Laser conditioning method for a nonlinear optical crystal

Abstract

The disclosure relates to a laser conditioning method (2) for a nonlinear optical crystal in which the nonlinear optical crystal is irradiated by a laser with a photon energy from Eg / 2 to Eg, where Eg is the band gap of the crystal. Comparative results show that when the 266 nm laser (2), which is much weaker than the 355 nm laser, is used, and provided that the laser power density is only 0.13 GW / cm², the zero probability volume damage threshold is 120% higher than that before conditioning. The laser conditioning for a potassium dihydrogen phosphate (KDP) crystal based on two-photon absorption according to the disclosure has higher conditioning efficiency and greater potential for improving the crystal volume damage threshold than the three-photon absorption laser conditioning.

Description

Title of the invention: Laser conditioning method for a nonlinear optical crystal Technical field

[0001] The present disclosure belongs to the technical field of laser conditioning, and relates in particular to a laser conditioning method for a nonlinear optical crystal. BACKGROUND

[0002] Nonlinear artificial crystal is an essential key optical element in both lasers and large-scale intense laser devices. Potassium dihydrogen phosphate (KDP) nonlinear optical crystal and other similar crystals with similar lattice structures, such as deuterated potassium dihydrogen phosphate (DKDP) with different deuterated ratios and ammonium dihydrogen phosphate (ADP), are important nonlinear artificial crystals that are widely used at present. These crystals are usually used as frequency doubling elements or electro-optical switching elements in laser devices and are frequently exposed to intense laser radiation.When the laser intensity I (in unit of W / cm2) irradiated on the crystal surface is higher than a certain threshold (volume damage threshold 1 th), the laser causes irreversible damage inside the crystal, so that the nonlinear artificial crystal loses its basic function, and the laser loses its function. Therefore, the ability of KDP and its similar crystals to withstand intense laser damage, i.e., the magnitude of the volume damage threshold I th, is one of its very important performance indicators.

[0003] In order to improve the ability of KDP and its similar crystals to withstand intense laser damage, a so-called laser conditioning technology has been developed over the past 40 years. The basic process of such technology is that the volume damage threshold of unconditioned KDP and its similar crystals is assumed to be I thJ and if the crystal is irradiated directly by the laser with a laser intensity higher than 1 thJ, irreversible volume damage will occur in the crystal. However, the crystal could be irradiated with a number of pulses using a laser with a laser intensity lower than I thJ, such as a laser with an intensity of 0.5 times I thJ, then the crystal will not be damaged when the crystal is subsequently irradiated using a laser with an intensity of I thJ.Such a method of increasing the volume damage threshold of the I th laser is called KDP laser conditioning technology. and its similar crystals. Taking DKDP crystal as an example, 17 thJ of the crystal grown using the most advanced crystal growth technology at present is about 4 J / cm2 / 3 ns. After conditioning using the 355 nm wavelength laser, 17 th of the crystal could increase by about 8 J / cm2 / 3 ns. In practice, in order to achieve the optimal conditioning effect, through the optimization of laser parameters, it is found that the conditioning effect is highly dependent on the conditioned laser intensity for the 355 nm wavelength laser. The more powerful the laser is, the better the conditioning effect will be. However, the laser should not be too powerful, otherwise it will directly damage the crystal. The laser intensity with the optimal conditioning effect is about 5 GW / cm2.

[0004] “Off-Line Sub-Nanosecond Laser Conditioning Technology On Large-Aperture Deuterated Potassium Dihydrogen Phosphate Crystals” (Liu Zhoho et al., Acta Phys. Sin., Vol. 70, No. 7 (2021), 074208) discloses the laser conditioning technology for KDP / DKDP crystals using triple frequency laser output (of 355 nm wavelength) by the Nd:YAG laser device. The conditioning experimental parameters are as follows: a pulsed laser applied to the DKDP crystal to be conditioned has a pulse width of 0.5 nanoseconds, a spot diameter of 0.68 mm, a wavelength of 355 nm, a maximum conditioned laser fluence of 2 J / cm2, and a maximum laser power density of 4 GW / cm2. Sub-nanosecond laser conditioning could increase the zero-probability volume damage threshold of the DKDP crystal by about one time.

