A single-stage and multi-stage amplification method for single-frequency tunable 1342nm continuous light

Abstract

The present invention discloses a single-stage and multi-stage amplification method of a single-frequency tunable 1342nm continuous light. The single-stage amplification method comprises the following steps: after the 1342nm seed light is shaped by a light shaping lens group, it is reflected by a first transflective mirror and injected into a first amplifying gain medium. The first pump coupling device shapes and converges the 880nm pump laser emitted by the optical fiber, and after passing through the first transflective mirror, it is focused into the first amplifying gain medium. The propagation direction of the seed laser is the same as that of the pump laser. The laser amplified by pumping is refocused from the first amplifying gain medium through a single lens to a second amplifying gain medium. At this time, the second pump coupling device shapes and focuses the pump light and injects it into the second amplifying gain medium. The laser propagation direction is opposite to that of the pump light, and it is amplified again after pumping. The amplified laser is reflected by the second transflective mirror. After multi-stage amplification, the laser power is increased from hundreds of milliwatts to hundreds of watts.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a method for amplifying single-stage single-frequency tunable 1342nm continuous light. Background Art

[0002] Lasers in the 1.3μm band have broad application prospects in the fields of optical fiber communications, video display, laser color holography, laser beauty and medical treatment, scientific research, etc. High-power and high-beam-quality 1342nm lasers can be used for nonlinear frequency conversion, such as double frequency to obtain high-power 671nm red light. The quadrupled 336nm light of 1342nm can be widely used in photobiology, photomedicine, and optical imaging.

[0003] Currently, solid-state lasers that emit continuously tunable 1342nm single-frequency lasers on the market have the disadvantage of low energy. In order to obtain a single-frequency continuously tunable laser with higher power, it is necessary to amplify the tunable 1342nm single-frequency continuous light so that the laser output meets the characteristics of single frequency, narrow line width, high frequency stability and high energy. The traditional amplifier structure in which the pump light is longitudinally pumped from both the forward and reverse directions to the same gain medium has the problems of high thermal effect, difficulty in laser alignment and low laser amplification efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a single-stage amplification method of single-frequency tunable 1342nm continuous light in view of the technical defects of the laser in the prior art.

[0005] Another object of the present invention is to provide a multi-stage amplification method for single-frequency tunable 1342nm continuous light.

[0006] The technical solution adopted to achieve the purpose of the present invention is:

[0007] A single-stage amplification method for single-frequency tunable 1342nm continuous light, after being shaped by a light shaping lens group, a 1342nm seed light is injected into a first amplifying gain medium through reflection by a first reflective mirror, a first pump coupling device shapes and converges an 880nm pump laser emitted from an optical fiber, and after passing through the first reflective mirror, focuses it into the first amplifying gain medium, the seed laser propagates in the same direction as the pump laser, the laser amplified by pumping is refocused from the first amplifying gain medium through a single lens into a second amplifying gain medium, at which time a second pump coupling device shapes and focuses the pump light and injects it into the second amplifying gain medium, the laser propagates in the opposite direction to the pump light, is amplified again after being pumped, and the amplified laser is reflected out through a second reflective mirror.

[0008] In the above technical solution, the single-frequency tunable 1342nm continuous light is amplified by a straight cavity amplifier, which includes a shaping lens group for shaping the seed light, a single lens arranged on the same optical axis, two pump coupling devices, two reflective mirrors and two amplifying gain media, wherein:

[0009] Two amplifying gain media are respectively located on both sides of the single lens, each transflective mirror is located between a pump coupling device and an amplifying gain medium, the light output directions of the two pump coupling devices are opposite, the first transflective mirror refracts the light emitted by the shaping lens group into the first amplifying gain medium, and the light emitted by the second amplifying gain medium is reflected out through the second transflective mirror.

[0010] In the above technical solution, the shaping lens group includes an isolator and a first lens and a second lens located on both sides of the isolator.

[0011] In the above technical solution, the first lens is a shaping lens, and the second lens is a focusing lens.

[0012] In the above technical solution, the angles between the first reflective mirror and the second reflective mirror and the optical axis are both 45°, the first reflective mirror and the second reflective mirror are arranged in parallel, and the first reflective mirror and the second reflective mirror fully reflect the seed light at 45 degrees and fully transmit the pump light at 45 degrees.

[0013] In the above technical solution, the amplifying gain medium is a YVO4-Nd:YVO4 bond and crystal.

[0014] In the above technical solution, the amplified gain medium is wrapped by copper and the temperature is controlled by a TEC cooling sheet.

