, via one or more wired or wireless networks (not shown).

[0050] III. General Discussion on Pulse Shape Information

[0051] As mentioned above, the controller (318) may receive pulse shape information to facilitate the performance of optical training operations during a customized optical training period (or may access such information via, for example, one or more wired or wireless networks (not shown)). The controller (318) may receive information indicating pulse shape information related to laser pulses to be generated by the laser source (104), or, if not, may derive such pulse shape information based on the received information. Such received information may be input by a user (for example, via the user interface (not shown) of the device (100)), set by an operator or technician of the device (100), read from a computer file transmitted or delivered to the controller (318), etc., or a combination thereof.

[0052] Pulse shape information may be stored in association with other information (also referred to herein as “supplementary information”) describing laser parameters (e.g., pulse duration of the laser pulse (402) generated by the laser source (104), pulse repetition frequency at which the laser pulse (402) is generated, average power at which the laser pulse (402) is generated, etc., or any combination thereof) of the laser energy beam (e.g., in a lookup table or other data structure in computer memory accessible to the controller (318)). Then, the controller (318) can determine when any optical training operation should be performed and for how long the optical training operation should be performed (duration of the customized optical training period (500)) by using pulse shape information and optionally any related supplementary information to maintain a substantially constant thermal gradient within the AO cell of the second AOD (304) during the operation of the device (100).

[0053] A. Discussion on the Generation of Pulse Shape Information

[0054] In one embodiment, pulse shape information may be generated using any known or suitable laser energy monitoring system included in the AOD scanning system (300) or in the device (100) including the AOD scanning system (300). For example, and referring to FIG. 8, a laser energy monitoring system (800) according to one embodiment of the present invention includes a mirror (802) and a laser sensor (804).

[0055] The mirror (802) is provided as a partial transmission mirror configured to be positioned within the beam path (806) and to reflect most of the light of the incident beam of laser energy propagating along the beam path (806) (to the beam path (806r)) and also to transmit a small portion of the light (e.g., about 2%) to the beam path (806t). In FIG. 8, the beam path (806) may be one of the zero-order beam paths (306 or 308) or one of the first-order beam paths (112' or 112"). Thus, the beam path (806r) may propagate to a first beam trap (310) (if the beam path (806) is the zero-order beam path (306), a second beam trap (312) (if the beam path (806) is the zero-order beam path (308), a second AOD (304) (if the beam path (806) is the first-order beam path (112'), or to a scan lens (108) or another optical element located optically downstream of the AOD scanning system (300) (if the beam path (806) is the first-order beam path (112")).

[0056] A laser sensor (804) is positioned to receive laser energy transmitted through a mirror (802) (e.g., propagating along a beam path (806t)). In one embodiment, the laser sensor (804) is configured to measure the instantaneous optical power of a laser energy beam incident thereon and to generate sensor data based on the detection or measurement. The sensor data may be output to a controller (318) by any suitable means (e.g., via wired or wireless communication as known in the art). The controller (318) causes the sensor data to be stored as pulse shape information describing the temporal optical power profile of the laser energy incident on the laser sensor (804) over a set time period (e.g., during a temporal "slice" of the laser pulse (402) as described in more detail below) (e.g., locally within the controller (318), in some computer memory within the device (100) accessible to the controller (318), or in some computer memory located remotely from the device (100) but communically connected to the device (100) via one or more networks).

[0057] In another embodiment, sensor data output to the controller (318) may be further processed (e.g., time integration) to derive the amount of energy of a laser energy beam incident on the laser sensor (804) over a set time period. In this embodiment, the processed sensor data may be stored as pulse shape information describing the amount of energy within the laser pulse energy over a set time period (e.g., during a temporal "slice" of the laser pulse (402) as described in more detail below) (e.g., as described above).

[0058] In another embodiment, the laser sensor (804) is provided as an integrating detector (e.g., configured to measure the instantaneous optical power of an incident laser energy beam and integrate the measured optical power to derive the amount of energy of the beam) and generates sensor data. The sensor data may be output to a controller (318) by any suitable means (e.g., via wired or wireless communication as known in the art) and may be stored as pulse shape information describing the amount of energy within the laser pulse energy over a set time period (e.g., during a temporal "slice" of the laser pulse (402) as described in more detail below) (e.g., as described above).

