Hollow-core fiber-filled gas laser

Abstract

The present invention provides a hollow-core fiber hybrid gas laser, comprising a pump laser, a reflector, a dichroic mirror, a coupling lens, an input sealed cavity, an output sealed cavity, a vacuum pumping and gas filling system, a hollow-core fiber, and a collimating lens. The laser output from the pump laser is combined and coupled into a hollow-core fiber. The hollow-core fiber is then vacuumed and filled with corresponding gain gases. By simultaneously filling the same section of hollow-core fiber with at least two gain gases, laser outputs in multiple different wavelength bands are generated, thereby achieving a wider output wavelength range and increasing the output wavelength range of the hollow-core fiber gas laser. Furthermore, the pressure of the gain gas is controlled to increase the output power of the hollow-core fiber gas laser. The present invention utilizes an optical fiber structure, making the hollow-core fiber hybrid gas laser simple and compact, highly stable, and providing high beam quality.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber lasers, and in particular relates to a hollow-core optical fiber mixed-gas laser. Background Art

[0002] As an important means of producing portable, stable, and efficient lasers, fiber lasers offer excellent beam quality and compact design, holding great promise for development in the laser field. Applications for lasers requiring high average power, compact size, high reliability, and the ability to transmit beams over long distances are rapidly increasing, particularly in the medical, materials processing, defense, and sensing fields.

[0003] Hollow-core fiber-based gas lasers are a new type of laser light source that has developed with the advent of hollow-core fiber. They combine many of the advantages of traditional gas lasers and fiber lasers and have garnered widespread attention in recent years. Fiber gas lasers use hollow-core fiber as the laser transmission medium and gas molecules as the gain medium, combining the advantages of both fiber and gas lasers. They boast a long operating range, excellent beam quality, good heat dissipation characteristics, and a high damage threshold. Furthermore, they can output lasers of varying wavelengths using interchangeable gain gases (such as CO2, CO, and HF).

[0004] Common fiber gas lasers are typically filled with only one gain gas. This single gain gas has limited output spectrum and places high demands on the output linewidth of the pump source. Summary of the Invention

[0005] In view of the defects of the existing technology, the present invention proposes a hollow-core fiber mixed gas laser to obtain a laser light source with a wide output band, high beam quality and flexible transmission.

[0006] In order to achieve the above technical objectives, the specific technical solutions adopted by the present invention are as follows:

[0007] Hollow-core fiber mixed gas laser, including pump laser, reflector, dichroic mirror, coupling lens, input sealed cavity, output sealed cavity, vacuum and filling system, hollow-core fiber, collimating lens;

[0008] The pump laser output by the pump laser is incident on a dichroic mirror after adjusting the optical path through a reflector. The dichroic mirror combines the pump laser beams and then injects them into a coupling lens. The coupling lens couples the combined pump laser beams into a hollow-core optical fiber. The input and output ends of the hollow-core optical fiber are sealed in an input sealed cavity and an output sealed cavity, respectively. A vacuum pumping and gas filling system is connected to the input sealed cavity or the output sealed cavity. The vacuum pumping and gas filling system is used to vacuum the hollow-core optical fiber and fill the hollow-core optical fiber with at least two gain gases having a set pressure, and to control the pressure of a single gain gas in the hollow-core optical fiber to not exceed 2 mbar, and the total pressure of the gain gases in the hollow-core optical fiber to not exceed 3 mbar. After the pump laser and the at least two gain gases interact in the hollow-core optical fiber, a mid-infrared laser with a wide output wavelength range is output. The mid-infrared laser with a wide output wavelength range output by the hollow-core optical fiber is collimated by a collimating lens and then emitted.

[0009] Furthermore, the number of the pump lasers corresponds to the type of gain gas, and the pump lasers are narrow-linewidth laser light sources whose central wavelengths correspond to the absorption lines of the gain gas.

[0010] Furthermore, the reflector is a plane reflector with high reflectivity corresponding to the central wavelength of the pump laser.