[0005] However, due to the limited laser energy output by the pulsed laser, in order to achieve the laser intensity of 4 GW / cm2 to 5 GW / cm2 required for the conditioning technology, the laser spot could only be reduced to a diameter of less than 1 mm (0.68 mm as indicated in the above document). Considering a maximum repetition rate of the energy output by the pulsed laser, the crystal area that could be conditioned by the laser conditioning per hour is only of the order of 20 cm2 currently in terms of conditioning efficiency.

[0006] In summary, the current laser packaging technology for KDP and its similar crystals has shortcomings of low packaging efficiency and high packaging cost. EXPOSED

[0007] The present disclosure aims to provide a laser conditioning method for a nonlinear optical crystal based on two-photon absorption. The laser conditioning method according to the present disclosure could greatly improve and effectively a nonlinear optical crystal laser volume damage threshold and reduce a packaging cost.

[0008] To achieve the above-mentioned objective, the present disclosure provides the following technological solutions.

[0009] The present disclosure provides a laser conditioning method for a nonlinear optical crystal based on two-photon absorption, comprising the following steps:

[0010] irradiating the nonlinear optical crystal with a laser, where the laser has a photon energy of Eg / 2 to Eg, Eg being a band gap of the nonlinear optical crystal.

[0011] In some embodiments, the laser has a wavelength of 165 nm to 305 nm.

[0012] In some embodiments, the laser has the wavelength of 266 nm.

[0013] In some embodiments, the laser is generated by a laser device, and the laser device is selected from the group consisting of a solid-state laser device and an excimer laser device.

[0014] In some embodiments, the nonlinear optical crystal comprises one selected from the group consisting of potassium dihydrogen phosphate, deuterated potassium dihydrogen phosphate, or ammonium dihydrogen phosphate.

[0015] In some embodiments, the laser has a pulse width of 0.3 ns to 40 ns or 100 fs to 100 ps.

[0016] In some embodiments, the laser has a spot diameter of 0.05 mm to 5 mm.

[0017] In some embodiments, a power density of the laser is 0.2 times to 1.5 times a volume damage threshold of the nonlinear optical crystal, and the volume damage threshold of the nonlinear optical crystal is a volume damage threshold corresponding to a wavelength of a conditioned laser.

[0018] In some embodiments, a number of pulses of the laser is 90% to 95% of a number of saturated pulses.

[0019] In some embodiments, the nonlinear optical crystal is deuterated potassium dihydrogen phosphate; the laser has a wavelength of 266 nm, a pulse width of 10 ns, a spot diameter of 1 mm, and a power density of 0.13 GW / cm2.

[0020] The present disclosure provides a laser conditioning method for a nonlinear optical crystal based on two-photon absorption, comprising the following steps: irradiating a nonlinear optical crystal with a laser, where the laser has a photon energy from Eg / 2 to Eg, Eg being a band gap of the crystal nonlinear optics. Since a 355 nm wavelength laser is used for laser conditioning in the prior art, valence band electrons of the nonlinear optical crystal need to absorb three photons at the same time before being ionized to a conduction band, which is a third-order nonlinear process. In the present disclosure, the laser with a photon energy of Eg / 2 to Eg is used for conditioning, and valence band electrons of the nonlinear optical crystal need to absorb only two photons at the same time before being ionized to a conduction band, which is a second-order nonlinear process.Since the probability of two-photon absorption is thousand times to tens of thousands of times higher than that of three-photon absorption, compared with laser conditioning based on three-photon absorption at present, in the present disclosure the laser conditioning method using the laser with photon energy of Eg / 2 to Eg, i.e., based on two-photon absorption, has greatly improved efficiency.As can be seen from the results of examples and comparative examples, in the present disclosure, the 266 nm wavelength laser, which is much weaker (more than 10 times) than that of 355 nm wavelength, is used for conditioning, and under the condition that a laser power density is only 0.13 GW / cm2, the zero-probability volume damage threshold of the DKDP crystal is 4.7 J / cm2 after conditioning, which is 120% higher than the zero-probability volume damage threshold of 2.3 J / cm2 before conditioning. Compared with the fact that the laser intensity of 4 GW / cm2 to 5 GW / cm2 is required in the prior art to achieve the same conditioning effect (the volume damage threshold is improved by about one time), the laser power density in the present disclosure is of course reduced, thereby improving the conditioning efficiency and reducing the packaging cost.Furthermore, compared with three-photon absorption laser conditioning, the laser conditioning of the KDP crystal based on two-photon absorption according to the present disclosure not only has higher conditioning efficiency, but also has greater potential for improving a crystal volume damage threshold. Brief description of the drawings

