Intracavity triple frequency laser

Abstract

The invention relates to an intracavity frequency tripling laser which comprises a laser resonant cavity, and a laser generation unit, a modulation unit, a frequency doubling unit and a frequency tripling unit are sequentially arranged in the laser resonant cavity along a light path. A dual-wavelength wave plate is arranged in a light path between the frequency doubling unit and the frequency tripling unit, the dual-wavelength wave plate is configured to be of a rotatable structure, the dual-wavelength wave plate has a full-wave-plate characteristic for fundamental frequency light and has a half-wave-plate characteristic for frequency doubling light, and the polarization direction of the frequency doubling light can be continuously adjusted by rotating the angle of the dual-wavelength wave plate. Therefore, the proportion of the frequency doubling light participating in the frequency tripling process is controlled, so that the photon number proportion of the fundamental frequency light to the frequency doubling light reaches 1: 1, and the optimal conversion efficiency requirement of the frequency tripling unit is met.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and in particular to an intracavity frequency tripled laser. Background Art

[0002] Laser frequency conversion technologies primarily include nonlinear frequency conversion methods such as frequency doubling, frequency tripling, and optical parametric oscillation, and are widely used to generate laser light sources with specific wavelengths. Frequency tripling, in particular, involves the interaction of two photons of different frequencies in a nonlinear medium to produce a photon of a new frequency. This technology can produce ultraviolet lasers with wavelengths of 300-400nm.

[0003] To maximize tripled frequency conversion efficiency, the most common phase matching method is Type II phase matching, which combines two orthogonally polarized photons to produce a tripled frequency photon of ordinary light. This matching method has a large nonlinear coefficient and can achieve high conversion efficiency. To achieve optimal tripled frequency efficiency, the fundamental and doubled frequency light must have the same number of photons.

[0004] However, in practical applications, traditional intracavity frequency-tripling lasers have significant drawbacks: due to their enclosed structure, it is difficult to directly observe the energy ratio of the fundamental and second-harmonic lasers within the cavity, making it impossible to adjust the optimal ratio in real time to maximize the tripled frequency efficiency. Existing solutions typically use doubled frequency crystals of different sizes and specifications to vary the doubled frequency efficiency, thereby indirectly controlling the intracavity laser ratio. This method requires preparing multiple frequency-tripling crystals of different specifications and conducting repeated experiments to determine the optimal configuration, which not only increases experimental costs but also prolongs the debugging cycle, significantly reducing R&D and production efficiency.

[0005] To address the above issues, a technical solution is urgently needed that can accurately adjust the ratio of fundamental frequency light to second-harmonic frequency light in the cavity in real time to simplify the debugging process, reduce R&D costs, and achieve optimal triple frequency efficiency. Summary of the Invention

[0006] The invention discloses an intracavity frequency tripled laser, which is used to solve the problems existing in the prior art.

[0007] An embodiment of the present invention provides an intracavity frequency tripled laser, comprising a laser resonant cavity, wherein a laser generating unit, a modulation unit, a frequency doubling unit, and a frequency tripled unit are sequentially arranged along an optical path in the laser resonant cavity; A dual-wavelength wave plate is provided in the optical path between the double frequency unit and the triple frequency unit. The dual-wavelength wave plate is configured as a rotatable structure. The dual-wavelength wave plate exhibits full-wave plate characteristics for fundamental frequency light and half-wave plate characteristics for double frequency light. By rotating its angle, the polarization direction of the double frequency light can be continuously adjusted to control the proportion of the double frequency light participating in the triple frequency process, so that the photon number ratio of the fundamental frequency light and the double frequency light reaches 1:1, thereby meeting the optimal conversion efficiency requirements of the triple frequency unit.

[0008] As a preferred technical solution, the laser generating unit includes a 0° total reflection mirror, a laser crystal, a pump source and a mode compensation lens; The 0° fully reflective mirror is set at one end of the laser resonant cavity; The laser crystal is located between the 0° total reflection mirror and the modulation unit; The pump source is configured to side-pump the laser crystal; The mode compensation lens is arranged between the laser crystal and the modulation unit, and is used to compensate for the thermal lens effect in the laser crystal and adjust the oscillation light mode.

[0009] As a preferred technical solution, a polarizer is further provided between the 0° total reflection mirror and the laser crystal. The polarizer is used to select the polarization mode to ensure that fundamental frequency light with a single polarization direction is formed in the cavity.

[0010] As a preferred technical solution, the pump source includes a continuous wave semiconductor laser, whose output power is configured to be in the range of 250W to 300W; the laser crystal is a neodymium-doped yttrium lithium fluoride crystal, and the crystal orientation and size of the neodymium-doped yttrium lithium fluoride crystal match the pump wavelength and pumping mode of the pump source.

