A praseodymium-doped third-harmonic generation deep-ultraviolet laser

Abstract

The application discloses a kind of praseodymium-doped third harmonic generation deep ultraviolet lasers, comprising: the first blue light semiconductor laser and second blue light semiconductor laser simultaneously emit pump laser respectively after focusing by first focusing lens and second focusing lens, respectively transmit first laser cavity end mirror and second laser cavity end mirror and be incident to first praseodymium-doped laser material, first praseodymium-doped laser material obtains gain after absorbing two pump lasers, and praseodymium-doped visible light fundamental laser is generated in the laser cavity, praseodymium-doped visible light fundamental laser obtains frequency-doubled laser after frequency doubling by frequency-doubling crystal, frequency-doubled laser and residual praseodymium-doped visible light fundamental laser are output from second laser cavity end mirror after sum frequency by sum frequency crystal, and then third harmonic deep ultraviolet laser is output after filtering other wavelength laser by filter piece.The application provides a simple and effective scheme for the generation of short-wavelength deep ultraviolet laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of deep ultraviolet lasers, in particular to a deep ultraviolet laser generated by three-harmonic of praseodymium doping. BACKGROUND

[0002] From the wavelength range of light waves, the short wavelength of 200nm-280nm is usually called "deep ultraviolet" band. The laser wavelength of this band is very short, has a very small diffraction limit, and therefore has high resolution. It has important application value in many fields such as Raman spectroscopy, photolithography, microscopic imaging, optical detection, sterilization and life science. Although shorter wavelengths less than 200nm undoubtedly have higher resolution, such as vacuum ultraviolet and extreme ultraviolet, the generation of wavelengths less than 200nm is more difficult, and the vacuum ultraviolet wavelength is quickly absorbed by oxygen in the air to form ozone. Therefore, the deep ultraviolet band is the best band that can meet these applications and can be easily applied. The application value of 213nm deep ultraviolet laser, which is close to the shortest wavelength limit of deep ultraviolet band, is self-evident.

[0003] Currently, there have been several reports on 213nm deep ultraviolet laser. For example, in 2000, Gruen et al. of the University of Chicago in the United States applied for a U.S. patent, using a high-power 1064nm Nd:YAG pulse laser as the fundamental wave, and converting the frequency to 213nm deep ultraviolet pulse laser by five times[1]. That is, the 1064nm laser is frequency doubled twice (i.e. four times), to obtain 266nm deep ultraviolet laser, and then the 1064nm and 266nm are frequency mixed to obtain 213nm deep ultraviolet laser. This is the most common method for developing 213nm deep ultraviolet laser. For example, in 2004, Sakuma et al. of Japan converted the frequency of Nd:YAG 1064nm near-infrared continuous wave laser to 213nm deep ultraviolet continuous wave laser by mixing the frequency of 1064nm and 266nm (i.e. four times harmonic of 1064nm) (as shown in 3+ ). Figure 1 The schematic diagram of the device is shown in FIG. 1). Because the peak power of continuous wave is very low, in order to improve the frequency conversion efficiency, Sakuma et al. used a resonant enhancement technique to precisely control the laser cavity, so as to effectively generate 213nm deep ultraviolet laser output. This is a common method for obtaining continuous wave laser by frequency conversion. However, whether it is pulse operation or continuous wave operation, the entire 213nm deep ultraviolet laser system is extremely complex, which will lead to problems such as large system, low efficiency, high cost, poor stability and difficult maintenance. In 2019, Kaneda et al. of Japan used a more complex system (as shown in Figure 2 ), that is, a 1.9 micron near-infrared laser amplifier doped with thulium (Tm 3+ ) and a 1.5 micron near-infrared laser amplifier doped with erbium (Er 3+The 213nm deep ultraviolet laser is obtained by using a 1.5-micron near-infrared laser amplifier of a 1.5-micron near-infrared laser of a 426nm visible light laser, and then the 426nm visible light laser is frequency doubled to generate a 426nm visible light laser, and finally the 426nm visible light laser is frequency doubled to finally obtain a 213nm deep ultraviolet laser; such a more complex system greatly limits the practical application of the 213nm deep ultraviolet laser. Overall, the current 213nm, or the deep ultraviolet laser near this band, is all obtained by using a fifth or higher harmonic, but the operation modes are different, some operate in continuous wave mode, and more operate in pulse mode. SUMMARY