[0011] Furthermore, the dichroic mirror is a plane dichroic mirror having high reflectivity for the pump laser wavelength band incident after adjustment by the reflector, and high transmittance for the pump laser wavelength band incident directly.

[0012] Furthermore, the coupling lens is a positive lens with high transmittance to the pump laser wavelength band, and the coupling lens can focus the pump beam to match the hollow-core optical fiber mode field.

[0013] Furthermore, the input sealed cavity and the output sealed cavity are respectively provided with an input window and an output window; the input window has high transmittance to the pump laser band and the output laser band; the output window has high transmittance to the output laser band.

[0014] Furthermore, the vacuuming and charging system includes a vacuum pump, a gas cylinder, a pressure regulating valve, and a barometer, which are used to adjust and monitor the pressure of the gain gas in the hollow-core optical fiber.

[0015] Furthermore, the hollow-core optical fiber can transmit the pump laser band and the output laser band with low loss.

[0016] Furthermore, the collimating lens is a positive lens with high transmittance to the output laser wavelength band.

[0017] Furthermore, the gain gas includes but is not limited to carbon monoxide, carbon dioxide, hydrogen bromide, and acetylene.

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention uses at least two gases as gain gases simultaneously, and generates laser outputs of multiple different wavelength bands through stimulated radiation of different gases, thereby obtaining a wider output wavelength band and improving the output wavelength range of the hollow-core fiber gas laser. In principle, the pump laser pumps the gain gas molecules from the ground state to the excited state by aligning with the P-branch or R-branch absorption line of the gain gas. The excited gain gas molecules transition to the lower laser energy level through stimulated radiation and output mid-infrared laser light. At the same time, the mutual collision between the at least two gain gas molecules changes the energy level relaxation rate, thereby improving the laser output power and efficiency. In addition, filling the hollow-core fiber with at least two gain gases can further improve gas collision broadening, thereby increasing the absorption linewidth of each gas and reducing the output linewidth requirements of the pump source. In the present invention, filling at least two gain gases does not reduce the stability of the laser output power. The present invention also improves the output power of the hollow-core fiber mixed gas laser by controlling the gas pressure of the gain gas in the hollow-core fiber.

[0020] The present invention adopts an optical fiber structure, and the light is bound in the hollow core optical fiber, which is not easily affected by the external environment. Therefore, the present invention has the advantages of simple and compact structure, high stability, and high beam quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0022] Figure 1 A schematic diagram of the structure of a hollow-core fiber mixed gas laser provided in one embodiment;

[0023] Figure 2 This is an output spectrum diagram of an embodiment provided by simultaneously filling HBr and CO gases;

[0024] Figure 3 A diagram showing the effect of gas pressure on the output power of a hollow-core fiber mixed-gas laser when CO gas is filled into 1.49 mbar HBr gas according to an embodiment;

[0025] Figure 4 A diagram showing the effect of gas pressure on the output power of a hollow-core fiber mixed-gas laser when CO gas is filled into 3 mbar HBr gas according to an embodiment;

[0026] Figure 5A diagram showing the effect of gas pressure on the output power of a hollow-core fiber mixed-gas laser when HBr gas is filled into 2.2 mbar CO gas according to an embodiment;

[0027] Figure 6 A diagram showing the effect of gas pressure on the output power of a hollow-core fiber mixed-gas laser when HBr gas is filled into 5.2 mbar CO gas according to an embodiment;

[0028] Figure 7 A schematic diagram of the output power of a hollow-core fiber mixed-gas laser provided in one embodiment;

[0029] Figure 8 A diagram showing the effect of gas pressure changes on the CO absorption linewidth increase in a hollow-core fiber mixed-gas laser provided in one embodiment;

[0030] Figure 9 This is a diagram showing the effect of gas pressure changes on the HBr absorption linewidth increase in a hollow-core fiber mixed gas laser provided by one embodiment.

