Method and apparatus for thermally stable AOD operation - Patents.com

Abstract

The system includes 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, a second AOD arranged to receive the first laser energy beam and for generating and output a third laser energy beam and a fourth laser energy beam by diffracting the received first laser energy beam, 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 communicatively coupled to the first AOD and the second AOD, the controller configured to operate the first AOD without operating the second AOD.

Description

[Technical field]

[0001] I.Technical field SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate generally to acousto-optic deflectors, laser processing devices incorporating same, and methods of operating same. [Background technology]

[0002] II. Description of Related Art 1, a laser processing apparatus 100 capable of processing a workpiece 102 often includes, among other components, a laser source 104, a positioner 106, and a scan lens 108. The apparatus also typically includes a controller 110 capable of controlling the operation of the laser source 104 and the positioner 106. The positioner 106 can reflect, refract, and / or diffract the laser energy beam to deflect a beam path 112 traversed by laser energy in the laser energy beam as it propagates from the laser source 104 to the scan lens 108. The laser energy deflected to the scan lens 108 is focused by the scan lens 108 and directed to propagate along a beam axis to reach the workpiece 102.

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

[0004] As will be appreciated by those skilled in the art, an AOD utilizes a diffraction effect caused by one or more acoustic waves propagating through the AO cell to diffract an incident optical wave (i.e., in the context of this application, a laser energy beam) propagating simultaneously through the AO cell. When the AOD is driven to diffract an incident laser energy beam, a diffraction pattern is generated that typically includes a zeroth order diffraction peak and a first order diffraction peak, and may also include other higher order (e.g., second order, third order, etc.) diffraction peaks. In general, the amount of optical power diffracted into the first order diffraction peak (e.g., compared to the zeroth order diffraction peak) depends on the manner in which the AOD is driven to diffract the incident laser energy beam. As is known in the art, the portion of the diffracted laser energy beam in the zeroth order diffraction peak is referred to as the "zeroth order" beam, and the portion of the diffracted laser energy beam in the first order diffraction peak is referred to as the "first order" beam, and so forth. In general, the zeroth order beam and the other diffraction order beams (e.g., first order beams) 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, the first order beam propagates along the first order beam path, and so on.

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

[0006] The AO cell of the AOD absorbs a portion of the laser energy beam propagating through it. If the power of the laser energy beam is high enough, the absorbed energy can locally heat the material forming the AO cell, causing 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 and of itself. If the thermal gradient within the AO cell is relatively constant and unchanging (e.g., while processing the workpiece 102), wavefront distortion effects (e.g., focusing effects, defocus effects, or other wavefront distortions as described above) can typically be taken into account to ensure that the workpiece 102 is satisfactorily processed. However, if the thermal gradient within the AO cell is not relatively constant and varies, it becomes very difficult to adequately compensate for the changes in the wavefront distortion effects.

[0007] 2, the optical component 208 ensures that the optical power incident on the AO cell of the second AOD 202 is substantially constant, but the position at which the zero order beam path 204 incidents on the AO cell of the second AOD 202 may vary slightly over time. It has been found that this can result in a thermal gradient within the AO cell of the second AOD 202 that is not suitably constant and unchanging, ultimately resulting in an asymmetric energy distribution (about the optical axis of the laser energy beam) in the laser energy irradiated on the workpiece 102, which in turn reduces the ability of the second AOD 202 to accurately deflect the beam path 112. Summary of the Invention

[0008] overview One embodiment of the present invention can be characterized as a system comprising a first acousto-optic deflector (AOD) for generating and outputting a first laser energy beam and a second laser light beam by diffracting an incident laser energy beam; a second AOD arranged to receive the first laser energy beam and for generating and outputting a third laser energy beam and a fourth laser energy beam by diffracting the received first laser energy beam; 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 communicatively coupled to the first AOD and the second AOD, the controller configured to operate the first AOD without operating the second AOD.

[0009] Another embodiment of the invention may be characterized as a system comprising a first AOD capable of generating and outputting a first and a second laser light beam by diffracting an incident laser light beam, a second AOD arranged to receive the first laser light beam and capable of generating and outputting a third laser light beam by diffracting the received first laser light beam, at least one first beam trap arranged and configured to absorb the second laser light beam output from the first AOD, at least one exercise beam trap arranged and configured to absorb the third laser light beam output from the second AOD, and a controller communicatively coupled to the first and second AODs, the controller configured to direct a first RF driver to apply a first drive signal to a transducer of the first AOD and to direct a second RF driver to apply a second drive signal to a transducer of the second AOD. The controller is operable to operate the first AOD to diffract the incident laser light beam along an exercise beam path to the second AOD, the second AOD configured to diffract the laser light beam from the first AOD along the exercise beam path to an exercise beam trap, the drive signal being modulated through a range of RF frequencies to control temperature gradients within the first AOD and the second AOD. [Brief description of the drawings]

[0010] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 illustrates diagrammatically a related art laser processing apparatus in which a positioner according to an embodiment of the present invention may be incorporated and operated in accordance with an embodiment of the present invention.

[0011] [Diagram 2] FIG. 2 is a schematic diagram of a positioner according to the related art.

[0012] [Diagram 3] FIG. 3 illustrates a schematic diagram of a positioner according to one embodiment of the present invention.

[0013] [Figure 4] FIG. 4 illustrates a timing diagram for performing a pulse slicing operation according to one embodiment of the present invention.

[0014] [Diagram 5] FIG. 5 illustrates a timing diagram for performing an optical exercise operation according to one embodiment of the present invention.

[0015] [Figure 6-7] 6 and 7 show timing diagrams for performing pulse slicing and optical exercise operations according to embodiments of the present invention.

[0016] [Figure 8] FIG. 8 illustrates a laser energy monitoring system according to one embodiment of the present invention.

[0017] [Figure 9-10] 9 and 10 illustrate aspects of a pulse shape analysis process using, among other components, the laser energy monitoring system shown in FIG. 8, in accordance with one embodiment of the present invention.

[0018] [Figure 11] FIG. 11 shows a timing diagram for performing pulse slicing for non-uniform incident power to an AOD scanning system.

[0019] [Figure 12] FIG. 12 illustrates a timing diagram for performing an RF exercise operation according to an embodiment of the present invention.

[0020] [Figure 13]FIG. 13 illustrates a schematic diagram of a positioner according to another embodiment of the present invention.

[0021] [Figure 14] FIG. 14 illustrates a timing diagram for performing pulse slicing and RF exercise operations according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Detailed Description Exemplary embodiments will now be described with reference to the accompanying drawings, in which, unless explicitly stated, the sizes, positions, etc. of components, features, elements, etc. and the distances therebetween are not necessarily to scale and have been exaggerated for ease of understanding.

[0023] The terms used in the specification are for the purpose of describing particular exemplary embodiments only and are not intended to be limiting. As used herein, the singular is intended to include the plural unless the content clearly indicates otherwise. Furthermore, it should be understood that the terms "comprises" and / or "comprising", when used herein, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise indicated, when a range of values ​​is described, the range includes the upper and lower limits as well as any subranges between the upper and lower limits of the range. Unless otherwise indicated, terms such as "first" and "second" are only used to distinguish elements from one another. For example, one node may be referred to as a "first node" and similarly another node may be referred to as a "second node" or vice versa. Section headings used herein, unless otherwise noted, are for organizational purposes only and should not be construed as limiting the subject matter described.

[0024] Unless otherwise indicated, "about," "around," "substantially," and the like mean that amounts, sizes, formulations, parameters, and other quantities and characteristics are not, and need not be, precise and may be approximate and / or larger or smaller, as appropriate or to reflect tolerances, conversion factors, rounding, measurement errors, and the like, as well as other factors known to those of ordinary skill in the art.

[0025] Spatially relative terms such as "below," "lower," "lower side," "upper," and "above" may be used herein for ease of description in describing the relationship of an element or feature to other elements or features as depicted in the figures. It should be understood that spatially relative terms are intended to include different orientations in addition to those depicted in the figures. For example, an element described as being "below" or "below" another element or feature would be oriented "above" the other element or feature if the object in the figure were inverted. Thus, the exemplary term "below" may include both an upward and downward orientation. If an object is oriented in another way (e.g., rotated 90 degrees or at another orientation), the spatially relative descriptors used herein may be interpreted accordingly.

[0026] Like numbers refer to like elements throughout the drawings, and thus the same or similar numbers may be described with reference to other drawings even if not mentioned or described in the corresponding drawing, and elements that are not numbered may be described with reference to other drawings.

