Yellow light self-frequency-doubled laser

Abstract

The application relates to a yellow light self-frequency-doubling laser, which comprises an excitation source, a laser crystal and a self-frequency-doubling crystal arranged in the light output direction of the excitation source. First excitation light output by the excitation source is incident on the laser crystal, so that the laser crystal outputs second excitation light. The second excitation light is subjected to wavelength conversion by using the laser effect and the frequency doubling effect of the self-frequency-doubling crystal, and yellow light laser output is realized. The application helps to improve the beam quality of the output frequency-doubled light.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser, in particular to a yellow light self-frequency-doubling laser. BACKGROUND

[0002] Yellow light refers to light with a wavelength between 570nm and 590nm, and yellow light has a wide range of applications in the fields of biomedicine, military research and atmospheric environment monitoring.

[0003] At present, the technologies for realizing yellow light laser include nonlinear sum frequency, Raman frequency shift after frequency doubling or laser frequency doubling after Raman frequency shift; among them, a solid laser can also be obtained by stimulated Raman scattering of 1μm laser and then frequency doubling or by sum frequency of 1.06μm and 1.3μm laser emission, but there are third-order nonlinear and second-order nonlinear optical effects, making the frequency conversion process of the self-frequency-doubling laser complex, and the Raman frequency shift technology itself is a third-order nonlinear optical process, which requires high light intensity, and no matter whether it is frequency doubling after Raman frequency shift or Raman after laser frequency doubling, the output light power will be reduced due to Raman scattering when the excitation light is incident into the resonant cavity, and a high-quality frequency-doubled light cannot be obtained. The yellow light self-frequency-doubling has always used a semiconductor laser as an excitation source, and the poor beam quality of the semiconductor laser is incompatible with the self-frequency-doubling mode, resulting in poor output beam quality of the self-frequency-doubling laser.

[0004] Therefore, there is an urgent need for a yellow light self-frequency-doubling laser. SUMMARY

[0005] In order to improve the beam quality of the output frequency-doubled light of the laser, the present application provides a yellow light self-frequency-doubling laser.

[0006] The following technical solutions are adopted:

[0007] A yellow light self-frequency-doubling laser includes an excitation source, a laser crystal and a self-frequency-doubling crystal arranged in the light output direction of the excitation source, the first excitation light output by the excitation source is incident into the laser crystal to make the laser crystal output second excitation light, and the second excitation light is wavelength-converted by using the laser effect and frequency-doubling effect of the self-frequency-doubling crystal to realize yellow light laser output.

[0008] By adopting the above technical solutions, the yellow light can be output by only using the excitation source, the laser crystal and the self-frequency-doubling crystal, without using a complex sum frequency process or Raman effect, i.e. without using a complex nonlinear laser system, thereby reducing the complexity of the laser structure design and coating, making the structure simpler and more compact, easy to implement and low in cost, so as to improve the spot quality and laser power of the output light and thereby improve the beam quality of the frequency-doubled light.

[0009] Optionally, a first lens is disposed between the excitation source and the laser crystal, and a second lens is disposed between the laser crystal and the self-frequency doubling crystal. The first lens is used to converge the first excitation light output by the excitation source, and the second lens is used to converge the second excitation light output by the laser crystal.

[0010] By adopting the above technical solution, converging lenses are set on both sides of the light-transmitting surface of the laser crystal, which helps to converge the laser emitted from the excitation source into the laser crystal and the excitation light excited by the laser crystal into the self-frequency doubling crystal. Since the near-infrared laser beam output from the laser crystal has good quality, it can be effectively compatible with the self-frequency doubling crystal mode, which can improve the laser output power and spot quality of the emitted light.

[0011] Optionally, the incident surface of the self-frequency doubling crystal is coated with a dielectric film with high transmittance of 1020-1030nm and high reflectance of 1140nm, and the emitting surface of the self-frequency doubling crystal is coated with a dielectric film with high reflectance of 1020-1030nm and 1140nm and high transmittance of 570nm.

[0012] Optionally, the cutting angle of the self-frequency doubling crystal is θ=120.6° and φ=38.7°.

