Short-wavelength pulse laser

Abstract

The invention relates to the technical field of lasers, and discloses a short-wavelength pulse laser, which comprises an external cavity semiconductor laser used for outputting first pulse laser with a preset central wavelength; the modulator is used for carrying out chopping modulation on the first pulse laser output by the external cavity semiconductor laser according to the chopping modulation signal output by the control unit and outputting second pulse laser, and the pulse width of the first pulse laser is larger than that of the second pulse laser; the control unit is used for controlling the external cavity semiconductor laser to output first pulse laser and controlling the modulator to perform chopping modulation on the first pulse laser; and the frequency multiplication device is used for carrying out frequency multiplication on the second pulse laser to obtain short-wavelength pulse laser. According to the invention, short-wavelength pulse laser with narrow linewidth, stable time domain and high power can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a short-wavelength pulse laser. Background Art

[0002] At present, there are two ways to realize nanosecond pulse short-wavelength lasers, mainly divided into solid solutions and fiber solutions. Among them, due to its structural characteristics, the solid solution has more and more complex space devices, relatively poor stability, and generally more than 100W solutions are difficult to achieve. In order to achieve higher frequency doubling efficiency, the fiber MOPA solution generally requires a narrower spectral width of the signal light source, which is related to the small allowable bandwidth of nonlinear crystals. Generally, the wider the fundamental frequency spectrum, the greater the phase mismatch and the lower the frequency doubling efficiency.

[0003] In the related technology, a technical solution is proposed based on superfluorescent fiber sources (SFSs) that use their low temporal coherence to output narrowband pulse light after narrowband filtering. One advantage of this type of solution over the DFB solution is that it is more cost-effective, but its time domain pulse stability is relatively general, and there is a certain amount of pulse amplitude jitter, which may affect the process processing effect during actual use.

[0004] In summary, there is an urgent need for a laser suitable for generating short-wavelength pulses to solve the technical problem of insufficient time-domain amplitude stability of the output short-wavelength pulses. Summary of the invention

[0005] In view of this, the present invention provides a short-wavelength pulse laser to solve or partially solve the technical problem of insufficient time-domain amplitude stability of the output pulse laser in the related art.

[0006] The technical solution proposed by the present invention is as follows:

[0007] The invention provides a short-wavelength pulse laser, comprising: an external cavity semiconductor laser, the external cavity semiconductor laser comprising an FP semiconductor laser and a low-reflection narrow-band grating, the FP semiconductor laser being used to output a first pulse laser, the low-reflection narrow-band grating being used to partially reflect a first pulse laser with a set central wavelength within a first spectral line width and form a stable laser oscillation mode, and output the first pulse laser with a preset central wavelength; a modulator being used to perform chopping modulation on the first pulse laser output by the external cavity semiconductor laser according to a chopping modulation signal output by a control unit, and output a second pulse laser, wherein the pulse width of the first pulse laser is greater than the pulse width of the second pulse laser; a control unit being used to control the external cavity semiconductor laser to output the first pulse laser and control the modulator to perform chopping modulation on the first pulse laser; and a frequency doubling device being used to perform frequency doubling on the second pulse laser, and obtain a short-wavelength pulse laser.

[0008] The short-wavelength pulse laser of the present invention is directly modulated by an FP semiconductor laser and a low-reflection narrow-band grating to output a first pulse laser with a narrow line width within a first spectral line width. For an external cavity semiconductor laser mainly composed of an FP semiconductor laser and a low-reflection narrow-band grating, as the pulse width increases, the feedback intensity of the low-reflection narrow-band grating to the inner cavity is also increased, the output spectrum width is correspondingly narrowed, and the side mode suppression ratio is also correspondingly improved. Therefore, the pulse width of the first pulse laser output by the external cavity semiconductor laser is wider, which is helpful to output the first pulse laser with a narrow line width, a high side mode suppression ratio and time domain stability. The first pulse laser is used as a polarization-maintaining pulse seed light and is chopped and modulated by a modulator to output a second pulse laser with adjustable pulse width. The second pulse laser has the same characteristics of narrow line width, high side mode suppression ratio and time domain stability as the first pulse laser, and can still maintain a relatively narrow spectrum output when high-power amplification is performed. After the second pulse laser is frequency-doubled, a short-wavelength pulse laser with a narrow line width, time domain stability and high power can be obtained.

