Laser device for performing laser modal shaping by using externally injected light spot

Abstract

The invention discloses a laser device for performing laser mode shaping by using an external injection light spot. The laser device comprises a laser cavity, end injection laser, a side pump source and a laser mode shaper, the laser cavity includes a gain medium surrounded by a pair of cavity mirrors and generates an output laser beam having a first wavelength in an axial direction of the laser cavity. The end-injection laser emits an end-injection laser beam having a second wavelength in an axial direction toward the laser cavity. The second wavelength is in an absorption band of the gain medium. The side pump source provides pump light for the gain medium and generates an output laser beam emitted from the laser cavity. The laser mode shaper is used for spatially redistributing the laser intensity of the end injection laser, so that the end injection laser beam emitted by the end injection laser and injected into the gain medium has the spatially redistributed intensity. The laser cavity is used for generating an output laser beam with an output mode, and the output mode is an injection mode for simulating an end injection laser beam projected to the gain medium, so that the generation of the required laser mode is relatively efficient and effective.

Description

Technical Field

[0001] This invention relates to a laser device, and more particularly to a laser device for laser mode shaping using an externally injected light spot. Background Technology

[0002] A laser is a device that generates coherent optical radiation. The coherence of laser radiation is manifested by a highly collimated radiation beam and a highly accurate radiation wavelength. The laser beam emitted from a laser cavity can be adjusted or configured to have different transverse modes suitable for different applications; a laser mode is a characteristic energy distribution of the electromagnetic radiation pattern within the laser cavity. Specifically, a laser cavity with a pair of planar cavity mirrors surrounding a large-diameter laser rod tends to generate a large number of transverse laser modes, resulting in complex transverse laser intensity outputs. In existing technologies, although it is possible to use an external cavity spatial light modulator to convert the existing laser output mode into an arbitrary laser mode, subsequent processing after laser generation wastes laser power, thus failing to effectively utilize valuable laser energy (see A. Forbes et al.'s paper "Creation and detection of optical modulators with spatial light modulators" in Advances in Optics and Photonics Vol.8, No.2, 2016). Generating arbitrary laser modes directly within a laser cavity using an intracavity spatial light modulator is relatively more efficient (see, for example, L Burger et al., "Implementation of a spatial light modulator for intracavity beam shaping", J. Opt. 17, (015604) 2015). However, the laser power of intracavity resonance is typically much higher than the output laser power. Therefore, the intracavity spatial light modulator is susceptible to damage from the high-intensity laser inside the laser cavity. Therefore, providing an effective and efficient solution to overcome the aforementioned drawbacks of the prior art, and to generate controlled laser modes from the laser cavity for specific applications, is an important issue in this technical field. In this invention, an external laser source and an external cavity spatial light shaper are combined to induce the desired laser mode from within the laser cavity. This invention avoids wasting valuable laser power, prevents intracavity laser damage as in the prior art, and offers a superior combination of simplicity, efficiency, and effectiveness compared to the prior art. Summary of the Invention

[0003] The purpose of this invention is to provide a laser device for laser mode shaping using an externally injected light spot.

[0004] This invention discloses a laser device for laser mode shaping using an externally injected laser spot, comprising a laser cavity, an end-injected laser, a side-pump source, and a laser mode shaper. The laser cavity includes a first cavity mirror that highly reflects a first wavelength, a second cavity mirror spatially spaced from the first cavity mirror and partially reflecting the first wavelength, and a gain medium located between the first and second cavity mirrors. The gain medium is used to generate laser light of the first wavelength, wherein the laser light travels along an axial direction extending from the first cavity mirror, passes through the gain medium, and reaches the second cavity mirror. The end-injected laser is used to emit an end-injected laser beam having a second wavelength toward the laser cavity in the axial direction. The side-pump source is used to provide pump light to the gain medium in a direction substantially angled to the axial direction, so that the gain medium generates an output laser beam of the first wavelength emitted from the second cavity mirror. The laser mode shaper is disposed between the end-injected laser and the first cavity mirror, and is used to spatially redistribute the laser intensity of the end-injected laser, so that the end-injected laser beam emitted via the end-injected laser and injected into the gain medium through the first cavity mirror has a spatially redistributed intensity. The laser cavity is used to generate the output laser beam having an output mode, the output mode being an injection mode simulating the end-injected laser beam projected onto the gain medium. In some embodiments, the laser mode shaper provides the end-injected laser beam with fixed spatial modulation or tunable spatial modulation to optimize the output mode of the output laser beam.

[0005] Preferably, in the laser device for laser mode shaping using an externally injected laser spot according to the present invention, the second wavelength emitted by the end-injected laser is within the absorption band of the gain medium.

[0006] Preferably, in the laser device for laser mode shaping using an externally injected laser spot according to the present invention, the gain medium absorbs the energy of the end-injected laser beam to induce one of spatially modulated laser gain and spatially modulated laser loss.

[0007] Preferably, in the laser device for laser mode shaping using an externally injected light spot according to the present invention, the gain medium of the laser is selected from any one of the following crystals: Nd:YAG, Nd:YAB, Yb:YAG, Ho / Cr / Tm:YAG, Nd:YVO4, Er:YAG, Cr:LiSAF, Ti:sapphire, Cr / Er:YSGG, Alexandrite, and Er:glass crystals.