[0027] It will be appreciated that many different forms and embodiments are possible without departing from the spirit and teachings of this disclosure, and that the disclosure should not be construed as limited to the example embodiments set forth herein, but rather, these examples and embodiments are provided so that this disclosure will be complete and all-inclusive, and will fully convey the scope of the disclosure to those skilled in the art.

[0028] I. Discussion of Positioners in General According to an embodiment of the present invention, the AOD scanning system in the positioner 106 described above with respect to Figure 1 may be provided as exemplarily shown in Figure 3 (i.e., as AOD scanning system 300). With reference to Figure 3, the AOD scanning system 300 includes a first AOD 302 positioned and configured to deflect the beam path 112 along a first axis, and a second AOD 304 positioned and configured to deflect the beam path 112 along a second axis (e.g., orthogonal to the first axis). In Figure 3, the zero order beam path of the first AOD 302 is identified at 306, and the zero order beam path of the second AOD 304 is identified at 308. Similarly, the primary beam path of the first AOD 302 is identified as 112' and the second AOD 304 is identified as 112". As can be appreciated, each of the primary beam path 112' and the primary beam path 112" represent specific examples of beam paths along which a laser energy beam can propagate (e.g., towards the scan lens 108). Accordingly, each of the beam path 112' and the beam path 112" may be collectively referred to herein as "beam path 112", and thus the first AOD 302 is positioned and configured to deflect the primary beam path 112' along a 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 a second axis of the AOD scanning system 300.

[0029] Additionally, the AOD scanning system 300 shown in FIG. 3 includes a first beam trap 310 positioned and configured to block laser energy propagating along the zeroth order beam path 306 (including laser energy propagating along the second or higher order beam paths) without blocking laser energy propagating along the first order beam path 112′. Similarly, the AOD scanning system 300 includes a second beam trap 312 positioned and configured to block laser energy propagating along the zeroth order beam path 308 (including laser energy propagating along the second or higher order beam paths) without blocking laser energy propagating along the first order beam path 112″. Although not shown, the AOD scanning system 300 may further include a galvanometer mirror scanning system (e.g., including a pair of galvanometer mirrors positioned and configured to deflect a laser energy beam along two axes, as known in the art) located optically downstream of the second AOD 304 in the beam path 112″.

[0030] In general, the AO cells of each of the first and second AODs 302 and 304 are formed from a material that is susceptible to thermal lensing (e.g., as described above) when a laser energy beam having a sufficiently high optical power propagates along the beam path 112. For example, the AO cells of each of the first and second AODs 302 and 304 may be formed from crystalline germanium. In this example, the laser energy beam propagating along the beam path 112 would have a wavelength in the range of 2 μm (or thereabouts) to 20 μm (or thereabouts) and would have a sufficiently high average power (e.g., 150 W or thereabouts or more) to cause thermal lensing in the AO cells of the first and second AODs 302 and 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 suitably high power carbon dioxide or carbon monoxide gas laser. Typically, high power carbon dioxide or carbon monoxide gas lasers are configured to produce a continuous wave (CW) or quasi-CW (QCW) laser energy beam, or to produce a laser energy beam made up of discrete pulses (typically tens of microseconds or longer in length).

[0031] Although not shown, each of the first AOD 302 and the second AOD 304 includes at least one transducer attached to its AO cell. Typically, the transducer is a piezoelectric transducer capable of vibrating in response to an externally applied RF signal (i.e., drive signal). The transducer is attached to the AO cell of the AOD to generate a corresponding acoustic wave that propagates within the vibrating transducer AO cell. As will be appreciated 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 in the applied drive signal.

[0032] The drive signal may be applied to the input of the transducer by an associated RF driver. Thus, the AOD scanning system 300 may include, for example, a first RF driver 314 electrically connected to each transducer of the first AOD 302, and a second RF driver 316 electrically connected to each transducer of the second AOD 304. In general, each of the RF driver 314 and the second RF driver 316 may include an RF combiner, an amplifier coupled to the output of the RF combiner, and an impedance matching circuit coupled to the output of the amplifier. The RF combiner (e.g., a DDS combiner) generates and outputs a preliminary signal at a desired frequency, and the amplifier converts the preliminary signal to a drive signal by amplifying the preliminary signal to a desired amplitude, and the drive signal is applied to the input of the transducer via the impedance matching circuit.

[0033] The operation of the first RF driver 314 and the second RF driver 316 may be controlled in response to command signals output by a controller (e.g., controller 318) to generate drive signals of different frequencies and amplitudes. The drive signals may be applied to the respective transducers of the respective AODs at high speeds (e.g., up to 1 MHz or higher). Thus, the controller 318 replaces the controller 110 shown in FIG. 1 and may control the operation of the laser source 104 in addition to the operation of the AOD scanning system 300 and other scanning systems (e.g., galvanometer mirror scanning systems) of the positioner 106. For simplicity of the present disclosure, the act of applying drive signals to the transducers of the AODs is also referred to herein as "driving" the AODs. Thus, when the first AOD 302 is driven by a drive signal provided by the first RF driver 314, a portion of the laser energy incident on the AO cell of the first AOD 302 is diffracted and propagates along its first order beam path 112′ to the AO cell of the second AOD 304, and another portion of the incident laser energy propagates along the zero order beam path 306. When no drive signal is provided by the first RF driver 314, the laser energy incident on the AO cell of the first AOD 302 simply propagates along the zero order beam path 306. Similarly, when the second AOD 304 is driven by a drive signal provided by 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 first order beam path 112') is diffracted and propagates along its first order beam path 112" (and ultimately onto the scan lens 108), and another portion of the incident laser energy propagates along the zero order beam path 308. When no drive signal is provided 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.

[0034] In general, when the AOD is driven in response to an applied drive signal, the ratio of optical power diffracted into the first beam path 112 to the optical power in the zeroth beam path is determined by the amplitude of the RF power in the applied drive signal and, in some cases, the frequency of the RF power in the applied drive signal. Furthermore, the amount of optical power diffracted into the first beam path 112 increases with increasing RF power until it reaches a maximum value at some saturation level of RF power. The act of setting or modulating the amplitude of the RF power in the drive signal applied to the AOD is referred to herein as "amplitude modulation control." The act of setting or adjusting the amount of optical power diffracted into the first beam path 112 can be considered to set or adjust the "transmittance" of the AOD.

[0035] When an AOD includes multiple transducers, the transmissivity of the AOD may also be adjusted by applying a drive signal to each of the transducers. Each applied drive signal has the same RF frequency but is slightly out of phase with respect to one another. As a result, acoustic waves generated within the AO cells of the AOD interfere with each other in at least some destructive manner. Such destructively interfering acoustic waves have the effect of reducing the transmissivity of the AOD, and the degree to which the AOD transmissivity is reduced corresponds to the degree to which the acoustic waves destructively interfere with each other within the AO cells. The act of selecting or modulating the phase relationship of the drive signals applied to different transducers of a common AOD is referred to herein as "phase modulation control." It should be noted, however, that phase modulation control cannot be used to completely prevent optical power from being diffracted into the primary beam path 112.

[0036] By sequentially driving the first AOD 302 and the second AOD 304 with drive signals of different frequencies, the AOD scanning system 300 can be operated to rapidly deflect the primary beam path 112" at different angles to different positions within a two-dimensional scan field. Furthermore, the amplitude of the RF power in each drive signal sequentially applied to the first AOD 302 and / or second AOD 304 can be varied (if necessary) as a function of the frequency of the drive signal to ensure that the amount of optical power propagating along the primary beam path 112" is at least substantially constant, regardless of the frequency of the drive signals applied to the first AOD 302 and the second AOD 304.

[0037] According to embodiments described herein, the laser energy beam propagating along 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 the 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 time-sliced ​​laser energy pulses from the incident beam. These time-sliced ​​laser energy pulses are output from the AOD scanning system 300 along beam path 112″ and propagate towards the scan lens 108.

[0038] For example, with reference to FIG. 4, the laser source 104 is operated to generate a laser energy beam including a laser pulse 402 (e.g., in response to an initial transition of a laser trigger command signal 400 output by the controller 318 to the laser source 104 from a low state to a high state). As illustratively illustrated, 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 in the laser pulse 402 first rises at time t2 before reaching a substantially constant level (e.g., from time t3 to time t6). At time t6 (i.e., when the laser trigger command signal 400 transitions from a high state back to a low state), the optical power of the laser pulse 402 begins to decay. For example, at time t7, the optical power of the laser pulse 402 decays to zero or a negligible value. In this specification, the portion of laser pulse 402 between time t2 and time t3 is referred to as the "head" of laser pulse 402, and the portion of laser pulse 402 between time t6 and time t7 is referred to as the "tail" of laser pulse 402. In this specification, the portion of laser pulse 402 between time t3 and time t6 (i.e., the portion of laser pulse 402 between the head and tail of laser pulse 402) is referred to as the "main" of laser pulse 402.

