Self-Raman intracavity frequency conversion five-wavelength selectable laser

Abstract

The invention discloses a self-Raman intracavity frequency conversion five-wavelength selectable laser which comprises a machine body, a pumping source, a total reflection lens, a neodymium-doped yttrium vanadate crystal, a Q switch, a middle lens, a first BBO crystal, a second BBO crystal and an output lens are sequentially arranged in the machine body, and the total reflection lens and the output lens form an oscillation cavity. The axial center lines of the pumping source, the total reflection lens, the neodymium-doped yttrium vanadate crystal, the Q switch, the middle lens, the first BBO crystal, the second BBO crystal and the output lens are overlapped, a horizontal rotation adjusting table is arranged at the lower end of the first BBO crystal, a fixed platform is arranged at the lower end of the second BBO crystal, and the first BBO crystal is rotated through fine tuning to adjust the axial center lines of the neodymium-doped yttrium vanadate crystal, the Q switch and the middle lens. And the light passing direction of the first BBO crystal is consistent with the phase matching angle required by the output of the corresponding wavelength, so that the frequency mixing of the corresponding fundamental frequency light or each order of Stokes light in the laser resonant cavity is selectively realized, and the visible band laser with different wavelengths is correspondingly output. The technical scheme is reasonable in structural design, high in laser efficiency, stable in output and good in practicability.

Description

Technical Field

[0001] The invention relates to the technical field of optoelectronic devices, and in particular to a self-Raman intracavity frequency conversion five-wavelength optional laser. Background Art

[0002] Visible band multi-wavelength lasers have important applications in laser display, biomedicine, radar remote sensing and other fields. Typical applications include the treatment of fundus diseases. Fundus diseases are the most common and frequently occurring diseases in the field of ophthalmology. According to the different color light absorption characteristics of different lesion tissues, different wavelength lasers are selected for treatment, which can improve the treatment effect, reduce damage to tissues, and expand the scope of clinical diagnosis and treatment of ophthalmology. Compared with single-wavelength lasers, multi-wavelength laser treatment can overcome the obstacle of turbidity of ocular refractive media in the treatment of fundus diseases, and become the development direction of clinical laser treatment in ophthalmology.

[0003] Multi-wavelength krypton laser therapy machine entered ophthalmology clinic early and is currently the most widely used multi-wavelength laser treatment device for fundus diseases. However, krypton laser is a gas laser, which has disadvantages such as large size, low efficiency, poor stability and reliability. In recent years, with the development of semiconductor-pumped solid-state laser technology, the visible band multi-wavelength optional laser based on all-solid-state Raman intracavity frequency doubling and frequency technology has become the most potential light source for the treatment of fundus diseases due to its advantages of all-solid-state, simple structure, and convenient wavelength switching. After searching, Chinese invention patent CN201910306311.3 discloses a five-wavelength laser light source for laser fundus photocoagulation treatment, including a body, in which a pump source, a fully reflective lens, a Nd:YAlO3 crystal, a Q switch, a YVO4 Crystal, BBO crystal, output lens, coupling lens system and optical fiber. The coupling lens system includes coupling lens, total reflection lens and output lens to form an oscillation cavity; the axial center lines of the pump source, total reflection lens, Nd:YAlO3 crystal, Q switch, YVO4 crystal, BBO crystal and output lens coincide; by rotating the BBO crystal, the light transmission direction of the BBO crystal is consistent with the phase matching angle required for the corresponding wavelength output, so as to select and achieve the mixing of the corresponding fundamental frequency light or each order of Stokes light in the laser resonant cavity, and output visible band lasers of different wavelengths. This technical solution overcomes the shortcomings of previous krypton multi-wavelength laser treatment equipment to a certain extent, and expands the scope of indications for fundus disease treatment. Because the broadband high-reflection film system design of the cavity mirror meets the requirements of cascade Raman, it is easy to cause gain competition involving higher-order Stokes during frequency doubling and frequency summing, thereby affecting the power and stability of the required wavelength laser. For example, when the first-order Stokes light is frequency-doubled, since the resonant cavity also has high reflection for the second-order Stokes light, or even close to total reflection, more first-order Stokes light will be converted into second-order Stokes light through the Raman crystal, that is, the second-order Stokes light participates in the consumption of the first-order Stokes light, affecting the frequency-doubled efficiency, output power and laser stability of the first-order Stokes light. In addition, the nonlinear optical frequency conversion crystal used in the above patent is a critical phase-matched BBO crystal with a walk-off angle of more than 50 mrad. The birefringence walk-off effect will cause the separation of the energy flow directions of the two different polarized lights involved in the frequency conversion, affecting the laser output beam quality and frequency-doubled conversion efficiency. Summary of the invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a five-wavelength selectable laser with self-Raman intracavity frequency conversion which has reasonable structural design, high laser efficiency, stable output and good practicality.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a self-Raman intracavity frequency conversion five-wavelength optional laser, comprising a body, wherein a pump source, a total reflection lens, a Nd:Yttrium vanadate crystal, a Q switch, an intermediate lens, a first BBO crystal, a second BBO crystal and an output lens are sequentially arranged in the body, the total reflection lens and the output lens form an oscillation cavity, the axial center lines of the pump source, the total reflection lens, the Nd:Yttrium vanadate crystal, the Q switch, the intermediate lens, the first BBO crystal, the second BBO crystal and the output lens are placed in a coincident manner, a horizontal rotation adjustment platform is arranged at the lower end of the first BBO crystal, and a fixed platform is arranged at the lower end of the second BBO crystal, and the light transmission direction of the first BBO crystal is made consistent with the phase matching angle required for the corresponding wavelength output by fine-tuning and rotating the first BBO crystal, so that the mixing of the corresponding fundamental frequency light or each order of Stokes light in the laser resonant cavity is selected and realized, and visible band lasers of different wavelengths are output accordingly.