[0011] As a preferred technical solution, the modulation unit includes an acousto-optic Q-switch, which is used to modulate the continuous light output by the laser generating unit to generate pulsed laser.

[0012] As a preferred technical solution, the acousto-optic Q-switch is driven by a 41 MHz RF frequency and is configured to output a pulse repetition frequency with an adjustable range of 1 kHz to 10 kHz, so that the laser produces a stable Q-switched pulse laser output.

[0013] As a preferred technical solution, a first spectrometer is provided between the modulation unit and the double frequency unit. The first spectrometer has high transmittance to the fundamental frequency light and high reflectivity to the double frequency light, and is used to reflect the double frequency light generated by the double frequency unit to the triple frequency unit.

[0014] As a preferred technical solution, the double frequency unit includes an LBO crystal using a type I phase matching method, which is used to convert the fundamental frequency light into double frequency light.

[0015] As a preferred technical solution, the frequency tripling unit includes an LBO crystal using a type II phase matching method, which is used to mix the fundamental frequency light with the second-harmonic frequency light to generate the third-harmonic frequency light.

[0016] As a preferred technical solution, a second spectrometer is provided after the triple frequency unit. The second spectrometer has high reflectivity for fundamental frequency light and high transmittance for triple frequency light. It is used to reflect the fundamental frequency light back into the laser resonant cavity for recycling, while allowing triple frequency light to be output.

[0017] Compared with the prior art, the technical solution adopted by the present invention can achieve the following beneficial effects: The present invention provides an intracavity frequency tripled laser. Compared with conventional technologies, the present invention employs a dual-wavelength wave plate disposed between a frequency doubler unit and a frequency tripler unit. The dual-wavelength wave plate exhibits full-wave plate characteristics for fundamental frequency light and half-wave plate characteristics for frequency doubler light. The ratio of fundamental frequency light to frequency doubler light in the frequency tripled process can be precisely adjusted by simply rotating the dual-wavelength wave plate angle, eliminating the need to prepare multiple frequency doubled crystals of different specifications for experiments, significantly reducing testing time and cost. Furthermore, the present invention enables the intracavity frequency tripled effect, which is difficult to observe and adjust, to be precisely controlled through the dual-wavelength wave plate, achieving a 1:1 photon ratio between fundamental frequency light and frequency doubler light, thereby meeting the optimal conversion efficiency requirements of the frequency tripled crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, which constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings: Figure 1 Schematic diagram of the structure of an intracavity frequency tripled laser in a preferred embodiment of the present invention.

[0019] Description of reference numerals: 0° total reflection mirror 1, polarizer 2, laser crystal 3, pump source 4, mode compensation lens 5, modulation unit 6, first beam splitter 7, double frequency unit 8, dual-wavelength wave plate 9, triple frequency unit 10, second beam splitter 11. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. In the description of the present invention, it should be noted that the term "or" is generally used in the sense of including "and / or" unless the content clearly indicates otherwise.

[0021] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. In addition, in the description of this application, the terms "first," "second," and the like are used only to distinguish descriptions and should not be understood as indicating or implying relative importance. Those skilled in the art will appreciate that in order to achieve their respective functions and meet the actual application requirements of the laser, the specific shapes / sizes / angles of each structure can be adaptively adjusted.

[0022] 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 ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] In order to solve the problems existing in the prior art, the present invention provides an intracavity frequency tripled laser in a preferred embodiment, referring to Figure 1 The laser includes a laser resonant cavity, in which a laser generating unit, a modulation unit 6, a double frequency unit 8 and a triple frequency unit 10 are sequentially arranged along the optical path; wherein the laser generating unit is used to generate fundamental frequency light and form a stable oscillation in the resonant cavity; the modulation unit 6 is used to modulate the continuous fundamental frequency light to generate a pulsed laser with high peak power; the double frequency unit 8 is used to convert the fundamental frequency light into double frequency light; the triple frequency unit 10 is used to mix the fundamental frequency light with the double frequency light to generate triple frequency light output.

[0024] Preferably, a dual-wavelength wave plate 9 is provided in the optical path between the doubler unit 8 and the tripler unit 10. The dual-wavelength wave plate 9 is configured as a rotatable structure. It exhibits full-wave plate properties for fundamental frequency light, maintaining the polarization state of the fundamental frequency light unchanged during rotation, and exhibits half-wave plate properties for doubler light. By rotating its angle, the polarization direction of the doubler light can be continuously adjusted to control the proportion of doubler light participating in the tripler process, ensuring a 1:1 ratio of photons between the fundamental frequency light and the doubler light, thereby meeting the optimal conversion efficiency requirements of the tripler unit 10. In this embodiment, the provision of the dual-wavelength wave plate 9 makes the intracavity photon ratio, which is difficult to directly observe, controllable, and achieves optimal tripler efficiency without having to replace multiple specifications of doubler crystals, significantly improving the practicality and debugging efficiency of the system.