[0015] In the above technical solution, the pump coupling device contains a lens group. Preferably, the diameter ratio of the seed light spot to the focusing spot of the pump coupling device is 0.8.

[0016] Another aspect of the present invention is a multi-stage amplification method of single-frequency tunable 1342nm continuous light, comprising the following steps:

[0017] Step 1, in the first stage straight cavity amplifier, after the 1342nm seed light is shaped by the light shaping lens group, it is reflected by the first reflective mirror and injected into the first amplifying gain medium. The first pump coupling device shapes and converges the 880nm pump laser emitted from the optical fiber, and after passing through the first reflective mirror, it is focused into the first amplifying gain medium. The propagation direction of the seed laser is the same as that of the pump laser. The laser amplified by the pump is refocused from the first amplifying gain medium through a single lens into the second amplifying gain medium. At this time, the second pump coupling device shapes and focuses the pump light and injects it into the second amplifying gain medium. The propagation direction of the laser is opposite to that of the pump light. After pumping, it is amplified again, and the amplified laser is reflected out by the second reflective mirror.

[0018] Step 2, the light reflected by the second reflective mirror of the first-stage direct cavity amplifier enters the light shaping lens group of the next-stage direct cavity amplifier;

[0019] Step 3, repeat steps 1-2 to amplify step by step until the second reflective mirror of the last stage of the direct cavity amplifier reflects the laser out.

[0020] In the above technical solution, the multi-stage amplification method is completed by an N-stage direct cavity amplifier, and the light reflected by the second reflective mirror of the previous direct cavity amplifier is irradiated into the light shaping lens group of the next adjacent direct cavity amplifier, and N is a natural number greater than or equal to 2;

[0021] Each stage of the straight cavity amplifier includes a shaping lens group for shaping the seed light, a single lens arranged on the same optical axis, two pump coupling devices, two reflective mirrors and two amplifying gain media, wherein:

[0022] Two amplifying gain media are respectively located on both sides of the single lens, each transflective mirror is located between a pump coupling device and an amplifying gain medium, the light output directions of the two pump coupling devices are opposite, the first transflective mirror refracts the light emitted by the shaping lens group into the first amplifying gain medium, and the light emitted by the second amplifying gain medium is reflected out through the second transflective mirror.

[0023] In the above technical solution, N=4 or 5.

[0024] In the above technical scheme, the multi-stage straight cavity amplifier has the same structure but different parameters. As the seed light laser power increases, the power of the pump light increases, the spot of the pump light after being focused by the pump coupling device increases, the doping concentration of the laser crystal (YVO4-Nd:YVO4 bond and crystal) decreases, and the length of the laser crystal increases.

[0025] In the above technical solution, when N=5, the ratios of the pump coupling devices of the first, second, third, fourth and fifth stage direct cavity amplifiers are 1:1.5, 1:2, 1:2, 1:3 and 1:4 respectively.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The amplification method of the present invention performs straight cavity amplification in both the forward and reverse directions of the low-energy single-frequency continuously tunable 1342nm seed light at both ends, and the amplification gain medium is divided into two. This can greatly reduce the thermal effect of the crystal, reduce the difficulty of laser alignment, and increase the laser amplification efficiency.

[0028] 2. The amplification method of the present invention can amplify low-power seed light to increase the energy and maintain the high-quality characteristics of the seed light.

[0029] 3. The multi-stage amplification method of the present invention can solve the disadvantage of low laser energy, while retaining the spectral characteristics of the seed source, and can obtain a laser with high beam quality. Through multi-stage amplification, a beam with single longitudinal mode, narrow line width, tunable frequency, high energy and high quality is obtained, so that the laser power is increased from hundreds of milliwatts to hundreds of watts. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the structure of the straight cavity amplifier of Example 1.

[0031] Figure 2 It is a schematic diagram of the structure of the multi-stage straight cavity amplification system of Example 3.

[0032] In the figure: 1-isolator, 2-first lens, 3-second lens, 4-first pump coupling device, 5-first reflective mirror, 6-first amplifying gain medium, 7-second amplifying gain medium, 8-second reflective mirror, 9-second pump coupling device, 10-single lens, 11-first stage direct cavity amplifier, 12-second stage direct cavity amplifier, 13-third stage direct cavity amplifier, 14-fourth stage direct cavity amplifier. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Example 1

[0035] The 1342nm seed light is a single-frequency continuous light. Although the optical power is relatively low, about a few hundred milliwatts, it has the characteristics of single longitudinal mode, narrow linewidth (linewidth less than 500KHZ), frequency tunability, and high beam quality (M2<1.2).