[0008] Preferably, in the laser device for laser mode shaping using an external injection spot according to the present invention, the side pump source is used to emit pump light with a wavelength in the laser excitation band of the gain medium, and the side pump source can be selected from any one of a light-emitting diode (LED), a flash lamp, and a laser diode.

[0009] Preferably, in the laser device for laser mode shaping using an external injection spot according to the present invention, the laser mode shaper is a fixed pattern shield, so that the end-injected laser beam is transmitted to the gain medium in the desired laser mode.

[0010] Preferably, in the laser device for laser mode shaping using an externally injected light spot according to the present invention, the fixed pattern shield is formed on the surface of the first cavity mirror.

[0011] Preferably, in the laser device for laser mode shaping using an external injection spot according to the present invention, the laser mode shaper is a pixel-addressable spatial light modulator, so that the end-injected laser beam is transmitted to the gain medium in the desired laser mode, wherein the desired laser mode can be modulated by the pixel-addressable spatial light modulator.

[0012] Preferably, the laser device for laser modal shaping using an external injection spot according to the present invention further includes a laser modal imager and a feedback circuit, wherein the laser modal imager and the feedback circuit are disposed outside the laser cavity.

[0013] Preferably, in the laser device for laser modal shaping using an external injection spot according to the present invention, the laser modal imager includes an image sensor, which can acquire a feedback image of the output modality emitted from the second cavity mirror and transmit the feedback image to the laser modal shaper via the feedback line.

[0014] Preferably, in the laser device for laser mode shaping using an external injection spot according to the present invention, the laser mode shaper can also use an iterative algorithm to adjust the injection mode of the end-injected laser beam based on the feedback image, wherein the iterative algorithm includes comparing the feedback image of the desired laser mode with that of the output mode.

[0015] Preferably, the laser device for laser mode shaping using an external injection spot according to the present invention further includes a laser mode imager disposed outside the laser cavity and a feedback circuit.

[0016] Preferably, the laser device for laser modal shaping using an external injection spot according to the present invention includes an image sensor in the laser modal imager. The image sensor can acquire a feedback image of the output modality emitted from the second cavity mirror and send the feedback image to the laser modal shaper through the feedback line.

[0017] Preferably, the laser device for laser mode shaping using an external injection spot according to the present invention includes a laser mode shaper for transmitting the end-injected laser beam having the desired laser mode to the gain medium, and the laser mode shaper can further use an iterative algorithm to adjust the injection mode of the end-injected laser beam based on the feedback image, the iterative algorithm including comparing the feedback image of the desired laser mode with the output mode.

[0018] The advantages of this invention are that, unlike some existing technologies that employ external cavity mode converters, which require the removal of valuable laser power due to laser mode switching, the present invention discloses a more efficient, effective, and direct method of generating the desired laser mode from the laser cavity. Attached Figure Description

[0019] Other features and effects of the present invention will be clearly presented in the embodiments with reference to the accompanying drawings, wherein:

[0020] Figure 1 This is a schematic diagram of an example of an existing laser device;

[0021] Figure 2 This is a schematic diagram summarizing the various Ers-Gaussian modes generated by existing laser cavities;

[0022] Figure 3 This is a schematic diagram of a laser device with improved output mode control in the prior art;

[0023] Figure 4 This is a schematic diagram of an alternative version of the improved laser device;

[0024] Figure 5 This is a schematic diagram of another improved laser device with output mode control in the prior art;

[0025] Figure 6 This is a schematic diagram of a laser device of a first example according to the first embodiment disclosed in the present invention, showing a schematic diagram of laser mode shaping by shielding the opposite end of the laser beam via a fixed pattern.

[0026] Figure 7 This is a schematic diagram of a laser device of a second example according to the first embodiment disclosed in the present invention, and shows laser mode shaping using the end-injected laser beam through a coating on a first cavity mirror;

[0027] Figure 8 These are embodiments of the laser modality pattern that can be emitted by the laser modality shaper projection of the laser device according to the present invention.

[0028] Figure 9 This is a schematic diagram of a laser device according to a second embodiment of the present invention, and illustrates laser mode shaping using the end-injected laser beam via the tunable laser mode shaper;

[0029] Figure 10 This is a schematic diagram of a laser device according to a third embodiment of the present invention, including a feedback circuit for outputting an image. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] Before the invention is described in detail, it should be noted that reference numerals or the last part of reference numerals are used repeatedly in the figures where appropriate to indicate corresponding or similar components that may have similar properties.