[0025] Some existing solutions include wave plates that can achieve dual-wavelength functionality. These wave plates behave like quarter-wave plates for fundamental light and half-wave plates for double-frequency light. Theoretically, these wave plates can adjust the optical field properties by rotating the wave plate angle. However, their physical mechanism has fundamental flaws and cannot meet the core requirement of type II phase matching for intracavity tripled frequency lasers. This is because type II phase matching requires that the polarization directions of the fundamental light (o light) and the double-frequency light (e light) be strictly orthogonal, that is, their polarization states be perpendicular, to achieve maximum tripled frequency conversion efficiency (equal photon numbers are required). However, in existing wave plates, the characteristics of the quarter-wave plate destroy the polarization orthogonality. When the wave plate is rotated, the fundamental light becomes circularly polarized, while the polarization direction of the double-frequency light rotates. The fundamental light cannot form a stable orthogonal polarization state with the double-frequency light, failing to meet the polarization conditions for type II phase matching. Therefore, the ratio of the fundamental light to the double-frequency light participating in the tripled frequency process cannot be effectively adjusted.

[0026] Compared to existing wave plates, the dual-wavelength wave plate 9 in this embodiment is configured as a full-wave plate for fundamental frequency light and as a half-wave plate for double frequency light. During rotation, the linear polarization state of the fundamental frequency light is unchanged, while only the polarization direction of the double frequency light is altered. This precisely controls the polarization orthogonality and energy ratio of the two beams, satisfying the Class II matching condition. In a preferred embodiment, the dual-wavelength wave plate 9 utilizes a multilayer film structure, optionally coated with a dual-wavelength antireflection film and a phase retardation film on the substrate surface. By precisely controlling the material composition and thickness of each dielectric film layer, the dual-wavelength wave plate 9 achieves full-wave plate characteristics with an optical path difference of 2π or an integer multiple of 2π for the fundamental frequency wavelength, while simultaneously achieving half-wave plate characteristics with an optical path difference of π or an odd multiple of π for the double frequency wavelength. This multilayer film structure utilizes the dispersion properties of the material and the principle of multilayer film interference to achieve independent phase modulation of two wavelengths of light within a single optical element.

[0027] In this embodiment, the specific technical parameters of the dual-wavelength wave plate 9, such as its material composition, thickness, surface treatment process, and coating specifications, are not specifically limited. Those skilled in the art can adapt and optimize the design of the dual-wavelength wave plate 9 based on specific requirements such as the laser wavelength, power level, and conversion efficiency required in actual applications, combined with existing optical thin film design technologies. The key to the dual-wavelength wave plate 9 is achieving full-wave plate properties for fundamental frequency light and half-wave plate properties for doubled frequency light. As long as this core functional requirement is met, various technical approaches are possible, all of which fall within the scope of this invention.

[0028] In a preferred embodiment, the dual-wavelength wave plate 9 is mounted on a rotating base that can achieve continuous and precise rotation adjustment within the range of 0 to 360 degrees in the horizontal or vertical direction; the rotating base is preferably fixed in the laser resonant cavity by an optical bracket to ensure that the dual-wavelength wave plate 9 is perpendicular to the laser propagation direction, while maintaining good mechanical stability to avoid the influence of system vibration on optical performance.

[0029] Specifically, when fundamental light passes through the dual-wavelength waveplate 9, its polarization state remains unchanged regardless of the angle to which it is rotated, due to its full-wave plate properties. However, for the second-harmonic frequency light, since the waveplate behaves like a half-wave plate, rotating the waveplate angle θ will cause the polarization direction of the second-harmonic frequency light to rotate by an angle of 2θ. This differentiated polarization control characteristic allows precise control of the polarization component of the second-harmonic frequency light entering the frequency tripling crystal without affecting the polarization state of the fundamental light. This allows for the adjustment of the proportion of the second-harmonic frequency light participating in the type II phase-matched frequency tripling process, achieving optimal matching of the photon counts of the fundamental and second-harmonic frequency light.