[0039] 4 shows the laser trigger command signal in a constant "on" state for the duration of the command, it will be understood that the laser trigger command signal can be modulated (e.g., pulse width modulated) as desired (e.g., to prevent the laser source 104 from overheating, to adjust the optical power generated by the laser source, to vary the pulse duration of the laser pulses generated in the laser source 104, or the like, or any combination thereof). Additionally, although FIG. 4 shows only a single laser pulse 402 in the laser energy beam generated by the laser source 104 in response to the laser trigger command signal 400, it will be understood that a series of laser trigger command signals, such as laser trigger command signal 400, can be output to the laser source 104, and the laser source 104 will generate a laser energy beam including a series of laser pulses, such as laser pulse 402.

[0040] 3 and 4, to generate a pulse 404 that is time-sliced ​​from the main portion of the laser pulse 402, during at least one common period 406 (also referred to herein as a "slice period"), the first AOD 302 and the second AOD 304 are driven (in response to drive signals provided by the first RF driver 314 and the second RF driver 316, respectively) so that laser energy incident on the AO cells of the first AOD 302 and the second AOD 304 is diffracted and propagates along the respective first order beam paths 112' and 112" . Laser energy that is not diffracted by the first AOD 302 and the second AOD 304 to the first order beam paths 112' or 112" (e.g., laser energy propagating along the zero order beam paths 306 and 308) is blocked by the first beam trap 310 and the second beam trap 312. In the example timing diagram shown in Figure 4, the first AOD 302 and the second AOD 304 diffract the 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 of these pulses 404 has a pulse duration at least approximately equal to the length of the associated slice period 406. It should be understood that the first AOD 302 and the second AOD 304 may be driven for more or less than two slice periods 406, each slice period 406 may have any length, and different slice periods 406 may have the same or different lengths.

[0041] In Figure 4, the temporal transmission profile of the first AOD 302 (i.e., the transmission of the first AOD 302 as a function of time) obtained by applying a drive signal to the first AOD 302 from the first RF driver 314 is shown by line 408. Similarly, the temporal transmission profile of the second AOD 304 (i.e., the transmission of the second AOD 304 as a function of time) obtained by applying a drive signal to the second AOD 304 from the second RF driver 316 is shown by line 410. Thus, Figure 4 illustrates an example in which two separate drive signals are applied to each of the first AOD 302 and the second AOD 304. Two separate drive signals are applied to the first AOD 302 to generate acoustic waves therein during the first slice period 406 described above and to generate acoustic waves therein during the second slice period 406 described above, and two separate drive signals are applied to the second AOD 304 to generate acoustic waves therein during the first slice period 406 described above and to generate acoustic waves therein during the second slice period 406 described above.

[0042] For ease of discussion herein, the drive signal applied to the first AOD 302 to impart a rising edge to the time transmission profile depicted by 408 will be assumed to have the same frequency, and the drive signal applied to the second AOD 304 to impart a rising edge to the time transmission profile depicted by 410 will be assumed to have the same frequency. However, the frequency of the drive signal applied to the first AOD 302 to impart a rising edge to the time transmission profile depicted by 408 during the first slice period 406 may alternatively be different from the frequency of the drive signal applied to the first AOD 302 to impart a rising edge to the time transmission profile depicted by 408 during the second slice period 406. Similarly, the frequency of the drive signal applied to the second AOD 304 to impart a rising edge to the time transmission profile depicted by 410 during the first slice period 406 may be different from the frequency of the drive signal applied to the second AOD 304 to impart a rising edge to the acoustic wave depicted by 410 during the second slice period 406. In these alternative cases, the amplitude and / or phase of the drive signals applied to the first AOD 302 and / or second AOD 304 can be set (e.g., as described above) to give the time transmission profile depicted by 408 and 410 a rise during the first slice period and the second slice period 406 so as to ensure that (in embodiments in which the first AOD 302 and / or the second AOD 304 include multiple converters) the average optical power of the laser pulses 404 generated during the first slice period 406 is at least substantially identical to the average optical power of the laser pulses generated during the second slice period 406.

[0043] 4, there is a minimum time delay between successive slice periods 406 (i.e., between times t4 and t5). This minimum time delay (also referred to herein as a “slice delay”) is selected to be long enough (e.g., equal to, close to, or between 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs, etc., 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 AOD optical aperture) to allow any transient acoustic waves in the AO cell of the first AOD 302 at the end of a previous slice period 406 to dissipate before the first AOD 302 is driven to diffract when the subsequent slice period 406 begins. Taking into account the duration of the main portion of the laser pulse 402, the number of slice periods 406 present in the main portion of the laser pulse 402, and the slice delay between successive slice periods 406, the slice periods 406 generated from a common laser pulse 402 may have a length of 0.1 μs or more (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, etc., or any value between these values).

[0044] Provided as described above, the first beam trap 310 of the AOD scanning system 300 blocks the zero-order beam path 306 from reaching the AO cell of the second AOD 304, thereby avoiding the problem discussed above with respect to Fig. 2 (regarding a thermal gradient in the AO cell of the second AOD 304 that is not preferably constant or stationary). 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, while the AO cell of the second AOD 304 is only exposed to laser energy propagating from the first AOD 302 along the primary beam path 112'. That is, the AO cell of the second AOD 304 is only exposed to laser energy when the first AOD 302 is driven by the first RF driver 314 to generate a primary beam propagating along the primary beam path 112'.

[0045] II. Discussion of Optical Exercises Because the AO cells of the second AOD 304 are formed from a material that is susceptible to thermal lensing in the presence of laser energy propagating along the primary beam path 112′ from the first AOD 302, the AO cells of the second AOD 304 may or may not introduce wavefront distortion effects as described above into the laser energy beam propagating along the primary beam path 112″ (and ultimately to the scan lens 108) from the second AOD 304, depending on how the first AOD 302 was previously driven. For example, prior to time t1 in FIG. 4 , the laser source 104 generates a laser energy beam including a series of laser pulses propagating along the beam path 112, but the first AOD 302 and the second AOD 304 are coupled together during a slicing period as described above to generate a sliced ​​pulse, such as pulse 404. is not activated, there is no thermal gradient in the AO cells of the second AOD 302 that can induce thermal lensing effects in the AO cells of the second AOD 304 just prior to the start of the first slice period (i.e., time t3). However, a thermal gradient may develop or evolve in the AO cells of the second AOD 304 during the first slice period (if the first slice period is long enough) or during subsequent slice periods (if successive slice periods are long enough and close enough in time). Thus, the thermal gradient in the AO cells of the second AOD 304 is not relatively constant, resulting in undesirable changes in wavefront distortion effects in the laser energy beam propagating from the second AOD 304 along the primary beam path 112″ (and ultimately to the scan lens 108).

[0046] To prevent or beneficially reduce undesirable development of thermal gradients in the AO cells of the second AOD 304, the first AOD 302 is activated (in response to one or more drive signals provided by the first RF driver 314 as commanded by the controller 318) during one or more periods (each of which is referred to herein as an “optical exercise period”) outside the slice periods. However, the second AOD 304 is not activated during the optical exercise periods. Thus, during the optical exercise periods, laser energy incident on the AO cells of the first AOD 302 is diffracted (e.g., as described above) and propagates along the respective primary beam paths 112′. The AO cells of the second AOD 304 then absorb a portion of the laser energy propagating along the primary beam paths 112′ of the first AOD 302, resulting in localized heating of the AO cells of the second AOD 304 (and thermal lensing within the AO cells of the second AOD 304). Heating the second AOD 304 in this manner may be described herein as optically “exercising” the second AOD 304 .

[0047] In general, the timing and length of the optical exercise periods are selected to ensure that thermal gradients within the AO cell of the second AOD 304 are relatively constant over time such that changes in wavefront distortion effects are negligible or sufficiently reduced to ensure sufficient processing of a workpiece such as the workpiece 102. For example, prior to time t1 in FIG. 4, the controller 318 may control operation of the laser source 104 to generate a laser energy beam including one or more laser pulses 402 propagating along the beam path 112, but may not control the AOD scanning system 300 (or to drive the first AOD 302) to generate sliced ​​pulses such as pulse 404 from the laser pulses 402. In this example, no thermal gradients that may induce thermal lensing effects within the AO cell of the second AOD 304 are present within the AO cell of the second AOD 304 at the start of the first slice period described above with respect to FIG. 4 (i.e., time t3 in FIG. 4). However, a thermal gradient that may induce a thermal lensing effect may develop or evolve within the AO cells of the second AOD 304 during the first slice period described above with respect to FIG. 4 (assuming the first slice period is sufficiently long) or during slice periods following the first slice period (assuming successive slice periods are sufficiently long and sufficiently close in time).

