Eigenfrequency detection, switch control and cutoff frequency stabilization method of laser system

Abstract

The present invention discloses a method for detecting the eigenfrequency of a laser system, switching control and stabilizing the cutoff frequency. The eigenfrequency detection method obtains the eigenfrequency of the laser by starting a non-local pump light source, injecting it into a laser oscillating cavity, starting a local detection light source, and starting a laser frequency scan. The switch control method is based on the suppression of the ultrashort pulse in the laser oscillating cavity by the local detection light at the resonant frequency. By controlling the frequency or power of the detection laser, the switch control operation can be realized. The cutoff frequency stabilization method controls the local detection light source to always be at the resonant frequency of the laser oscillating cavity through a feedback control circuit, and always maintains a stable frequency deviation between the output frequency of the laser and the resonant frequency. It is very necessary to develop effective eigenfrequency switch control technology, detection technology and cutoff frequency stabilization method for ultrashort pulse laser systems.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to a method for detecting the intrinsic frequency, controlling the switch and stabilizing the cut-off frequency of a laser system. Background Art

[0002] Any system has an eigenfrequency, and the system can induce a change of state when operating at this frequency. Therefore, measuring the eigenfrequency of the system is an important way to characterize the characteristics of the system. For ultrashort pulse laser systems, the measurement of the eigenfrequency requires the system to be in an online working state, and there are currently few technologies that can accomplish this. At the same time, pulsed lasers have the characteristics of wide spectrum and high power in a short time, and play an important role in laser detection, laser manufacturing and other fields. The generation of ultrashort pulse lasers relies on laser mode locking technology. The spontaneous pulse forming process requires a certain amount of establishment time and may be accompanied by extremely high-power pre-pulse signals, which can damage the laser and the application system. Therefore, it is very necessary to develop effective eigenfrequency switch control technology, detection technology and cutoff frequency stabilization methods for ultrashort pulse laser systems. Summary of the invention

[0003] In order to solve the above problems, the present invention aims to provide a method for detecting the eigenfrequency of a laser system, controlling the switch and stabilizing the cutoff frequency.

[0004] In order to achieve the above-mentioned purpose, the present invention provides the following technical solution: the laser system is a non-local pump ultrashort pulse laser system, including a non-local pump light source, a laser oscillator cavity, an optoelectronic detection component, a feedback control circuit and a local detection light source.

[0005] The frequency or wavelength of the non-local pump light source is outside the frequency or wavelength range of the output pulse laser; the frequency or wavelength of the local detection light source is within the frequency or wavelength range of the output pulse laser and is generally a single-frequency laser component that emits continuous light, and can achieve frequency or wavelength tuning, or can achieve frequency tuning and frequency scanning functions through an external electro-optical, acousto-optical or other optical modulator, and the tuning method is an analog or digital electronic control method;

[0006] The laser oscillator cavity includes a gain medium, an active or passive light intensity modulation device, and an optical reflection device, and is applicable to a free space laser cavity, a fiber laser cavity, an optical body medium cavity, and a micro-nano optical waveguide resonant cavity;

[0007] The photoelectric detection component includes an optical detection component and an electrical detection component, wherein the optical detection component includes a spectrometer, a spectrum analyzer, an optical power meter, and an optical autocorrelator, and the electrical detection component includes a photoelectric converter, a splitter, a filter, an oscilloscope, and an electronic spectrometer.

[0008] An eigenfrequency detection method for a non-locally pumped ultrashort pulse laser system comprises the following steps:

[0009] Step 1: Turn on the non-local pump light source and inject it into the laser oscillator cavity. By adjusting the intensity of the pump light source, the laser oscillator cavity generates a pulsed laser output, that is, mode-locked pulse laser generation is achieved;

[0010] Step 2: While the pulsed laser is outputting normally, turn on the local detection light source and start the laser frequency scan;

[0011] Step 3: Electrically detect the output pulse laser. After the laser passes through the photoelectric converter and low-pass filter, one or more "resonance peak" waveforms are observed on the oscilloscope. The waveform presents a Lorentz line shape, which is the inherent characteristic of the laser system.

[0012] Step 4: Read the frequency or wavelength information of the local detection laser, obtain the frequency at the peak of the resonance peak in step 3, and measure the eigenfrequency of the laser system.

[0013] The mode-locked pulse laser is output by a classic mode-locked pulse laser system composed of a non-local pump light source and a laser oscillator cavity.

[0014] A switch control method is used for a non-locally pumped ultrashort pulse laser system. Based on the fact that local probe light at a resonant frequency has an inhibitory effect on the generation of ultrashort pulses in a laser oscillator cavity, the switch control operation of the output laser pulse can be achieved by controlling the frequency or power of the probe laser. The switch control includes the following steps:

[0015] Step 1: Measure the intrinsic resonance peak;

[0016] Step 2: Stop the frequency scanning of the local detection laser, and set the frequency or wavelength of the local detection laser to the peak value of the resonance peak, or control the frequency tuning state of the laser through a feedback circuit so that the laser frequency or wavelength is always at the peak value of the resonance peak;

[0017] Step 3: Adjust the power of the local detection laser to a high level until the pulsed laser of the laser oscillator cavity stops outputting, which corresponds to the laser "off" state;

[0018] Step 4: Turn off the local detection laser, or move the laser frequency or wavelength out of the peak of the resonance peak, and the laser oscillator cavity resumes the pulsed laser output, which corresponds to the laser "on" state.