[0059] In one embodiment, the laser source (104), the AOD scanning system (300), and the laser energy monitoring system (800) may be operated to perform pulse shape analysis processing to generate pulse shape information. During pulse shape analysis processing, the laser source (104) is operated to generate a laser energy beam comprising a sequence of laser pulses (402) generated under a specific set of laser parameters (e.g., as described above). For example, all laser pulses in the laser pulse sequence may have the same (or substantially the same) pulse duration, and all laser pulses may be generated at the same (or substantially the same) pulse repetition frequency.

[0060] The AOD scanning system (300) is operated during pulse shape analysis processing (e.g., as previously described) so that the laser energy of each laser pulse (402) of a sequence of laser pulses propagates along a beam path (806) for at least one period (each period is referred to herein as the temporal "slice" or, more simply, a "slice window" of the laser pulse (402) mentioned above). When the laser energy propagates along the beam path (806), the slice window may be considered "open." When the laser energy does not propagate along the beam path (806), the slice window may be considered "closed." The duration of each slice window may be about 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs, 0.05 μs, etc., or between these values, and all slice windows generated during the sequence of laser pulses have the same duration.

[0061] When the slice window is opened, the laser sensor (804) generates sensor data and outputs it to the controller (318). The sensor data is stored in association with other information, such as supplementary information mentioned above and slice information describing the temporal aspect of the slice window in which the sensor data was generated (e.g., as discussed above). Examples of slice information may include the time when the slice window is opened (e.g., the time when the laser trigger command signal transitions from a low state to a high state), the time when the slice window is closed (e.g., the time when the laser trigger command signal transitions from a low state to a high state), the duration of the slice window, or any combination thereof.

[0062] Generally, the duration of each slice window associated with a laser pulse (402) is shorter than the pulse duration of the laser pulse (402), but the slice windows associated with other laser pulses (402) in the sequence of laser pulses (402) are opened and closed at different times, so that the sensor data generated by the laser sensor (804) effectively represents all parts of the representative laser pulse (402) of the sequence of laser pulses (402). For example, and referring to FIG. 9, the laser source (104) is operated to generate a laser energy beam comprising a plurality of laser pulses (402) (for simplification, only the first laser pulse (402') and the second laser pulse (402'') of the sequence of laser pulses are shown) (e.g., as previously described). The AOD scanning system (300) is operated to allow laser energy to propagate along a beam path (806) during at least one slice window associated with each laser pulse of a sequence of laser pulses (e.g., during the first slice window (900') associated with the first laser pulse (402') and also during the second slice window (900") associated with the second laser pulse (402") (e.g., as previously described). As understood, each of the slice windows (900' and 900") represents a specific example of a slice window and may therefore be collectively referred to as a slice window (900) in this specification. The position of the second slice window (900") within the temporal optical power profile of the associated laser pulse (402'') is temporally offset from the position of the first slice window (900') within the temporal optical power profile of the associated laser pulse (402'), as indicated by 902. The offset is generally equal to the duration of the slice window, but can be smaller or larger than the duration of the slice window.The AOD scanning system (300) is further operated to allow the laser energy of the next laser pulse (402) of the sequence of laser pulses to propagate along the beam path (806) during slice windows offset from each other (e.g., as described above), so that a slice window (900) is created for all parts of the laser pulses representing all laser pulses (402) of the sequence of laser pulses (402) (thus sensor data is created) (e.g., see FIG. 10).

[0063] IV. Discussion on RF Training

[0064] As mentioned above, the AO cells of each of the first AOD (302) and the second AOD (304) are formed of a material sensitive to thermal lenticating when laser energy propagates along the beam path (112) or the primary beam path (112'). However, when the first AOD (302) and the second AOD (304) are driven, the internal AO cells will be heated in a manner sufficient to create a thermal gradient capable of inducing a thermal lenticating effect as described above. The thermal gradient characteristics within the AO cells of the AOD will vary depending on how the AOD is driven (e.g., considering the amount of RF energy and RF frequency(s) applied to the AOD during the slicing period). However, the thermal gradient within the AO cell that induces the thermal lenting effect may be extinguished when there is no laser energy propagating through it (e.g., when the AOD is not operating, during the period between time t17 of pulse (402') and time t22 of pulse (402") as shown in FIG. 6; time t17 of pulse (402') corresponds to t7 shown in FIG. 4 and time t22 of pulse (402") corresponds to t2 shown in FIG. 4). Consequently, when pulse slicing operation is performed (e.g., for a laser pulse (402) as shown in FIG. 6), the thermal gradient within the AO cells of the first AOD (302) and the second AOD (304) may be undesirably different from the thermal gradient within the AO cells of the first AOD (302) and the second AOD (304) when pulse slicing operation is performed (e.g., for a laser pulse (402') as shown in FIG. 6). Thus, over the period during which laser energy from a continuous laser pulse (402) propagates through the AO cells of the first AOD (302) and the second AOD (304), the thermal gradient within these AO cells may change undesirably, and consequently, inconsistent deflection of the laser pulse (402) incident on the AOD scanning system (300) occurs.