[0031] Figure annotation:

[0032] 1. First pump laser; 2. Second pump laser; 3. Reflector; 4. Dichroic mirror; 5. Coupling lens; 6. Input window; 7. Input sealed cavity; 8. Vacuuming and inflation system; 9. Hollow-core optical fiber; 10. Output sealed cavity; 11. Output window; 12. Collimating lens. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] In one embodiment, a hollow-core fiber mixed gas laser includes a first pump laser 1, a second pump laser 2, a reflector 3, a dichroic mirror 4, a coupling lens 5, an input window 6, an input sealed cavity 7, a vacuum pumping and gas filling system 8, a hollow-core fiber 9, an output sealed cavity 10, an output window 11, and a collimating lens 12.

[0035] The first pump laser output by the first pump laser 1 passes through the reflector 3 and the dichroic mirror 4 in sequence, and is combined with the second pump laser output by the second pump laser 2 through the dichroic mirror 4. The combined pump laser is focused by the coupling lens 5 to achieve mode field matching between the pump laser and the core of the hollow core optical fiber 9. The pump laser is coupled to the core of the hollow core optical fiber 9 through the input window 6. The input end and the output end of the hollow core optical fiber 9 are respectively sealed in the input sealed cavity 7 and the output sealed cavity 10; the vacuum and inflation system 8 is connected to the input sealed cavity 7 or the output sealed cavity 10, and the vacuum and inflation system 8 is used to vacuum the hollow core optical fiber 9 and fill the hollow core optical fiber 9 with at least two gain gases of set pressure, and control the single gain in the hollow core optical fiber 9 The gas pressure does not exceed 2 mbar, and the total gas pressure of the gain gas in the hollow-core optical fiber 9 does not exceed 3 mbar; the hollow-core optical fiber 9 effectively confines the pump laser in the fiber core, providing an effective interaction distance between the pump laser and the gain gas; after the hollow-core optical fiber 9 is filled with at least two gain gases, on the one hand, the radiation spectrum range of the laser can be increased, and on the other hand, the collision between the gain gas molecules can be enhanced, the absorption linewidth of the gas molecules is increased, and the energy level lifetime of the gain gas is improved; after the pump laser and the multiple gain gases interact in the hollow-core optical fiber 9, a mid-infrared laser with a wide output wavelength range is output. The mid-infrared laser with a wide output wavelength range output by the hollow-core optical fiber 9 passes through the output window 11 and is collimated by the collimating lens 12 before being emitted.

[0036] like Figure 1 In one embodiment, the hollow-core fiber mixed gas laser includes a first pump laser 1, a second pump laser 2, a reflector 3, a dichroic mirror 4, a coupling lens 5, an input window 6, an input sealed cavity 7, a vacuum pumping and filling system 8, a hollow-core fiber 9, an output sealed cavity 10, an output window 11, and a collimating lens 12.

[0037] The first pump laser output by the first pump laser 1 passes through the reflector 3 and the dichroic mirror 4 in sequence, and is combined with the second pump laser output by the second pump laser 2 passing through the dichroic mirror 4. The combined pump laser is focused by the coupling lens 5 to achieve mode field matching between the pump laser and the core of the hollow core optical fiber 9. The pump laser is coupled to the core of the hollow core optical fiber 9 through the input window 6. The input end and the output end of the hollow core optical fiber 9 are respectively sealed in the input sealed cavity 7 and the output sealed cavity 10; the vacuum and inflation system 8 is connected to the input sealed cavity 7 or the output sealed cavity 10, and the vacuum is pumped. The vacuum and gas filling system 8 is used to evacuate the hollow-core optical fiber 9 and fill the hollow-core optical fiber 9 with 1 mbar of HBr gas and 0.1 mbar of CO gas; the hollow-core optical fiber 9 effectively confines the pump laser in the fiber core, providing an effective interaction distance between the pump laser and the HBr and CO gases; after the pump laser interacts with the HBr and CO gases in the hollow-core optical fiber 9, a mid-infrared laser with a wide output wavelength range is output. The mid-infrared laser with a wide output wavelength range output by the hollow-core optical fiber 9 passes through the output window 11 and is collimated by the collimating lens 12 before being emitted.