[0006] The present invention is further configured as follows: the first BBO crystal and the second BBO crystal are two crystals with the same size and optical parameters, and are cut according to the phase matching angle of 1313nm frequency doubling, with the angle between the light transmission direction and the crystal optical axis being 20.4°.

[0007] The present invention is further configured such that the rotatable angle of the horizontal rotation adjustment platform is greater than 2.5 degrees.

[0008] The present invention is further configured such that the optical axes of the first BBO crystal and the second BBO crystal are placed in a mirror image, so as to play a role in birefringence walk-off compensation in nonlinear frequency conversion.

[0009] The present invention is further configured such that: the oscillation cavity realizes the oscillation of the fundamental frequency laser, the first-order Stokes light and the second-order Stokes light in the cavity at the same time.

[0010] The present invention is further configured as follows: the fully reflective lens is coated with a high-reflective film for lasers in the wavelength range of 1.06 microns to 1.32 microns; the intermediate lens is coated with an anti-reflective film for lasers in the wavelength range of 1.06 microns to 1.32 microns and a high-reflective film for lasers in the wavelength range of 0.56 microns to 0.62 microns; the output lens is coated with a high-reflective film for lasers in the wavelength range of 1.06 microns to 1.32 microns and a high-transmittance film for lasers in the wavelength range of 0.53 microns to 0.66 microns.

[0011] The present invention is further configured such that: the pump source is a semiconductor laser with an output wavelength of 808 nanometers or 880 nanometers.

[0012] The present invention is further configured as follows: the Q switch is an acousto-optic Q switch with high transmittance in the 1.06 micron to 1.32 micron band.

[0013] The beneficial effects of the present invention are as follows: compared with the prior art, the present invention has a reasonable structural design, two mirror-set BBO crystals are used in the whole body, and the first BBO crystal is rotated by fine-tuning so that the light transmission direction of the first BBO crystal is consistent with the phase matching angle required for the corresponding wavelength output, thereby selecting to achieve the mixing of the corresponding fundamental frequency light or each order of Stokes light in the laser resonant cavity, and correspondingly outputting visible band lasers of different wavelengths. Among them, the second BBO crystal plays a role in regulating the Stokes light, and when the frequency doubling and sum frequency do not require the participation of the second-order Stokes, it plays a role in increasing the loss of the second-order Stokes light, thereby reducing the efficiency of the conversion from the first order to the second-order Stokes light, thereby reducing the loss of the first-order Stokes light. In addition, the birefringence walk-off effect of the first BBO crystal can also be compensated, which is beneficial to the beam quality of the mixed output laser. Both of these regulating effects of the second BBO crystal can play a role in improving the conversion efficiency of the frequency doubling of the first-order Stokes light. Finally, a visible band laser with high efficiency and high beam quality is achieved.

[0014] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a principle diagram of an optical path of an embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of the principle of generating five wavelengths in the visible band according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In the description of this embodiment, it should be noted that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "front", "back", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore, cannot be understood as limiting the present invention. In addition, if the terms "first", "second", and "third" appear, they are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0018] See also Figure 1 to Figure 2The present invention discloses a self-Raman intracavity frequency conversion five-wavelength selectable laser, comprising a body, wherein a pump source 1, a total reflection lens 2, a Nd-doped yttrium vanadate crystal 3, a Q switch 4, an intermediate lens 5, a first BBO crystal 6, a second BBO crystal 8 and an output lens 10 are sequentially arranged in the body, wherein the total reflection lens 2 and the output lens 10 form an oscillation cavity, wherein the axial center lines of the pump source 1, the total reflection lens 2, the Nd-doped yttrium vanadate crystal 3, the Q switch 4, the intermediate lens 5, the first BBO crystal 6, the second BBO crystal 8 and the output lens 10 are overlapped and placed, wherein a horizontal rotation adjustment platform 7 is arranged at the lower end of the first BBO crystal 6, and a fixed platform 9 is arranged at the lower end of the second BBO crystal 8, wherein the light transmission direction of the first BBO crystal 6 is consistent with the phase matching angle required for the corresponding wavelength output by fine-tuning and rotating the first BBO crystal 6, thereby selecting and realizing the mixing of the corresponding fundamental frequency light or each order of Stokes light in the laser resonant cavity, and correspondingly outputting visible band lasers of different wavelengths.