[0065] In order to prevent or minimize undesirable changes in the thermal gradient within the AO cells of the first AOD (302) and the second AOD (304) over the period during which laser energy from a continuous laser pulse (402) propagates, the first AOD (302) and the second AOD (304) may be driven during the interval between pulses. As used herein, “inter-pulse interval” refers to a time period during which laser energy from a continuous laser pulse (402) is not propagated through the first AOD (302) and the second AOD (304) (e.g., the interval (600) occurring during the period between time t7 of the pulse (402') as shown in FIG. 6 and time t2 of the pulse (402)). Driving the first AOD (302) and the second AOD (304) during the inter-pulse interval (600) is referred to herein as “RF training,” and this training may be performed during RF training operation.

[0066] Referring to FIG. 12, the controller (318) may enable RF training operation to be performed during a pulse interval such as a pulse interval (600). In FIG. 12, the driving signal applied to the first AOD (302) from the first RF driver (314) includes a first RF training pulse (1202), and the driving signal applied to the second AOD (304) from the second RF driver (316) includes a second RF training pulse (1204). As shown in FIG. 12, the duration during which the first RF training pulse (1202) and the second RF training pulse (1204) are applied is referred to herein as the RF training period (1200). The timing and duration of the RF training period (1200) can be selected to ensure that the thermal gradient within the AO cell of the second AOD (304) remains relatively constant over time, so that changes in the wavefront distortion effect can be ignored or sufficiently reduced so that a workpiece such as the workpiece (102) can be processed satisfactorily.

[0067] The controller (318) controls the operation of the first RF driver (314) and the second RF driver (316) so that there is a time delay between the RF training period (1200) and the next consecutive slice period (occurring after time t22 as discussed above). Generally, the duration of the time delay must be long enough to allow the transient acoustic waves in the AO cells of the first AOD (302) and the second AOD (304) to dissipate at the end of the RF training period (1200) before the first AOD (302) and the second AOD (304) are driven to diffract at the start of the slice period (406) (e.g., about 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs or more, etc., depending on one or more factors such as the amplitude and speed of the acoustic waves propagating in the AO cells and the size of the optical aperture of the AOD, or between these values). Although not illustrated, the driving signal applied to the first AOD (302) and the second AOD (304) may be any other RF of any appropriate frequency, amplitude, and duration to generate the laser pulse (404) discussed above, to perform any of the optical training operations discussed above, or to form any combination thereof. It must be understood that it may include pulses (as symbolically represented by dotted lines).

[0068] The amplitudes and durations of the first RF training pulse (1202) and the second RF training pulse (1204) can also be selected in any desired or advantageous manner to ensure that the thermal gradient within the AO cell of the first AOD (302) and the second AOD (304) remains relatively constant over time, so that changes in wavefront distortion effects are negligible or sufficiently reduced so that a workpiece, such as the workpiece (102), can be satisfactorily processed in the embodiment shown in FIG. 12. The first and second RF training pulses (1202, 1204) are represented as step functions. Alternatively, the amplitudes of the first and second RF training pulses (1202, 1204) can be shaped in a different way (e.g., as a sinusoid) to obtain a desired thermal gradient in the AO cell. In another embodiment, the RF training pulses (1202, 1204) may have different durations.

[0069] The RF frequency component of the RF training pulse (1202, 1204) may also be selected in any desired or advantageous manner. In some cases (e.g., depending on the configuration of the transducer(s) attached to the AO cell, the efficiency with which the transducer can emit acoustic waves into the AO cell, etc.), the absorption of RF energy by the AO cell may vary depending on the frequency of the driving signal. In one embodiment, the RF training pulse (1202, 1204) may include a subset of one or more individual frequencies within a frequency band, or may include all such individual frequencies. Additionally, the frequency of the RF training pulse (1202, 1204) applied during different RF training periods may be the same or different. That is, the frequency (or frequencies) of the RF training pulse applied during the first RF training period may be the same or different from the frequency (or frequencies) of the RF training pulse applied during the second RF training period. For example, during the first RF training period (1200), the frequencies of the first subset may be output to the converters of the first AOD (302) and / or the second AOD (304) for the entire duration of the RF training period (1200), and during the next RF training period (1200), the frequencies of the second subset (which may or may not include a portion of the same frequencies included in the first subset) are output to the converters of the first AOD (302) and / or the second AOD (304).

