A solid-state laser and an intracavity optical polarization element for a solid-state laser

Abstract

The present invention discloses a solid-state laser and an intracavity optical polarization element for a solid-state laser. The polarization element includes a Sm:GdCa4O(BO3)3 polarization wafer, which is used to achieve the polarization output of 1-μm band laser. The laser includes a laser pumping device and a resonant cavity adjacent to the laser pumping device, and a laser crystal and a polarization element are arranged in the resonant cavity. The present invention can control the laser oscillation in the 1-μm band, achieve linearly polarized output, provide a new method and a new device for simply and flexibly controlling the laser polarization in the cavity, avoid the large optical loss and lifetime problems brought by the beam splitter prism, and there is no need to be placed obliquely, which is beneficial to saving the intracavity space of the resonant cavity.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and more particularly to a solid-state laser and an intracavity optical polarization element for a solid-state laser. Background Art

[0002] Linearly polarized lasers have wide applications in optoelectronic detection, spectral measurement, photon entanglement, information processing and storage, etc. As an important means to broaden the laser wavelength, nonlinear optical frequency conversion has special requirements for the polarization characteristics of the fundamental frequency light, and only lasers along a specific linearly polarized direction can achieve effective conversion. Unfortunately, some important laser crystals are isotropic (such as Nd:YAG), and the emitted lasers are not single-linearly polarized. Therefore, certain methods need to be taken to convert them into single-linearly polarized light before application. In addition, for anisotropic laser crystals, the gain coefficient, polarization state, and wavelength of the excited laser will change with the crystal direction, which will bring two more inconveniences: (1) When the emission cross-sections of two laser wavelengths with orthogonal polarization states are similar, they often oscillate simultaneously at a slightly higher pump power, and it is difficult to obtain a single-polarization, single-wavelength laser. For example, for the Nd:YAP crystal, the c-polarized emission peak is at 1065 nm, and the b-polarized emission peak is at 1079 nm. Both often output simultaneously and cannot be used separately. (2) When the emission cross-sections of two laser wavelengths with orthogonal polarization states differ greatly, even at a very high pump power, it is impossible to make the polarized laser with a smaller emission cross-section oscillate and output, so the corresponding wavelength cannot be utilized. For example, for the Nd:YVO4 crystal, the c-polarized emission peak is at 1064 nm, and the b-polarized emission peak is at 1067 nm. For the commonly used a-cut crystal, it is difficult to obtain the 1067 nm output with a smaller emission cross-section of the b polarization in reality. Although the c-cut crystal can partially solve this problem, the obtained 1067 nm output is not single-linearly polarized. Therefore, in either of the above cases, simple and flexible means are needed to control the laser polarization, which is of great significance for making full use of the characteristic differences of the polarization spectra of laser crystals, enriching the laser wavelength, and realizing special applications of lasers.

[0003] The currently commonly used schemes for intracavity control of laser polarization can generally be divided into two categories. One is to place a polarization beam splitter prism in the laser cavity. By utilizing the screening effect of the prism on polarized light beams, the laser with one polarization direction can oscillate in the cavity and form an output. This method has high costs, large sizes, and high optical losses. It is easy for the two parts before and after the beam splitter prism to come unglued after heating, so its lifespan is limited. The other is to place glass sheets at the Brewster angle in the laser cavity. Although this method can play a role in polarization selection, the inclined glass sheets greatly increase the size of the resonator cavity and are not suitable for miniaturized and highly integrated laser devices. Secondly, the output power is very sensitive to the placement angle of the glass sheets, thus posing relatively high requirements for assembly accuracy. Moreover, the Brewster angles for different laser wavelengths are also different, further increasing the assembly difficulty. Fourthly, the thermal conductivity of the glass sheets is relatively low, far less than that of crystal optical components, which is not conducive to the stable operation of high-power lasers.

[0004] Therefore, how to provide a solid-state laser and an intracavity optical polarization element for a solid-state laser, which can avoid the limitations of the two types of lasers in the prior art, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a solid-state laser and an intracavity optical polarization element for a solid-state laser, which can control the oscillation of 1-μm lasers, achieve linearly polarized output, provide a new method and new device for simply and flexibly controlling laser polarization in the cavity, avoid the large optical losses and lifespan problems brought by the beam splitter prism, and do not require inclined placement, which is conducive to saving the intracavity space of the resonator cavity.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An intracavity optical polarization element for a solid-state laser, comprising a Sm:GdCa4O(BO3)3 polarization wafer, and the polarization wafer is used to achieve the output of polarized laser in the 1-μm band.