[0032] According to one embodiment of the present invention, a laser device for laser mode shaping using an external injection spot includes: a laser cavity having a gain medium between two cavity mirrors; a side pump source for providing pump energy to the gain medium to generate a laser beam having a first wavelength; an end-injected laser for emitting an end-injected laser beam having a second wavelength; and a laser mode shaper disposed between the end-injected laser and the laser cavity. The laser mode shaper receives the end-injected laser beam to spatially adjust the intensity of the end-injected laser beam and emits the end-injected laser beam of the mode (hereinafter referred to as the "injection mode") to one end of the gain medium in the laser cavity. The laser cavity generates an output laser beam having a mode simulating the injection mode (hereinafter referred to as the output mode). In some embodiments, the end-injected laser beam is absorbed by the gain medium to provide additional laser gain or thermally induced refractive index modulation in the gain medium. It should be noted that in multi-mode laser cavities, such as large-area planar mirror cavities, the highest-gain laser mode is established first, and several other lower-gain laser modes are suppressed. The side-pumped source provides laser gain to all laser modes in the laser cavity, while the end-injected laser beam through the laser mode shaper can provide additional laser gain or laser loss modulation to establish the desired laser mode in the laser cavity. In one embodiment, the laser mode shaper emits a pattern of a fixed mode onto one end of the gain medium. In another embodiment, the laser mode shaper is an externally adjustable spatial light modulator that can project an adjustable mode pattern onto one end of the gain medium. In other embodiments, the laser mode imager, located at the output port of the laser cavity (i.e., at the end of the laser cavity emitting the output laser beam), sends a feedback image of the output mode back to the externally adjustable spatial light modulator via a feedback line to optimize the output mode using an iterative algorithm.

[0033] See Figure 1 , Figure 1This is an example of an existing laser device having a laser cavity 7 including a gain medium 72 disposed between a first cavity mirror 70 and a second cavity mirror 71. The gain medium 72 receives an end-pump light 74 or a side-pump light 75 to generate an output laser beam 77 traveling along an axial direction of the laser cavity 7. Generally, the first cavity mirror 70 is highly reflective of the wavelength emitted by the output laser beam 77, and the second cavity mirror 71 (or output coupler) is partially reflective of the wavelength of the output laser beam 77. To provide laser gain, the wavelengths of the end-pump light 74 and the side-pump light 75 need to be within a laser excitation band of the gain medium 72 to generate laser light, wherein the laser excitation band includes wavelengths of the end-pump light 74 and the side-pump light 75 that are strongly absorbed by the gain medium 72 to generate laser light. The optical amplification in the laser cavity 7 can be described by a first equation (Eq.(1)):

[0034]

[0035] Where P i With P o These represent the light entering and leaving the gain medium 72, respectively. g is the gain coefficient, α is the loss coefficient, and L is the length of the gain medium 72 in one axial direction. The gain coefficient g is a function of the pump wavelength and pump power. The loss coefficient α is related to the absorption, scattering, and output coupling of the second cavity mirror 71. For the laser to achieve resonant amplification, the laser gain must exceed the loss (i.e., g ≥ α). In ordinary lasers without mode control, there is a non-net-zero gain (i.e., g... net All laser modes (=g-α>0) have the opportunity to grow and compete to produce the output laser beam 77 with multiple mode superpositions. Although both the end-pump beam 74 and the side-pump beam 75 can provide laser gain to all possible laser modes, the side-pump beam 75 particularly promotes the growth of higher-order transverse modes of the laser cavity 7 in general lasers.

[0036] Figure 2 Some Ers-Gaussian laser modes were shown (using TEM). mn The Ers-Gaussian laser mode (TEM) is an intrinsic mode of a conventional laser cavity (e.g., laser cavity 7, where the laser propagates in the z direction) with xy-plane symmetry. Specifically, TEM represents transverse electromagnetic; however, for each laser mode, integers m and n represent TEM respectively. mn The horizontal (x) and vertical (y) ordinal numbers of the laser mode. For example, the fundamental transverse mode (i.e., TEM). 00 The mode (TEM) has a circular mode and is suitable for laser circular hole machining. It should be noted that the first higher-order mode (TEM)10 or TEM 01 Each laser cavity 7 has a node in the horizontal direction (m=1) or a node in the vertical direction (n=1). However, since the output mode generated by the laser cavity 7 is generated by competition among multiple laser modes in the laser cavity 7, it would be advantageous to control the gain and loss of a specific laser mode in the laser cavity 7 in order to generate the output laser beam with the desired mode.

[0037] See Figure 3 , Figure 3 It is an improved laser device that improves upon existing technology, enabling... Figure 1 A spatial filter 81 (or iris aperture) is provided in the laser cavity 7 shown. The spatial filter 81 introduces losses into undesirable laser modes (e.g., high-order laser modes with large mode regions), thereby establishing low-order laser modes (e.g., TEM) from mode competition within the laser cavity 7. 00 (Mode). In this scheme, the first equation (Eq.(1)) is corrected by the spatially dependent loss coefficient α(x,y) to obtain a second equation (Eq.(2)):

[0038]

[0039] Laser amplification exhibits spatial dependence, and some laser modes with large areas suffer more losses than others. However, in Figure 3 In the laser cavity 7, a portion of the laser light generated by the gain medium 72 is blocked by the spatial filter 81 within the laser cavity 7, thus reducing the overall efficiency of laser generation. Furthermore, the spatial filter 81 in the laser cavity 7 is susceptible to damage from high-energy laser power originating from within the laser cavity 7. See further... Figure 4 In alternative versions of the improved laser device, the spatial filter 81 and the first cavity mirror 70 are sometimes combined and collectively referred to as a laser beam shaper 89 (in... Figure 4(See L Burger et al., “Implementation of a spatial light modulator for intracavity beam shaping”, 2015 J.Opt.17015604), the laser beam shaper 89 can spatially modulate the laser beam in the laser cavity 7, making the output mode of the output laser beam 77 adjustable. In this scheme, the second equation (Eq.(2)) is used again, introducing spatially dependent amplification in the laser cavity 7 through the spatially correlated loss coefficient α(x,y). However, since the spatial filter 81 is usually made of liquid crystal or transmissive or reflective microstructures, the high-intensity laser power in the laser cavity 7 can easily damage the surface of the spatial filter 81.