[0048] To prevent or beneficially reduce undesirable development of thermal gradients in the AO cells of the second AOD 304 during a slice period or over successive slice periods, the controller 318 may perform an optical exercise operation, for example as shown in Fig. 5, by controlling the operation of the first RF driver 314 to drive the first AOD 302 (during the optical exercise period 500) to diffract the incident laser energy of each of the laser pulses 402 generated before the above-mentioned time t1 into its primary beam path 112' so as to propagate the primary beam from the first AOD 302 to the AO cells of the second AOD 304. Such driving of the first AOD 302 is exemplarily shown in Fig. 5, although only a single laser pulse 402 is shown for simplicity. 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 exercise 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.

[0049] 5 shows that the optical exercise period 500 lasts for the entire length of the laser pulse 402 (including the entire head and tail of the laser pulse 402), it will be appreciated that the optical exercise period 500 may be shorter than the entire length of the laser pulse 402, or the first AOD 302 may be activated during successive optical exercise periods that span the duration of the pulse 402. In this case, the first AOD 302 may not be activated during all or a portion of the head of the laser pulse 402, during all or a portion of the tail of the laser pulse 402, during all or a portion of the laser pulse 402 between the head and tail, or any combination thereof.

[0050] As mentioned above, although FIG. 4 shows only a single laser pulse 402 in the laser energy beam generated by the laser source 104, typically a series of laser trigger command signals 400 are output to the laser source 104 such that the laser source 104 generates a laser energy beam including a series of laser pulses 402, such as, for example, shown in FIG. 6. If the length between successively generated laser pulses 402 is long enough, a thermal gradient in the AO cell of the second AOD 304 during a preceding slice period 406 (e.g., slice period 406′ as shown in FIG. 6) associated with a preceding laser pulse 402 (e.g., laser pulse 402′ as shown in FIG. 6) may dissipate or decrease in an undesirable manner before a slice pulse such as pulse 404 is generated during a subsequent slice period 406 (e.g., slice period 406″ as shown in FIG. 6) associated with a subsequent laser pulse 402 (e.g., laser pulse 402″ as shown in FIG. 6). As a result, the wavefront distortion effect imparted to the pulse 404 by the AO cells of the second AOD 304 during the preceding slice period 406' may be different from that imparted to the pulse 404 by the AO cells of the second AOD 304 during the subsequent slice period 406". As can be appreciated, each of the laser pulses 402' and 402" represents an example of a laser pulse and therefore may also be referred to collectively as laser pulse 402 in this specification.

[0051] To prevent or beneficially reduce undesirable dissipation or reduction of thermal gradients in the AO cell of the second AOD 304 between slice periods associated with successively generated laser pulses 402 (e.g., between slice periods 406′ and 406″ associated with laser pulses 402′ and 402″, respectively), the controller 318 controls the first AOD 302 to propagate the primary beam from the first AOD 302 to the AO cell of the second AOD 304, and / or to diffract incident laser energy in the tail of the laser pulse 402′ into its primary beam path 112′. Alternatively, one or more optical exercise operations may be performed, for example as shown in FIG. 6, by controlling the operation of the first RF driver 314 to drive the first AOD 302 to diffract the incident laser energy at the tail of the laser pulse 402' (and / or to diffract the incident laser energy at the head of the laser pulse 402"). Thus, the period during which the first AOD 302 is driven to diffract the incident laser energy at the tail of the laser pulse 402' (and / or to diffract the incident laser energy at the head of the laser pulse 402") is an example of the "optical exercise period" described above.

[0052] 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 exercise, so that all laser energy incident on the AO cell of the second AOD 304 during the optical exercise 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 at the head of the laser pulse 402′ into its primary beam path 112′ (and / or diffract the incident laser energy at the tail of the laser pulse 402″) so as to propagate the primary beam from the first AOD 302 to the AO cell of the second AOD 304 as needed or desired.

[0053] 6, the controller 318 controls the operation of the first RF driver 314 to provide a time delay between the optical exercise period and the subsequent successive slice period (and vice versa). If there is a time delay between the optical exercise period 500 and the subsequent successive slice period 406 (such as between the optical exercise period 500 and the slice period 406" associated with the laser pulse 402"), the length of the time delay is sufficiently long (e.g., equal to, close to, or between 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs, etc., 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) to allow the transient acoustic wave in the AOD of the first AOD 302 at the end of the optical exercise period 500 to dissipate before the first AOD 302 is driven to diffract when the subsequent successive slice period 406 begins. If there is a time delay between a slice period 406 and a subsequent successive optical exercise period 500 (such as between a slice period 406' and an optical exercise period 500 associated with a laser pulse 402'), the length of the time delay may be shorter than, equal to, or longer than the first time delay.

[0054] 6 shows that only one optical exercise period 500 occurs during the head or tail of the laser pulse 402, it will be understood that multiple intermittent optical exercise periods 500 may occur during any head or tail of the laser pulse 402. Additionally, while FIG. 6 shows that the optical exercise period 500 associated with the laser pulse 402 lasts for less than the entire head or tail of the laser pulse 402, it will be understood that the optical exercise period 500 associated with the laser pulse 402 may last for the entire head or tail of the laser pulse 402.

[0055] 4 and 6 show an embodiment in which the pulse slicing operation is performed such that the slice period 406 occupies the entire duration of the laser pulse 402 between the head and tail, excluding the slice delay therebetween as described above. However, in other embodiments, the controller 318 may cause one or more pulse slicing operations to be performed such that there is at least one period between the head and tail of the laser pulse 402 that is longer than (or is shorter than) twice the length of the slice delay and that is located outside the slice period. Such a period is referred to below as a "non-slice period." The controller 318 may cause an optical exercise operation (e.g., as described above) to be performed during a non-slice period, provided that there is a first time delay (e.g., as described above) between the associated optical exercise period 500 and the subsequent slice period. For example, a non-slice period is exemplarily identified in FIG. 7 as 700, and an optical exercise operation is performed during the optical exercise period 500 within the non-slice period 700. As shown in Figure 7, there is a first time delay between the optical exercise period 500 occurring during the non-slice period 700 and the subsequent slice period 406''', and there is also a time delay between the optical exercise period 500 occurring during the non-slice period 700 and the preceding slice period 406. Also, as shown in Figure 7, optical exercise operations may be performed at the head and / or tail of the laser pulse 402 (e.g., in the manner exemplarily described above with respect to Figure 6).

[0056] From the embodiments described above, it will be appreciated that the controller 318 may be configured to perform one or more optical exercise operations (as described above) over the entire non-slicing period, over the entire head of the laser pulse, over the entire tail of the laser pulse, or over any combination thereof. In other embodiments, the controller 318 causes the optical exercise operations to be performed only during a portion of the non-slicing period, only during a portion of the head of the laser pulse, only during a portion of the tail of the laser pulse, or any combination thereof. In embodiments where the controller 318 causes the optical exercise operations to be performed only during a portion of the non-slicing period (rather than the entire non-slicing period), only during a portion of the head of the laser pulse (rather than the entire head of the laser pulse), and / or only during a portion of the tail of the laser pulse (rather than the entire tail of the laser pulse), the optical exercise period 500 may be referred to as a "adjusted optical exercise period" 500.

[0057] According to an embodiment of the present invention, the length of the adjusted optical exercise period 500 during which the optical exercise operation is performed may correspond to the optical power of the laser pulse (e.g., the laser pulse 402) during the adjusted optical exercise period 500. For example, less laser energy is diffracted to the AO cell of the second AOD 304 during the adjusted optical exercise period 500 occurring near the beginning of the head (or near the end of the tail) of the laser pulse 402 compared to the adjusted optical exercise period 500 occurring near the end of the head (or near the beginning of the tail) of the laser pulse 402. Thus, the controller 318 may be configured to perform the optical exercise operation during a relatively long adjusted optical exercise period 500 occurring near the beginning of the head of the laser pulse 402 or during a relatively short adjusted optical exercise period 500 occurring near the end of the head of the laser pulse 402. Similarly, the controller 318 may be configured to perform optical exercise operations during relatively short adjusted optical exercise periods 500 occurring near the beginning of the tail of the laser pulse 402 or during relatively long adjusted optical exercise periods 500 occurring near the end of the tail of the laser pulse 402.