[0008] Further, the Sm in the polarization wafer 3+ has a concentration of 1-50 at.%.

[0009] Further, the light passing direction of the polarization wafer is along the refractive index main axis Nz, the light passing surface is polished, and the light passing thickness is 0.1-20 mm.

[0010] Further, the light passing surface of the polarization wafer is coated with an antireflection film in the 1020-1130 nm band.

[0011] A solid-state laser, adopting any one of the above intracavity optical polarization elements for a solid-state laser, comprising a laser pumping device and a resonator cavity adjacent to the laser pumping device, and a laser crystal and a polarization element are arranged in the resonator cavity.

[0012] Further, the laser pumping device includes a pumping source and a focusing system, the resonant cavity includes an incident mirror and an output mirror. The incident mirror is coated with an antireflection film for the pumping light and a high-reflection film for 1.05 - 1.1 μm; the output mirror is coated with a partially transmissive dielectric film for the 1.05 - 1.1 μm band, and the transmittance of the partially transmissive dielectric film in the 1.064 μm band is 5%.

[0013] Further, an intracavity frequency doubling crystal is also arranged in the resonant cavity for doubling the frequency of the polarization-selected laser to output continuous frequency-doubled laser.

[0014] Further, the output mirror is coated with a 1.06 μm high-reflection film and a 0.53 μm antireflection film to replace the partially transmissive dielectric film.

[0015] Further, a Q-switch is also arranged in the resonant cavity. The Q-switch is located behind the polarization element and is used to modulate and generate pulsed laser.

[0016] Further, after the resonant cavity, a convex lens, an extracavity frequency doubling crystal, and a filter are sequentially arranged along the optical path adjacent to the resonant cavity. After the pulsed laser is focused by the convex lens, it is incident as fundamental frequency light into the extracavity frequency doubling crystal that satisfies the phase matching condition. After the frequency-doubled light emitted from the extracavity frequency doubling crystal is filtered by the filter to remove the remaining fundamental frequency light, pure pulsed frequency-doubled light is output.

[0017] Advantages of the present invention:

[0018] As can be seen from the above technical solutions, compared with the prior art, the present invention overcomes many disadvantages of traditional intracavity polarization-selective optical elements. Compared with a polarization beam splitter prism, it has a lower cost, smaller size, lower optical loss, a glue-free integrated design, and a long service life. Compared with a glass sheet placed at the Brewster angle, it has a smaller size, is easy to integrate, easy to assemble, plug-and-play, is not sensitive to angle changes, can rotate for polarization selection, has a high thermal conductivity, and operates stably at high power. The Sm:GdCOB crystal of the present invention can be grown by the Czochralski method, with a fast growth rate, short period, low cost of the polarization element, stable properties, high polarization degree, easy to process, easy for mass production, and easy to promote. In addition to the above advantages, as shown in the appendix Figure 3 The Sm:GdCOB crystal exhibits obvious polarization absorption anisotropy in a relatively wide wavelength band near 1 μm (1020 - 1130 nm). Therefore, the intracavity polarization element of the present invention is applicable to a variety of laser materials, laser wavelengths, and even broadband lasers, and has very important and broad application prospects. Description of the Drawings

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on the provided drawings.

[0020] Figure 1 It is a position distribution diagram of the optical principal axis and the crystallographic axis of the Sm:GdCOB crystal of the present invention determined by orientation;

[0021] Figure 2 For the N of the present invention Z Processing drawing of the tangential Sm:GdCOB polarization element of the present invention;

[0022] Figure 3 It is the polarization transmission spectrum diagram of the 3at.%, 1mm thick Sm:GdCOB crystal;

[0023] Figure 4 It is a structural diagram of a solid laser provided by an embodiment of the present invention;

[0024] Figure 5 It is a structural diagram of an intracavity frequency-doubled solid laser provided by another embodiment of the present invention;

[0025] Figure 6 It is a structural diagram of an extracavity frequency-doubled solid laser provided by another embodiment of the present invention;

[0026] Among them, 1 - pump source, 2 - focusing system, 3 - incident mirror, 4 - laser crystal, 5 - polarization element, 6 - output mirror, 7 - Q-switch, 8 - convex lens, 9 - frequency-doubling crystal, 10 - filter, 11 - frequency-doubling output cavity mirror. Detailed implementation manners

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0028] Embodiment 1

[0029] The embodiment of the present invention discloses a processing method for an intracavity optical polarization element for a solid laser, as Figure 1 shown. The element material is a Sm:GdCa4O(BO3)3 crystal, which is processed into a wafer with a certain thickness along the principal axis N Z direction.