[0040] See Figure 5 , Figure 5 This is an improved laser device based on existing technology, comprising an end-pump source 10, a laser cavity 9 having a gain medium 92 disposed between a first surface 90 and a second surface 91, and a focusing lens 6 disposed between the laser cavity 9 and the end-pump source 10. The first surface 90 is highly reflective of the wavelength of the emitted laser 97, and the second surface 91 is partially reflective of the wavelength of the emitted laser 97. The focusing lens 6 is used to focus the pump light received from the end-pump source 10 onto the gain medium 92 to form a circular pump point 15. Generally, the end-pump source 10 is a focusable diode laser beam capable of emitting a wavelength located in the laser excitation band of the gain medium 92. The focusable diode laser beam generates heat at the circular pump point 15 of the gain medium 92. In this scheme, the second equation (Eq.(2)) is replaced by the gain coefficient (g(I)). TEM00 Modify the code to obtain a third-party program (Eq.(3)), which is beneficial to the basic TEM of the laser cavity 9. 00 Modal growth

[0041]

[0042] Among them, I TEM00 The pump strength at the circular pump point 15, and I TEM00 The intensity distribution matches the fundamental mode of the laser cavity 9. Furthermore, the refractive index of the gain medium 92 has a positive temperature gradient, and the gain medium 92 forms a thermal lens at the circular pump point 15, thereby enhancing the low-order laser mode TEM. 00To provide higher gain, the prior art can only directly increase the power of the end-pump source 10 in order to increase the power of the laser beam 97 output from the second surface 91 (i.e., increase the laser output power). However, this implementation often causes uncontrollable thermal runaway of the gain medium 92, resulting in unstable laser generation. A good laser device should be able to control the laser emission power and output mode separately.

[0043] See Figures 6 to 8 According to a first embodiment disclosed in this invention, two examples of a laser device for laser mode shaping are provided. The first embodiment relates to laser mode shaping using an end-injected laser 2 and a laser mode shaper 4, wherein the laser mode shaper 4 injects a fixed intensity pattern into the end-injected laser 2. In this embodiment, the laser device includes a laser cavity 1 capable of emitting an output laser beam 150 having a first wavelength, an end-injected laser 2 capable of emitting an end-injected laser beam 200 having a second wavelength, at least one side-pumped source 3, and a laser mode shaper 4. In the first embodiment, in... Figure 6 Two side pump sources are presented in the middle.

[0044] The laser cavity 1 includes a first cavity mirror 11, optically coated and highly reflective to the first wavelength and transmissive to the second wavelength; a second cavity mirror 12, spatially spaced from the first cavity mirror 11 and partially reflective to the first wavelength; and a gain medium 13 mounted between the first cavity mirror 11 and the second cavity mirror 12, capable of receiving a pump light from the side pump source 3. In this embodiment, the first cavity mirror 11 is a highly reflective element for the first wavelength. The gain medium 13, excited by the pump light emitted from the side pump source 3, provides gain to the laser cavity 1 for generating the output laser beam 150. The output laser beam 150 travels along an axial direction of the laser cavity 1 and is emitted from the second cavity mirror 12. In the embodiments described above, the gain medium 13 may be a neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal, a neodymium-doped yttrium aluminum perovskite (Nd:YAP) crystal, a ytterbium-doped yttrium aluminum garnet (Yb:YAG) crystal, a holmium-chromium-thulium triple-doped yttrium aluminum garnet (Ho / Cr / Tm:YAG) crystal, a neodymium-doped yttrium vanadate (Nd:YVO4) crystal, an erbium-doped yttrium aluminum garnet (Er:YAG) crystal, a chromium-doped LiSAF (Cr:LiSAF) crystal, a titanium-doped sapphire (Ti:sapphire) crystal, a chromium / erbium-doped YSGG (Cr / Er:YSGG) crystal, an alexandrite crystal, or an erbium-doped glass (Er:glass) crystal.

[0045] The end-injected laser 2 is configured to emit the end-injected laser beam 200 toward the laser cavity 1 along the axial direction. Each of the side-pump sources 3 is configured in a direction substantially angled to the axial direction to provide the energy of the pump light (hereinafter referred to as "pump energy") to the gain medium 13, so that the gain medium 13 generates a laser beam from within the laser cavity 1. In the embodiment, each of the side-pump sources 3 is provided to emit pump light with a wavelength in the laser excitation band of the gain medium 13, and each of the side-pump sources 3 may be selected from any one of a light-emitting diode (LED), a flash lamp, or a laser diode. More specifically, the laser excitation band includes a plurality of laser excitation wavelengths. When the wavelength of the pump light matches any of the laser excitation wavelengths of the gain medium 13, the gain medium 13 absorbs the pump light and amplifies the laser in the laser cavity 1, thereby establishing the output laser beam 150 from the laser cavity 1. In some embodiments, multiple side-pump sources 3 may simultaneously irradiate (i.e., provide the pump light to) the gain medium 13.