[0058] According to other embodiments of the present invention, the length of the conditioning optical exercise period 500 during which the optical exercise operation is performed may also correspond to an actual or predicted thermal gradient in the AO cell of the second AOD 304 immediately prior to the conditioning optical exercise period 500. To improve the performance of the optical exercise operation during the conditioning optical exercise period, the controller 318 may have pulse shape information describing the temporal optical power profile of the laser pulse 402 (i.e. from the beginning of the head to the end of the tail) or the amount of energy in the laser pulse 402 at various temporal "slices" of the laser pulse 402 (or may have access to such information, for example, via one or more wired or wireless networks, not shown).

[0059] III. Discussion of Pulse Shape Information in General As described above, the controller 318 may have pulse shape information (or may have access to such information, for example, via one or more wired or wireless networks, not shown) to improve performance of the optical exercise operation during the conditioning optical exercise period. The controller 318 may receive information indicative of pulse shape information associated with the laser pulses generated by the laser source 104, or may derive such pulse shape information based on the received information. Such received information may be entered by a user (e.g., via a user interface, not shown, of the device 100), read from a computer file set by an operator or technician of the device 100 and sent or transmitted to the controller 318, or any combination thereof.

[0060] The pulse shape information may be stored (e.g., in a computer memory of the controller 318 or in a look-up table or other data structure accessible to the controller 318) in association with other information (also referred to herein as “supplemental information”) describing the laser parameters at which the laser pulses 402 in the laser energy beam are generated (e.g., the pulse duration of the laser pulses 402 generated by the laser source 104, the pulse repetition frequency at which the laser pulses 402 are generated, the average power at which the laser pulses 402 are generated, etc., or any combination thereof). The controller 318 may then use the supplemental information, optionally associated with the pulse shape information, to determine when and how long to perform the optical exercise operation (i.e., the length of the adjustment optical exercise period 500) between generating the sliced ​​pulses 404 from the laser pulses 402 in order to maintain a substantially constant thermal gradient within the AO cell of the second AOD 304 during operation of the apparatus 100.

[0061] A. Discussion of the Generation of Pulse Shape Information In one embodiment, the pulse shape information may be generated using any known or suitable laser energy monitoring system incorporated within the AOD scanning system 300 or within an apparatus 100 that includes the AOD scanning system 300. For example, referring to Figure 8, a laser energy monitoring system 800 according to one embodiment of the present invention includes a mirror 802 and a laser sensor 804.

[0062] Mirror 802 is disposed in beam path 806 and is provided as a partially transmitting mirror configured to reflect (to beam path 806r) a majority of the light in an incident laser energy beam propagating along beam path 806 and transmit a small amount of light (e.g., 2% or thereabouts) to beam path 806t. In FIG. 8, beam path 806 can be either the zeroth order beam path 306 or 308 or either the first order beam path 112' or 112". Thus, beam path 806r can propagate to the first beam trap 310 (if beam path 806 is the zeroth order beam path 306), to the second beam trap 312 (if beam path 806 is the zeroth order beam path 308), to the second AOD 304 (if beam path 806 is the first order beam path 112'), or to the scan lens 108 or other optical component located optically downstream of the AOD scanning system 300 (if beam path 806 is the first order beam path 112").

[0063] The laser sensor 804 is positioned to receive the laser energy transmitted through the mirror 802 (e.g., propagating along beam path 806t). In one embodiment, the laser sensor 804 is configured to measure the instantaneous optical power in the incident laser energy beam and generate sensor data based on the detection or measurement. The sensor data may be output to the controller 318 by any suitable means (e.g., via wired or wireless communication as known in the art). The controller 318 stores the sensor data (e.g., locally within the controller 318, on a computer memory within the device 100 accessible to the controller 318, on a computer memory located remotely from the device 100 but communicatively connected to the device 100 via one or more networks) as pulse shape information describing the temporal optical power of the laser energy incident on the laser sensor 804 over a set length of time (e.g., during a temporal "slice" of the laser pulse 402, as described in more detail below).

[0064] In another embodiment, the sensor data output to the controller 318 may be further processed (e.g., time integrated) to obtain the energy content of the laser energy beam incident on the laser sensor 804 over a set length of time. In this embodiment, the processed sensor data may be stored (e.g., as described above) as pulse shape information describing the amount of energy within the laser pulse energy (e.g., during a temporal "slice" of the laser pulse 402, as described in more detail below) over a set length of time.

[0065] In other embodiments, the laser sensor 804 is provided as an integrating detector (e.g., configured to measure the instantaneous optical power of the laser energy beam incident thereon and integrate the measured optical power to obtain an energy content of the beam to generate sensor data). The sensor data may be output to the controller 318 by any suitable means (e.g., via wired or wireless communication as known in the art) and stored (e.g., as described above) as sensor data as pulse shape information describing the amount of energy in the laser energy over a set length of time (e.g., during a temporal "slice" of the laser pulse 402, as described in more detail below).

[0066] In one embodiment, the laser source 104, the AOD scanning system 300, and the laser energy monitoring system 800 may be operated to perform a pulse shape analysis process to generate pulse shape information. During the pulse shape analysis process, the laser source 104 is operated (e.g., as described above) to generate a laser energy beam that includes a series of laser pulses 402 generated under a particular set of laser parameters. For example, all of the laser pulses in the series of laser pulses may have the same (or substantially the same) pulse duration, and all of the laser pulses may be generated at the same (or substantially the same) pulse repetition frequency.

[0067] The AOD scanning system 300 operates (e.g., as described above) to propagate laser energy in each laser pulse 402 of a series of laser pulses along the beam path 806 during at least one period (each period is also referred to herein as a temporal "slice" of the laser pulse 402 described above, or more simply, a "slice window") during the pulse shape analysis process. When the laser energy is propagating along the beam path 806, the slice window can be considered "open". When the laser energy is not propagating along the beam path 806, the slice window can be considered "closed". The duration of each slice window can be equal to, close to, or between 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs, 0.05 μs, etc. All slice windows generated during a series of laser pulses have the same length.

[0068] When the slice window is open, the laser sensor 804 generates sensor data and outputs it to the controller 318. The sensor data is stored (e.g., as described above) in association with slice information describing the temporal aspects of the slice window during which the sensor data was generated along with other information, such as the supplemental information described above. Examples of slice information include the time the slice window opened (e.g., relative to when the laser trigger command signal transitioned from a low state to a high state), the time the slice window closed (e.g., relative to when the laser trigger command signal transitioned from a low state to a high state), the length of the slice window, or any combination thereof.

[0069] Generally, the length 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 different laser pulses 402 in the series of laser pulses 402 open and close at different times such that the sensor data generated by the laser sensor 804 effectively represents all portions of a representative laser pulse 402 in the series of laser pulses 402. For example, with reference to FIG. 9 , the laser source 104 operates (e.g., as described above) to generate a laser energy beam including a plurality of laser pulses 402 (for simplicity, only a first laser pulse 402′ and a second laser pulse 402″ in the series of laser pulses are shown). The AOD scanning system 300 operates (e.g., as described above) to propagate laser energy along the beam path 806 in at least one slice window associated with each laser pulse in the series of laser pulses (e.g., in a first slice window 900′ associated with the first laser pulse 402′ and a second slice window 900″ associated with the second laser pulse 402″). As will be appreciated, each of slice windows 900′ and 900″ represent an example of a slice window and thus may be referred to collectively as slice windows 900 in this specification. The position of the second slice window 900" within the temporal optical power profile of its associated laser pulse 402" is offset in time, as shown at 902, relative to the position of the first slice window 900' within the temporal optical power profile of its associated laser pulse 402'. This offset is generally equal to the length of the slice window, but may be less than or greater than the length of the slice window.The AOD scanning system 300 further operates to propagate laser energy of subsequent laser pulses 402 in the series of laser pulses along the beam path 806 in slice windows that are offset from one another (e.g., as described above) such that slice windows 900 are generated (and thereby sensor data is generated) for every portion of a laser pulse representing every laser pulse 402 in the series of laser pulses 402 (see, e.g., FIG. 10 ).