[0019] The oscillation cavity realizes the simultaneous oscillation of fundamental frequency laser, first-order Stokes light and second-order Stokes light in the cavity.

[0020] In order to make the structural design of the present invention more reasonable, as a preferred embodiment, the first BBO crystal 6 and the second BBO crystal 8 of this embodiment are two crystals with the same size and optical parameters, and are cut according to the phase matching angle of 1313nm frequency doubling and the angle between the light transmission direction and the crystal optical axis is 20.4°. The rotatable angle of the horizontal rotation adjustment table 7 is greater than 2.5 degrees.

[0021] The optical axes of the first BBO crystal 6 and the second BBO crystal 8 are placed in a mirror image, which plays a role in birefringence walk-off compensation in nonlinear frequency conversion.

[0022] The total reflection lens 2 is coated with a high reflection film for lasers in the wavelength range of 1.06 microns to 1.32 microns; the intermediate lens 5 is coated with an anti-reflection film for lasers in the wavelength range of 1.06 microns to 1.32 microns and a high reflection film for lasers in the wavelength range of 0.56 microns to 0.62 microns; the output lens 10 is coated with a high reflection film for lasers in the wavelength range of 1.06 microns to 1.32 microns and a high transmittance film for lasers in the wavelength range of 0.53 microns to 0.66 microns.

[0023] The pump source 1 is a semiconductor laser with an output wavelength of 808 nanometers or 880 nanometers.

[0024] The Q switch 4 is an acousto-optic Q switch with high transmittance in the 1.06 μm to 1.32 μm band.

[0025] In actual application, under the action of the pump source, the Nd:YVO crystal forms fundamental frequency light in the 1.06-micron band in the cavity composed of the total reflection lens and the output lens, and oscillates and strengthens continuously; when the intensity of the fundamental frequency light reaches the Raman conversion threshold of the Nd:YVO crystal, part of the fundamental frequency light in the 1.06-micron band generates the first-order Stokes light in the 1.18-micron band through a Raman frequency shift, and at the same time, oscillates and strengthens in the cavity composed of the total reflection lens and the output lens; when the intensity of the first-order Stokes light in the 1.18-micron band reaches the Raman conversion threshold of the Nd:YVO crystal, part of the first-order Stokes light in the 1.18-micron band generates the second-order Stokes light in the 1.31-micron band through Raman frequency shift again, and also oscillates and strengthens in the cavity composed of the total reflection lens and the output lens. Therefore, in the cavity composed of the total reflection lens and the output lens, there can be fundamental frequency light in the 1.06 micron band, first-order Stokes light in the 1.18 micron band, and second-order Stokes light in the 1.31 micron band at the same time. The Q switch is mainly used to realize Q-switched pulse laser operation and increase the peak power of the fundamental frequency light and the first and second order Stokes light in the cavity.

[0026] Table 1 BBO crystal matching angle and walk-off angle corresponding to each wavelength mixing

[0027]

[0028] Table 1 gives the theoretically calculated matching angle of the BBO crystal corresponding to each wavelength mixing. This matching angle is the value corresponding to the angle between the light direction and the crystal optical axis when realizing the laser frequency doubling or sum frequency in the "wavelength combination". The lasers of various wavelengths in the oscillator cavity are fine-tuned by rotating the horizontal rotary adjustment table to fine-tune the angle of the first BBO crystal so that the angle between the light direction and the crystal optical axis corresponds to the "BBO matching angle" value in Table 1, so that the sum frequency or respective frequency doubling between different wavelengths can be achieved, thereby realizing the conversion to the visible band laser of the wavelength corresponding to the "output wavelength" in Table 1. The intermediate lens is used to reflect the visible band laser transmitted in the opposite direction, and finally the visible band laser is output by the output lens. The first BBO crystal is placed in a mirror image with the second BBO crystal, which can play the role of pulling back the stray light beam, thereby improving the frequency conversion efficiency and the output laser beam quality. In addition, the second BBO crystal is cut according to the phase matching angle of the second-order Stokes light frequency doubling, which will convert the second-order Stokes light in the cavity to double the frequency. When the second-order Stokes light participates in the frequency doubling, it plays a role in increasing the frequency doubling efficiency. When the second-order Stokes light is not required, it also has an important function of increasing the loss of the second-order Stokes light, thereby reducing the efficiency of the conversion from the first-order to the second-order Stokes light and improving the conversion efficiency of the first-order Stokes light frequency doubling.