[0046] The laser mode shaper 4 is disposed between the end-injected laser 2 and the first cavity mirror 11, and the end-injected laser 2 is located on the side of the first cavity mirror 11 opposite to the gain medium 13. The laser mode shaper 4 is used to spatially redistribute the laser intensity of the end-injected laser 200 so that the end-injected laser beam 200 having an injection mode is emitted onto one end of the gain medium 13. The present invention discloses a new laser amplification mechanism improved from the first equation (Eq.(1)), which is derived from the spatial correlation amplification of a fourth equation (Eq.(4)).

[0047]

[0048] Among them, G(I s ) is composed of a pump with uniform pump strength I s The main laser gain coefficient provided by the side pump source 3, while g(I e (x,y)) is the spatial modulation gain coefficient, which depends on the... Figure 6 and Figure 7 The laser mode shaper 4 or the laser mode shaper 4 disposed outside the laser cavity 1 Figure 9 and Figure 10 The intensity distribution I of the end-injected laser beam 200 in the spatial light modulator (which will be described in further detail later) e (x,y). Due to the exponential amplification in the laser cavity 1, the small spatial modulation gain coefficient g(I) e(x,y) is sufficient to control the mode of the output laser. Furthermore, some laser gain materials, such as Nd:YAG or Nd:YVO4, can exhibit thermally induced refractive index changes or gain bleaching (explained below). When the spatially modulated end-injected laser beam 200 is absorbed by the gain medium 13 to generate heat, the spatially modulated end-injected laser beam 200 causes a spatial thermal mode and a spatially dependent loss coefficient in the gain medium 13. Therefore, the first equation (Eq.(1)) can be modified into a fifth equation (Eq.(5)):

[0049]

[0050] In this situation, the wavelength of the end-injected laser beam 200 is within the absorption band of the gain medium 13, and the absorption band of the gain medium 13 includes the laser excitation band, but the wavelength is not necessarily within the laser excitation band of the gain medium 13. It should be noted that the absorption band includes wavelengths of light that are easily absorbed by the gain medium 92. The laser excitation band is a wavelength band useful for the absorption band of the gain medium (e.g., the gain medium 92). Similarly, due to the exponential amplification in the laser cavity 1, the spatially dependent loss coefficient α(I0) is... e (x,y) is sufficient to control the mode of the output laser.

[0051] The spatial modulation gain coefficient g(I) in the fourth equation e (x,y)) and the space-dependent loss coefficient α(I) in the fifth equation e (x,y) is flexibly controlled by the end-injected laser beam 200, which provides an efficient way for the output of the laser cavity 1 to generate the required laser mode.

[0052] See Figure 6 In the first example of the first embodiment, the laser mode shaper 4 is a fixed-pattern shield 41 disposed outside the laser cavity 1, used to spatially redistribute the laser intensity of the end-injected laser 200 and emit the end-injected laser beam 200 with the desired laser mode onto the gain medium 13, thereby forcing the laser cavity 1 to resonate with the desired laser mode corresponding to the desired mode. It should be noted that the desired laser mode can be set by a user-defined mask (i.e., the fixed-pattern shield 41). Since the fixed-pattern shield 41 is mounted outside the laser cavity 1, it will not be damaged by the strong laser power inside the laser cavity 1. Furthermore, since the laser power of the output laser beam 150 is mainly supplied by the side-pump source 3, the end-injected laser 2 can be used independently to control and optimize the output mode of the output laser beam 150.

[0053] See Figure 7 In a second example of the first embodiment, the laser modality shaper 4 is combined with the first cavity mirror 11. Specifically, the laser modality shaper 4 is coated onto the first cavity mirror 11. In this embodiment, the first cavity mirror 11 is a patterned dichroic mirror that transmits the second wavelength and reflects the first wavelength. Such a patterned dichroic mirror can be manufactured using both thin-film coating and photolithography techniques. For example, firstly, a pair of dichroic coatings that are highly reflective of the first wavelength and highly transmittive of the second wavelength are formed on an intracavity mirror surface 305 of the first cavity mirror 11. An optical coating that is highly reflective of the second wavelength is formed on an outer cavity mirror surface 405 of the first cavity mirror 11. Finally, the optical coating on the outer cavity mirror surface 405 is etched using photolithography to form the fixed pattern shield 41 for the end-injected laser 2. The end-injected laser beam 200 having the second wavelength can be transmitted between the patterned external cavity mirror surface 405 (i.e., through the etched portion) and the internal cavity mirror surface 305, and the end-injected laser beam 200 having the desired laser mode is emitted onto one end of the gain medium 13. Figure 8 Several possible laser mode patterns (A, B, and C) emitted by the laser mode shaper 4 are shown. Figure 8 The top row), and the corresponding output mode of the laser cavity 1 ( Figure 8 (The bottom row). In the embodiment, the laser mode shaper 4 is the fixed pattern shield 41 coated on the surface 405 of the external cavity mirror and outside the laser cavity 1.