[0070] IV. Discussion of RF Exercise As discussed above, the AO cells of each of the first AOD 302 and the second AOD 304 are formed from a material that is susceptible to thermal lensing in the presence of laser energy propagating along the beam path 112 or along the primary beam path 112'. However, driving the first AOD 302 and the second AOD 304 also heats the AO cells therein sufficiently to create thermal gradients that can induce thermal lensing, as discussed above. The characteristics of the thermal gradient within the AO cells of an AOD change depending on how the AOD is driven (e.g., considering the amount and frequency of RF energy applied to the AOD during a slice period). However, the thermal gradient within the AO cell that induces the thermal lensing effect can dissipate in the absence of laser energy propagating therethrough (e.g., during the period between time t17 of pulse 402' and time t22 of pulse 402", when the AOD is not activated, 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). As a result, the thermal gradients in the AO cells of the first AOD 302 and the second AOD 304 when a pulse slicing operation is performed (e.g., for laser pulse 402'' as shown in FIG. 6) may differ in an undesirable manner from the thermal gradients in the AO cells of the first AOD 302 and the second AOD 304 when a pulse slicing operation is performed (e.g., for laser pulse 402' as shown in FIG. 6). As a result, over a period of time as laser energy from successive laser pulses 402 propagates through the AO cells of the first AOD 302 and the second AOD 304, the thermal gradients in these AO cells may change in an undesirable manner, causing inconsistent deflection of the laser pulses 402 entering the AOD scanning system 300.

[0071] The first AOD 302 and the second AOD 304 may be driven during inter-pulse intervals to prevent or minimize undesired changes in thermal gradients within the AO cells of the first AOD 302 and the second AOD 304 over the period during which laser energy from successive laser pulses 402 propagates therethrough. As used herein, "inter-pulse interval" refers to a period during which laser energy from successive laser pulses 402 does not propagate within the first AOD 302 and the second AOD 304 (e.g., the interval 600 occurring during the period between time t7 of pulse 402' and time t2 of pulse 402" shown in FIG. 6). Driving the first AOD 302 and the second AOD 304 during the inter-pulse interval 600 is referred to herein as "RF exercise," and this RF exercise may be performed during an RF exercise operation.

[0072] 12, the controller 318 may cause an RF exercise operation to be performed during an inter-pulse interval, such as inter-pulse interval 600. In FIG. 12, the drive signal applied from the first RF driver 314 to the first AOD 302 includes a first RF exercise pulse 1202, and the drive signal applied from the second RF driver 316 to the second AOD 304 includes a second RF exercise pulse 1204. As shown in FIG. 12, the period during which the first RF exercise pulse 1202 and the second RF exercise pulse 1204 are applied is referred to herein as an RF exercise period 1200. The timing and length of the RF exercise period 1200 may be selected to ensure that the thermal gradient within the AO cell of the second AOD 304 is relatively constant over time, such that changes in wavefront distortion effects are negligible or sufficiently reduced to ensure sufficient machining of a workpiece, such as the workpiece 102.

[0073] The controller 318 controls the operation of the first RF driver 314 and the second RF driver 316 to provide a time delay between the RF exercise period 1200 and the subsequent successive slice period (which occurs after time t22 as described above). In general, the length of the time delay should be long enough (e.g., greater than, equal to, close to, or between 2 μs, 1 μs, 0.5 μs, 0.25 μs, 0.1 μs, 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 apertures of the AODs) to allow transient acoustic waves in the AO cells of the first AOD 302 and the second AOD 304 at the end of the RF exercise period 1200 to dissipate before the first AOD 302 and the second AOD 304 are activated to diffract when the slice period 406 begins. Although not shown, it should be understood that the drive signals applied to the first AOD 302 and the second AOD 304 may include other RF pulses of any suitable frequency, amplitude and length (as symbolically represented by dashed lines) to generate the laser pulses 404 described above, or to perform any of the optical exercise operations described above, or the like, or any combination thereof.

[0074] The amplitude and length of the first and second RF exercise pulses 1202, 1204 may also be selected in any desired or useful manner to ensure that the thermal gradients in the AO cells of the first and second AODs 302, 304 are relatively constant over time such that changes in wavefront distortion effects are negligible or sufficiently reduced to ensure sufficient machining of a workpiece such as the workpiece 102. In the embodiment shown in FIG. 12, the first and second RF exercise pulses 1202, 1204 are shown as step functions. Alternatively, the amplitudes of the first and second RF exercise pulses 1202, 1204 may be shaped in other ways (e.g., sinusoidally) to achieve a desired thermal gradient in the AO cells. In yet other embodiments, the RF exercise pulses 1202 and 1204 may have different lengths.

[0075] The RF frequency components of the RF exercise pulses 1202 and 1204 may also be selected in any desired or beneficial manner. In some cases (e.g., depending on the configuration of the transducer attached to the AO cell, the efficiency with which the transducer can inject acoustic waves into the AO cell, etc.), the absorption of RF energy by the AO cell may depend on the frequency of the drive signal. In one embodiment, the RF exercise pulses 1202 and 1204 may include a subset of one or more discrete frequencies in a frequency band, or may include all such discrete frequencies. Furthermore, the frequencies of the RF exercise pulses 1202 and 1204 applied during different RF exercise periods may be the same or different. That is, the frequency (or frequencies) of the RF exercise pulse applied during a first RF exercise period may be the same or different from the frequency (or frequencies) of the RF exercise pulse applied during a second RF exercise period. For example, during the first RF exercise period 1200, a first frequency subset may be output to the transducers of the first AOD 302 and / or the second AOD 304 throughout the entire RF exercise period 1200. During a subsequent RF exercise period 1200, a second subset of frequencies (which may or may not include some of the same frequencies that were included in the first subset) is output to the transducers of the first AOD 302 and / or the second AOD 304.

[0076] In other embodiments, RF exercise pulses 1202 and 1204 may include some or all of the frequencies within a particular frequency band by chirping or "smearing" the frequency of the RF exercise pulse during the RF exercise period. Creating and delivering such chirped or "smeared" RF exercise pulses may be beneficial over RF exercise pulses that include one or more discrete frequencies (each also referred to herein as a "discrete frequency RF exercise pulse") when the discrete frequency RF exercise pulses emit undesirable levels of electromagnetic radiation (e.g., that may interfere with electronic devices near the laser processing apparatus 100).

[0077] Although the RF exercises have been described above with respect to AOD scanning system 300, it will be appreciated that the RF exercises may be performed with any system having any number of suitably arranged AODs (e.g., a system having only one AOD or a system having more than two AODs).

[0078] V. Discussion on Beam Trap Exercise As discussed above, optical exercises may be beneficially used to maintain the thermal state of the AO cells in the first AOD 302 and the second AOD 304 when laser energy propagating therein is not propagating to the workpiece 102. Also, as discussed above, RF exercises may be utilized to maintain the thermal state of the AO cells in the first AOD 302 and the second AOD 304 when laser energy is not propagating in the first AOD 302 or the second AOD 304 (and thus is not propagating to the workpiece 102), for example, during the inter-pulse intervals discussed above.

[0079] However, there may be situations where it is desirable to prevent laser energy from being applied to the workpiece 102 while the laser source 104 generates a laser energy beam (e.g., to maintain stable operation of the laser source 104) unless the optical exercise is effective or feasible for a relatively long period of time (e.g., because the second AOD 304 is not activated during a relatively long period of time when the first AOD 302 is activated). Such situations may arise, for example, during workpiece processing where a long distance occurs between features formed in succession on the workpiece when the processed workpiece is removed from (or loaded into) the system. To maintain the thermal state of the AO cells in the first AOD 302 and the second AOD 304 during such situations, referring to FIG. 13, the AOD scanning system 1300 may be provided as exemplarily described with respect to the AOD scanning system 300, but may further include a third beam trap 1302 (also referred to herein as the “exercise beam trap 1302”) positioned and configured to block laser energy propagating thereto. The first AOD 302 and second AOD 304 of the AOD system 1300 may be driven to deflect the primary beam path 112" to the exercise beam trap 1302 (e.g., as shown by arrow 1304) such that the exercise beam trap 1302 blocks laser energy propagating along the primary beam path 112". Driving the first AOD 302 and second AOD 304 in this manner is referred to herein as a "beam trap exercise", and this beam trap exercise may be performed during a beam trap exercise operation.

[0080] 14, the controller 318 may perform a beam trap exercise operation by controlling the operation of the first RF driver 314 and the second RF driver 312 to provide drive signals to the first AOD 302 and the second AOD 304 while the laser energy in a series of multiple sequentially generated laser pulses 402 propagates inside the AO cell. In FIG. 14, the optical power in the primary beam path 112″ deflected into the exercise beam trap 1302 is shown by line 1400.

[0081] The amplitude of the drive signals applied to the first AOD 302 and the second AOD 304 may be constant or may vary in any desired or beneficial manner to ensure that the thermal gradient within the AO cells of the first AOD 302 and the second AOD 304 is 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 adequately processed.