[0038] The first pump laser 1 is a Tm fiber laser with a central wavelength of 1971.67 nm and a line width of 10 MHz; the second pump laser 2 is a Tm fiber laser with a central wavelength of 2331.93 and a line width of 10 MHz.

[0039] The reflector 3 is a plane reflector with a silver film coated on its surface, and has a high reflectivity for laser light with a central wavelength of 1971.67 nm.

[0040] The dichroic mirror 4 is a flat dichroic mirror with a dichroic film coated on its surface, which has high reflectivity for laser light with a central wavelength of 1971.67 nm and high transmittance for laser light with a central wavelength of 2331.93 nm.

[0041] The coupling lens 5 is a plano-convex lens with a focal length of 50 mm, has high transmittance for lasers with central wavelengths of 1971.67 nm and 2331.93 nm, and can focus the pump beam to match the hollow-core optical fiber mode field.

[0042] The input sealed cavity 7 and the output sealed cavity 10 are respectively provided with an input window 6 and an output window 11; the input window 6 is a flat glass window with high transmittance for lasers with central wavelengths of 1971.67nm and 2331.93nm; the output window 11 is a flat glass window with high transmittance for lasers in the 3.5-4.8μm band.

[0043] The hollow-core optical fiber 9 has low transmission loss for lasers in the wavelength bands of 1971.67 nm, 2331.93 nm, and 3.5-4.8 μm.

[0044] The collimating lens 12 is a plano-convex lens having high transmittance to laser beams in the 3.5-4.8 μm wavelength range.

[0045] like Figure 2 As shown, Figure 2 This is an output spectrum diagram of an embodiment provided by the simultaneous injection of HBr and CO gases. As can be seen from the figure, the simultaneous injection of HBr and CO gases produces laser output, indicating that the hollow-core fiber mixed-gas laser provided by the present invention can operate when simultaneously filled with HBr and CO gases.

[0046] In a hollow-core fiber mixed-gas laser, the more HBr and CO gas filled into the hollow-core fiber, the better. When the HBr gas in the hollow-core fiber is constant, the amount of CO gas filled into the hollow-core fiber will affect the output power of the hollow-core fiber mixed-gas laser. Specifically, Figure 3 This is a diagram showing the effect of the CO gas pressure in 1.49mbar HBr gas on the output power of a hollow-core fiber mixed gas laser provided in one embodiment. In this embodiment, the central wavelength of the first pump laser is 1971.67nm, the output linewidth is less than 10MHz, and the output power is maintained at a constant 3W; the central wavelength of the second pump laser is 2331.93, the output linewidth is less than 10MHz, and the output power is maintained at a constant 1W. The hollow-core fiber length is 5m and the core diameter is 100μm. Figure 3 It can be seen that at the initial moment, the hollow-core fiber mixed gas laser is only filled with HBr gas, and the pressure of HBr gas is 1.49mbar. At this time, the output power of the hollow-core fiber mixed gas laser is about 2.7mW. CO gas is filled into the hollow-core fiber using the vacuum pumping and filling system, and the output power of the hollow-core fiber mixed gas laser is monitored in real time. Figure 3 As can be seen in the figure, the amount of CO gas filled will affect the output power of the hollow-core fiber mixed gas laser. When 0.1mbar of CO gas is filled, the output power of the hollow-core fiber mixed gas laser reaches its maximum value. Then, as the CO gas filled in the hollow-core fiber increases, the output power of the hollow-core fiber mixed gas laser continues to decrease. When the CO gas filled in the hollow-core fiber exceeds 0.3mbar, the output power of the hollow-core fiber mixed gas laser will begin to gradually decrease compared to the output power of the hollow-core fiber mixed gas laser when only 1.49mbar of HBr gas is filled at the initial moment.