[0013] By adopting the above technical solution, the conversion efficiency is significantly improved while ensuring that the frequency doubling bandwidth does not decrease, so that the self-frequency doubling crystal can have a better conversion efficiency of 1140nm light to 570nm at this cutting angle.

[0014] Optionally, the light transmission length of the laser crystal is 20-100 nm, and the light transmission length of the self-frequency doubling crystal is 0.5-20 nm.

[0015] By adopting the above technical solution, the light transmission length of the laser crystal is 20-100mm. In laser crystals with excitation function, an appropriate light transmission length helps to improve the pulse energy of the output beam and increase the output power of the output beam. The light transmission length of the self-frequency doubling crystal is 0.5-20mm. Selecting a suitable light transmission length in the self-frequency doubling crystal helps to achieve phase matching, thereby improving the conversion efficiency of fundamental frequency light to frequency-doubled light.

[0016] Optionally, both the laser crystal and the self-frequency doubling crystal are yttrium oxy-3-di(2, ...

[0017] By adopting the above technical solution, yttrium oxy-3-doped calcium yttrium borate crystals can be easily grown into large-size crystals, which can relatively reduce the cost of self-frequency doubling crystals. At the same time, they have high second-order nonlinear optical coefficients and high optical damage thresholds, enabling yttrium oxy-3-doped calcium yttrium borate crystal devices to output high-beam-quality yellow lasers. Furthermore, they can increase the maximum laser power that can be borne per unit area of ​​the crystal device, which helps to further increase the output yellow laser power by increasing the laser power output from the excitation source.

[0018] Optionally, the yellow self-frequency doubling laser further includes an input mirror and an output mirror, the input mirror being disposed between the second lens and the self-frequency doubling crystal, and the output mirror being disposed on the light output path of the self-frequency doubling crystal.

[0019] By adopting the above technical solution, and by setting input and output mirrors on both sides of the light-transmitting surface of the self-frequency doubling crystal to form a resonant cavity, after obtaining excitation light with high beam quality, it is possible to form yellow laser with relatively high beam quality through the laser effect and frequency doubling effect of the self-frequency doubling crystal.

[0020] Optionally, the light-transmitting surface of the input mirror is coated with a dielectric film with high transmittance of 1020-1030nm and high reflectance of 1140nm and 570nm, and the light-transmitting surface of the output mirror is coated with a dielectric film with high reflectance of 1020-1030nm and 1140nm and high transmittance of 570nm.

[0021] By adopting the above technical solution, dielectric films are deposited on the light-transmitting surfaces of the input and output mirrors to reduce the loss of the excitation light in the 1020-1030nm band. At the same time, high-reflectivity dielectric films of 1140nm and 570nm are deposited on the input mirror to increase the frequency of fundamental light in the resonant cavity, thereby achieving effective output of the yellow light band.

[0022] Optionally, the output mirror is a concave mirror with a radius of curvature of 50mm-1000mm.

[0023] By adopting the above technical solution, in the resonant cavity formed by the input mirror, the self-frequency doubling crystal and the output mirror, the use of a concave mirror as the output mirror is beneficial for the fundamental frequency light to oscillate in the resonant cavity. When the radius of curvature is selected between 50nm and 1000nm, the larger the radius of curvature, the more times the fundamental frequency light reflected to the self-frequency doubling crystal oscillates, thereby increasing the absorption efficiency of the self-frequency doubling crystal for the fundamental frequency light.

[0024] Optionally, the excitation source can be any one of a semiconductor laser, a solid-state laser, or a fiber laser.

[0025] In summary, this application includes at least one of the following beneficial technical effects:

[0026] 1. Frequency-doubled output yellow light can be achieved using only an excitation source, a laser crystal, and a self-frequency-doubled crystal, eliminating the need for complex sum-frequency processes or Raman effects. This means that a complex nonlinear laser system is not required, reducing the complexity of laser structure design and coating. The structure is simpler, more compact, easier to implement, and lower in cost, thereby improving the beam quality of the output light and the laser power, and thus improving the beam quality of the frequency-doubled light.