[0070] In another embodiment, the RF training pulse (1202, 1204) may include some or all of the frequencies within a specific frequency band by chirping or "smearing" the frequency of the RF training pulse during the RF training period. If the individual frequency RF training pulse emits an undesirable level of electromagnetic radiation (e.g., may interfere with electronic devices near the laser processing device (100)), generating and applying such chirped or "smeared" RF training pulse may be more advantageous for an RF training pulse containing one or more individual frequencies (each also referred to herein as an "individual frequency RF training pulse").

[0071] Although RF training has been discussed above in relation to the AOD scanning system (300), it will also be understood that RF training can be performed with any system having any number of AODs that are properly equipped (e.g., a system having only one AOD, or a system having two or more AODs).

[0072] V. Discussion on Beam Trap Training

[0073] As described above, optical training can be advantageously used to maintain the thermal state of the AO cells of the first AOD (302) and the second AOD (304) when laser energy propagated through the first AOD (302) and the second AOD (304) is not propagated to the workpiece (102). Also, as described above, RF training can be used to maintain the thermal state of the AO cells of the first AOD (302) and the second AOD (304) when laser energy is not propagated through the first AOD (302) or the second AOD (304) (and thus not propagated to the workpiece (102)) (e.g., during the pulse interval mentioned above).

[0074] However, there may be situations where it is desirable to prevent the workpiece (102) from being irradiated with laser energy while the laser source (104) is still generating a laser energy beam (e.g., to maintain stable operation of the laser source (104)), but while optical training is not effective or feasible (e.g., because the second AOD (304) is not running for a relatively long period while the first AOD (302) is running). Such situations may occur during workpiece processing where there is a long distance between features to be formed continuously on the workpiece, for example, when the processed workpiece is being removed from the system (or loaded into the system). In order to maintain the thermal state of the AO cells of the first AOD (302) and the second AOD (304) during such circumstances, and with reference to FIG. 13, the AOD scanning system (1300) may be provided as exemplarily described for the AOD scanning system (300), but may further include a third beam trap (1302) (also referred to herein as "training beam trap (1302)") which is positioned and configured to block the laser energy propagating therefrom, and the first AOD (302) and the second AOD (304) of the AOD system (1300) may be driven to deflect the primary beam path (112'') toward the training beam trap (1302) (e.g., as indicated by arrow (1304)), so that the training beam trap (1302) blocks the laser energy propagating along the primary beam path (112''). Driving the first AOD (302) and the second AOD (304) in this manner is referred to in this specification as "beam trap training," and this training may be performed during beam trap training operation.

[0075] Referring to FIG. 14, the controller (318) can enable beam trap training operation to be performed by controlling the operation of the first RF driver (314) and the second RF driver (312) to apply a driving signal to the first AOD (302) and the second AOD (304) when the laser energy of a series of consecutively generated laser pulses (402) is propagated through the AO cell. In FIG. 14, the optical power of the primary beam path (112'') deflected toward the training beam trap (1302) is indicated by the line (1400).

[0076] The amplitude of the driving signal applied to the first AOD (302) and the second AOD (304) may be constant, or may vary in any desired or advantageous way to ensure that the thermal gradient within the AO cell of the first AOD (302) and the second AOD (304) remains relatively constant over time, so that the change in the wavefront distortion effect may be ignored or sufficiently reduced so that a workpiece such as the workpiece (102) can be processed satisfactorily.

[0077] In one embodiment, while the phase modulation control is driving the first AOD (302) and / or the second AOD (304), the phase modulation control is additionally used to reduce the optical power propagated along the beam path (112'') to the training beam trap (1302). If the average or peak power of the laser energy propagated along the beam path (112'') to the training beam trap (1302) would otherwise undesirably damage or aggravate the beam trap (1302), it may be desirable to do so.

[0078] As shown in FIG. 14, the duration of the driving signal applied to the first AOD (302) and the second AOD (304) from the first RF driver (314) and the second RF driver (316), respectively, is significantly longer than the duration of a single laser pulse (402). In the illustrated embodiment, the driving signal applied from the first RF driver (314) and the second RF driver (316) at once is synchronized with the beginning of the head portion of the laser pulse (402) incident on the AO cell of the first AOD (302) (i.e., at time t12 corresponding to the time t2 mentioned above). However, in other embodiments, the driving signal may be applied before time t12 (e.g., between time t12 and time t11 corresponding to the time t1 mentioned above, or before time t11).