[0029] The structure of the present invention is reasonable. Two mirror-image BBO crystals are used in the whole body. By fine-tuning and rotating the first BBO crystal, the light transmission direction of the first BBO crystal is consistent with the phase matching angle required for the corresponding wavelength output, so as to select and realize the mixing of the corresponding fundamental frequency light or each order of Stokes light in the laser resonant cavity, and output visible band lasers of different wavelengths. The second BBO crystal plays a role in regulating the Stokes light. When the frequency doubling and sum frequency do not require the participation of the second-order Stokes, it plays a role in increasing the loss of the second-order Stokes light, thereby reducing the efficiency of the conversion from the first order to the second-order Stokes light, thereby reducing the loss of the first-order Stokes light. In addition, it can also compensate for the birefringence walk-off effect of the first BBO crystal, which is beneficial to the beam quality of the mixed output laser. The two regulating effects of the second BBO crystal can both play a role in improving the conversion efficiency of the frequency doubling of the first-order Stokes light. Finally, a high-efficiency, high-beam-quality visible band laser is achieved.

[0030] The specific description of the present invention in the above embodiments is only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Technical engineers in this field may make some non-essential improvements and adjustments to the present invention based on the contents of the above invention, which fall within the scope of protection of the present invention.

Claims

1. A self-Raman intracavity frequency conversion five-wavelength selectable laser, comprising a body, characterized in that: The body is provided with a pump source (1), a fully reflective lens (2), a neodymium-doped yttrium vanadate crystal (3), a Q switch (4), an intermediate lens (5), a first BBO crystal (6), a second BBO crystal (8) and an output lens (10) in sequence. The fully reflective lens (2) and the output lens (10) form an oscillation cavity. The axial center lines of the pump source (1), the fully reflective lens (2), the neodymium-doped yttrium vanadate crystal (3), the Q switch (4), the intermediate lens (5), the first BBO crystal (6), the second BBO crystal (8) and the output lens (10) are placed so as to overlap. A horizontal rotation adjustment platform (7) is provided at the lower end of the first BBO crystal (6), and a fixed platform (9) is provided at the lower end of the second BBO crystal (8). By fine-tuning and rotating the first BBO crystal (6), the light transmission direction of the first BBO crystal (6) is made consistent with the phase matching angle required for the output of the corresponding wavelength, thereby selectively realizing the mixing of the corresponding fundamental frequency light or each order of Stokes light in the laser resonant cavity, and correspondingly outputting visible band lasers of different wavelengths.

2. The self-Raman intracavity frequency conversion five-wavelength selectable laser according to claim 1, characterized in that: The first BBO crystal (6) and the second BBO crystal (8) are two crystals with the same size and optical parameters, and are cut according to the phase matching angle of 1313nm frequency doubling, with the angle between the light transmission direction and the crystal optical axis being 20.4°.

3. The self-Raman intracavity frequency conversion five-wavelength selectable laser according to claim 2, characterized in that: The rotatable angle of the horizontal rotation adjustment platform (7) is greater than 2.5 degrees.

4. The self-Raman intracavity frequency conversion five-wavelength selectable laser according to claim 3, characterized in that: The optical axes of the first BBO crystal (6) and the second BBO crystal (8) are placed in a mirror-image manner, which plays a role in birefringence walk-off compensation in nonlinear frequency conversion.

5. The self-Raman intracavity frequency conversion five-wavelength selectable laser according to claim 1 or 4, characterized in that: The oscillation cavity realizes the simultaneous oscillation of fundamental frequency laser, first-order Stokes light and second-order Stokes light in the cavity.

6. The self-Raman intracavity frequency conversion five-wavelength selectable laser according to claim 5, characterized in that: The total reflection lens (2) is coated with a high reflection film for lasers in the wavelength range of 1.06 microns to 1.32 microns; the intermediate lens (5) is coated with an anti-reflection film for lasers in the wavelength range of 1.06 microns to 1.32 microns and a high reflection film for lasers in the wavelength range of 0.56 microns to 0.62 microns; and the output lens (10) is coated with a high reflection film for lasers in the wavelength range of 1.06 microns to 1.32 microns and a high transmittance film for lasers in the wavelength range of 0.53 microns to 0.66 microns.

7. The self-Raman intracavity frequency conversion five-wavelength selectable laser according to claim 6, characterized in that: The pump source (1) is a semiconductor laser with an output wavelength of 808 nanometers or 880 nanometers.

8. The self-Raman intracavity frequency conversion five-wavelength selectable laser according to claim 7, characterized in that: The Q switch (4) is an acousto-optic Q switch with high transmittance in the 1.06 micron to 1.32 micron band.

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