[0027] 2. Yttrium borate (YBO) crystals are easy to grow into large-size crystals, which can relatively reduce the cost of self-frequency doubling crystals. At the same time, they have a high second-order nonlinear optical coefficient and a high optical damage threshold, which enables YBO crystal devices to output high-beam-quality yellow laser light. Furthermore, they can increase the maximum laser power that can be borne per unit area of ​​the crystal device, which helps to further increase the output yellow laser power by increasing the laser power output by the excitation source. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the optical path of a yellow self-frequency doubling laser provided in the first embodiment of this application;

[0029] Figure 2 This is a schematic diagram of the optical path of a yellow self-frequency doubling laser provided in the second embodiment of this application;

[0030] Figure 3 This is a schematic diagram of the working principle of a yellow light self-frequency doubling laser provided in the second embodiment of this application;

[0031] Figure 4 This is the absorption spectrum of the calcium yttrium oxide crystal doped with ytterbium borate provided in this application.

[0032] Explanation of reference numerals in the attached diagram: 1. Excitation source; 2. Laser crystal; 3. Self-frequency doubling crystal; 4. First lens; 5. Second lens; 6. Input mirror; 7. Output mirror. Detailed Implementation

[0033] The following is in conjunction with the appendix Figures 1-3 This application provides a further detailed description of a yellow light self-frequency doubling laser.

[0034] Before introducing the embodiments of the present invention, some terms involved in the embodiments of the present invention will be defined and explained.

[0035] Nonlinear optical effects: These are phenomena caused by electromagnetic radiation, but whose response is not proportional to the illuminance. Incident light of a certain frequency can be converted into light of other frequencies through interaction with the medium. In addition to the original frequency ω, higher harmonics such as 2ω and 3ω will appear, and a series of light with different frequencies and intensities periodically distributed across the spectrum can be generated.

[0036] Raman scattering (Raman effect): When a laser of a certain frequency irradiates the surface of a sample, energy transfer occurs between the molecules and photons in the material, and the vibrational state (e.g., the wobbling and twisting of atoms, the wobbling and vibration of chemical bonds) changes in different ways and to different degrees, and then light of different frequencies is scattered.

[0037] In this invention, "high reflectivity" and "high transmittance" have the meanings known in the art.

[0038] "High reflectivity" refers to a reflectivity of more than 99% for incident light of a specific wavelength or band.

[0039] "High transmittance" means that the transmittance of light of a specific wavelength or band is greater than 95%.

[0040] refer to Figure 1 The first embodiment of this application provides a yellow self-frequency doubling laser, including an excitation source 1 and a laser crystal 2 and a self-frequency doubling crystal 3 disposed in the light output direction of the excitation source 1.

[0041] Excitation source 1 is used to emit the first excitation light. Excitation source 1 is a continuous wave laser. The excitation method of the continuous wave laser can be semiconductor laser excitation or solid-state laser excitation.

[0042] The laser crystal 2 is used to convert the first excitation light output from the excitation source 1 into a second excitation light, wherein the wavelengths of the first excitation light and the second excitation light are different.

[0043] In one example, the first excitation light may be light with a wavelength of 976 nm emitted by a semiconductor laser or a solid-state laser, and the second excitation light may be near-infrared laser generated by the first excitation light through a laser crystal. Near-infrared lasers include, but are not limited to, lasers with a wavelength of 1020-1030 nm.

[0044] The self-frequency doubling crystal 3 is used to double the frequency of the near-infrared laser input to the self-frequency doubling crystal 3 according to the second-order nonlinear optical effect, so that the 1140nm fundamental frequency light is doubled to form a 570nm yellow light laser.

[0045] Among them, laser crystal 2 and self-frequency doubling crystal 3 are both ytterbium borate calcium oxide yttrium crystals. Yttrium borate calcium oxide crystals are easy to grow into large-size crystals, which can relatively reduce the cost of self-frequency doubling crystal 3. At the same time, they have high second-order nonlinear optical coefficients and high optical damage thresholds, which enable the ytterbium borate calcium oxide yttrium crystal device to output high beam quality yellow laser light. It can also increase the maximum laser power that can be borne per unit area of ​​the crystal device, which helps to further increase the output yellow laser power by increasing the laser power output by excitation source 1.