[0021] [Fig.l] is a schematic flowchart of laser conditioning of a DKDP crystal based on two-photon absorption according to one embodiment of the present disclosure.

[0022] [Fig.2] is a schematic diagram of an experimental optical path system for quadruple frequency laser conditioning of a DKDP crystal based on two-photon absorption according to one embodiment of the present disclosure.

[0023] [Fig.3] is a schematic diagram of a volume damage probability curve of a crystal measured by a small aperture laser and a triple frequency laser conditioning optical path system.

[0024] [Fig.4] is an electron paramagnetic resonance spectrogram of a DKDP crystal before and after laser conditioning in Embodiment 1.

[0025] [Fig.5] is a measurement result diagram of a damage probability curve of a DKDP crystal before and after laser conditioning in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present disclosure provides a laser conditioning method for a nonlinear optical crystal based on two-photon absorption, comprising (or consisting of) the following steps:

[0027] irradiating a nonlinear optical crystal with a laser, where the laser has a photon energy of Eg / 2 to Eg, Eg being a band gap of the nonlinear optical crystal.

[0028] In the present disclosure, unless otherwise indicated, all raw materials / preparation components are commercially available products well known to those skilled in the art.

[0029] According to the present disclosure, based on the physical phenomenon of two-photon absorption of the crystal, the nonlinear optical crystal is subjected to laser conditioning, greatly and effectively increasing the laser volume damage threshold of these crystals, wherein the nonlinear optical crystal comprises one selected from the group consisting of potassium dihydrogen phosphate (KDP) nonlinear optical crystals and similar crystals having lattice structures similar to KDP. In some embodiments, the similar crystals comprise (or are) one selected from the group consisting of deuterated potassium dihydrogen phosphate (DKDP) and ammonium dihydrogen phosphate (ADP) and the like.

[0030] There is no special requirement on the preparation method of the nonlinear optical crystal, and the nonlinear optical intraocular lens which is well known to those skilled in the art and which is obtained by artificial growth and annealing treatment can be used. In some embodiments, prior to irradiation, the nonlinear optical crystal is subjected to cutting and surface polishing in sequence. There is no special requirement on the specific implementation of the cutting and surface polishing. In some embodiments, the cutting is performed according to the required direction and size when the nonlinear optical crystal is used. In some embodiments, the surface of the nonlinear optical crystal obtained after surface polishing achieves optical quality uniformity.

[0031] In some embodiments, the nonlinear optical crystal comprises one selected from the group consisting of potassium dihydrogen phosphate (KDP), deuterated potassium dihydrogen phosphate (DKDP), or ammonium dihydrogen phosphate (ADP). In some embodiments, the deuterated ratio of DKDP is in a range of 5% to 98%. In a specific embodiment of the present disclosure, DKDP is taken as an example to illustrate the laser conditioning method according to the present disclosure in detail. The deuterated ratio of DKDP crystal 4 is 70%. DKDP crystal 4 is an insulator with a wide band gap (Eg). The band gap of DKDP crystal 4 is in a range of 7.5 ev to 9 ev.