[0004] The existing scheme uses near-infrared laser as the fundamental wave, and therefore the purpose of the present application is to provide a praseodymium-doped third-harmonic deep ultraviolet laser using visible light as the fundamental wave, which can solve the above problems.

[0005] The present application provides a praseodymium-doped third-harmonic deep ultraviolet laser, comprising:

[0006] A first blue light semiconductor laser, a second blue light semiconductor laser, a first focusing lens, a second focusing lens, a first laser cavity end mirror, a second laser cavity end mirror, a third laser cavity end mirror, a fourth laser cavity end mirror, a first praseodymium-doped laser material, a frequency doubling crystal, a sum frequency crystal, and a filter;

[0007] The first focusing lens, the first laser cavity end mirror, the first praseodymium-doped laser material, and the second laser cavity end mirror are sequentially arranged on the incident light path of the first blue light semiconductor laser; the second focusing lens, the second laser cavity end mirror, the first praseodymium-doped laser material, and the first laser cavity end mirror are sequentially arranged on the incident light path of the second blue light semiconductor laser; the sum frequency crystal and the third laser cavity end mirror are sequentially arranged on the reflected light path of the second laser cavity end mirror; the frequency doubling crystal, the fourth laser cavity end mirror are sequentially arranged on the first reflected light path of the third laser cavity end mirror; the sum frequency crystal, the second laser cavity end mirror, and the filter are sequentially arranged on the second reflected light path of the third laser cavity end mirror; and the incident light path of the first blue light semiconductor laser, the incident light path of the second blue light semiconductor laser, the reflected light path of the second laser cavity end mirror, the first reflected light path of the third laser cavity end mirror, and the second reflected light path of the third laser cavity end mirror constitute a laser cavity light path.

[0008] The first blue light semiconductor laser and the second blue light semiconductor laser emit pump lasers at the same time, the pump lasers are focused by the first focusing lens and the second focusing lens respectively, and then are transmitted to the first laser cavity end mirror and the second laser cavity end mirror respectively to be incident into the first praseodymium-doped laser material, the first praseodymium-doped laser material absorbs the two pump lights to obtain praseodymium-doped visible light fundamental laser through gain conversion, the praseodymium-doped visible light fundamental laser is transmitted along the optical path in the annular laser cavity optical path, and in the process, the praseodymium-doped visible light fundamental laser passes through the frequency doubling crystal to obtain frequency-doubled laser, the frequency-doubled laser and the praseodymium-doped visible light fundamental laser pass through the sum frequency crystal to be output from the second laser cavity end mirror, and then other wavelength lasers are filtered out through the filter to output deep ultraviolet laser.

[0009] The first laser cavity end mirror is a plane mirror, and the coating of the first laser cavity end mirror is high-transmissive to the pump laser wavelength and high-reflective to the praseodymium-doped visible light fundamental laser.

[0010] In addition, the coating of the first laser cavity end mirror can be directly prepared at the front end of the first praseodymium-doped laser material, which is beneficial to reducing loss and improving output laser performance.

[0011] The second laser cavity end mirror is a curved concave mirror, and the coating of the second laser cavity end mirror is high-reflective to the praseodymium-doped visible light fundamental laser and high-transmissive to the deep ultraviolet laser.

[0012] The third laser cavity end mirror is a curved mirror, and the coating of the third laser cavity end mirror is high-reflective to the praseodymium-doped visible light fundamental laser and the frequency-doubled laser.