[0036] A single-stage amplification method of single-frequency tunable 1342nm continuous light comprises the following steps: after the seed light is shaped by the light shaping lens group, it is reflected by the first reflective mirror 5 and then injected into the first amplifying gain medium 6. The first pump coupling device 4 shapes and converges the 880nm pump laser emitted by the optical fiber, and after passing through the first reflective mirror 5, it is injected into the first amplifying gain medium 6 in the same direction as the 1342nm seed light, so that the 1342nm laser is gain-amplified. The propagation direction of the seed laser is the same as that of the pump laser. The laser amplified by pumping enters the second amplifying gain medium 7 from the first amplifying gain medium 6 through a single lens 10 again. The single lens 10 has the function of shaping the light, matching the size of the reverse pumping and the seed light. At this time, the second pump coupling device 9 shapes and focuses the 880nm pump light and injects it into the second amplifying gain medium 7, amplifying the 1342nm seed light again. The propagation direction of the laser is reverse to that of the pump light, and it is amplified again after pumping. The amplified laser is reflected out through the second reflective mirror 8. At this point the amplifier completes the first stage of double-ended straight-cavity amplification.

[0037] The single-stage amplification method is carried out in a straight cavity amplifier. The working principle of the straight cavity amplifier is to perform straight cavity amplification on low-power 1342nm seed light. The straight cavity amplifier includes a shaping lens group and a single lens arranged on the same optical axis, two pump coupling devices, two reflective mirrors and two amplification gain media, wherein:

[0038] Two amplifying gain media are respectively located on both sides of the single lens 10, and each reflector is located between a pump coupling device and an amplifying gain medium. The first reflector 5 refracts the light emitted by the shaping lens group into the first amplifying gain medium, and the light emitted by the second amplifying gain medium is reflected by the second reflector 8.

[0039] Example 2

[0040] The shaping lens group includes an isolator 1 and a first lens 2 and a second lens 3 located on both sides of the isolator 1. The function of the isolator 1 is to isolate the seed light returning along the original path to avoid interfering with the seed light and ensure the stability of the seed light. The first lens 2 shapes the seed light so that the divergent seed light is transmitted as parallel as possible. The second lens 3 is a focusing lens, which mainly focuses the shaped seed light to a suitable spot size and injects it into the gain medium, so that the seed light meets the requirements of efficient amplification. The focusing spot size is determined by the lens group parameters.

[0041] In the straight cavity amplifier, the shaping lens group needs to shape the spot diameter to 320um, while the first pump coupling device 4 and the second pump coupling device 9 need to shape the pump light to 300um, so that the spot diameter ratio of the seed light and the pump light is about 0.8, meeting the mode matching requirements.

[0042] The first reflective mirror 5 and the second reflective mirror 8 fully reflect the seed light at 45 degrees and fully transmit the 880nm pump light at 45 degrees, which plays a key role in adjusting the longitudinal mode matching of the seed light and the pump light. The pump coupling device has a lens group inside, which shapes and focuses the 880nm pump light emitted from the optical fiber in different proportions.

[0043] The pump light uses a fiber-coupled laser diode laser with an output central wavelength of 880nm, a fiber diameter of 200um, a numerical aperture NA of 0.22, and a magnification of 1:1.5, 1:2, 1:3, and 1:1.4. Different magnifications can be selected according to different amplification requirements to match the seed light spot size. The pump light output by the optical fiber is injected into the first amplification gain medium 6 and the second amplification gain medium 7 from the forward and reverse directions after passing through the first pump coupling device 4 and the first pump coupling device 4, respectively, so that the seed light is amplified efficiently. The laser emitted by the pump laser is then transmitted through the optical fiber, and the optical fiber is connected to the pump coupling device. The pump coupling device contains a lens group to shape and converge the pump light. The pump light spot size refers to the spot size of the pump light after being focused by the coupling device, and the focus is in the crystal.

[0044] The first gain medium 6 and the second gain medium 7 are both YVO4-Nd:YVO4 bonded crystals. The bonded crystals can effectively improve the thermal effect caused by the low thermal conductivity of the Nd:YVO4 crystal, avoid the end film layer from being damaged by high temperature and thermal stress, and improve the light damage resistance. The seed light and pump light are focused inside the crystal, and the overall heat is large. It is wrapped in copper, which has good conductivity and is conducive to heat dissipation. The water cooling takes away the entire heat, and the TEC refrigeration sheet performs precise temperature control. The TEC temperature control mode is more flexible and accurate, and easy to adjust.