[0032] In some embodiments, the laser is generated by a laser device. The laser device is selected from the group consisting of a solid-state laser device and an excimer laser device. In other embodiments, the laser device is a solid-state laser device. Compared with the excimer laser device, the solid-state laser device is more environmentally friendly. In the present disclosure, the solid-state laser device is preferably used for laser conditioning of the nonlinear optical crystal. The conditioning process is green and environmentally friendly, and suitable for wide industrial application. In a specific embodiment of the present disclosure, the laser device used in the laser conditioning is an Nd:YAG 1 laser device.The pulse width of Nd:YAG laser device 1 is nanosecond to sub-nanosecond, which could output high-efficiency quadruple-frequency laser.

[0033] In some embodiments, the photon energy (hv) of the laser is in a range from Eg / 2 to Eg. The laser photons with the photon energy of Eg / 2 to Eg could ionize valence band electrons in the nonlinear optical crystal to the conduction band of the crystal through the two-photon absorption process of the nonlinear optical crystal. The nonlinear optical crystal is irradiated by a laser with a number of pulses at a laser intensity lower than its volume damage threshold, and the volume damage threshold of the nonlinear optical crystal is greatly and effectively improved.

[0034] In some embodiments, the wavelength of the laser is in a range of 165 nm to 305 nm, preferably 175 nm to 295 nm, and more preferably 205 nm to 275 nm. In a specific embodiment of the present disclosure, the laser has a wavelength of 266 nm. In some embodiments, the quadruple frequency laser used herein has a wavelength of 266 nm, a photon energy of 4.66 eV, and a photon energy between 3.75 ev and 7.5 ev, thus satisfying the photon energy requirement for laser conditioning of the DKDP 4 crystal based on two-photon absorption.

[0035] In some embodiments, the pulse width of the laser is in a range of 0.3 ns to 40 ns or 100 fs to 100 ps, ​​preferably 5 ns to 40 ns or 150 fs to 80 ps, ​​and more preferably 15 ns to 30 ns or 500 fs to 50 ps. In some embodiments, the spot diameter of the laser is in a range of 0.05 mm to 5 mm, preferably 0.1 mm to 5 mm, and more preferably 1 mm to 5 mm. In some embodiments, the power density of the laser is 0.2 times to 1.5 times the volume damage threshold of the nonlinear optical crystal, preferably 0.3 times to 1.5 times the volume damage threshold of the nonlinear optical crystal, more preferably 0.4 to 1.5 times the volume damage threshold of the nonlinear optical crystal, and most preferably 0.5 to 1.5 times the volume damage threshold of the nonlinear optical crystal.The volume damage threshold of the nonlinear optical crystal is a volume damage threshold corresponding to the wavelength of the conditioned laser. In some embodiments, the volume damage threshold of the nonlinear optical crystal to be conditioned varies with the wavelength of the conditioned laser. In some embodiments, the power density of the laser is 0.2 times to 1.5 times the volume damage threshold of the nonlinear optical crystal. The volume damage threshold is the volume damage threshold of the nonlinear optical crystal corresponding to the wavelength of the conditioned laser.

[0036] In a specific embodiment of the present disclosure, the laser power density is 0.565 times the volume damage threshold of the nonlinear optical crystal. In some embodiments, the volume damage threshold of the nonlinear optical crystal is the maximum laser power density (in unit of W / cm2) when the nonlinear optical crystal is irreversibly damaged by laser radiation before conditioning. In some embodiments, before laser conditioning, the nonlinear optical crystal to be conditioned is evaluated and calculated to obtain its volume damage threshold. In some embodiments, the number of pulses of the laser is in a range of 90% to 95% of the number of saturated pulses, and preferably 95% of the number of saturated pulses.In the present disclosure, in the laser conditioning process, the volume damage threshold of the nonlinear optical crystal gradually increases with the increase of the number of laser pulses, but after the number of laser pulses reaches a certain value, the volume damage threshold of the nonlinear optical crystal no longer increases to be saturated when the number of laser pulses increases again. In the present disclosure, the number of saturated pulses is defined as a number . of laser pulses that the volume damage threshold of the nonlinear optical crystal no longer increases with increasing number of laser pulses in the laser conditioning process.