[0013] The fourth laser cavity end mirror is any one of a plane mirror and a concave mirror, and the coating of the fourth laser cavity end mirror is high-reflective to the praseodymium-doped visible light fundamental laser and the frequency-doubled laser.

[0014] The frequency-doubled crystal is an LBO crystal, which is used for frequency doubling the praseodymium-doped visible light fundamental laser, and the coating of the frequency-doubled crystal is high-transmissive to the praseodymium-doped visible light fundamental laser and the frequency-doubled laser; the sum frequency crystal is a BBO crystal, which is used for sum frequency of the praseodymium-doped visible light fundamental laser and the frequency-doubled laser, and the coating of the sum frequency crystal is high-transmissive to the praseodymium-doped visible light fundamental laser, the frequency-doubled laser and the deep ultraviolet laser.

[0015] In addition, the incident light path of the first blue light semiconductor laser further sequentially comprises the first focusing lens, the first laser cavity end mirror, the first praseodymium-doped laser material, the frequency-doubled crystal, the sum frequency crystal, the second laser cavity end mirror and the filter.

[0016] In addition, the laser cavity comprises a fifth plane mirror and a second praseodymium-doped laser material; the fifth plane mirror is coated to be high-reflective to the praseodymium-doped visible light fundamental laser and high-transmissive to the frequency-doubled laser.

[0017] In addition, the incident light path of the first blue light semiconductor laser is sequentially provided with the first focusing lens, a first laser cavity end mirror, a first praseodymium-doped laser material, a frequency doubling crystal, a fifth plane mirror, a sum frequency crystal, a fourth laser cavity end mirror and a filter.

[0018] The incident light path of the second blue light semiconductor laser is sequentially provided with the second focusing lens, a second praseodymium-doped laser material and a fifth plane mirror.

[0019] The present application has the following advantages:

[0020] First, the praseodymium-doped visible light fundamental wave laser is selected at a visible light wavelength, so that the 213nm deep ultraviolet laser can be generated by three times of harmonic wave, and the system is simple, compact and low in cost.

[0021] Second, the coating film with high transmittance to the pump laser wavelength and high reflectivity to the praseodymium-doped visible light fundamental wave laser is directly prepared on the praseodymium-doped laser material, so that the overall structure can be further slightly reduced, the loss is reduced, and the output laser performance (i.e. the power and the efficiency) is improved. By preparing various coating films and using nonlinear crystals, the conversion of the laser wavelength can be realized in the laser cavity, and the deep ultraviolet laser can be simply and efficiently generated.

[0022] Third, the laser can also be extended to other fundamental wave wavelengths of praseodymium doping and the generation of deep ultraviolet laser by three times of harmonic wave, which can solve the application in different scenes. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 is a simplified deep ultraviolet laser implementation structure diagram in the background art of the present application.

[0025] Figure 2 is a simplified deep ultraviolet laser implementation device diagram in the background art of the present application.

[0026] Figure 3 is a deep ultraviolet laser overall structure diagram in the first embodiment of the present application.

[0027] Figure 4is a deep ultraviolet laser continuous wave laser spectrum diagram in example one of the present application.

[0028] Figure 5 is a deep ultraviolet laser spot diagram in example one of the present application.

[0029] Figure 6 is a deep ultraviolet laser overall structure diagram in example two of the present application.

[0030] Figure 7 is a deep ultraviolet laser overall structure diagram in example three of the present application.

[0031] Figure 8 is a deep ultraviolet laser overall structure diagram in example four of the present application.

[0032] Figure 9 is a deep ultraviolet laser overall structure diagram in example five of the present application. DETAILED DESCRIPTION

[0033] In order to facilitate those skilled in the art to understand, the structure of the present application will be further described in detail in combination with the drawings.