[0082] In one embodiment, phase modulation control is additionally utilized while driving the first AOD 302 and / or the second AOD 304 to reduce the optical power propagating along the beam path 112'' to the exercise beam trap 1302. This may be desirable if the average or peak power in the laser energy that would propagate along the beam path 112'' to the exercise beam trap 1302 would damage or degrade the beam trap 1302 to an undesirable extent.

[0083] 14, the length of the drive signals provided from the first RF driver 314 and the second RF driver 316 to the first AOD 302 and the second AOD 304, respectively, is significantly longer than the length of a single laser pulse 402. In the illustrated embodiment, the drive signals provided from the first RF driver 314 and the second RF driver 316 at a time are synchronized to the start of the head portion of the laser pulse 402 incident on the AO cell of the first AOD 302 (i.e., at time t12, which corresponds to time t2 described above). However, in other embodiments, the drive signals may be provided before time t12 (e.g., between time t12 and time t11, which corresponds to time t1 described above, or before time t11).

[0084] As should be apparent, the frequencies of the respective drive signals provided by the first RF driver 314 and the second RF driver 316 are selected to direct laser energy propagating along the primary beam path 112″ to the exercise beam trap 1302. In general, the frequency of the drive signal provided by the first RF driver 314 (also referred to herein as the “first frequency”) can be any frequency within a first frequency range. Similarly, the frequency of the drive signal provided by the second RF driver 316 (also referred to herein as the “second frequency”) can be any frequency within a second frequency range. The bandwidth of the first frequency range can be wider than, equal to, or narrower 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 other embodiments, the first frequency range does not overlap with the second frequency range (ie, frequencies included in the first frequency range are not included in the second frequency range, and vice versa).

[0085] The RF frequency content of the drive signals applied to the first AOD 302 and the second AOD 304 during the beam trapping exercise operation may be selected in any desired or useful manner. For example, the drive signal applied to the first AOD 302 may include one or more discrete frequencies within a first frequency range, or may include multiple frequencies within the first frequency range that are chirped or "smeared" as described in the above embodiment for the RF exercise. Similarly, the drive signal applied to the second AOD 304 may include one or more discrete frequencies within a second frequency range, or may include multiple frequencies within the second frequency range that are chirped or "smeared" as described in the above embodiment for the RF exercise.

[0086] While the beam trap exercise has been described above as involving the use of an exercise beam trap in connection with an AOD scanning system 1300 including an exercise beam trap 1302, it will be understood that in other embodiments, the exercise beam trap 1302 may be replaced with one or more optical components (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 the beam trap exercise operation and redirect the laser energy to the first beam trap 310 or the second beam trap 312. In yet other embodiments, the second beam trap 312 may be configured to block laser energy propagating along the primary beam path 112" from the second AOD 304 during the beam trap exercise operation.

[0087] Although the beam trapping exercise is described above in relation to the AOD scanning system 1300, it will be appreciated that the RF exercise may be performed with any system having any number of suitably arranged AODs (e.g., a system having only one AOD or a system having more than two AODs) and a beam trap. Furthermore, although Figure 14 shows an embodiment in which the beam trapping exercise is performed to deflect two successive laser pulses 402 into the beam trap 1302, it will be appreciated that the beam trapping exercise may be performed to deflect any number of such laser pulses 402 into the beam trap 1302.

[0088] VI. Discussion on Adjusting the Temporal Optical Power Profile As described above, the temporal transmission profiles of the first AOD 302 and the second AOD 304 during the slice period, depicted by 408 and 410, respectively, are constant (or at least substantially constant) during the entire slice period 406. As a result, the temporal optical power profile of the laser pulse 404 generated during the slice period (i.e., the optical power as a function of time of the laser pulse 404 output from the AOD scanning system 300) is approximately congruent with the temporal optical power profile of the portion of the laser pulse 402 incident on the AOD scanning system 300 during the slice period. For example, during any of the slice periods shown in Figures 4-7 or 8-10, the temporal optical power profiles of the laser pulse 402 incident on the AOD scanning system 300 and the laser pulse 404 output from the AOD scanning system 300 are essentially horizontally flat, indicating that the optical power in the incident laser pulse 402 and the output laser pulse 404 is approximately constant during the slice period 406. Thus, the temporal optical power profiles of portions of the laser pulses 402 during different slice periods will be the same (or approximately equal), and the temporal optical power profiles of the laser pulses 404 generated during those slice periods will also be the same (or approximately equal). Ensuring that the temporal optical power profiles of the laser pulses 404 generated during the slice periods are the same (or approximately equal) can be beneficial in facilitating the development of laser-based processes for forming features in a workpiece (e.g., for forming through or blind vias in a workpiece such as a printed circuit board or integrated circuit board) or for forming multiple features using different laser pulses 404 sliced ​​from a common laser pulse 402.

[0089] However, the optical power of the main portion of the laser pulse 402 often varies in an undesirable manner, resulting in the temporal optical power profiles of portions of the laser pulse 402 during different slicing periods being sufficiently different from one another that it becomes difficult to efficiently develop a laser-based process to form multiple features using different laser pulses 404 sliced ​​from a common laser pulse 402. In certain embodiments, the temporal optical power profile of the laser pulse 402 can be adjusted by modifying the manner in which the laser source 104 is operated (e.g., by varying the optical power of the laser pulses generated, by varying the pulse repetition rate, by varying the pulse duration of the laser pulses generated, by modulating the duty cycle of a laser trigger command signal provided to the laser source 104 (e.g., via pulse width modulation), the like, or any combination thereof).

[0090] As an alternative (or in relation to) modifying the operation of the laser source 104, the amplitude and / or phase during the slice period 406 of the drive signal applied to the first AOD 302 and / or second AOD 304 (in embodiments in which the first AOD 302 and / or second AOD 304 include multiple transducers), which induces a rise in the temporal transmission profile depicted by 408 and / or 410, respectively, may be varied during the slice period 406 (e.g., as described above). According to an embodiment of the invention, the amplitude and / or phase of the drive signal applied to the first AOD 302 and / or second AOD 304 during the slice period 406 may be varied such that the temporal optical power profile of the laser pulse 404 generated during the slice period 406 is not substantially congruent with the temporal optical power profile of the portion of the laser pulse 402 incident on the AOD scanning system 300 during the slice period 406.

[0091] For example, referring to FIG. 11, it can be seen that the optical power of the laser pulse 402 varies significantly (e.g., steadily decreases from a relatively high optical power "Hi" at time t3 described above to a relatively low optical power "Lo" at time t6 described above, where the optical power Lo can be in the range of 5% to 15% lower than the optical power Hi). If the temporal transmission profiles of the first AOD 302 and the second AOD 304 during the first slice period 406 described above were constant, the optical power of the laser pulse 404 generated during the first slice period 406 would undesirably vary over the length of the first slice period (e.g., steadily decrease to produce a temporal optical power profile congruent with the temporal optical power profile of the portion of the laser pulse 402 incident on the AOD scanning system 300 during the first slice period 406). Similarly, if the temporal delivery profile during the second slice period 406 described above were constant, the optical power of the laser pulses 404 generated during the second slice period 406 would undesirably vary over the length of the second slice period (e.g., steadily decrease to produce a temporal optical power profile congruent with the temporal optical power profile of the portion of the laser pulses 402 incident on the AOD scanning system 300 during the second slice period 406). Furthermore, if the pulse durations of the laser pulses 404 generated during the first slice period and the second slice period 406 were equal, the laser pulses 404 generated during the second slice period 406 would undesirably have lower pulse energy than the laser pulses 404 generated during the first slice period 406.

[0092] 11, the temporal transmission profile of each drive signal applied to the first AOD 302 during the first and second slice periods 406 may be varied (e.g., using amplitude modulation control, phase modulation control, or a combination thereof) such that the temporal optical power profile of the laser pulses 404 generated during the first and second slice periods 406 is at least substantially horizontally flat (i.e. substantially constant over time). For example, amplitude modulation control and / or phase modulation control may be used 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 is the inverse of the temporal optical power profile of the portion of the laser pulses 402 incident on the AOD scanning system 300 during the first and second slice periods 406. Additionally, the amplitude and / or phase modulation control can be performed such that the temporal optical power of the laser pulses 404 generated during the first slice period and the second slice period 406 is at least substantially equal. As a result, the laser pulses 404 generated during the second slice period 406 preferably have the same pulse energy as the laser pulses 404 generated during the first slice period 406, assuming equal pulse durations of the laser pulses 404 generated during the first slice period 406.