[0009] In some optional embodiments, the pulse width of the first pulse laser is 100 ns to 200 ns.

[0010] Within the pulse width range, the first pulse laser output by the external cavity semiconductor laser has a good wavelength locking effect, and the pulse width range meets the duty cycle requirement under the semiconductor laser pulse modulation.

[0011] In some alternative embodiments, the modulator is an electro-optic modulator or an acousto-optic modulator.

[0012] In this way, fast response and high modulation accuracy can be achieved through either electro-optic modulators or acousto-optic modulators.

[0013] In some optional embodiments, the FP semiconductor laser, the low-reflection narrow-band grating and the modulator are all polarization-maintaining devices.

[0014] In this method, the FP semiconductor laser, low-reflection narrowband grating and modulator are all polarization-maintaining devices, which can effectively maintain the polarization state of the laser and reduce the impact of polarization state changes on laser performance. This helps to improve the stability of the laser and the output beam quality.

[0015] In some optional embodiments, the preset central wavelength is 1030 nm or 1064 nm, and the first spectral line width is 0.1 nm to 0.5 nm.

[0016] In some optional embodiments, the short-wavelength pulse laser further includes a first isolator, which is disposed between the low-reflection narrow-band grating and the modulator.

[0017] In this manner, a first isolator is provided between the low-reflection narrowband grating and the modulator, which can effectively prevent the interference of light reflection on the laser resonant cavity and improve the stability of the laser and the output beam quality.

[0018] In some optional embodiments, the short-wavelength pulse laser further includes a step-by-step amplifier, the input end of the step-by-step amplifier is connected to the output end of the modulator, and the output end of the step-by-step amplifier is connected to the frequency multiplication device.

[0019] In this method, adding a step-by-step amplifier can amplify the modulated second pulse laser step by step, thereby increasing the power of the laser and meeting the application requirements of high-power short-wavelength pulse laser.

[0020] In some optional embodiments, the step-by-step amplifier includes several power amplifiers connected in series, each power amplifier includes a pump source, a combiner and an active optical fiber, one input end of the combiner is connected to the output end of the modulator, the other input end of the combiner is connected to the pump source, and the output end of the combiner is connected to one end of the active optical fiber.

[0021] In this way, efficient energy conversion and power amplification can be achieved, and the output power of the laser can be further increased by cascading multiple power amplifiers.

[0022] In some optional embodiments, a second isolator is provided between the first series-connected power amplifier and the modulator, and a third isolator is provided between each power amplifier.

[0023] In this method, isolators are provided between the first power amplifier and the modulator and between each power amplifier, which can effectively isolate reverse light reflection and reduce the impact of optical feedback on laser performance.

[0024] In some optional embodiments, the control unit is further configured to adjust the pulse width of the second pulse laser by controlling the pulse width or delay of the first pulse laser and / or the chopping modulation signal.

[0025] In this manner, by adjusting the pulse width or delay of the first pulse laser and / or the chopper modulation signal, the pulse width of the second pulse laser can be flexibly controlled, thereby improving the flexibility and applicability of the output short-wavelength pulse laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly express the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. 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 these drawings without creative work.

[0027] Figure 1 Schematic diagram of the structure of a short-wavelength pulse laser in an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of spectrum of different pulse widths in an embodiment of the present invention;

[0029] Figure 3 Schematic diagram of modulation of the second pulse laser in an embodiment of the present invention;

[0030] Figure 4 Schematic diagram of comparison of the time domain waveforms of the second pulsed laser and the pulsed laser generated based on the superfluorescent fiber light source in an embodiment of the present invention;

[0031] Figure numerals: 1. FP semiconductor laser; 2. low-reflection narrow-band grating; 3. modulator; 4. control unit; 5. frequency doubling device; 6. step-by-step amplifier; 61. power amplifier; 7. first isolator; 8. second isolator. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described clearly and completely below 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] At present, there are two ways to realize nanosecond pulse short-wavelength lasers, mainly divided into solid solutions and fiber solutions. Among them, one of the solutions based on fiber solutions to realize nanosecond short-wavelength lasers is based on direct modulation of DFB semiconductor lasers for amplification. Due to the single longitudinal mode structure characteristics of DFB semiconductor lasers, the spectrum width of its direct output is generally in the order of hundreds of KHZ to several GHZ, and its spectrum cannot be naturally widened. Therefore, a serious SBS effect will occur during the amplification process, and it can generally only be used for narrow pulse width (less than 5ns) amplification, which limits the final output pulse energy.