[0054] To explain in more detail Figure 7 In the embodiment described above, the patterned dichroic mirror (i.e., the first cavity mirror 11 of the second example of the first embodiment) transmits the end-injected laser beam 200 having the intensity mode defined by the laser mode shaper 4 to the laser cavity 1, and the patterned dichroic mirror reflects the laser beam generated by the gain medium 13 inside the laser cavity 1 to resonate. The second cavity mirror 12 is an output coupler and partially reflects the laser generated from the gain medium 13. Therefore, the output coupler allows a portion of the laser to exit the laser cavity 1 as the output laser beam 150. Because the end-injected laser beam 200 with a pattern modulated by the laser mode shaper 4 increases the net gain of the desired laser mode in the laser cavity 1, the desired laser mode is selectively established inside the laser cavity 1, and the output laser beam 150 with the desired laser mode is generated.

[0055] In one example, the laser mode shaper 4 is configured such that if the desired laser mode of the output laser beam 150 is TEM... 00 In the laser mode, the end-injected laser beam 200, which has a circular spot, is emitted through the first cavity mirror 11 onto one end of the gain medium 13. Preferably, the size of the circular spot emitted by the laser mode shaper 4 is related to the resonant TEM in the laser cavity 1. 00 Matching of circular regions of the pattern.

[0056] In some embodiments, the second wavelength of the end-injected laser beam 200 emitted by the end-injected laser 2 matches one of the absorption wavelengths of the laser excitation band of the gain medium 13, and according to the fourth equation (Eq. (4)), the energy in the end-injected laser beam 200 having the injection mode helps to establish a desired laser mode in the laser cavity 1 having a similar injection mode, so the laser cavity 1 produces the output laser beam 150 having the desired laser mode. In some embodiments, the second wavelength of the end-injected laser beam 200 emitted by the end-injected laser 2 matches one of the absorption wavelengths of the gain medium 13, and the absorption wavelength is not within the laser excitation band of the gain medium 13. For example, the end-injected laser 2 is a CO2 laser, and the CO2 laser is strongly absorbed by, for example, an Nd:YAG laser gain medium, but the CO2 laser does not contribute to the Nd:YAG laser. The absorption of the end-injected laser beam 200 by the gain medium 13 may cause thermal scattering or thermal gain bleaching in the gain medium 13. To further explain, thermal scattering of light is related to thermally induced refractive index changes in the gain medium 13. Thermal gain bleaching occurs when the ground-state atoms of the gain medium 13 are thermally excited to a higher energy level and can no longer maintain the population inversion necessary for laser operation. Therefore, according to the fifth equation (Eq. (5)), thermal scattering and thermal gain bleaching can be used to manipulate the laser loss of different laser modes in the laser cavity 1. It should be noted that the pump energy used to generate the output laser beam 150 mainly depends on the pump light provided by the side pump source 3. Therefore, the end-injected laser 2 is set to relatively low power and can be used alone to control or optimize the output mode at the output end of the laser cavity 1 if necessary.

[0057] In some embodiments, the laser mode shaper 4 is configured to inject the end-injected laser beam 200 having a higher-order mode (i.e., Figure 2 TEM with nonzero "m" and "n" mnThe end-injected laser beam 200, having the higher-order mode, is emitted through the first cavity mirror 11 onto the gain medium 13. The end-injected laser beam 200, having the higher-order mode, can redistribute the net gain of different laser modes within the laser cavity 1, and preferentially establishes the output mode that mimics the higher-order mode. In other embodiments, the laser mode shaper 4 is configured to emit the end-injected laser beam 200 having a user-desired mode for certain applications. In this case, the injection mode of the end-injected laser beam 200 (i.e., the user-desired mode) can be selected such that the injection mode of the end-injected laser beam 200 induces multiple TEMs within the laser cavity 1. mn The resonance of the mode produces the output mode that simulates the mode desired by the user, wherein the output mode matches a specific application.

[0058] Further reading Figure 9 According to a second embodiment of the present invention, a laser device for laser mode shaping is provided. The second embodiment relates to laser mode shaping using the end-injected laser 2 and the laser mode shaper 4 emitting a tunable pattern. The second embodiment is similar to the first embodiment, except that the laser mode shaper 4 in the second embodiment is tunable. In the second embodiment, the laser device is the same as the first example of the first embodiment (e.g., Figure 6 The difference lies in that the fixed pattern shield 41 is replaced by a pixel-addressable spatial light modulator, which can adjust the injection mode to control or optimize the output mode. The pixel-addressable spatial light modulator may include, for example, a display controller, a display driver, a reflective liquid crystal display (LCD), or a transmissive LCD, and can transmit any mode of the end-injected laser beam 200 through the first cavity mirror 11 to one end of the gain medium 13. Unlike the fixed pattern shield 41 (see...), this is a different approach. Figure 6 (or the patterned dichroic mirror of the first embodiment), wherein the pixel-addressable spatial light modulator provides flexibility to inject tunable end-injected laser modes into the laser cavity 1 to meet applications requiring tunability.

[0059] Further reading Figure 10According to a third embodiment of the present invention, a laser device for laser modality shaping is provided. This third embodiment relates to laser modality shaping using an output image feedback circuit. The third embodiment is similar to the second embodiment, except that it further includes a laser modality imager 5 and a feedback circuit 54, wherein the laser modality imager 5 and the feedback circuit 54 are disposed at the output end of the laser cavity 1 (i.e., at one end of the laser cavity 1 that emits the output laser beam 150). Specifically, the laser modality imager 5 and the feedback circuit 54 form a feedback loop.