[0079] As is apparent, the frequency of each driving signal applied from the first RF driver (314) and the second RF driver (316) is selected to direct laser energy propagating along the primary beam path (112'') toward the training beam trap (1302). Generally, the frequency of the driving signal applied from the first RF driver (314) (also referred to herein as the “first frequency”) may be any frequency within the first frequency range. Likewise, the frequency of the driving signal applied from the second RF driver (316) (also referred to herein as the “second frequency”) may be any frequency within the second frequency range. The bandwidth of the first frequency range may be greater than, equal to, or smaller than the bandwidth of the second frequency range. In one embodiment, the first frequency range overlaps with the second frequency range (i.e., frequencies included in the first frequency range are included in the second frequency range). In another embodiment, the first frequency range does not overlap with the second frequency range (i.e., frequencies included in the first frequency range are not included in the second frequency range, and vice versa).

[0080] During beam trap training operation, the RF frequency components of the driving signal applied to the first AOD (302) and the second AOD (304) may be selected in any desired or advantageous manner. For example, the driving signal applied to the first AOD (302) may include one or more individual frequencies within a first frequency range, or may include multiple frequencies within the first frequency range that are chirped or "smeared" as described above in embodiments relating to RF training. Likewise, the driving signal applied to the second AOD (304) may include one or more individual frequencies within a second frequency range, or may include multiple frequencies within the second frequency range that are chirped or "smeared" as described above in embodiments relating to RF training.

[0081] Although beam trap training has been described above as involving the use of a training beam trap in connection with an AOD scanning system (1300) including a training beam trap (1302), it will be understood that in other embodiments, the training beam trap (1302) may be replaced by one or more optical elements (e.g., one or more mirrors, lenses, etc., or any combination thereof) positioned and configured to block laser energy propagating along the primary beam path (112'') during beam trap training operation and also to redirect that laser energy back into the first beam trap (310) or the second beam trap (312). In another embodiment, the second beam trap (312) may be configured to block laser energy propagating from the second AOD (304) along the primary beam path (112") during beam trap training operation.

[0082] Although beam trap training was discussed above in relation to the AOD scanning system (1300), RF training is available for any system having any number of appropriately equipped AODs (e.g., a single jiIt will be understood that this can be performed with a system having one AOD (or a system having two or more AODs) and a beam trap. Furthermore, FIG. 14 illustrates an embodiment in which beam trap training is performed to deflect two consecutive laser pulses (402) into a beam trap (1302), but it will be understood that beam trap training may also be performed to deflect any number of such laser pulses (402) into a beam trap (1302).

[0083] VI. Discussion on the Adjustment of Temporal Optical Power Profiles

[0084] As discussed above, the temporal transmission profiles of the first AOD (302) and the second AOD (304) during the slice period, denoted as 408 and 410 respectively, are constant (or at least substantially constant) for the entire duration of the slice period (406). Consequently, the temporal optical power profile of the laser pulse (404) generated during the slice period (i.e., the optical power of the laser pulse (404) output from the AOD scanning system (300) as a function of time during the slice period) will approximately match the temporal optical power profile of a portion of the laser pulse (402) incident on the AOD scanning system (300) during the slice period. For example, during any slice period shown in FIG. 4-7 or 8-10, the temporal optical power profile of the laser pulse (402) incident on the AOD scanning system (300) and the laser pulse (404) output from the AOD scanning system (300) is essentially horizontally flat, which means that the optical power of the incident laser pulse (402) and the output laser pulse (404) is approximately constant during the slice period (406). Therefore, during different slice periods, the temporal optical power profile of a portion of the laser pulse (402) will be the same (or approximately the same), and the temporal optical power profile of the laser pulse (404) generated during the slice period will also be the same (or approximately the same). Ensuring that the temporal optical power profile of the laser pulse (404) generated during the slicing period is the same (or approximately the same) may be advantageous for promoting the development of a laser-based process for forming features on a workpiece (e.g., for forming through- or blind vias on a workpiece such as a printed circuit board or an integrated circuit board) or for forming multiple features using different laser pulses (404) sliced ​​from a common laser pulse (402).