[0034] Example one

[0035] As shown in Figure 3 , the present application provides a praseodymium-doped third harmonic generation deep ultraviolet laser, comprising: a first blue light semiconductor laser, a second blue light semiconductor laser, a first focusing lens, a second focusing lens, a first laser cavity end mirror, a second laser cavity end mirror, a third laser cavity end mirror, a fourth laser cavity end mirror, a first praseodymium-doped laser material, a frequency doubling crystal, a sum frequency crystal, and a filter;

[0036] The first focusing lens, the first laser cavity end mirror, the first praseodymium-doped laser material, and the second laser cavity end mirror are sequentially arranged on the incident light path of the first blue light semiconductor laser; the second focusing lens, the second laser cavity end mirror, the first praseodymium-doped laser material, and the first laser cavity end mirror are sequentially arranged on the incident light path of the second blue light semiconductor laser; the sum frequency crystal and the third laser cavity end mirror are sequentially arranged on the reflected light path of the second laser cavity end mirror; the frequency doubling crystal, the fourth laser cavity end mirror are sequentially arranged on the first reflected light path of the third laser cavity end mirror; the sum frequency crystal, the second laser cavity end mirror, and the filter are sequentially arranged on the second reflected light path of the third laser cavity end mirror; the incident light path of the first blue light semiconductor laser, the incident light path of the second blue light semiconductor laser, the reflected light path of the second laser cavity end mirror, the first reflected light path of the third laser cavity end mirror, and the second reflected light path of the third laser cavity end mirror constitute a laser cavity light path;

[0037] The first blue light semiconductor laser and the second blue light semiconductor laser emit pump laser at the same time, which is focused by the first focusing lens and the second focusing lens respectively, and then transmitted to the first laser cavity end mirror and the second laser cavity end mirror respectively to be incident into the first praseodymium-doped laser material, the first praseodymium-doped laser material absorbs two pump lights and converts them into praseodymium-doped visible light fundamental laser, the praseodymium-doped visible light fundamental laser is transmitted along the optical path in the annular laser cavity optical path, and the praseodymium-doped visible light fundamental laser is frequency doubled by the frequency doubling crystal to obtain frequency doubled laser, the frequency doubled laser and the praseodymium-doped visible light fundamental laser are summed by the sum frequency crystal, and then output from the second laser cavity end mirror, and then output deep ultraviolet laser after filtering other wavelength laser by the filter.

[0038] The first laser cavity end mirror is a plane mirror, and the coating film thereof is high-transmissive to the pump laser wavelength and high-reflective to the praseodymium-doped visible light fundamental laser.

[0039] The second laser cavity end mirror is a curved concave mirror, and the coating film thereof is high-reflective to the praseodymium-doped visible light fundamental laser and high-transmissive to the deep ultraviolet laser.

[0040] The third laser cavity end mirror is a curved mirror, and the coating film thereof is high-reflective to the praseodymium-doped visible light fundamental laser and the frequency doubled laser.

[0041] The fourth laser cavity end mirror is a plane mirror or a concave mirror, and the coating film thereof is high-reflective to the praseodymium-doped visible light fundamental laser and the frequency doubled laser.

[0042] The frequency doubling crystal is an LBO crystal, which is used for frequency doubling the praseodymium-doped visible light fundamental laser, and the coating film thereof is high-transmissive to the praseodymium-doped visible light fundamental laser and the frequency doubled laser; the sum frequency crystal is a BBO crystal, which is used for summing the praseodymium-doped visible light fundamental laser and the frequency doubled laser, and the coating film thereof is high-transmissive to the praseodymium-doped visible light fundamental laser, the frequency doubled laser and the deep ultraviolet laser.

[0043] In the embodiment, a full solid-state Pr-doped red light (about 640 nm) is used as a fundamental laser, a 320 nm ultraviolet laser is generated by frequency doubling, the sum frequency of the 640 nm fundamental laser and the 320 nm frequency-doubled ultraviolet laser is also the third harmonic, and then a 213 nm deep ultraviolet laser is generated. The prerequisite for obtaining the 213 nm deep ultraviolet laser is to obtain the 640 nm red light and the 320 nm frequency-doubled ultraviolet laser. The 640 nm fundamental laser is relatively easy to obtain directly by Pr-doped laser with high power and high efficiency. Therefore, by constructing a suitable "640 nm + 320 nm" sum frequency laser cavity, the 213 nm deep ultraviolet laser can be realized. The sum frequency laser cavity can have different designs, as long as the fundamental 640 nm laser and the frequency-doubled 320 nm laser can be efficiently overlapped in the BBO crystal with a small spot size, so as to form a high power density, which is beneficial to improve the conversion efficiency.