[0046] Furthermore, the Yb ion doping concentration in laser crystal 2 and self-frequency doubling crystal 3 is selected according to equipment requirements. The aforementioned yttrium borate-doped calcium oxy-ttrium crystal maintains a slightly strong absorption capacity in the 850-1050nm range. Laser crystal 2 is cut along the optical principal axis Y-axis, and the cutting angle of self-frequency doubling crystal 3 is θ=120.6° and φ=38.7°, which is the optimal crystal phase matching direction at 570nm. This ensures that the fundamental frequency light achieves a type I phase match, significantly improving the conversion efficiency while ensuring that the frequency doubling bandwidth does not attenuate. This allows self-frequency doubling crystal 3 to have a superior conversion efficiency of converting 1140nm fundamental frequency light to 570nm frequency-doubled light at this cutting angle.

[0047] Yttrium-doped calcium oxy borate crystals can also be replaced with yttrium-doped calcium oxy borate crystals capable of emitting yellow light. The chemical formula of the yttrium-doped calcium oxy borate crystal is Yb:ReCa4O(BO3)3 (Yb:ReCOB), where Re represents Y (yttrium) and the lanthanide rare earth elements Gd and La. These crystals belong to space group Cm and point group m, are bicyclic crystals with low symmetry, are chemically stable, not easily deliquescent, and exhibit second-order nonlinear optical properties and a moderate nonlinear optical coefficient (d). 11 =1.5 pm / V) High damage resistance threshold (>1 GW / cm) 2 Yb has advantages such as ease of growth into large-size, high-optical-quality crystals. It also possesses a broad transmission spectrum (200-3700 nm), making ytterbium-doped rare-earth calcium oxide borate crystals important for self-frequency-doubling second-order nonlinear optics applications. 3+ Due to the lanthanide contraction effect, it has a small ionic radius, and the electron-phonon coupling of this ion-doped crystal is strong, enabling laser emission beyond the fluorescence spectrum and outputting yellow light based on the frequency doubling effect. Meanwhile, YCOB is a crystal that combines self-frequency doubling and strong electron-phonon coupling; after Yb3+ ion doping, high-power, high-efficiency self-frequency doubling yellow laser output from Yb:YCOB crystals can be achieved.

[0048] The transmission length of laser crystal 2 is 20-100 mm. In laser crystal 2 with excitation function, an appropriate transmission length helps to improve the pulse energy of the output beam and increase the output power of the output beam. Preferably, the transmission length of laser crystal 2 is 60 nm. At this transmission length, the near-infrared laser generated by laser crystal 2 has the optimal laser output power. The transmission length of self-frequency doubling crystal 3 is 0.5-20 mm. Selecting a suitable transmission length in self-frequency doubling crystal 3 helps to achieve phase matching. Preferably, when the transmission length of self-frequency doubling crystal 3 is 8 mm, the conversion efficiency of the fundamental frequency light 1140 nm to the frequency-doubled light 570 nm is the highest.

[0049] A first lens 4 is disposed between the excitation source 1 and the laser crystal 2, and a second lens 5 is disposed between the laser crystal 2 and the self-frequency doubling crystal 3. The focal point of the first lens 4 is on the incident surface of the laser crystal 2, and the focal point of the second lens 5 is on the incident surface of the self-frequency doubling crystal 3. The first lens 4 is used to converge the laser output from the excitation source 1, and the second lens 5 is used to converge the near-infrared laser output from the laser crystal 2. Converging lenses are disposed on both sides of the light-transmitting surface of the laser crystal 2, which helps to converge the laser emitted from the excitation source 1 into the laser crystal 2, and to converge the excitation light excited by the laser crystal 2 into the self-frequency doubling crystal 3, thereby improving the laser output power and spot quality of the emitted light. The optical axes of the excitation source 1, the first lens 4, the laser crystal 2, the second lens 5, and the self-frequency doubling crystal 3 are all on the same straight line.