[0037] In a specific embodiment of the present disclosure, the nonlinear optical crystal is deuterated potassium dihydrogen phosphate; the laser has a wavelength of 266 nm, a pulse width of 10 ns, a spot diameter of 1 mm, a power density of 0.13 GW / cm2, and a pulse number of 5. The pulse number is the number of laser pulses from which the nonlinear optical crystal receives the laser pulse radiation at the same position. The pulse number is 5, which means that the number of laser pulses from which the nonlinear optical crystal receives the laser pulse radiation at the same position is 5.

[0038] In a specific embodiment of the present disclosure, a schematic flowchart of the laser conditioning process for the nonlinear optical crystal is shown in [Fig.l], and a block diagram of the optical path system is shown in [Fig.2]. [Fig.l] illustrates the Nd:YAG laser device 1, the 266 nm laser 2, the focusing lens 3 and the DKDP crystal to be conditioned 4. As shown in [Fig.2], the optical path system used in the laser conditioning system according to the present disclosure consists of a laser device and an optical path adjustment and transmission system, wherein: the laser device is an Nd:YAG 1 laser device; The optical path adjustment and transmission system consists of an elevation mirror 6, an energy meter (29:1) 7, a spectroscope 8, a 532 nm high-reflectivity mirror 9, a convex lens 10, a concave lens 11, a triple-beam reduction system 12, a quadruple-frequency crystal 13, a prism 14, a convex lens (f:1000 mm) 1 5 and a sequence reflector 16. The diameter of the 532 nm spot is about 12 mm and the energy of the 532 nm spot is 664 rnJ, the diameter of the 266 nm focal spot is about 1 mm and the energy of the 266 nm focal spot is 10 mJ.The laser pulse width is 10 ns and the power density of the 266 nm laser is 0.13 GW / cm2. In a specific embodiment of the present disclosure, as shown in [Fig. 2], the 266 nm ultraviolet laser output from the Nd:YAG laser device 1 is focused by a long focal length focusing lens 3 and is incident on the nonlinear optical crystal to be conditioned. Usually, the area of ​​the crystal to be conditioned is much larger than that of the laser spot. In some embodiments, the entire crystal is conditioned to be uniform by a laser spot scanning method.

[0039] In the present disclosure, the selection of the laser photon energy is the key to improving the laser volume damage threshold of the nonlinear optical crystal of significantly and efficiently. In the prior art when a triple-frequency laser of wavelength 355 nm is used for laser conditioning, valence band electrons of the nonlinear optical crystal need to absorb three photons at the same time before being ionized on a conduction band, which is a third-order nonlinear process. In the present disclosure, a quadruple-frequency laser of wavelength 266 nm is used for laser conditioning; valence band electrons of the nonlinear optical crystal need to absorb only two photons at the same time before being ionized on a conduction band, which is a second-order nonlinear process.Since the probability of two-photon absorption is a thousand times to tens of thousands of times higher than that of three-photon absorption, compared with the laser conditioning based on three-photon absorption at present, the laser conditioning technology based on two-photon absorption according to the present disclosure could greatly improve the efficiency of laser conditioning.

[0040] In order to further illustrate the present disclosure, the technical solutions of the present disclosure are described in detail in conjunction with examples below, but these examples should not be understood as limiting the scope of the present disclosure.

[0041] Example 1

[0042] The DKDP 4 crystal (with a deuterated ratio of 70%) was subjected to laser conditioning according to the laser conditioning flowchart shown in [Fig.l] and the optical path diagram shown in [Fig.2], where the laser conditioning was conducted as follows.

[0043] An artificially grown DKDP 4 crystal that had been treated by a thermal annealing process was selected and then cut according to the direction and size required for crystal application. After that, a cut crystal was subjected to surface polishing so that the surface achieved optical quality smoothness.