[0037] There is another method of adding phase modulation to the DFB semiconductor laser. This solution is complex and expensive because it requires devices such as an electro-optical phase modulator 3, so it cannot be used on a large scale.

[0038] In the related technology, a technical solution is proposed based on superfluorescent fiber sources (SFSs) that use their low temporal coherence to output narrowband pulse light after narrowband filtering. One advantage of this type of solution over the DFB solution is that it is more cost-effective, but its time domain pulse stability is relatively general, and there is a certain amount of pulse amplitude jitter, which may affect the process processing effect during actual use.

[0039] However, the light source itself is composed of many incoherent wavelength components of different frequencies, and the different components will form optical beat noise, also known as excess intensity noise. In the case of narrowband filtering, these optical beat noises will increase as the bandwidth of the filter decreases, thereby affecting the stability of the time domain signal output by the final filter. That is, it will affect the time domain amplitude stability of the final modulated pulse. Generally speaking, the smaller the bandwidth of the narrowband filter, the more serious the output pulse peak jitter. Therefore, for the superfluorescent fiber light source solution, when it outputs narrow bandwidth pulse lasers, there is a relatively serious jitter and insufficient time domain stability.

[0040] In view of this, an embodiment of the present invention provides a short-wavelength pulse laser, which can output a pulse seed light source with a narrow linewidth spectrum, good time domain stability and adjustable pulse width.

[0041] like Figure 1 As shown, an embodiment of the present invention provides a short-wavelength pulse laser, including:

[0042] An external cavity semiconductor laser comprises an FP semiconductor laser 1 and a low-reflection narrowband grating 2, wherein the FP semiconductor laser 1 is used to output a first pulse laser, and the low-reflection narrowband grating 2 is used to partially reflect a first pulse laser with a set central wavelength within a first spectral line width and form a stable laser oscillation mode, and output a first pulse laser with a preset central wavelength; a modulator 3 is used to perform chopping modulation on the first pulse laser output by the external cavity semiconductor laser according to a chopping modulation signal output by a control unit 4, and output a second pulse laser, wherein the pulse width of the first pulse laser is greater than the pulse width of the second pulse laser, so that the pulse width of the first pulse laser is wider; a control unit 4 is used to control the external cavity semiconductor laser to output the first pulse laser and control the modulator 3 to perform chopping modulation on the first pulse laser; a frequency doubling device 5 is used to perform frequency doubling on the second pulse laser to obtain a short-wavelength pulse laser.

[0043] Specifically, an external-cavity semiconductor laser (ECSL) is mainly composed of a FP semiconductor laser 1 and a low-reflection narrow-band grating 2, and outputs a first pulse laser within a first spectral linewidth through direct electrical modulation, and performs external pulse modulation with a specific time delay with the chopping modulation signal of an external modulator 3, and outputs a second pulse laser with a narrow linewidth spectrum that is stable in the time domain and has an adjustable pulse width.

[0044] It should be understood that a general semiconductor laser will form a laser resonant cavity through the front and back cleavage surfaces of the chip active layer. In the laser resonant cavity, due to the competition of gain saturation modes, only the longitudinal mode with gain greater than loss can stably oscillate to form laser output. Since the gain curve of a free-running semiconductor laser is relatively flat and there is more spontaneous radiation of carriers, semiconductor lasers often operate in a multi-longitudinal mode, resulting in a wider output spectrum width.

[0045] In the embodiment of the present invention, a low-reflection narrowband grating 2 is added in the output direction of the FP semiconductor laser 1 to form an external cavity semiconductor laser. The portion of the laser output by the FP semiconductor laser 1 that is within the reflection bandwidth of the low-reflection narrowband grating 2 will be partially reflected by the low-reflection narrowband grating 2 and fed back to the inner cavity of the FP semiconductor laser 1, resulting in a reduction in mode loss within the corresponding range. The gain-greater-than-loss effect within the bandwidth range is enhanced to form a stable laser oscillation, while the modes of other bands are suppressed, thereby achieving wavelength locking and spectral line narrowing.