[0050] To achieve effective output in the yellow light band and reduce losses in the near-infrared laser, the incident surface of the self-frequency doubling crystal 3 is coated with a dielectric film with high transmittance of 1020-1030nm and high reflectance of 1140nm, while the emitting surface of the self-frequency doubling crystal 3 is coated with a dielectric film with high reflectance of 1020-1030nm and 1140nm and high transmittance of 570nm. Coating the corresponding dielectric film on the transmitting surface of the self-frequency doubling crystal 3 improves the light input rate of the excitation light while minimizing the simultaneous emission of the excitation light and the frequency-doubled light during emission.

[0051] This scheme only requires excitation source 1, laser crystal 2, and self-frequency doubling crystal 3 to achieve frequency doubling output of yellow light, eliminating the need for complex sum-frequency processes or Raman effects. This means that a complex nonlinear laser system is not required, reducing the complexity of laser structure design and coating. The structure is simpler, more compact, easier to implement, and lower in cost. Since the near-infrared laser (1020-1030nm) output from the laser crystal has good beam quality, it can be effectively compatible with the self-frequency doubling crystal mode, which can improve the laser output power and beam quality of the emitted light.

[0052] Implementation principle: The excitation light emitted from the excitation source 1 is focused onto the laser crystal 2 by the first lens 4. The laser crystal 2 absorbs the excitation light to generate near-infrared laser with a wavelength of 1020-1030nm. The near-infrared laser is focused onto the self-frequency doubling crystal 3 by the second lens 5. Due to the laser effect and second-order nonlinear optical effect of the yttrium borate-doped crystal, the near-infrared laser input into the self-frequency doubling crystal 3 generates laser with twice the frequency. That is, a high beam quality yellow laser with a wavelength of 570nm is achieved through nonlinear optical frequency conversion.

[0053] Please see Figure 2 , Figure 2This is a schematic diagram of a yellow self-frequency doubling laser provided in the second embodiment of this application. The structure of the yellow self-frequency doubling laser provided in the second embodiment is basically the same as that of the yellow self-frequency doubling laser in the first embodiment. The difference is that in this embodiment, an input mirror 6 and an output mirror 7 are respectively provided on both sides of the self-frequency doubling crystal 3. The input mirror 6 is disposed between the second lens 5 and the self-frequency doubling crystal 3, and the output mirror 7 is disposed on the light output path of the self-frequency doubling crystal 3.

[0054] The added input mirror 6 and output mirror 7 form a laser resonant cavity. To reduce the loss of excitation light and suppress oscillation in the 1020-1030nm band, a dielectric film with high transmittance for this band needs to be deposited on the resonant cavity. Specifically, the input mirror 6 is coated with a dielectric film with high transmittance for 1020-1030nm in the light-transmitting direction, and the output mirror 7 is coated with a dielectric film with high transmittance for 570nm. To achieve effective output in the yellow light band, the input mirror 6 also needs to be coated with a dielectric film with high reflectance for 1140nm and 570nm, and the output mirror 7 is coated with a dielectric film with high reflectance for both 1020-1030nm and 1140nm. Preferably, a dielectric film with a transmittance greater than 95% for 570nm is deposited on the light-transmitting surface of the output mirror 7. Furthermore, both light-transmitting surfaces of the self-doubling crystal 3 are coated with dielectric films with high transmittance for 1020-1030nm, 1140nm, and 570nm.

[0055] The output mirror 7 is a concave mirror with a radius of curvature of 50-1000 mm, and the excitation source 1 is a fiber laser. In the resonant cavity formed by the input mirror 6 and the output mirror 7, using a concave mirror as the output mirror 7 is beneficial for the fundamental frequency light to oscillate within the resonant cavity. A radius of curvature of 50-1000 mm is chosen; the larger the radius of curvature, the more oscillations the fundamental frequency light reflected to the self-frequency doubling crystal 3 will have, thus increasing the absorption efficiency of the self-frequency doubling crystal 3 for the fundamental frequency light. The distance between the output mirror 7 and the input mirror 6 is chosen to be 15-200 mm, which is also beneficial for the oscillation of the fundamental frequency light.