[0060] In a further detailed description, the laser modality imager 5 includes an image sensor configured to obtain a feedback image of an output modality from the laser cavity 1, and to provide the feedback image of the output modality to the laser modality shaper 4 in real time via the feedback line 54. In this embodiment, the image sensor may be, for example, a camera, and the feedback line 54 may be, for example, a signal line capable of sending data of the feedback image back to the laser modality shaper 4. In this embodiment, the laser modality shaper 4 is further configured to iteratively adjust the injection modality of the end-injected laser beam 200 using an iterative algorithm based on the data of the feedback image, so that the output modality generated by the laser cavity 1 gradually approaches the desired laser modality. Specifically, the iterative algorithm is executed by the laser modality shaper 4, and spatially modulates the intensity of the end-injected laser beam 200 based on a comparison between the feedback image returned from the feedback line 54 and a target modality, so that the injection modality of the end-injected laser beam 200 gradually approaches the target modality. It should be noted that the target mode is used to help establish the desired laser mode of the output laser beam 150. In this embodiment, an iterative cycle begins with the laser mode shaper 4 emitting the end-injected laser beam 200 having the injection mode into the laser cavity 1, followed by the laser mode imager 5 capturing the output mode (i.e., as the feedback image), the feedback line 54 transmitting the captured image (i.e., the feedback image) back to the laser mode shaper 4, the laser mode shaper 4 comparing the target mode with the returned image (i.e., the feedback image), and the laser mode shaper 4 emitting the end-injected laser beam 200 of the injection mode that is modified to be closer to the target mode, so that the output laser beam 150 having the desired laser mode is gradually obtained after multiple iterations.

[0061] Compared to some existing laser devices that receive pump energy solely from the end-injected laser beam and suffer from thermal instability at high pump power, the laser device disclosed herein primarily receives pump energy from the side-pump source 3. Since the side-pump source 3 provides sufficient energy for the generated laser from the laser cavity 1, the end-injected laser 2 used to manipulate the output mode can be relatively low-power and decoupled from most fundamental laser operating parameters, such as laser threshold, laser efficiency, laser stability, and output laser power. Of course, before thermal instability below the laser cavity 1 takes effect, if the wavelength of the end-injected laser 2 is one of the wavelengths located in the laser excitation band of the gain medium 13, the end-injected laser 2 can also act as an amplifying pump source to increase the overall laser output power when controlling the output mode of the laser cavity 1. This design advantageously simplifies the operation of the laser system when a particular application requires both laser efficiency (e.g., the laser power of the output laser beam 150) and the desired laser mode.

[0062] In summary, the laser device disclosed in this invention includes a laser mode shaper 4 located outside the laser cavity 1, and the laser mode shaper 4 is capable of manipulating the output mode by adjusting the injection mode of the end-injected laser beam 200. By adding the laser mode imager 5 and the feedback line 54 to the laser device, the laser mode shaper 4 can further iteratively control or optimize the injection mode in real time based on the feedback image obtained by the laser mode imager 5 and the feedback line 54. Furthermore, since the side pump source 3 provides sufficient pump energy to generate the output laser beam 150, the wavelength of the end-injected laser beam 200 is not limited to the laser excitation wavelength of the gain medium 13. In one example, thermally induced refractive index modulation can be achieved by using an 808 nm end-injected laser or a CO2-injected laser in the gain medium of the Nd:YVO4 crystal, wherein the wavelength of the CO2-injected laser is not the laser excitation wavelength of the Nd:YVO4 crystal.

[0063] This invention discloses an external cavity assembly, including the laser mode shaper 4, the end-injected laser 2, the laser mode imager 5, and the feedback circuit 54, to shape the laser mode of the laser cavity 1 and control the output mode of the output laser beam 150. Unlike existing technologies that use in-cavity assemblies for laser mode shaping, the external cavity solution disclosed in this invention avoids damage to materials caused by the high laser power inside the laser cavity 1. Another important feature of this invention is that the end-injected laser beam 200 with the injection mode is injected into the laser cavity 1 from the outside, so as to preferentially establish the desired laser mode by controlling the net gain (gain coefficient minus loss coefficient) of the laser modes within the laser cavity 1. The exponential growth of the laser process allows small gain / loss perturbations in the laser cavity 1 to selectively establish some laser modes within the laser cavity 1. Unlike some existing technologies that employ external cavity mode converters, which require the removal of valuable laser power due to laser mode switching, the present invention discloses a more efficient, effective, and direct method of generating the desired laser mode from within the laser cavity.

[0064] In the foregoing description, numerous specific details have been set forth for illustrative purposes to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that one or more other embodiments may be practiced without some of these specific details. It should also be understood that the terms "an embodiment," "an embodiment," and embodiments indicated by a number, etc., as used in this specification, indicate that a particular morphology, structure, or feature may be included when implementing the disclosures of this invention. It should be further understood that in this specification, various features are sometimes combined in a single embodiment, drawing, or description for the purpose of rationalizing the disclosures and aiding in the understanding of various inventive forms; this does not mean that each of these features needs to be implemented in the presence of all other features. In other words, in any described embodiment, when the implementation of one or more features or details does not affect the implementation of another one or more features or details, said one or more features or details may be selected and implemented individually without the other one or more features or details. It should also be noted that in the implementations disclosed in this invention, where appropriate, one or more features or details from one embodiment may be implemented together with one or more features or details from another embodiment.