[0047] like Figure 4 As shown, Figure 4 The diagram of the effect of gas pressure on the output power of a hollow-core fiber mixed gas laser when CO gas is filled into 3 mbar HBr gas provided by an embodiment. Figure 3 The embodiment shown is the same, from Figure 4It can be seen that at the initial moment, the hollow-core fiber gas-filled laser is only filled with HBr gas, and the pressure of HBr gas is 3mbar. At this time, the output power of the hollow-core fiber gas-filled laser is about 4.2mW. CO gas is filled into the hollow-core fiber using the vacuum pumping and filling system, and the output power of the hollow-core fiber gas-filled laser is monitored in real time. Figure 4 It can be seen from the figure that the amount of CO gas filled in affects the output power of the hollow-core fiber mixed gas laser. Subsequently, as the amount of CO gas filled in the hollow-core fiber increases, the output power of the hollow-core fiber mixed gas laser decreases continuously. This indicates that when the HBr gas pressure in the hollow-core fiber mixed gas laser is too high, the addition of CO gas will reduce the output power of the hollow-core fiber mixed gas laser.

[0048] like Figure 5 As shown, Figure 5 The diagram of the effect of gas pressure on the output power of a hollow-core fiber mixed gas laser when HBr gas is filled into 2.2 mbar CO gas provided in one embodiment. Figure 3 The embodiment shown is the same, from Figure 5 It can be seen that at the initial moment, the hollow-core fiber mixed gas laser is only filled with CO gas, and the CO gas pressure is 2.2mbar. At this time, the output power of the hollow-core fiber mixed gas laser is about 5.4mW. HBr gas is filled into the hollow-core fiber using the vacuum pumping and filling system, and the output power of the hollow-core fiber mixed gas laser is monitored in real time. Figure 5 As can be seen in the figure, the amount of HBr gas filled will affect the output power of the hollow-core fiber mixed gas laser. When 0.8 mbar of HBr gas is filled, the output power of the hollow-core fiber mixed gas laser reaches its maximum value. Then, as the HBr gas filled in the hollow-core fiber increases, the output power of the hollow-core fiber mixed gas laser decreases continuously. When the HBr gas filled in the hollow-core fiber exceeds 2.9 mbar, the output power of the hollow-core fiber mixed gas laser will gradually decrease compared to the output power of the hollow-core fiber mixed gas laser when only 2.2 mbar of CO gas is filled at the initial moment.

[0049] like Figure 6 As shown, Figure 6 The diagram of the effect of gas pressure on the output power of a hollow-core fiber mixed gas laser when HBr gas is filled into 5.2 mbar CO gas provided in one embodiment. Figure 3 The embodiment shown is the same, from Figure 6It can be seen that at the initial moment, the hollow-core fiber mixed gas laser is only filled with CO gas, and the CO gas pressure is 5.2mbar. At this time, the output power of the hollow-core fiber mixed gas laser is about 2.4mW. HBr gas is filled into the hollow-core fiber using the vacuum pumping and filling system, and the output power of the hollow-core fiber mixed gas laser is monitored in real time. Figure 6 As can be seen in the figure, the amount of HBr gas filled in affects the output power of the hollow-core fiber hybrid gas laser. Subsequently, as the amount of HBr gas filled in the hollow-core fiber increases, the output power of the hollow-core fiber hybrid gas laser decreases continuously. This indicates that when the CO gas pressure in the hollow-core fiber hybrid gas laser is too high, the addition of HBr gas will reduce the output power of the hollow-core fiber hybrid gas laser.

[0050] When the gain gases filled in the hollow-core fiber are CO and HBr, the gas pressure of a single gain gas should not exceed 2 mbar, and the total gas pressure of the gain gases filled in the hollow-core fiber should not exceed 3 mbar. If the total gas pressure of the gain gases filled in the hollow-core fiber exceeds 3 mbar, it will not only fail to increase the output power of the hollow-core fiber mixed gas laser, but will cause the output power of the hollow-core fiber mixed gas laser to decrease.

[0051] like Figure 7 As shown, Figure 7 Schematic diagram of the output power of a hollow-core fiber mixed gas laser provided in one embodiment. Figure 3 The embodiment shown is the same. In the figure, the root mean square of the output power of the hollow-core fiber mixed gas laser is 1.1%, indicating that the hollow-core fiber mixed gas laser has good power stability.