[0045] Example 3

[0046] A multi-stage amplification method for single-frequency tunable 1342nm continuous light, comprising the following steps:

[0047] Step 1, in the first stage straight cavity amplifier, after the 1342nm seed light is shaped by the light shaping lens group, it is reflected by the first reflective mirror and injected into the first amplifying gain medium. The first pump coupling device shapes and converges the 880nm pump laser emitted from the optical fiber, and after passing through the first reflective mirror, it is focused into the first amplifying gain medium. The propagation direction of the seed laser is the same as that of the pump laser. The laser amplified by the pump is refocused from the first amplifying gain medium through a single lens into the second amplifying gain medium. At this time, the second pump coupling device shapes and focuses the pump light and injects it into the second amplifying gain medium. The propagation direction of the laser is opposite to that of the pump light. After pumping, it is amplified again, and the amplified laser is reflected out by the second reflective mirror.

[0048] Step 2, the light reflected by the second reflective mirror of the first-stage direct cavity amplifier enters the light shaping lens group of the next-stage direct cavity amplifier;

[0049] Step 3, repeat steps 1-2 to amplify step by step until the second reflective mirror of the last stage of the direct cavity amplifier reflects the laser out.

[0050] Each stage of the direct cavity amplifier adopts the direct cavity amplifier described in Example 1 or Example 2, but the parameters of each stage of the direct cavity amplifier will vary with the change of laser power. When the 1342nm laser power increases, the power and spot size of the pump light will increase, the doping concentration of the laser crystal will decrease successively, and the crystal length will also increase.

[0051] The light reflected by the second reflective mirror 8 of the preceding straight cavity amplifier is irradiated into the light shaping lens group of the following adjacent straight cavity amplifier. Figure 2 As shown, the laser amplified by the first stage direct cavity amplifier 11 enters the second stage direct cavity amplifier 12 for amplification again, and is amplified step by step by the third stage direct cavity amplifier 13 and the fourth stage direct cavity amplifier 14, forming a multi-stage amplification system. Because the energy of the 1342nm laser changes with each amplification stage, the light energy density injected into the laser crystal also changes, so the spot size of the 1342nm laser and the pump spot size also change, and the specific parameters are shown in Table 1.

[0052] Taking the five-stage connected direct cavity amplifier as an example, the doping concentration of the crystal (YVO4-Nd:YVO4 bond and crystal) in Table 1 decreases with the increase of 1342nm laser power, and the pump spot size (the spot size of the pump light after being focused by the coupling device, the spot is located in the crystal) and the optical power increase with the increase of 1342nm laser power. The change of the pump spot size is determined by the pump coupling device with different magnifications. The magnification of the first stage direct cavity amplifier is 1:1.5, the magnification of the second and third stage direct cavity amplifiers is 1:2, the magnification of the fourth stage direct cavity amplifier is 1:3, and the magnification of the fifth stage direct cavity amplifier is 1:4.

[0053] Table 1. Main design parameters of multi-stage straight cavity amplification system

[0054]

[0055] In the first-stage direct-cavity amplifier 11, the seed light entering the first amplifying gain medium 6 is 1W. After leaving the first amplifying gain medium 6, the power is amplified to 1.5W, that is, when entering the second amplifying gain medium 7, the seed light is 1.5W. 1W can be saturated with 20W pump light. 1.5W is not easy to saturate due to its high power, so 30W pump light can be selected. As the number of direct-cavity amplifiers increases, the power of the seed light gradually increases, and the same power pump light can be used before and after in the subsequent levels of direct-cavity amplifiers.

[0056] For ease of explanation, spatial relative terms such as "upper", "lower", "left", "right" and the like are used in the embodiments to illustrate the relationship of one element or feature shown in the figure relative to another element or feature. It should be understood that, in addition to the orientation shown in the figure, the spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figure is inverted, the element described as being "under" other elements or features will be positioned "on" other elements or features. Therefore, the exemplary term "under" can include both upper and lower orientations. The device can be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used here can be interpreted accordingly.

[0057] Furthermore, relational terms such as “first” and “second” and the like are merely used to distinguish one component from another having the same name, but do not necessarily require or imply any such actual relationship or order between these components.