[0056] Implementation principle: The excitation light emitted from the excitation source 1 is focused onto the laser crystal 2 by the first lens 4. The laser crystal 2 absorbs the excitation light to generate near-infrared lasers with wavelengths of 1020-1030nm and 1140nm. The near-infrared lasers are focused onto the resonant cavity composed of the input mirror 6, the self-frequency doubling crystal 3, and the output mirror 7 by the second lens 5. The near-infrared lasers oscillate continuously in the resonant cavity and undergo Raman scattering to generate lasers with twice the frequency.

[0057] like Figure 2 and Figure 3 As shown, the excitation source 1, the first lens 4, and the laser crystal 2 can be replaced with a fiber laser with an output wavelength of 1020-1030nm. By using a fiber laser to provide a beam with high energy density and high spot quality, the power loss caused by Raman scattering in the resonant cavity can be reduced.

[0058] refer to Figure 4 The absorption spectrum of yttrium ytterbium borate (YYB) crystal is plotted with wavelength on the x-axis and transmittance on the y-axis. It is clear that the transmittance of P- and S-beams is low around 900 nm and 975 nm, while the transmittance of P- and S-beams is highest at wavelengths less than 850 nm and greater than 1025 nm. Theoretical calculations show that when light with wavelengths greater than 1025 nm passes through the YYB crystal, as long as the doping concentration is high, effective absorption of the excitation laser can still be achieved, resulting in high-power, higher-quality frequency-doubled light.

[0059] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A yellow-light self-frequency-doubled laser, characterized in that: The device includes an excitation source (1) and a laser crystal (2) and a self-frequency doubling crystal (3) disposed in the light output direction of the excitation source (1). Both the laser crystal (2) and the self-frequency doubling crystal (3) are yttrium-doped calcium oxy-xylene crystals. The first excitation light output from the excitation source (1) is incident on the laser crystal (2) so that the laser crystal (2) outputs a second excitation light. The second excitation light uses the laser effect and frequency doubling effect of the self-frequency doubling crystal (3) to perform wavelength conversion and realize yellow laser output.

2. The yellow-light self-frequency-doubled laser according to claim 1, characterized in that: A first lens (4) is provided between the excitation source (1) and the laser crystal (2), and a second lens (5) is provided between the laser crystal (2) and the self-frequency doubling crystal (3). The first lens (4) is used to converge the first excitation light output by the excitation source (1), and the second lens (5) is used to converge the second excitation light output by the laser crystal (2).

3. The yellow-light self-frequency doubling laser according to claim 1, characterized in that: The incident surface of the self-frequency doubling crystal (3) is coated with a dielectric film with high transmittance of 1020-1030nm and high reflectance of 1140nm, and the emitting surface of the self-frequency doubling crystal (3) is coated with a dielectric film with high reflectance of 1020-1030nm and 1140nm and high transmittance of 570nm.

4. The yellow-light self-frequency doubling laser according to claim 1, characterized in that: The cutting angle of the self-frequency doubling crystal (3) is θ=120.6° and φ=38.7°.

5. The yellow-light self-frequency-doubled laser according to claim 1, characterized in that: The transmission length of the laser crystal (2) is 20-100nm, and the transmission length of the self-frequency doubling crystal (3) is 0.5-20nm.

6. The yellow-light self-frequency doubling laser according to claim 2, characterized in that: The yellow self-frequency doubling laser also includes an input mirror (6) and an output mirror (7). The input mirror (6) is disposed between the second lens (5) and the self-frequency doubling crystal (3), and the output mirror (7) is disposed on the light output path of the self-frequency doubling crystal (3).

7. The yellow-light self-frequency-doubled laser according to claim 6, characterized in that: The light-transmitting surface of the input mirror (6) is coated with a dielectric film with high transmittance of 1020-1030nm and high reflectance of 1140nm and 570nm, and the light-transmitting surface of the output mirror (7) is coated with a dielectric film with high reflectance of 1020-1030nm and 1140nm and high transmittance of 570nm.

8. The yellow self-frequency doubling laser according to claim 7, characterized in that: The output mirror (7) is a concave mirror with a radius of curvature of 50-1000mm.

9. The yellow self-frequency doubling laser according to any one of claims 1-8, characterized in that: The excitation source (1) is any one of a semiconductor laser, a solid-state laser, or a fiber laser.

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