[0085] However, there may often be cases where the optical power of the main portion of the laser pulse (402) changes in an undesirable way. Consequently, the temporal optical power profiles of the portions of the laser pulse (402) during different slice periods will be sufficiently different from each other, and thus it becomes difficult to efficiently develop laser-based processes and to form multiple features using different laser pulses (404) sliced ​​from a common laser pulse (402). In some embodiments, the temporal optical power profile of the laser pulse (402) can be adjusted by changing the way the laser source (104) is operated (e.g., by changing the optical power of the generated laser pulse, by changing the pulse repetition rate, by changing the pulse duration of the generated laser pulse, by modulating the duty cycle of the laser trigger command signal applied to the laser source (104) (e.g., through pulse width modulation), or through any combination of these).

[0086] As an alternative to (or together with) modifying the operation of the laser source (104), the amplitude and / or phase of the driving signals applied to the first AOD (302) and / or the second AOD (304), which generate the temporal transmission profiles indicated by 408 and / or 410 respectively during the slice period (406) (in an embodiment in which the first AOD (302) and / or the second AOD (304) comprises a plurality of transducers) may be variable during the slice period (406) (e.g., as described above). According to an embodiment of the present invention, the amplitude and / or phase of the driving signal applied to the first AOD (302) and / or the second AOD (304) during the slice period (406) may be variable such that the temporal optical power profile of the laser pulse (404) generated during the slice period (406) does not approximately match the temporal optical power profile of a portion of the laser pulse (402) incident on the AOD scanning system (300) during the slice period (406).

[0087] For example, and referring to FIG. 11, it was found that the optical power of the laser pulse (402) varies significantly (e.g., steadily decreasing from the relatively high optical power "Hi" at the previously mentioned time t3 to the relatively low optical power "Lo" at the previously mentioned time t6, where optical power Lo may be in the range 5% to 15% lower than optical power Hi). If the temporal transmission profiles of the first AOD (302) and the second AOD (304) are constant during the previously mentioned first slice period (406), the optical power of the laser pulse (404) generated during the first slice period (406) will vary undesirably during the first slice period (e.g., steadily decreasing to produce a temporal optical power profile that matches the temporal optical power profile of a portion of the laser pulse (402) incident on the AOD scanning system (300) during the first slice period (406). Likewise, if the temporal transmission profile is constant during the previously mentioned second slice period (406), the optical power of the laser pulse (404) generated during the second slice period (406) will change undesirably during the second slice period (e.g., steadily decreasing to produce a temporal optical power profile that matches the temporal optical power profile of a portion of the laser pulse (402) incident on the AOD scanning system (300) during the second slice period (406). Furthermore, assuming that the pulse durations of the laser pulse (404) generated during the first and second slice periods (406) are the same, the laser pulse (404) generated during the second slice period (406) will undesirably have less pulse energy than the laser pulse (404) generated during the first slice period (406).

[0088] Accordingly, according to an embodiment of the present invention, and as exemplarily shown in FIG. 11, the temporal optical power profile of the laser pulse (404) generated during the first and second slice periods (406) may be at least substantially horizontally flat (i.e., substantially constant over time), and the temporal transmission profile of each driving signal applied to the first AOD (302) during the first and second slice periods (406) may be variable (e.g., using amplitude modulation control, phase modulation control, or a combination thereof). For example, amplitude modulation control and / or phase modulation control may be performed to drive the first AOD (302) during the first and second slice periods such that the temporal transmission profile of the first AOD (302) during the first and second slice periods becomes the inverse of the temporal optical power profile of a portion of the laser pulse (402) incident on the AOD scanning system (300) during the first and second slice periods (406). Furthermore, amplitude modulation control and / or phase modulation control can be performed such that the temporal optical power of the laser pulse (404) generated during the first and second slice periods (406) is at least substantially the same. Consequently, assuming that the pulse durations of the laser pulse (404) generated during the first and second slice periods (406) are the same, the laser pulse (404) generated during the second slice period (406) will preferably have the same pulse energy as the laser pulse (404) generated during the first slice period (406).

[0089] FIG. 11 illustrates an embodiment in which the optical power of the laser pulse (402) is shown to be steadily decreasing, but it will be understood that the optical power of the laser pulse (402) may be steadily increasing or decreasing or increasing in a sinusoidal, quasi-erratic, or other nonlinear manner, or a combination thereof, depending on one or more factors such as the laser source (104) used to generate the laser energy beam, the manner in which the laser source (104) is operated, the temperature of the laser source (104), environmental conditions within the surrounding environment surrounding the laser source (104) (e.g., humidity, temperature), or a combination thereof.