[0046] In some embodiments, the reflectivity of the low-reflection narrowband grating 2 is between 2% and 10%, the first spectral linewidth is between 0.1nm and 0.5nm, and the preset central wavelength is 1030nm or 1064nm, thereby outputting a first pulse laser with narrow linewidth and high side mode suppression ratio.

[0047] In particular, the locking effect is related to the working state of the FP semiconductor laser 1, that is, the output spectrum is related to the actual working state.

[0048] When the external cavity semiconductor laser is in continuous operation, since the inner cavity can continuously receive feedback from the external low-reflection narrowband grating 2, and due to the effect of mode competition, only the signal wavelength components within the reflection peak bandwidth of the external low-reflection narrowband grating 2 can form stable oscillations, and may eventually output a single longitudinal mode with an extremely narrow linewidth, which can be used for single-frequency laser related applications. In this case, due to the extremely narrow spectral linewidth and extremely high side mode suppression ratio, the SBS effect threshold is low during the amplification process, and it cannot be directly used for high-power or high-energy pulse seed sources after external modulation.

[0049] like Figure 2As shown in the figure, when the external cavity semiconductor laser is in the pulse modulation state, since the actual intensity and time of the feedback from the low-reflection narrowband grating 2 to the inner cavity are related to the actual pulse modulation time, when the pulse width is too narrow (less than 2ns), the feedback from the external low-reflection narrowband grating 2 to the active region inside the seed source is limited, and the actual wavelength locking effect is not obvious. At this time, the output spectrum is still close to the state of the semiconductor free operation. As the pulse width increases, the feedback intensity of the external grating to the inner cavity also increases, the output spectrum width is narrowed accordingly, the wavelength locking effect is more obvious, and the side mode suppression ratio is also improved accordingly, so that a relatively narrow spectrum output can be maintained during high power amplification.

[0050] The embodiment of the present invention utilizes this property of the external cavity semiconductor laser and directly modulates the external cavity semiconductor laser to output a first pulse laser with a specific pulse width. The pulse width of the first pulse laser must meet the following requirements:

[0051] On the one hand, the pulse width of the first pulse laser needs to be able to obtain a good wavelength locking effect, so the pulse width cannot be too narrow; on the other hand, it is limited by the duty cycle requirements under the semiconductor laser pulse modulation (too high duty cycle will affect the life or damage of the semiconductor laser, generally required not to be greater than 25%: that is, if the modulated pulse width is 500ns, the maximum adjustable pulse frequency is 500kHz, because (500*10 -9 )s*500*10 3 =0.25s, that is, the actual light emitting time of the seed source per second is at most 0.25 seconds), and at the same time, the adjustable range of the modulated pulse frequency cannot be too small (to meet the requirements of high-frequency applications, generally the pulse repetition frequency below 2MHz needs to be adjustable), so the modulated pulse width cannot be too wide.

[0052] In one embodiment, the pulse width of the first pulse laser is 100 ns to 200 ns.

[0053] For example, the pulse width of the first pulse laser is 100 ns, 150 ns, 200 ns, etc.

[0054] Within the pulse width range, the first pulse laser output by the external cavity semiconductor laser has a good wavelength locking effect, and the pulse width range meets the duty cycle requirement under the semiconductor laser pulse modulation.

[0055] Through the above analysis, it can be known that the pulse width of the first pulse laser cannot be too small. A too narrow pulse width cannot obtain a good wavelength locking effect, and a too large pulse width will result in the final output pulse peak power being too low, which cannot meet the requirements of the process processing effect. Therefore, by adding a modulator 3, the first pulse laser output by the external cavity semiconductor laser is subjected to secondary chopping modulation, and the relative delay between the two or the pulse width of the chopping modulation signal is controlled by the control unit 4, so that a second pulse laser with a smaller pulse width can be obtained in the overlapping part of the two. The pulse width of the second pulse laser is smaller than the pulse width of the first pulse laser. For example, the pulse width of the second pulse laser is 10ns, 5ns, 2ns, etc.