[0065] While the disclosure of this invention is illustrated in connection with embodiments that are considered exemplary, it is to be understood that the disclosure is not limited to the disclosed embodiments, but is intended to cover various different configurations within the spirit and scope of the broadest interpretation, so as to include all such modifications and equivalent configurations.

Claims

1. A laser device for laser mode shaping with an exogenous light spot, characterized by: Comprising: a laser cavity including a first cavity mirror having high reflectivity for a first wavelength, a second cavity mirror spatially separated from the first cavity mirror and partially reflective for the first wavelength, and a gain medium located between the first cavity mirror and the second cavity mirror for generating laser light of the first wavelength, wherein the laser light travels along an axial direction extending from the first cavity mirror, through the gain medium and to the second cavity mirror; an end-pumped laser for emitting an end-pumped laser beam having a second wavelength in the axial direction toward the laser cavity; a side-pump source for providing pump light to the gain medium in a direction substantially angled with respect to the axial direction to cause the gain medium to generate an output laser beam of the first wavelength emitted from the second cavity mirror; and a laser mode shaper disposed between the end-pumped laser and the first cavity mirror for spatially redistributing laser intensity of the end-pumped laser so that the end-pumped laser beam injected into the gain medium through the first cavity mirror has a spatially redistributed intensity. wherein the laser cavity is configured to generate the output laser beam having an output mode that is an analog of an injection mode of the end-pumped laser beam projected onto the gain medium.

2. The laser device using an external injection spot for laser mode shaping according to claim 1, characterized in that: The second wavelength emitted by the end-pumped laser is within an absorption band of the gain medium.

3. The laser device of claim 1, wherein the laser device is configured to perform the laser mode shaping using an external light spot. The gain medium absorbs energy of the end-pumped laser beam to induce one of spatially modulated laser gain and spatially modulated laser loss.

4. The laser device of claim 1, wherein the laser device is configured to perform the laser mode shaping using an external injection spot. The gain medium is selected from any one of the following crystals: Nd:YAG, Nd:YAB, Yb:YAG, Ho / Cr / Tm:YAG, Nd:YVO4, Er:YAG, Cr:LiSAF, Ti:sapphire, Cr / Er:YSGG, alexandrite, and Er:glass crystal.

5. The laser device of claim 1, wherein the laser device is configured to perform the laser mode shaping using an external injection spot. The side-pump source is configured to emit pump light having a wavelength within a laser excitation band of the gain medium, and the side-pump source can be selected from any one of a light-emitting diode, a flash lamp, and a laser diode.

6. The laser device for laser mode shaping with an external injection spot according to claim 1, characterized in that: The laser mode shaper is a fixed-pattern mask to cause the end-pumped laser beam to be transmitted to the gain medium in a desired laser mode.

7. The laser device of claim 6, wherein the laser device is configured to perform the laser mode shaping by: generating a plurality of laser beams; and focusing the plurality of laser beams to form a plurality of outer injection spots on the target surface. The fixed-pattern mask is formed on a surface of the first cavity mirror.

8. The laser device of claim 1, wherein the laser device is configured to perform laser mode shaping using an external light spot. The laser mode shaper is a pixel-addressable spatial light modulator to cause the end-pumped laser beam to be transmitted to the gain medium in a desired laser mode, wherein the desired laser mode is modulated by the pixel-addressable spatial light modulator.

9. The laser device of claim 8, wherein the laser device is configured to perform the laser mode shaping by: generating a plurality of laser beams; and focusing the plurality of laser beams to form a plurality of outer injection spots on the target surface. Further comprising a laser mode imager and a feedback line, and the laser mode imager and the feedback line are disposed outside the laser cavity.

10. The laser device of claim 9, wherein the laser device is configured to perform the laser mode shaping using an external light spot. The laser mode imager includes an image sensor that acquires a feedback image of the output mode emitted from the second cavity mirror and transmits the feedback image to the laser mode shaper via the feedback line.

11. The laser device for laser mode shaping with an external injection spot according to claim 10, characterized in that: The laser mode shaper can further adjust the end-injected laser beam based on the injection mode of the feedback image using an iterative algorithm that includes comparing the desired laser mode to the feedback image of the output mode.

12. The laser device of claim 1, wherein: Also included is a laser mode imager disposed outside the laser cavity, and a feedback line.

13. The laser device of claim 12, wherein the laser device is configured to perform the laser mode shaping using an external light spot. The laser mode imager includes an image sensor that can acquire a feedback image of the output mode emitted from the second cavity mirror and send the feedback image to the laser mode shaper through the feedback line.

14. The laser device of claim 13, wherein the laser device is configured to perform the laser mode shaping using an external light spot. The laser mode shaper is used to deliver the end-injected laser beam having a desired laser mode to the gain medium, and the laser mode shaper can further adjust the end-injected laser beam based on the injection mode of the feedback image using an iterative algorithm that includes comparing the desired laser mode to the feedback image of the output mode. The laser mode shaper can further adjust the end-injected laser beam based on the injection mode of the feedback image using an iterative algorithm that includes comparing the desired laser mode to the feedback image of the output mode.

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