[0058] The above description is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention, and these improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A single-stage amplification method for single-frequency tunable 1342nm continuous light, characterized in that: After the 1342nm seed light is shaped by the light shaping lens group, it is reflected by the first reflective mirror and injected into the first amplifying gain medium. The first pump coupling device shapes and converges the 880nm pump laser emitted from the optical fiber, and after passing through the first reflective mirror, it is focused into the first amplifying gain medium. The propagation direction of the seed laser is the same as that of the pump laser. The laser amplified by the pump is refocused from the first amplifying gain medium through a single lens into the second amplifying gain medium. At this time, the second pump coupling device shapes and focuses the pump light and injects it into the second amplifying gain medium. The propagation direction of the laser is opposite to that of the pump light. After being pumped, it is amplified again and the amplified laser is reflected out by the second reflective mirror. The single-frequency tunable 1342nm continuous light is amplified by a straight cavity amplifier, which includes a shaping lens group for shaping the seed light, a single lens arranged on the same optical axis, two pump coupling devices, two reflective mirrors and two amplification gain media, wherein: Two amplifying gain media are respectively located on both sides of the single lens, each transflective mirror is located between a pump coupling device and an amplifying gain medium, the light emitting directions of the two pump coupling devices are opposite, the first transflective mirror refracts the light emitted by the shaping lens group into the first amplifying gain medium, and the light emitted by the second amplifying gain medium is reflected by the second transflective mirror; The included angles between the first reflective mirror and the second reflective mirror and the optical axis are both 45°, the first reflective mirror and the second reflective mirror are arranged in parallel, and the first reflective mirror and the second reflective mirror fully reflect the seed light at 45 degrees and fully transmit the pump light at 45 degrees.

2. The single-stage amplification method according to claim 1, characterized in that: The shaping lens group includes an isolator and a first lens and a second lens located on both sides of the isolator.

3. The single-stage amplification method according to claim 2, characterized in that: The first lens is a shaping lens, and the second lens is a focusing lens.

4. The single-stage amplification method according to claim 1, characterized in that: The amplification gain medium is a YVO4-Nd:YVO4 bond and crystal.

5. The single-stage amplification method according to claim 1, characterized in that: The amplified gain medium is wrapped by copper and the temperature is controlled by a TEC cooling sheet.

6. The single-stage amplification method according to claim 1, characterized in that: The pump coupling device contains a lens group, and the diameter ratio of the seed light spot to the focusing spot of the pump coupling device is 0.

8.

7. A multi-stage amplification method for single-frequency tunable 1342nm continuous light, characterized in that: The following steps are involved: Step 1, in the first stage straight cavity amplifier, after the 1342nm seed light is shaped by the light shaping lens group, it is reflected by the first reflective mirror and injected into the first amplifying gain medium. The first pump coupling device shapes and converges the 880nm pump laser emitted from the optical fiber, and after passing through the first reflective mirror, it is focused into the first amplifying gain medium. The propagation direction of the seed laser is the same as that of the pump laser. The laser amplified by the pump is refocused from the first amplifying gain medium through a single lens into the second amplifying gain medium. At this time, the second pump coupling device shapes and focuses the pump light and injects it into the second amplifying gain medium. The propagation direction of the laser is opposite to that of the pump light. After pumping, it is amplified again, and the amplified laser is reflected out by the second reflective mirror. Step 2, the light reflected by the second reflective mirror of the first-stage direct cavity amplifier enters the light shaping lens group of the next-stage direct cavity amplifier; Step 3, repeating steps 1-2 to amplify step by step until the second reflective mirror of the last stage of the direct cavity amplifier reflects the laser out; The multi-stage amplification method is completed by using N-stage direct cavity amplifiers, and the light reflected by the second reflective mirror of the previous direct cavity amplifier is irradiated into the light shaping lens group of the next adjacent direct cavity amplifier, where N is a natural number greater than or equal to 2; Each stage of the straight cavity amplifier includes a shaping lens group for shaping the seed light, a single lens arranged on the same optical axis, two pump coupling devices, two reflective mirrors and two amplifying gain media, wherein: Two amplifying gain media are respectively located on both sides of the single lens, each transflective mirror is located between a pump coupling device and an amplifying gain medium, the light output directions of the two pump coupling devices are opposite, the first transflective mirror refracts the light emitted by the shaping lens group into the first amplifying gain medium, and the light emitted by the second amplifying gain medium is reflected out through the second transflective mirror.

8. The multi-stage amplification method according to claim 7, characterized in that: N=4 or 5.

9. The multi-stage amplification method according to claim 7, characterized in that: The multi-stage straight cavity amplifier has the same structure but different parameters. As the seed light laser power increases, the pump light power increases, the pump light spot increases after being focused by the pump coupling device, the doping concentration of the laser crystal decreases, and the length of the laser crystal increases.

10. The multi-stage amplification method according to claim 9, characterized in that: When N=5, the ratios of the pump coupling devices of the first, second, third, fourth and fifth stage direct cavity amplifiers are 1:1.5, 1:2, 1:2, 1:3 and 1:4 respectively.

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