[0093] While FIG. 11 illustrates an embodiment in which the optical power of the laser pulse 402 is seen to decrease steadily, it will be understood that the optical power of the laser pulse 402 may increase steadily or may decrease or increase in a sinusoidal, quasi-random or other non-linear manner, the like, or a combination thereof, depending on one or more factors such as the laser source 104 used to generate the laser energy beam, the method of operating the laser source 104, the temperature of the laser source 104, the environmental conditions of the environment surrounding the laser source 104 (e.g., humidity, temperature), and the like, or a combination thereof.

[0094] Furthermore, while FIG. 11 illustrates an embodiment in which the temporal transmission profile of the first AOD 302 during the first slice period and the second slice period 406 is varied to ensure that the temporal optical power profile of the laser pulses 404 generated during the first slice period and the second slice period 406 is at least substantially horizontally flat, it will be appreciated that alternatively or in addition, the temporal transmission profile of the second AOD 304 during the first slice period and the second slice period 406 may be varied to achieve the same purpose.

[0095] Finally, although it has been described above that the temporal transmission profile of the first AOD 302 and / or the second AOD 304 may be varied in the presence of a portion of a laser pulse 402 having a temporal optical power profile that is not substantially horizontally flat, which is changed during the slice period to generate a laser pulse 404 having at least a substantially horizontally flat temporal optical power profile, it will be appreciated that the amplitude of the applied drive signal may be varied in any other manner to generate a laser pulse 404 having another temporal optical power profile that may or may not be approximately congruent to the temporal optical power profile of the portion of the laser pulse 402 present during the slice period.

[0096] To the extent that the pulse shape information describes or approximates a temporal optical power profile of a laser pulse generateable by the laser source 104, such pulse shape information can be accessed by the controller 318. The controller 318 can then generate data characterizing a temporal amplitude profile of at least one drive signal generated by at least one RF driver (e.g., the first RF driver 314, the second RF driver 316, or a combination thereof) such that a laser pulse 404 is generated having a desired temporal optical power profile that is not congruent with the temporal optical power profile of a portion of the laser pulse 402 generated therefrom. The controller 318 can then output the data to the appropriate RF driver in the form of a command signal for the RF driver.

[0097] VII. Additional Comments In general, the controller 118 includes one or more processors operable to generate the command and control signals described above (e.g., upon execution of one or more instructions). The processor may be provided as a programmable processor operable to execute instructions (e.g., one or more general purpose computer processors, microprocessors, digital signal processors, or any suitable form of circuitry (including digital, analog, mixed analog / digital circuitry) including programmable logic devices (PLDs), central processing units (CPUs), graphic processing units (GPUs), advanced processing units (APUs), real-time processing units (RPUs), field programmable gate arrays (FPGAs), field programmable object arrays (FPOAs), application specific integrated circuits (ASICs), or the like), or the like, or any combination thereof). Execution of instructions may occur on a single processor, distributed across multiple processors, in parallel across multiple processors within a device or across a network of devices, or the like, or any combination thereof.

[0098] Generally, instructions may be embodied as software (e.g., executable code, files, library files, etc., or any combination thereof), hardware configurations (e.g., in the case of FPGAs, ASICs, etc.), etc., which may be readily identified by one of ordinary skill in the art from the description herein (written in a hardware description language such as C, C++, Visual Basic, Java, Python, Tel, Perl, Scheme, Ruby, assembly language, LUCID, VHDL, VERILOG, etc.). Software is typically stored in one or more data structures carried by a tangible medium, such as computer memory, accessible by a 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 drives, etc.), optical disks, volatile or non-volatile semiconductor memory (e.g., RAM, ROM, NAND flash memory, NOR flash memory, SONOS memory, etc.), etc., or any combination thereof, which may be locally accessible or remotely accessible (e.g., over a network), or any combination thereof.

[0099] 1-11 in the context of operating the AOD scanning system 300 in the presence of laser pulses 402, it will be appreciated that these embodiments may be similarly implemented to operate the AOD scanning system 300 in the presence of a CW laser energy beam or a QCW laser energy beam. Similarly, while the beam trapping exercise has been described above with reference to Figures 13 and 14 in the context of deflecting a laser energy beam represented by a laser pulse train 402, it should be appreciated that the beam trapping exercise technique may also be used when the laser energy beam generated by the laser source 104 is represented as a CW laser energy beam or a QCW laser energy beam. In addition, although Figures 4, 6, 7, and 14 show embodiments in which the first AOD 302 is driven to a higher transmission level than the second AOD 304, it will be appreciated that the first AOD 302 and the first AOD 304 may be driven to equal transmission levels, or the second AOD 304 may be driven to a higher transmission level than the first AOD 302, or the first AOD 302 may be driven alternately to higher and lower transmission levels than the second AOD 304. Furthermore, the embodiments described above with respect to obtaining and processing pulse shape information and adjusting the temporal optical profile may be applied to a CW or QCW laser energy beam to ensure that the sliced ​​laser pulse 404 has a constant temporal optical power profile or other desired or suitable temporal optical power profile distribution over successive pulse slices.

[0100] VIII. Conclusion The above describes embodiments and examples of the present invention and is not to be construed as being limiting thereto. Although several specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily recognize that many modifications are possible to the disclosed embodiments and examples and other embodiments without significantly departing from the novel teachings and advantages of the present invention. For example, while the embodiment relating to the exercise operation is 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 exercise 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 the subject matter of any sentence, paragraph, example, or embodiment may be combined with some or all of the subject matter of any other sentence, paragraph, example, or embodiment, except where such combinations would be mutually exclusive. Accordingly, the scope of the present invention should be determined by the following claims and any equivalents of such claims to be included therein.

Claims

1. a first acousto-optic deflector (AOD) operable to diffract an incident laser energy beam to generate and output a first laser energy beam and a second laser energy beam; a second AOD disposed to receive the first laser energy beam and operable to generate and output a third laser energy beam and a fourth laser energy beam by diffracting the received first laser energy beam; 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 beam of laser energy output from the second AOD; a controller communicatively coupled to the first AOD and the second AOD, the controller configured to operate the first AOD without operating the second AOD; A system comprising:

2. 2. The system of claim 1, wherein at least one selected from the group consisting of the first AOD and the second AOD includes an AO cell formed from a material susceptible to thermal lensing in the presence of the laser energy.

3. The system of claim 1 , wherein at least one selected from the group consisting of the first AOD and the second AOD includes an AO cell formed from germanium.

4. The controller operating the first AOD without operating the second AOD during a first period; Activating the first AOD while activating the second AOD during a second period. The system of claim 1 configured to:

5. The system of claim 4 , wherein the second period of time is after the first period of time.

6. the portion of the incident laser energy beam can be characterized by a first temporal optical power profile; 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; the at least one laser pulse has a second temporal optical power profile; the first temporal optical power profile and the second temporal optical power profile are not congruent; The system of claim 1 .

7. The system of claim 6 , wherein the laser energy beam is a quasi-continuous wave (QCW) laser energy beam.

8. The system of claim 6 , wherein the first temporal optical power profile is non-flat.

9. The system of claim 6 , wherein the second temporal optical power profile is at least substantially flat.

10. the laser energy beam is represented as a series of laser pulses propagated along a beam path, the laser pulses being separated in time from one another by inter-pulse intervals; the controller is further configured to operate the first AOD and the second AOD during the inter-pulse interval by driving the first AOD and the second AOD at a plurality of frequencies. The system of claim 1 .

11. a first AOD capable of diffracting an incident laser light beam to generate and output a first laser light beam and a second laser light beam therefrom; a second AOD arranged to receive the first laser light beam and capable of diffracting the received first laser light beam to generate and output a third laser light beam; at least one first beam trap arranged and configured to absorb the second laser light beam output from the first AOD; at least one exercise beam trap positioned and configured to absorb the third laser light beam output from the second AOD; a controller communicatively coupled to the first AOD and the second AOD, the controller configured to command a first RF driver to apply a first drive signal to a transducer of the first AOD and to command a second RF driver to apply a second drive signal to a transducer of the second AOD; wherein the controller During a high state of a laser trigger command, a drive signal can be applied to a transducer of the first AOD and a drive signal can be applied to the second AOD to operate the first AOD to diffract the incident laser light beam along an exercise beam path to the second AOD, the second AOD being configured to diffract the first laser light beam from the first AOD along the exercise beam path to an exercise beam trap, the drive signal being modulated through a range of RF frequencies to thereby control temperature gradients within the first AOD and the second AOD. system.

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