[0056] It should be understood that the control unit 4 can be a central processing unit, a network processor or a combination thereof. The control unit 4 can further include a hardware chip. The hardware chip can be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device can be a complex programmable logic device, a field programmable gate array (FPGA), a general array logic or any combination thereof.

[0057] like Figure 4 As shown, the second pulse laser output by the short-wavelength pulse laser in the embodiment of the present invention has better stability in the time domain than the pulse laser output by the superfluorescent fiber light source. At the same time, it has the advantages of narrow linewidth and high side mode suppression ratio like the first pulse laser. After being multiplied by 5 times by the frequency doubling device, it can output short-wavelength pulse lasers such as green light and purple light that can meet the frequency doubling efficiency of 70%.

[0058] After the second pulse laser is frequency-doubled by the frequency-doubling device 5, it outputs a green light pulse of 515nm or 532nm, and can finally output a green light pulse with a line width of 0.1nm to 0.5nm, which has wide application value in industrial processing, medical treatment, scientific research and other fields.

[0059] The short-wavelength pulse laser of the embodiment of the present invention is directly modulated by the FP semiconductor laser 1 and the low-reflection narrow-band grating 2 to output a first pulse laser with a narrow linewidth within the first spectral linewidth. For the external cavity semiconductor laser mainly composed of the FP semiconductor laser 1 and the low-reflection narrow-band grating 2, as the pulse width increases, the feedback intensity of the low-reflection narrow-band grating 2 to the inner cavity is also increased, the output spectrum width is correspondingly narrowed, and the side mode suppression ratio is also correspondingly improved. Therefore, the pulse width of the first pulse laser output by the external cavity semiconductor laser is made greater than that of the second pulse laser, which is helpful to output the first pulse laser with narrow linewidth, high side mode suppression ratio and time domain stability. The first pulse laser is used as a polarization-maintaining pulse seed light and is chopped and modulated by the modulator 3 to output a second pulse laser with adjustable pulse width. The second pulse laser has the same characteristics of narrow linewidth, high side mode suppression ratio and time domain stability as the first pulse laser, and can still maintain a relatively narrow spectrum output when high-power amplification is performed. After the second pulse laser is frequency-doubled, a short-wavelength pulse laser with narrow linewidth, time domain stability and high power can be obtained.

[0060] In some embodiments, the modulator 3 is an electro-optic modulator or an acousto-optic modulator.

[0061] In one example, the modulator 3 is an electro-optic modulator, and the control unit 4 is connected to the electro-optic modulator to control the delay between the chopping modulation signal of the electro-optic modulator and the first pulse laser output by the FP semiconductor laser 1, so as to obtain a second pulse laser with adjustable pulse width and narrow line width and high side mode suppression ratio. Fast response and high modulation accuracy can be achieved by using an electro-optic modulator or an acousto-optic modulator.

[0062] Furthermore, the FP semiconductor laser 1, the low-reflection narrow-band grating 2 and the modulator 3 are all polarization-maintaining devices.

[0063] In this method, the FP semiconductor laser 1, the low-reflection narrowband grating 2 and the modulator 3 are all polarization-maintaining devices, which can effectively maintain the polarization state of the laser and reduce the influence of the polarization state change on the laser performance. It can achieve that a relatively narrow spectral width can be maintained after amplification, and the output short-wavelength pulse laser is stable.

[0064] In some embodiments, the short-wavelength pulse laser further includes a first isolator 7 , which is disposed between the low-reflection narrow-band grating 2 and the modulator 3 .

[0065] Specifically, the first isolator 7 is an optical isolator (ISO), which is a passive optical device that only allows light to be transmitted in one direction and blocks light transmission in the opposite direction, thereby protecting the FP semiconductor laser 1 and ensuring that the spectrum output by the FP semiconductor laser 1 is not affected by the return light.

[0066] In this manner, a first isolator 7 is provided between the low-reflection narrowband grating 2 and the modulator 3, which can effectively prevent the interference of light reflection on the laser resonant cavity and improve the stability of the laser and the output beam quality.

[0067] In some embodiments, the short-wavelength pulse laser further includes a step-by-step amplifier 6 , the input end of the step-by-step amplifier 6 is connected to the output end of the modulator 3 , and the output end of the step-by-step amplifier 6 is connected to the frequency multiplication device 5 .