[0030] In a preferred embodiment, the laser generating unit is configured as a side-pumped flat-flat resonant cavity structure, which includes a 0° total reflection mirror 1, a polarizer 2, a laser crystal 3, a pump source 4, and a mode compensation lens 5. Among them, the 0° total reflection mirror 1 is arranged at one end of the laser resonant cavity for total reflection of the fundamental frequency light; the polarizer 2 is located between the 0° total reflection mirror 1 and the laser crystal 3, which can not only force the laser to operate in a single polarization state, but also suppress stray oscillation modes and improve the quality and stability of the laser beam. In addition, the polarizer 2 also has a wavelength selection function. When the polarization direction is parallel to the C-axis of the laser crystal 3, the output wavelength is 1047nm. When the polarization direction is perpendicular to the C-axis of the laser crystal 3, the output wavelength is 1053nm. In practical applications, the embodiments of the present invention Preferably, a laser with a wavelength of 1053 nm is used; the laser crystal 3 is located after the polarizer 2, and preferably a neodymium-doped yttrium lithium fluoride (Nd:YLF) crystal is used, and the crystal orientation and size of the neodymium-doped yttrium lithium fluoride crystal match the pump wavelength and pumping mode of the pump source 4; the pump source 4 is configured to side-pump the laser crystal 3, and is preferably a continuous wave semiconductor laser, and its output power is configured to be in the range of 250~300W; the mode compensation lens 5 is arranged between the laser crystal 3 and the modulation unit 6, and is used to compensate for the thermal lens effect in the laser crystal 3 and adjust the oscillation light mode.

[0031] Preferably, the continuous light output power of the laser generating unit is 70-80W.

[0032] In a preferred embodiment, modulation unit 6 is configured as an acousto-optic Q-switch, which is used to modulate the continuous light output by the laser generating unit to generate pulsed laser light. Preferably, the acousto-optic Q-switch is driven by a 41 MHz radio frequency and is configured to output a pulse repetition frequency adjustable from 1 kHz to 10 kHz, enabling the laser to generate stable Q-switched pulsed laser output.

[0033] Specifically, the upper energy level lifetime of the Nd:Yttrium-doped lithium fluoride crystal is approximately 500μs, and the output Q-switched laser power under 1kHz pulse modulation is 35-40W. It should be noted that this power value was measured when the output mirror transmittance was 30% during fundamental frequency debugging. That is, at this time, the position of the second beam splitter 11 is the output mirror at T = 30%. When performing frequency doubling debugging, the output mirror in this position needs to be replaced with a dichroic mirror.

[0034] In a preferred embodiment, the frequency doubling unit 8 includes an LBO crystal employing Type I phase matching, which is used to convert the fundamental frequency light into the second-harmonic frequency light. Specifically, this crystal exhibits a high damage threshold, a wide phase-matching temperature bandwidth, and a large effective nonlinear coefficient, enabling it to demonstrate excellent performance in frequency conversion applications involving high-power fundamental frequency light. Type I phase matching means that the incident fundamental frequency light has the same polarization direction as the generated second-harmonic frequency light, while the polarization direction is perpendicular to that of the fundamental frequency light. This configuration fully utilizes the nonlinear properties of the LBO crystal to achieve efficient frequency multiplication.

[0035] Preferably, a first beam splitter 7 is provided between the modulation unit 6 and the double frequency unit 8. The first beam splitter 7 has a high transmittance to the fundamental frequency light and a high reflectivity to the double frequency light, so that the fundamental frequency light in the resonant cavity can efficiently pass through the first beam splitter 7 and enter the double frequency unit 8, while the generated double frequency light is reflected to the triple frequency unit 10, forming an optical one-way channel, which significantly improves the extraction efficiency and utilization rate of the double frequency light.

[0036] Specifically, when high-peak-power Q-switched fundamental pulsed light passes through the frequency doubler 8, a portion of the fundamental photons are converted into frequency doublers with doubled energy due to second-order nonlinear effects. Due to the high intracavity power density, good beam quality, and precise phase matching, the frequency doubler process achieves high conversion efficiency. At a repetition rate of 1kHz, the frequency doubler 8 can stably output approximately 30W of frequency doubler light.

[0037] In a preferred embodiment, the frequency tripling unit 10 includes an LBO crystal using a type II phase matching method, and achieves frequency summation of fundamental frequency light and doubled frequency light to generate tripled frequency light through precisely controlled crystal orientation.

[0038] Preferably, the frequency tripling unit 10 can convert the incident fundamental frequency light and second frequency light into frequency tripling ultraviolet light with an efficiency of about 50%, and finally output a 1 kHz frequency tripling pulse laser of about 15 W.