[0030] Specifically, a crystallographic axis orientation of the Sm:GdCa4O(BO3)3 crystal is performed using an X-ray orientator; the angles between the crystallographic axes and the optical principal axes are oriented with a polarizing microscope for Sm:GdCa4O(BO3)3, and the results are (a,N Z ) = 26.7°, (c,N X ) = 15.4°. The crystallographic axis b is opposite to the optical principal axis N Y . The optical principal axes N X , N Y , N Z follow the right-hand screw rule; wafers are processed along the optical principal axis N Z of the Sm:GdCa4O(BO3)3 crystal to make polarization elements, and the normal directions of the side surfaces of the polarization elements are N X and N Y .

[0031] Example 2

[0032] As Figure 2 and Figure 3 show, an intracavity optical polarization element for a solid-state laser disclosed in an embodiment of the present invention includes a Sm:GdCa4O(BO3)3 polarization wafer, and the polarization wafer is used to achieve polarization laser output in the range of 1020 - 1130 nm. In the 1-μm band, the transmittances of the Sm:GdCOB crystal for different linearly polarized lights vary greatly (T NX << T NZ < T NY ). Therefore, for the wafer device processed along the N Z direction, the two linearly polarized directions N X , N Y on its cross-section have the largest transmittance difference, and the linearly polarized light in the N Y direction is basically not absorbed. Based on this unique property, placing this element in the resonator cavity of a solid-state laser with a wavelength of 1 μm can play a role in polarization selection, making the polarization of the output laser only along the N Y direction with a larger transmittance. The present invention has the advantages of low production cost, convenient processing, small size, high polarization degree, easy adjustment, and easy popularization.

[0033] In one embodiment, the Sm 3+ concentration of the Sm:GdCOB crystal is 1 - 50 at.%, the wafer is polished on both sides, and the thickness in the light-transmitting direction is 0.1 - 20 mm. Preferably, antireflection films in the 1-μm band are coated on the two light-transmitting surfaces of the wafer to reduce the overall loss in the cavity, lower the pump threshold, and improve the conversion efficiency.

[0034] Example 3

[0035] An embodiment of the present invention discloses a solid-state laser, which includes a laser pumping device and a resonant cavity adjacent to the laser pumping device. A laser crystal and a polarization element are arranged in the resonant cavity. Among them, the polarization element can adopt the polarization element in Embodiment 2.

[0036] In one embodiment, the laser pumping device includes a pump source and a focusing system, and the resonant cavity includes an incident mirror and an output mirror. The incident mirror is coated with an antireflection film for pump light and a high-reflection film of 1.05 - 1.1 μm; the output mirror is coated with a partially transmissive dielectric film for the 1.05 - 1.1 μm band, and the transmittance of the partially transmissive dielectric film in the 1.064 μm band is 5%.

[0037] Specifically, the pump source 1, the pump focusing system 2, the incident mirror 3, the laser crystal 4, the Sm:GdCOB polarization element 5, and the output mirror 6 are arranged in sequence to form a concave-plane resonant cavity. The laser wavelength emitted by the pump source 1 is 808 nm. The beam compression ratio of the focusing system 2 is 1:1. The incident mirror 3 is coated with an antireflection film for pump light and a high-reflection film of 1.06 μm. The laser crystal 4 is 3+ Nd doped with 0.5 at.%, with dimensions of 3 × 3 × 10 mm 3 in the shape of a cuboid, and both ends are coated with an antireflection film of 1.06 μm. The polarization element 5 is a Sm 3+ Sm:GdCOB wafer with a concentration of 3 at.%, and the tangential direction is N Z , with dimensions of 3 × 3 × 1 mm 3 , and both sides are polished. The output mirror 6 is coated with a partially transmissive dielectric film for the 1.05 - 1.1 μm band, and the transmittance at 1.064 μm is 5%.

[0038] When the laser crystal 4 is a

[111] -cut Nd:YAG crystal, the pump light emitted by the pump source 1 passes through the focusing system 2 and is incident into the Nd:YAG crystal 4, generating laser oscillation and amplification. After the polarization selection by the element 5, 1064 nm laser output with polarization along the N Y direction of the Sm:GdCOB wafer is achieved.