[0044] As shown in Figure 4 the 213 nm laser spectrum measured by an Ocean Optics spectrometer USB4000 (range 177 nm-896 nm) is shown, and the peak wavelength is 213.2 nm. As shown in Figure 5 the 213.2 nm deep ultraviolet laser spot pattern measured by a Thorlabs BC106-UV CCD (range 190 nm-350 nm) is shown. Through experiments, it can be demonstrated that the deep ultraviolet laser generation can be realized by the present application.

[0045] It should be noted that the present embodiment only takes the 213 nm deep ultraviolet laser as an example to specifically show the scheme proposed in the present patent, but in fact, the scheme (i.e. Pr-doped third harmonic) can also be extended to other fundamental wavelengths and their third harmonic wavelengths generated by Pr-doped laser, for example:

[0046] (1) the blue light semiconductor laser is used to generate pump laser, and then the Pr-doped laser material is converted into Pr-doped 720 nm laser, and the third harmonic is 240 nm deep ultraviolet laser;

[0047] (2) the blue light semiconductor laser is used to generate pump laser, and then the Pr-doped laser material is converted into Pr-doped 607 nm and 604 nm orange light, and the third harmonic is 202.3 nm and 201 nm deep ultraviolet laser, respectively;

[0048] (2) the blue light semiconductor laser is used to generate pump laser, and then the Pr-doped laser material is converted into Pr-doped 522 nm green light, and the third harmonic is 174 nm laser.

[0049] Embodiment two

[0050] As shown in Figure 6As shown, this embodiment of the invention provides a deep ultraviolet laser generated by praseodymium-doped third harmonic. Based on embodiment one, the coating of the first laser cavity end face mirror can be directly prepared on the front end of the first praseodymium-doped laser material to reduce losses during laser transmission.

[0051] In this embodiment, the overall structure can be further reduced slightly, and the loss is reduced, which is beneficial to improving the power and generation efficiency of deep ultraviolet laser.

[0052] Example 3

[0053] like Figure 7 As shown, this embodiment of the invention provides a deep ultraviolet laser generated by praseodymium-doped third harmonic laser, which reduces the second blue semiconductor laser, the second focusing lens, the third laser cavity end mirror, and the fourth laser cavity end mirror based on embodiment one.

[0054] In addition, the incident optical path of the first blue semiconductor laser is also provided with the first focusing lens, the first laser cavity end face mirror, the first praseodymium-doped laser material, the frequency doubling crystal, the sum frequency crystal, the second laser cavity end face mirror, and the filter in sequence.

[0055] In this embodiment, a praseodymium-doped third harmonic deep ultraviolet laser device is constructed using two end-face mirrors. This structure is more suitable for pulsed third harmonic lasers with high pulse energy, but the conversion efficiency will be very low for continuous wave third harmonic lasers.

[0056] Example 4

[0057] like Figure 8 As shown, this embodiment of the invention provides a deep ultraviolet laser generated by praseodymium-doped third harmonic laser, which adds a fifth plane mirror and a second praseodymium-doped laser material to the first embodiment; the fifth plane mirror is coated with a film for high reflectivity of the praseodymium-doped visible light fundamental laser and high transmittance of the ultraviolet laser.

[0058] In addition, the incident optical path of the first blue semiconductor laser is sequentially provided with the first focusing lens, the first laser cavity end face mirror, the first praseodymium-doped laser material, the frequency doubling crystal, the fifth plane mirror, the sum-frequency crystal, the fourth laser cavity end face mirror, and the filter; the incident optical path of the second blue semiconductor laser is sequentially provided with the second focusing lens, the second praseodymium-doped laser material, the fifth plane mirror, and the third laser cavity end face mirror.