[0090] Furthermore, FIG. 11 illustrates an embodiment in which the temporal transmission profile of the first AOD (302) during the first and second slice periods (406) is varied to ensure that the temporal optical power profile of the laser pulse (404) generated during the first and second slice periods (406) is at least substantially horizontally flat, but it will be understood that the temporal transmission profile of the second AOD (304) during the first and second slice periods (406) may be varied alternatively or additionally to achieve the same goal.

[0091] Finally, it will be understood that although it has been discussed above that the temporal transmission profile of the first AOD (302) and / or the second AOD (304) may be changed when there is a portion of the laser pulse (402) having a temporal optical power profile that is not substantially horizontally flat and varies during the slice period in order to produce a laser pulse (404) having at least a substantially horizontally flat temporal optical power profile, the amplitude of the applied driving signal(s) may be changed in any other way to produce a laser pulse (404) having a different temporal optical power profile that is approximately or not consistent with the temporal optical power profile of the portion of the laser pulse (402) present during the slice period.

[0092] Temporal optical wave of a laser pulse that can be generated by a laser source (104) woah As much as pulse shape information describing or approximating the profile, such pulse shape information can be accessed by the controller (318). Then, the controller (318) can generate data characterizing the temporal amplitude profile of at least one driving signal to be generated by at least one RF driver (e.g., the first RF driver (314), the second RF driver (316), or a combination thereof), thereby generating a laser pulse (404) having a desired temporal optical power profile that does not match the temporal optical power profile of a portion of the generated laser pulse (402). Then, the controller (318) can output the data to the appropriate RF driver in the form of a command signal to the RF driver.

[0093] VII. Additional Comments

[0094] Generally, the controller (118) includes one or more processors that operate to generate the above-mentioned command and control signals (e.g., during the execution of one or more commands). The processor may be provided as a programmable processor that operates to execute commands (e.g., one or more general-purpose computer processors, microprocessors, digital signal processors, or programmable logic devices (PLDs), central processing units (CPUs), graphics processing units (GPUs), acceleration processing units (APUs), real-time processing units (RPUs), field programmable gate arrays (FPGAs), field programmable object arrays (FPOAs), application-specific integrated circuits (ASICs) (including digital, analog, and mixed analog / digital circuits), etc., or any other suitable form of circuit including any combination thereof). The execution of commands may be performed on a single processor or distributed among a number of processors in parallel across a processor within a device or a network of devices, or a combination thereof.

[0095] Generally, instructions may be implemented in software (e.g., executable code, files, library files, etc., or any combination thereof), hardware configurations (e.g., in the case of FPGAs, ASICs, etc.), or any combination thereof, which can be easily identified by an expert from the description provided herein (e.g., written in hardware description languages ​​such as C, C++, Visual Basic, Java, Python, Tel, Perl, Scheme, Ruby, assembly language, LUCID, VHDL, or VERILOG). Software is generally stored in one or more data structures delivered by a tangible medium, such as computer memory, which is accessible by the processor (e.g., via one or more wired or wireless communication links). Examples of tangible media include magnetic media (e.g., magnetic tape, hard disk drive, etc.), optical disks, volatile or non-volatile semiconductor memory (e.g., RAM, ROM, NAND flash memory, NOR flash memory, SONOS memory, etc.) or any combination thereof, and may be accessed locally, remotely (e.g., through a network), or any combination thereof.

[0096] Although various embodiments of the present invention have been described above in relation to operating the AOD scanning system (300) when a laser pulse (402) is present, it will be understood that these embodiments can likewise be implemented to operate the AOD scanning system (300) when a CW or QCW beam of laser energy is present. Likewise, although beam trap training has been described above in relation to deflecting the laser energy beam appearing as a heat of the laser pulse (402) in relation to FIGS. 13 and FIGS. 14, it will be understood that beam trap training techniques can be used when the laser energy beam generated by the laser source (104) appears as a CW or QCW beam of laser energy. Additionally, FIGS. 4, 6, 7 and 14 illustrate embodiments in which the first AOD (302) is driven at a higher transmission level than the second AOD (304), but the first AOD (302) and the first AOD (304) same It will be understood that the second AOD (304) can be driven at a transmission level higher than the first AOD (302), or the first AOD (302) can be driven alternately and repeatedly at a transmission level higher than the second AOD (304) and a transmission level lower. Furthermore, in order to ensure that the sliced ​​laser pulse (404) has a consistent temporal optical power profile or any other desired or appropriate distribution of the temporal optical power profile over a continuous pulse slice, the embodiments discussed above regarding the acquisition and processing of pulse shape information and the adjustment of the temporal optical profile may be applied to a CW or QCW beam of laser energy.