[0039] When the laser crystal 4 is an X-cut Nd:LYSO crystal, the pump light emitted by the pump source 1 passes through the focusing system 2 and is incident into the Nd:LYSO crystal 4, generating laser oscillation and amplification. After the polarization selection by the element 5, laser output with polarization along the N Y direction of the Sm:GdCOB wafer is achieved. When the N Y direction of the polarization element coincides with the Z-axis of the laser crystal, the output laser wavelengths are 1076 nm and 1080 nm. When the N Y direction of the polarization element coincides with the Y-axis of the laser crystal, the output laser wavelengths are 1069 nm and 1076 nm.

[0040] When the laser crystal 4 is a Y-cut Nd:LYSO crystal, the pump light emitted by the pump source 1 passes through the focusing system 2 and enters the interior of the Nd:LYSO crystal 4, generating laser oscillation and amplification. After the polarization selection by the element 5, the laser output with polarization along the N direction of the Sm:GdCOB wafer is achieved. Y When the polarization direction of the polarization element N Y coincides with the Z-axis of the laser crystal, the output laser wavelengths are 1076 nm and 1080 nm. When the polarization direction of the polarization element N Y coincides with the X-axis of the laser crystal, the output laser wavelengths are 1060 nm and 1080 nm.

[0041] When the laser crystal 4 is a Z-cut Nd:LYSO crystal, the pump light emitted by the pump source 1 passes through the focusing system 2 and enters the interior of the Nd:LYSO crystal 4, generating laser oscillation and amplification. After the polarization selection by the element 5, the laser output with polarization along the N direction of the Sm:GdCOB wafer is achieved. Y When the polarization direction of the polarization element N Y coincides with the Y-axis of the laser crystal, the output laser wavelength is 1076 nm. When the polarization direction of the polarization element N Y coincides with the X-axis of the laser crystal, the output laser wavelengths are 1061 nm, 1076 nm, and 1080 nm.

[0042] In another embodiment, an intracavity frequency doubling crystal is further arranged in the resonant cavity for doubling the frequency of the polarization-selected laser to output continuous frequency-doubled laser. The output mirror is coated with a 1.06 μm high-reflection film and a 0.53 μm antireflection film to replace part of the transmissive dielectric film.

[0043] Specifically, the structure of the laser is as shown in the appendix Figure 5 The pump source 1, the pump focusing system 2, the incident mirror 3, the laser crystal 4, the Sm:GdCOB polarization element 5, the frequency doubling crystal 9, and the frequency doubling output cavity mirror 11 are arranged in sequence along the optical path: The laser emitted by the pump source 1 has a wavelength of 808 nm. The beam compression ratio of the focusing system 2 is 1:1. The incident mirror 3 is coated with an antireflection film for the pump light and high-reflection films of 1.06 μm and 0.53 μm. The laser crystal 4 is a

[111] -cut, 0.5 at.%, 3×3×10 mm 3 Nd:YAG crystal, with both ends coated with 1.06 μm and 0.53 μm antireflection films. The polarization element 5 is a Sm 3+ :GdCOB wafer with a concentration of 3 at.%, the cut direction is N Z , and the size is 3×3×1 mm 3, Double-sided polishing. The frequency doubling crystal 9 meets the phase matching condition, which can be LBO, or YCOB, BIBO. The frequency doubling output mirror 11 is coated with a high reflection film at 1.06 μm and an antireflection film at 0.53 μm. When the pump light emitted by the pump source 1 passes through the focusing system 2 and is incident into the Nd:YAG crystal 4, 1064 nm laser oscillation and amplification are generated. After passing through the polarization selection of the component 5 and the frequency doubling of the frequency doubling crystal 9, continuous frequency doubled light is output from the mirror 11.

[0044] In another embodiment, a Q-switch is also arranged in the resonant cavity. The Q-switch is located behind the polarization element and is used to modulate the generation of pulsed laser. After the resonant cavity, a convex lens, an extracavity frequency doubling crystal and a filter are sequentially arranged along the optical path adjacent to the resonant cavity. After the pulsed laser is focused by the convex lens, it is incident into the extracavity frequency doubling crystal that meets the phase matching condition as the fundamental frequency light. After the frequency doubled light emitted from the extracavity frequency doubling crystal is filtered by the filter to remove the remaining fundamental frequency light, pure pulsed frequency doubled light is output.