[0068] Specifically, the step-by-step amplifier 6 includes a plurality of power amplifiers 61 connected in series, each power amplifier 61 includes a pump source, a combiner and an active optical fiber, one input end of the combiner is connected to the output end of the modulator 3, the other input end of the combiner is connected to the pump source, and the output end of the combiner is connected to one end of the active optical fiber.

[0069] The second pulse laser enters the active optical fiber through the beam combiner and is amplified under the stimulation of the pump energy of the pump source.

[0070] For example, the wavelength of the pump light output by the pump source is 975 nm or 915 nm, and it can be forward pumping or reverse pumping. Preferably, reverse pumping can be used to reduce the spectrum broadening caused by nonlinear effects.

[0071] In this manner, adding a step-by-step amplifier 6 can amplify the modulated second pulse laser step-by-step, thereby increasing the power of the laser and meeting the application requirements of high-power short-wavelength pulse laser.

[0072] By connecting multiple power amplifiers 61 in series, the power of the laser can be gradually increased, so that the laser can output higher energy pulsed laser, which is suitable for applications requiring high power laser, such as industrial processing, medical surgery, etc., while maintaining the spectral characteristics of the laser.

[0073] In some embodiments, a second isolator 8 is provided between the first series-connected power amplifier 61 and the modulator 3 , and a third isolator is provided between each power amplifier 61 .

[0074] The second isolator 8, the third isolator and the first isolator 7 are all optical isolators. By providing the second isolator 8 between the power amplifier 61 and the modulator 3 and the third isolator between the power amplifiers 61, the reverse propagation and mutual interference of light can be prevented, thereby improving the stability of the laser output by the short-wavelength pulse laser.

[0075] In some embodiments, the control unit 4 is further configured to adjust the pulse width of the second pulse laser by controlling the pulse width or delay of the first pulse laser and / or the chopping modulation signal.

[0076] Specifically, Figure 3As shown, the second pulse laser output after chopping modulation is the overlapping part of the first pulse laser and the chopping modulation signal. Therefore, when the output delay is fixed, the overlapping width of the first pulse laser and the chopping modulation signal can be changed by the pulse width of the first pulse laser and / or the chopping modulation signal, thereby adjusting the pulse width of the second pulse laser. For example, the pulse width of the first pulse laser is appropriately increased, thereby increasing the pulse width of the second pulse laser.

[0077] When the pulse widths of the first pulse laser and the chopping modulation signal are fixed, the overlapping width of the first pulse laser and the chopping modulation signal can be changed by controlling the time delay, thereby adjusting the pulse width of the second pulse laser, for example, reducing the time delay of the chopping modulation signal to increase the pulse width of the second pulse laser.

[0078] In this manner, by adjusting the pulse width or delay of the first pulse laser and / or the chopper modulation signal, the pulse width of the second pulse laser can be flexibly controlled, thereby improving the flexibility and applicability of the output short-wavelength pulse laser.

[0079] The short-wavelength pulse laser of the embodiment of the present invention has the following effects:

[0080] The short-wavelength pulse laser of the embodiment of the present invention is directly modulated by the FP semiconductor laser 1 and the low-reflection narrow-band grating 2 to output a first pulse laser with a narrow line width within a first spectral line width. For an external cavity semiconductor laser mainly composed of the FP semiconductor laser 1 and the low-reflection narrow-band grating 2, as the pulse width increases, the feedback strength of the low-reflection narrow-band grating 2 to the inner cavity is also increased, the output spectral width is correspondingly narrowed, and the side mode suppression ratio is also correspondingly improved. Therefore, the pulse width of the first pulse laser output by the external cavity semiconductor laser is greater than that of the second pulse laser. Light helps to output a first pulse laser with narrow linewidth, high side mode suppression ratio and time domain stability. The first pulse laser is chopped and modulated by the modulator 3 as a polarization-maintaining pulse seed light to output a second pulse laser with adjustable pulse width. The second pulse laser has the same characteristics as the first pulse laser, such as narrow linewidth, high side mode suppression ratio and time domain stability. It can still maintain a relatively narrow spectral output during high-power amplification. After frequency doubling, the second pulse laser can obtain a short-wavelength pulse laser with narrow linewidth, time domain stability and high power. The output short-wavelength pulse laser can achieve a frequency doubling efficiency of 70%.