[0052] like Figure 8 As shown, Figure 8 The figure shows the effect of pressure change on the CO absorption line width increase in a hollow-core fiber mixed gas laser according to an embodiment. As can be seen from the figure, as the total pressure in the hollow-core fiber increases, the CO absorption line width increase also increases. Figure 9 , Figure 9 A graph shows the effect of pressure changes on the HBr absorption linewidth increase in a hollow-core fiber mixed-gas laser according to one embodiment. As can be seen, as the total pressure in the hollow-core fiber increases, the HBr absorption linewidth increase also increases. This demonstrates that the hollow-core fiber mixed-gas laser provided by the present invention can increase the absorption linewidth of the gain gas, thereby reducing the output linewidth requirements of the pump source.

[0053] Matters not covered by the present invention are known technologies.

[0054] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

[0056] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. Hollow-core fiber mixed gas laser, characterized by: Including pump laser, reflector, dichroic mirror, coupling lens, input sealed cavity, output sealed cavity, vacuum and inflation system, hollow core optical fiber, collimating lens; The pump laser output by the pump laser is incident on a dichroic mirror after adjusting the optical path through a reflector. The dichroic mirror combines the pump laser beams and then injects them into a coupling lens. The coupling lens couples the combined pump laser beams into a hollow-core fiber. The input and output ends of the hollow-core fiber are sealed in an input sealed cavity and an output sealed cavity, respectively. A vacuum pumping and gas filling system is connected to the input sealed cavity or the output sealed cavity. The vacuum pumping and gas filling system is used to evacuate the hollow-core fiber and fill the hollow-core fiber with two gain gases with set pressures. The two gain gases are HBr and CO gases, and the pressure of a single gain gas in the hollow-core fiber is controlled to not exceed 2 mbar, and the total pressure of the gain gases in the hollow-core fiber is controlled to not exceed 3 mbar. After the pump laser and the two gain gases interact in the hollow-core fiber, a mid-infrared laser with a wide output wavelength range is output. The mid-infrared laser with a wide output wavelength range output by the hollow-core fiber is collimated by a collimating lens and then emitted.

2. The hollow-core fiber mixed gas laser according to claim 1, characterized in that: The number of the pump lasers corresponds to the type of gain gas, and the pump lasers are narrow-linewidth laser light sources whose central wavelengths correspond to the absorption lines of the gain gas.

3. The hollow-core fiber mixed gas laser according to claim 1, wherein: The reflector is a plane reflector with high reflectivity corresponding to the central wavelength of the pump laser.

4. The hollow-core fiber mixed gas laser according to claim 1, wherein: The dichroic mirror is a plane dichroic mirror having high reflectivity for the pump laser wave band incident after adjustment by the reflector and high transmittance for the pump laser wave band incident directly.

5. The hollow-core fiber mixed gas laser according to claim 1, wherein: The coupling lens is a positive lens with high transmittance for the pump laser wavelength band, and the coupling lens can focus the pump beam to match the hollow-core optical fiber mode field.

6. The hollow-core fiber mixed gas laser according to claim 1, characterized in that: The input sealed cavity and the output sealed cavity are respectively provided with an input window and an output window; the input window has high transmittance to the pump laser band and the output laser band; the output window has high transmittance to the output laser band.

7. The hollow-core fiber mixed gas laser according to claim 1, wherein: The vacuuming and filling system includes a vacuum pump, a gas cylinder, a pressure regulating valve, and a barometer, and is used to adjust and monitor the pressure of the gain gas in the hollow-core optical fiber.

8. The hollow-core fiber mixed gas laser according to claim 1, wherein: The hollow-core optical fiber can transmit the pump laser band and the output laser band with low loss.

9. The hollow-core fiber mixed gas laser according to claim 1, characterized in that: The collimating lens is a positive lens with high transmittance to the output laser wavelength band.

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