[0045] Specifically, the structure of the laser is as shown in the appendix Figure 6 . The pump source 1, the pump focusing system 2, the incident mirror 3, the laser crystal 4, the Sm:GdCOB polarization element 5, the Q-switch 7, the output mirror 6, the focusing convex lens 8, the frequency doubling crystal 9, and the filter 10 are arranged in sequence along the optical path. It is characterized in that: the laser wavelength emitted by the pump source 1 is 808 nm. The beam compression ratio of the focusing system 2 is 1:1. The incident mirror 3 is coated with an antireflection film for the pump light and a high reflection film at 1.06 μm. The laser crystal 4 is a Nd:YAG crystal with a

[111] cut, 0.5 at.%, and 3×3×10 mm 3 . The two ends are coated with an antireflection film at 1.06 μm. The polarization element 5 is a Sm:GdCOB wafer with a Sm3+ concentration of 3 at.%, and the cut direction is N Z , with a size of 3×3×1 mm 3 , double-sided polished. The Q-switch 7 is an active or passive pulse wave modulator, such as an electro-optic Q-switch, an acousto-optic Q-switch, and a passive Q-switch made of a crystal or two-dimensional material with saturable absorption properties, etc. The output mirror 6 is coated with a dielectric film that is partially transmissive in the 1.05 - 1.1 μm band, and the transmittance at 1.064 μm is 5%. When the pump light emitted by the pump source 1 passes through the focusing system 2 and is incident into the Nd:YAG crystal 4, laser oscillation and amplification are generated. After passing through the polarization selection of the component 5 and the modulation of the Q-switch 7, 1064 nm pulsed laser output with polarization along the N Y direction of the Sm:GdCOB wafer is achieved. The output laser is focused by the convex lens 8 and then incident into the frequency doubling crystal 9 that meets the phase matching condition as the fundamental frequency light. After the frequency doubled light emitted from 9 is filtered by the filter 10 to remove the remaining fundamental frequency light, pure 532 nm pulsed light is output.

[0046] In the present specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0047] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An intracavity optical polarization element for a solid-state laser, characterized in that, It includes a Sm:GdCa4O(BO3)3 polarization wafer, which is used to achieve polarized laser output in the 1-μm band.

2. An intracavity optical polarization element for a solid-state laser according to claim 1, characterized in that, Sm in the polarization crystal 3+ The concentration is 1-50 at.%.

3. An intracavity optical polarization element for a solid-state laser according to claim 1, characterized in that, The optical axis direction of the polarization wafer is along the refractive index principal axis Nz, the optical surface is polished, and the optical thickness is 0.1 - 20 mm.

4. An intracavity optical polarization element for a solid-state laser according to claim 3, characterized in that, The optical surface of the polarization wafer is coated with an antireflection film in the 1-μm band.

5. A solid-state laser, characterized in that, Any one of the intracavity optical polarization elements for solid-state lasers described in claims 1 - 4 is adopted, including a laser pumping device and a resonant cavity adjacent to the laser pumping device, and a laser crystal and a polarization element are arranged in the resonant cavity.

6. A solid-state laser according to claim 5, characterized in that, The laser pumping device includes a pump source and a focusing system. The resonant cavity includes an input mirror and an output mirror. The input mirror is coated with an antireflection film for pump light and a high-reflection film at 1.05 - 1.1 μm; the output mirror is coated with a partially transmissive dielectric film at 1.05 - 1.1 μm, and the transmittance of the partially transmissive dielectric film in the 1.064-μm band is 5%.

7. A solid-state laser according to claim 5, characterized in that, An intracavity frequency doubling crystal is also arranged in the resonant cavity, which is used to double the frequency of the polarization-selected laser and output continuous frequency-doubled laser.

8. A solid-state laser according to claim 7, characterized in that, The output mirror is coated with a 1.06-μm high-reflection film and a 0.53-μm antireflection film to replace the partially transmissive dielectric film.

9. A solid-state laser according to claim 5, characterized in that, A Q-switch is also arranged in the resonant cavity. The Q-switch is located behind the polarization element and is used to modulate and generate pulsed laser.

10. A solid-state laser according to claim 9, characterized in that, After the resonant cavity, a convex lens, an extracavity frequency doubling crystal, and a filter are arranged adjacent to the resonant cavity and in sequence along the optical path. After the pulsed laser is focused by the convex lens, it is incident on the extracavity frequency doubling crystal that satisfies the phase matching condition as the fundamental frequency light. After the frequency-doubled light emitted from the extracavity frequency doubling crystal is filtered by the filter to remove the remaining fundamental frequency light, pure pulsed frequency-doubled light is output.

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