[0097] VIII. Conclusion

[0098] The foregoing is illustrative of embodiments and examples of the present invention and should not be construed as limiting. Although some specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily understand that many modifications and other embodiments of the disclosed embodiments and examples are possible without substantially departing from the novel teachings and benefits of the present invention. For example, although an embodiment relating to a training operation has been described above as being used with the beam positioner shown in FIG. 3, it will be understood that the first AOD (200) in the beam positioner (106) shown in FIG. 2 may also be driven to perform the training operation described herein. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the claims. For example, those skilled in the art will understand that any sentence, paragraph, example, or subject of an embodiment may be combined with the subject of any other sentence, paragraph, example, or embodiment, in whole or in part (except where such combinations are mutually exclusive). Accordingly, the scope of the present invention shall be determined by the following claims, and equivalents to the claims shall also be included in the claims.

Claims

Claim 1 A system comprising: a first acousto-optic deflector (AOD) that operates to diffract an incident laser energy beam to generate and output a first laser energy beam and a second laser light beam therefrom; a second AOD that is positioned to receive the first laser energy beam and operates to diffract the received first laser energy beam to generate and output a third laser energy beam and a fourth laser energy beam therefrom; at least one first beam trap that is positioned and configured to absorb the second laser energy beam output from the first AOD; at least one second beam trap that is positioned and configured to absorb the fourth laser energy beam output from the second AOD; and a controller that is communicably connected to the first AOD and the second AOD, wherein the controller is configured to operate the first AOD without operating the second AOD. Claim 2 A system according to claim 1, wherein at least one selected from the group consisting of the first AOD and the second AOD comprises an AO cell formed of a material sensitive to thermal lensing when laser energy is present. Claim 3 A system according to claim 1, wherein at least one selected from the group consisting of the first AOD and the second AOD comprises an AO cell formed of germanium. Claim 4 A system according to claim 1, wherein the controller is configured to operate the first AOD without operating the second AOD during a first period, and also to operate the first AOD while operating the second AOD during a second period. Claim 5 In paragraph 4, the system, wherein the second period is after the first period. Claim 6 In claim 1, a portion of the incident laser energy beam can be characterized by a first temporal optical power profile, and the controller is further configured to simultaneously operate the first AOD and the second AOD to generate at least one laser pulse from the incident laser energy beam, and the at least one laser pulse has a second temporal optical power profile, and the first temporal optical power profile and the second temporal optical power do not match, a system. Claim 7 In paragraph 6, the system wherein the laser energy beam is a quasi-continuous wave (QCW) beam of laser energy. Claim 8 In paragraph 6, the above first temporal optical power profile is a non-flat system. Claim 9 In paragraph 6, the above second temporal optical power profile is at least substantially flat, system. Claim 10 A system according to claim 1, wherein the laser energy beam appears as a sequence of laser pulses capable of propagating along a beam path, and a plurality of laser pulses are temporally separated from each other by an interval between pulses, and the controller is further configured to operate the first AOD and the second AOD during the interval between pulses by driving the first AOD and the second AOD at a plurality of frequencies. Claim 11 As a system, a first AOD that operates to diffract an incident laser light beam to generate and output a first laser light beam and a second laser light beam therefrom; a second AOD that is positioned to receive the first laser light beam and operates to diffract the received first laser light beam to generate and output a third laser light beam therefrom; at least one first beam trap that is positioned and configured to absorb the second laser light beam output from the first AOD; and at least one training beam trap that is positioned and configured to absorb the third laser light beam output from the second AOD. A system comprising a controller that is communicatably connected to the first AOD and the second AOD, wherein the controller is configured to command a first RF driver to apply a first driving signal to a transducer of the first AOD and also to command a second RF driver to apply a second driving signal to a transducer of the second AOD, wherein the controller operates the first AOD to diffract the incident laser light beam along a training beam path to the second AOD by applying the driving signal to the transducer of the first AOD and the driving signal to the second AOD during a high state of a laser trigger command, and wherein the second AOD is configured to diffract the laser light beam from the first AOD along a training beam path to a training beam trap, and wherein the driving signal is modulated through an RF frequency of a certain range to control a temperature gradient within the first AOD and the second AOD.

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