[0039] In a preferred embodiment, a second spectrometer 11 is provided after the frequency tripling unit 10. The second spectrometer 11 has high reflectivity for fundamental frequency light and high transmittance for frequency tripling light, thereby ensuring that the unconverted fundamental frequency light can be reflected back into the resonant cavity to continue participating in the oscillation process, while the generated frequency tripling light is efficiently output through the spectrometer.

[0040] Specifically, the second beam splitter 11 not only has a wavelength selection function, but also serves as an output coupler. Its position and inclination are adaptively adjusted to ensure that the fundamental frequency light reflected back into the cavity can accurately return along the original optical path, maintaining the stable oscillation of the resonant cavity. At the same time, the transmitted output tripled frequency light has good beam quality and stability and can be directly used in downstream applications.

[0041] Compared with the existing technology, the embodiment of the present invention solves the problem of difficult precise control of the ratio of fundamental frequency light to doubled frequency light in the traditional tripled frequency system through the innovative application of dual-wavelength wave plate 9, improves the tripled frequency conversion efficiency, simplifies the system structure, improves stability and reliability, and provides a more excellent technical solution for the practical application of high-power ultraviolet lasers.

[0042] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. An intracavity frequency tripled laser, characterized in that: It includes a laser resonant cavity, in which a laser generating unit, a modulation unit, a frequency doubling unit and a frequency tripling unit are sequentially arranged along an optical path; A dual-wavelength wave plate is provided in the optical path between the double frequency unit and the triple frequency unit. The dual-wavelength wave plate is configured as a rotatable structure. The dual-wavelength wave plate exhibits full-wave plate characteristics for fundamental frequency light and half-wave plate characteristics for double frequency light. By rotating its angle, the polarization direction of the double frequency light can be continuously adjusted to control the proportion of the double frequency light participating in the triple frequency process, so that the photon number ratio of the fundamental frequency light to the double frequency light reaches 1:1, thereby meeting the optimal conversion efficiency requirement of the triple frequency unit.

2. The intracavity frequency tripled laser according to claim 1, characterized in that: The laser generating unit includes a 0° total reflection mirror, a laser crystal, a pump source and a mode compensation lens; The 0° total reflection mirror is arranged at one end of the laser resonant cavity; The laser crystal is located between the 0° total reflection mirror and the modulation unit; The pump source is configured to side-pump the laser crystal; The mode compensation lens is arranged between the laser crystal and the modulation unit, and is used to compensate for the thermal lens effect in the laser crystal and adjust the oscillation light mode.

3. The intracavity frequency tripled laser according to claim 2, characterized in that: A polarizer is further provided between the 0° total reflection mirror and the laser crystal, and the polarizer is used to select a polarization mode to ensure that fundamental frequency light with a single polarization direction is formed in the cavity.

4. The intracavity frequency tripled laser according to claim 2, characterized in that: The pump source includes a continuous wave semiconductor laser, whose output power is configured to be in the range of 250W to 300W; the laser crystal is a neodymium-doped yttrium lithium fluoride crystal, and the crystal orientation and size of the neodymium-doped yttrium lithium fluoride crystal match the pump wavelength and pumping mode of the pump source.

5. The intracavity frequency tripled laser according to claim 1, characterized in that: The modulation unit includes an acousto-optic Q-switch, which is used to modulate the continuous light output by the laser generating unit to generate pulsed laser.

6. The intracavity frequency tripled laser according to claim 5, characterized in that: The acousto-optic Q-switch is driven by a 41 MHz radio frequency and is configured to output a pulse repetition frequency in an adjustable range of 1 kHz to 10 kHz, so that the laser generates a stable Q-switched pulse laser output.

7. The intracavity frequency tripled laser according to claim 1, characterized in that: A first spectroscope is provided between the modulation unit and the frequency doubling unit. The first spectroscope has high transmittance to fundamental frequency light and high reflectivity to frequency doubling light, and is used to reflect the frequency doubling light generated by the frequency doubling unit to the frequency tripling unit.

8. The intracavity frequency tripled laser according to claim 1, characterized in that: The double frequency unit includes an LBO crystal using a type I phase matching method, and is used to convert fundamental frequency light into double frequency light.

9. The intracavity frequency tripled laser according to claim 1, characterized in that: The frequency tripling unit includes an LBO crystal using a type II phase matching method, and is used for mixing fundamental frequency light with doubled frequency light to generate tripled frequency light.

10. The intracavity frequency tripled laser according to claim 1, characterized in that: A second spectrometer is provided behind the triple frequency unit. The second spectrometer has high reflectivity for fundamental frequency light and high transmittance for triple frequency light. It is used to reflect the fundamental frequency light back into the laser resonant cavity for recycling while allowing triple frequency light to be output.

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