[0059] This embodiment shows a schematic diagram of a composite ring-cavity praseodymium-doped third harmonic deep ultraviolet laser device. (See diagram below.) Figure 8 As shown, the newly added element is a fifth plane mirror 8, whose coating is highly reflective to praseodymium-doped visible light fundamental laser and highly transparent to frequency-doubled laser. This causes the praseodymium-doped visible light fundamental laser and the frequency-doubled light to converge and merge in the frequency-doubled crystal 6, converting them into third-harmonic deep ultraviolet laser output.

[0060] Example Five

[0061] As Figure 9 shown, the embodiment of the present application provides a deep ultraviolet laser of praseodymium-doped third harmonic generation. On the basis of the embodiment one, the praseodymium-doped visible fundamental laser and the frequency-doubled laser are subjected to third harmonic and frequency mixing outside the laser cavity. That is, the 640 nm visible fundamental laser and the 320 nm frequency-doubled laser are simultaneously injected into an external cavity containing a frequency mixing crystal BBO after being generated from the laser cavity. This scheme needs to use the resonance enhancement technology mentioned in the background art.

[0062] In this embodiment, the 640 nm visible fundamental laser can be obtained by a blue semiconductor laser and a praseodymium-doped laser material. The visible fundamental laser is subjected to frequency doubling by a frequency doubling crystal to obtain a frequency-doubled laser. The visible fundamental laser and the frequency-doubled laser are subjected to frequency mixing in a frequency mixing crystal outside the laser cavity to generate a deep ultraviolet laser.

[0063] It is to be noted that any reference signs placed between parentheses in a claim do not constitute limitations to the scope or the meaning of the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. It is further to be understood that a specific measure can be an alternative to, or in combination with, a corresponding generally framed measure. The application can be implemented by means of both hardware and software, and any combination thereof. In a unit claim, several elements can be presented - the use of "each" before the first of these elements does not exclude the presence of additional such elements nor exclude introduction of new elements after the first one. The word "another" preceding the use of an element does not preclude the presence of a plurality of such elements. He word "first", "second", "third", and the like in the description do not necessarily have a chronological meaning since the recited order can be altered in other implementations. The terms "first", "second", and the like, can be understood as names.

[0064] Although preferred embodiments of the application have been described, a person of ordinary skill in the art can make additional changes and modifications to these embodiments once armed with the present disclosure. Therefore, the appended claims are intended to cover all such changes and modifications that fall within the scope of the application.

[0065] Obviously, many modifications and variations of the present application are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

[0066] In the present application, unless specifically defined otherwise and limited in the specification, the terms "mounting", "connected", "connecting", "fixed", and the like should be understood broadly, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0067] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. Furthermore, the skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