[0044] The 266 nm ultraviolet laser output from the Nd:YAG laser device 1 is focused by a long focal length focusing lens 3, and is incident on the DKDP crystal 4 to be conditioned. The entire crystal was subjected to conditioning to be uniform by a laser spot scanning method. During the conditioning, the laser parameters are as follows: the wavelength of 266 nm, the spot diameter of 1 mm, the power density of 0.13 GW / cm2, the number of pulses of 5 (the DKDP crystal is irradiated by five laser pulses at the same position), the pulse width of 10 ns, and the fluence of 1.3 J / cm2.

[0045] In Example 1, the number of intrinsic “point defects” of the DKDP 4 crystal before and after laser conditioning was measured against a spectrometer electron paramagnetic resonance spectra with a microwave frequency of 9.4 GHz at a sample temperature of 30 K. The obtained electron paramagnetic spectrum is shown in [Fig.4]. In [Fig.4], the solid curve represents the spectrum of the crystal without laser conditioning, and the broken curve represents the spectrum of the crystal after laser conditioning. As can be seen in [Fig.4], the number of hole-type "point defects" [H2PO4]0 directly related to the laser volume damage threshold after laser conditioning is reduced to only 60% of the point defects before laser conditioning.

[0046] Comparative example 1

[0047] The DKDP crystal 4 was subjected to laser conditioning according to the laser conditioning flowchart shown in [Fig.l] and the optical path diagram shown in [Fig.3]; wherein the optical path diagram shown in [Fig.3] is not only suitable for damage probability curve measurement, but also suitable for laser conditioning using a 355 nm laser. [Fig.3] more specifically illustrates a laser device 18, a CW semiconductor laser 19, an energy meter (29:1) 7, a spectroscope 8, a convex lens (f:1000 mm) 15, a focal length of 1000 mm, bulk damage point scattering observation 24, and a DKDP sample 4 to be measured; The DKDP 4 sample is placed at the focal point, and the focal spot diameter of the 355 nm laser is 0.470 mm. The laser conditioning was conducted as follows.

[0048] An artificially grown DKDP 4 crystal that had been treated by a thermal annealing process was selected and then cut according to the direction and size required for crystal application. After that, a cut crystal was subjected to surface polishing so that the surface achieved optical quality smoothness.

[0049] The 355 nm ultraviolet laser output from the Nd:YAG laser device 1 is focused by a long focal length focusing lens, and is incident on the DKDP crystal 4 to be conditioned. The entire crystal was subjected to conditioning to be uniform by a laser spot scanning method. In the conditioning, the laser parameters were as follows: the wavelength of 355 nm, the spot diameter of 1 mm, the power density of 0.1 GW / cm2, the number of pulses of 5 (the DKDP crystal 4 is irradiated by five laser pulses at the same position), the pulse width of 10 ns, and the fluence of 1.0 J / cm2.