[0081] Combined with the modulator 3, by controlling the time delay or pulse width of the FP semiconductor laser 1 and the modulator 3, a second pulse laser with a narrow linewidth, stable time domain and adjustable polarization-maintaining pulse width can be obtained, and through multi-stage amplification, a polarization-maintaining fundamental frequency pulse laser with high peak value, high energy, narrow linewidth and high time domain stability can be output. After being frequency-doubled by the frequency-doubling device 5, a short-wavelength pulse laser output with a frequency-doubling efficiency of up to 70% can be achieved.

[0082] The present invention also avoids the high cost of the phase modulator 3 in the DFB seed source plus phase modulation scheme, and can achieve more stable time domain pulse output than the superfluorescent fiber light source scheme, and can achieve efficient nonlinear frequency conversion efficiency, so it is a low-cost and efficient short-wavelength laser implementation scheme.

[0083] Although example embodiments and their advantages have been described in detail, those skilled in the art may make various changes, substitutions and modifications to these embodiments without departing from the spirit and defined scope of the present invention, and such modifications and variations are all within the defined scope.

Claims

1. A short wavelength pulse laser, characterized in that: include: An external cavity semiconductor laser, the external cavity semiconductor laser comprising an FP semiconductor laser (1) and a low-reflection narrowband grating (2), the FP semiconductor laser (1) being used to output a first pulse laser, the low-reflection narrowband grating (2) being used to partially reflect the first pulse laser of a set central wavelength within a first spectral line width and form a stable laser oscillation mode, and output the first pulse laser of a preset central wavelength; A modulator (3) is used to perform chopping modulation on the first pulse laser output by the external cavity semiconductor laser according to the chopping modulation signal output by the control unit (4), so as to output a second pulse laser, wherein the pulse width of the first pulse laser is greater than the pulse width of the second pulse laser; The control unit (4) is used to control the external cavity semiconductor laser to output a first pulse laser and control the modulator (3) to perform chopping modulation on the first pulse laser; The frequency doubling device (5) is used for frequency doubling the second pulse laser to obtain a short-wavelength pulse laser.

2. The short-wavelength pulse laser according to claim 1, characterized in that: The pulse width of the first pulse laser is 100 ns to 200 ns.

3. The short-wavelength pulse laser according to claim 1, characterized in that: The modulator (3) is an electro-optic modulator (3) or an acousto-optic modulator (3).

4. The short-wavelength pulse laser according to claim 1, characterized in that: The FP semiconductor laser (1), the low-reflection narrow-band grating (2) and the modulator (3) are all polarization-maintaining devices.

5. The short-wavelength pulse laser according to claim 1, characterized in that: The preset central wavelength is 1030 nm or 1064 nm, and the first spectral line width is 0.1 nm to 0.5 nm.

6. The short-wavelength pulse laser according to claim 1, characterized in that: It also comprises a first isolator (7), wherein the first isolator (7) is arranged between the low-reflection narrow-band grating (2) and the modulator (3).

7. The short-wavelength pulse laser according to claim 1, characterized in that: It also comprises a step-by-step amplifier (6), the input end of the step-by-step amplifier (6) is connected to the output end of the modulator (3), and the output end of the step-by-step amplifier (6) is connected to the frequency multiplication device (5).

8. The short-wavelength pulse laser according to claim 7, characterized in that: The step-by-step amplifier (6) comprises a plurality of power amplifiers (61) connected in series, each of the power amplifiers (61) comprising a pump source, a beam combiner and an active optical fiber, one input end of the beam combiner being connected to the output end of the modulator (3), the other input end of the beam combiner being connected to the pump source, and the output end of the beam combiner being connected to one end of the active optical fiber.

9. The short-wavelength pulse laser according to claim 8, characterized in that: A second isolator (8) is provided between the first power amplifier (61) and the modulator (3) connected in series, and a third isolator is provided between each power amplifier (61).

10. The short-wavelength pulse laser according to claim 1, characterized in that: The control unit (4) is also used to adjust the pulse width of the second pulse laser by controlling the pulse width or time delay of the first pulse laser and / or the chopping modulation signal.

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