Claims

1. A deep ultraviolet laser generated by praseodymium-doped third harmonic laser, characterized in that, include: First blue semiconductor laser, second blue semiconductor laser, first focusing lens, second focusing lens, first laser cavity end mirror, second laser cavity end mirror, third laser cavity end mirror, fourth laser cavity end mirror, first praseodymium-doped laser material, frequency doubling crystal, sum-frequency crystal, filter; The first blue semiconductor laser has a first focusing lens, a first laser cavity end mirror, a first praseodymium-doped laser material, and a second laser cavity end mirror arranged sequentially in the incident light path; the second blue semiconductor laser has a second focusing lens, a second laser cavity end mirror, a first praseodymium-doped laser material, and a first laser cavity end mirror arranged sequentially in the incident light path; the second laser cavity end mirror has a sum-frequency crystal and a third laser cavity end mirror arranged sequentially in the reflected light path; the third laser cavity end mirror has a frequency-doubling crystal and a fourth laser cavity end mirror arranged sequentially in the first reflected light path; and the third laser cavity end mirror has a sum-frequency crystal, a second laser cavity end mirror, and a filter arranged sequentially in the second reflected light path; the incident light path of the first blue semiconductor laser, the incident light path of the second blue semiconductor laser, the reflected light path of the second laser cavity end mirror, the first reflected light path of the third laser cavity end mirror, and the second reflected light path of the third laser cavity end mirror constitute a laser cavity; The first and second blue semiconductor lasers simultaneously emit pump lasers, which are focused by the first and second focusing lenses respectively and then transmitted through the first and second laser cavity end-face mirrors to the first praseodymium-doped laser material. The first praseodymium-doped laser material absorbs the two pump laser beams and gains gain, generating a 640nm praseodymium-doped visible fundamental laser in the laser cavity. The praseodymium-doped visible fundamental laser propagates in the laser cavity. During this process, the praseodymium-doped visible fundamental laser is frequency-doubled by the frequency-doubled crystal to obtain a frequency-doubled laser. The frequency-doubled laser and the residual praseodymium-doped visible fundamental laser are frequency-doubled by the sum-frequency crystal and output from the second laser cavity end-face mirror. Then, after filtering out other wavelengths of laser light by the filter, a 213nm third harmonic deep ultraviolet laser is output. The first laser cavity end face mirror is a plane mirror, and its coating can be highly transparent to the pump laser wavelength and highly reflective to the praseodymium-doped visible light fundamental laser. The coating of the first laser cavity end face mirror is directly prepared on the front end of the first praseodymium-doped laser material, which helps to reduce losses and improve the performance of the output laser.

2. The deep ultraviolet laser generated by praseodymium-doped third harmonic laser as described in claim 1, characterized in that, The second laser cavity end face mirror is a concave mirror, and its coating can be highly reflective of the praseodymium-doped visible light fundamental laser and highly transparent to the deep ultraviolet laser.

3. The deep ultraviolet laser generated by praseodymium-doped third harmonic laser as described in claim 1, characterized in that, The third laser cavity end face mirror is a curved mirror, and its coating can be highly reflective of the praseodymium-doped visible fundamental laser and the frequency-doubled laser.

4. The deep ultraviolet laser generated by praseodymium-doped third harmonic laser as described in claim 1, characterized in that, The fourth laser cavity end face mirror can be either a plane mirror or a concave mirror, and its coating can be highly reflective of the praseodymium-doped visible fundamental laser and the frequency-doubled laser.

5. A deep ultraviolet laser generated by praseodymium-doped third harmonic laser as described in claim 1, characterized in that, The frequency doubling crystal is an LBO crystal used for frequency doubling of the praseodymium-doped visible fundamental laser, and its coating is highly transparent to both the praseodymium-doped visible fundamental laser and the frequency doubling laser. The sum-frequency crystal is a BBO crystal used for summing the praseodymium-doped visible fundamental laser and the frequency doubling laser, and its coating is highly transparent to the praseodymium-doped visible fundamental laser, the frequency doubling laser, and the deep ultraviolet laser.

6. The deep ultraviolet laser generated by praseodymium-doped third harmonic laser as described in claim 1, characterized in that, The incident optical path of the first blue semiconductor laser is also provided with the first focusing lens, the first laser cavity end face mirror, the first praseodymium-doped laser material, the frequency doubling crystal, the sum frequency crystal, the second laser cavity end face mirror, and the filter in sequence.

7. A deep ultraviolet laser generated by praseodymium-doped third harmonic laser as described in claim 1, characterized in that, The incident optical path of the first blue semiconductor laser is sequentially provided with the first focusing lens, the first laser cavity end face mirror, the first praseodymium-doped laser material, the frequency doubling crystal, the fifth plane mirror, the sum-frequency crystal, the fourth laser cavity end face mirror, and the filter. The incident optical path of the second blue semiconductor laser is sequentially provided with a second focusing lens, a second praseodymium-doped laser material, a fifth plane mirror, and a third laser cavity end face mirror.

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