[0050] In Example 1 and Comparative Example 1, the DKDP 4 crystals before and after laser conditioning were tested according to the optical path diagram of the crystal volume damage probability curve measured by the small aperture laser as shown in [Fig.3]. The results are shown in [Fig.5]. [Fig.5] shows the damage probability curves of the DKDP 4 crystals before and after laser conditioning in Example 1 and Example Comparative Example 1. It can be concluded from [Fig.5] that the zero-probability volume damage threshold of the DKDP 4 crystal before laser conditioning is 2.3 J / cm2, the zero-probability volume damage threshold of the DKDP 4 crystal after quadruple-frequency conditioning in Example 1 is 4.7 J / cm2, and the zero-probability volume damage threshold of the DKDP 4 crystal after triple-frequency conditioning in Comparative Example 1 is 2.7 J / cm2.After comparing the results of Example 1 and Comparative Example 1, it can be seen that when the laser pulse width is the same, and the laser power (intensity) is almost the same, but the laser wavelength is different, the zero-probability volume damage threshold of the crystal conditioned by a 266 nm laser based on two-photon absorption in Example 1 increases by 120%, while the zero-probability volume damage threshold of the crystal conditioned by a 355 nm laser based on three-photon absorption in Comparative Example 1 increases by only 20%. [Fig. 5] proves the effectiveness of an efficient laser conditioning method for a nonlinear optical crystal based on two-photon absorption according to the present disclosure.Furthermore, in this example, the 266 nm wavelength laser, which is much weaker (more than 10 times) than 355 nm, is used for conditioning, and under the condition that a laser power density is only 0.13 GW / cm2, it is found that the zero-probability volume damage threshold of the DKDP 4 crystal is 4.7 J / cm2 after conditioning, which is 120% higher than the zero-probability volume damage threshold of 2.3 J / cm2 before conditioning. Compared with Comparative Example 1, the conditioning method according to Example 1 of the present disclosure has a remarkable effect of improving the volume damage threshold of the crystal, and achieves the same conditioning effect as that of the prior art (the volume damage threshold is improved by about one time).According to the present disclosure, the laser power density (0.13 GW / cm2) of the 266 nm wavelength laser is only a few tenths of that (4 GW / cm2 to 5 GW / cm2) of the 355 nm wavelength laser, thereby improving the laser conditioning efficiency and reducing the conditioning cost. Finally, the laser conditioning of the KDP crystal based on two-photon absorption according to the present disclosure not only has a higher conditioning efficiency than that of three-photon absorption laser conditioning, but also has a greater potential for improving a crystal volume damage threshold than that of three-photon absorption laser conditioning. Such potential lies in the ability to obtain a higher conduction band electron density when the laser conditioning based on two-photon absorption is used.

[0051] Although the present disclosure is described in detail according to the above-mentioned examples, the examples are only some of the embodiments of the present disclosure, rather than all of the embodiments. Other embodiments could be obtained without creative effort according to these embodiments, all of which fall within the scope of the present disclosure.

Claims

Claims

1. 1 A method of laser conditioning a nonlinear optical crystal, comprising the following steps: irradiating the nonlinear optical crystal with a laser (2), wherein the laser (2) has a photon energy of Eg / 2 to Eg, Eg being a band gap of the nonlinear optical crystal.

2. 2 A laser conditioning method according to claim 1, wherein the laser (2) has a wavelength of 165 nm to 305 nm.

3. 3 A laser conditioning method according to claim 2, wherein the laser (2) has the wavelength of 266 nm.

4. 4 A laser conditioning method according to any one of claims 1 to 3, wherein the laser (2) is generated by a laser device (1), and the laser device (1) is selected from the group consisting of a solid-state laser device and an excimer laser device.

5. 5 A laser conditioning method according to any one of claims 1 to 4, wherein the nonlinear optical crystal comprises one selected from the group consisting of potassium dihydrogen phosphate, deuterated potassium dihydrogen phosphate and ammonium dihydrogen phosphate.

6. 6 A laser conditioning method according to any one of claims 1 to 5, wherein the laser (2) has a pulse width of 0.3 ns to 40 ns or 100 fs to 100 ps.

7. 7 A laser conditioning method according to any one of claims 1 to 6, wherein the laser (2) has a spot diameter of 0.05 mm to 5 mm.

8. 8 A laser conditioning method according to any one of claims 1 to 7, wherein a power density of the laser (2) is 0.2 times to 1.5 times a volume damage threshold of the nonlinear optical crystal, and the volume damage threshold of the nonlinear optical crystal is a volume damage threshold corresponding to a wavelength of a conditioned laser.

9. 9 A laser conditioning method according to any one of claims 1 to 8, wherein a number of pulses of the laser (2) is 90% to 95% of a number of saturated pulses.

10. 10 A laser conditioning method according to any one of claims 1 to 9, wherein the nonlinear optical crystal is deuterated potassium dihydrogen phosphate (4); the laser (2) has a wavelength of 266 nm, a pulse width of 10 ns, a spot diameter of 1 mm, and a power density of 0.13 GW / cm2.

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