[0019] The electronically controlled frequency tuning function contained in the local detection laser source can be used in combination with a feedback control circuit to quickly and arbitrarily switch the above switching state.

[0020] A cutoff frequency stabilization method is used for a non-locally pumped ultrashort pulse laser system. Through a feedback control circuit, a local detection light source is controlled to always be located at the resonant frequency of the laser oscillation cavity, and a stable frequency deviation is always maintained between the output frequency of the laser and the resonant frequency. The cutoff frequency stabilization method includes the following steps:

[0021] Step 1: The pulsed laser output by the laser oscillator corresponds to a set of discrete, equally spaced frequency elements in the frequency domain;

[0022] Step 2: Select one of the frequency elements and perform frequency shift through an electro-optical modulator, where the shift amount is controlled by an external reference signal source;

[0023] Step 3: The selected frequency element is injected into the laser oscillation cavity again as a local detection laser;

[0024] Step 4: The intensity of the non-local pump light source is regulated by a feedback control circuit so that the local detection laser is always located at the intrinsic frequency of the laser system, thereby stabilizing the deviation between the selected laser frequency element and the system resonant frequency, i.e., the cutoff frequency, which is equal to the external reference signal source.

[0025] The offset can be derived from a standard low-noise ultra-stable RF signal source, or an atomic clock; the frequency tuning of the local detection light source can be controlled by the current of the non-local pump light source.

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

[0027] 1. The proposed method for detecting the eigenfrequency of a non-locally pumped ultrashort pulse laser system can obtain the eigenfrequency of the laser and play a better role in the fields of laser detection and laser manufacturing.

[0028] 2. The proposed switching control method for the non-locally pumped ultrashort pulse laser system is independent of the laser wavelength, bandwidth, power and other performance parameters, and is compatible with laser oscillator cavities of different transmission media such as space, optical fiber, micro-nano optical waveguide, and can achieve a higher switching rate.

[0029] 3. A cutoff frequency stabilization method for a non-locally pumped ultrashort pulse laser system is proposed. This method is used to stabilize the laser frequency. In particular, this method can be completed within the existing frequency range of the laser without the need for external frequency extension components. Therefore, it is suitable for achieving frequency stabilization of ultrashort pulse lasers with low power levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings required for use in the description of the embodiments will be 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 paying creative work.

[0031] Figure 1 This is a configuration diagram of the non-locally pumped ultrashort pulse laser system in the present invention;

[0032] Figure 2 This is a schematic diagram of the implementation principle of the non-locally pumped ultrashort pulse laser system configuration in the present invention;

[0033] Figure 3 It is a schematic diagram of the implementation principle of the feedback control circuit in the present invention;

[0034] Figure 4 (a) is the time domain superposition signal diagram of the measured system resonance peak and laser pulse; (b) is the time domain signal diagram after the local detection laser is locked with the system resonance peak; (c) is the beat frequency spectrum diagram formed by the local detection laser and the partial frequency of the mode-locked pulse laser after the local detection laser is locked with the system resonance peak.

[0035] Figure 5 (a) is a graph showing the pulse signal result of the ultrashort pulse laser switch operation test; (b) is a graph showing the frequency modulation signal of the ultrashort pulse laser switch operation test;

[0036] In the figure, 1-980nm laser light source; 2-980 / 1550nm wavelength division multiplexer; 3-fiber laser oscillator cavity; 4-erbium-doped fiber; 5-1550nm tunable continuous laser light source; 6-2×2 coupler; 7-fiber polarization controller; 8-saturable absorber; 9-fiber isolator; 10-feedback control circuit based on PDH technology; 11-electro-optic phase modulator; 12-acousto-optic modulator. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but it should not be understood that the scope of the subject matter described in the present invention is limited to the following embodiments. Without departing from the above-mentioned technical ideas of the present invention, various modifications, substitutions and changes made according to the common technical knowledge and customary means in the field are included in the scope of the present invention.

[0038] Reference Figure 1 A non-local pumped ultrashort pulse laser system includes a non-local pump light source, a laser oscillator cavity, an optoelectronic detection component, a feedback control circuit and a local detection light source.

[0039] Reference Figure 2, a non-local pumped ultrashort pulse laser system configuration, wherein the non-local pump light source is a laser light source 1 with a wavelength of 980nm, which is injected into the laser oscillator cavity 3 through a 980 / 1550nm wavelength division multiplexer 2. The laser oscillator cavity is a fiber laser oscillator cavity 3, which includes an erbium-doped fiber 4 that generates intracavity gain in the 1550nm band under the excitation of a 980nm light source, and a saturable absorber is also connected in the cavity to help achieve passive mode-locked pulse laser generation in the 1550nm band, and the pulse width is generally in the sub-picosecond level, that is, an ultrashort pulse.

[0040] The local detection light source is a tunable continuous laser light source 5 with a wavelength of about 1550nm. The light source supports electronically controlled laser frequency tuning, which is injected into the laser oscillation cavity through a 2×2 coupler 6, and the pulsed laser in the cavity is output at the other output end of the 2×2 coupler 6. The output intracavity laser is photoelectrically characterized, wherein the electrical characterization includes using a photoelectric converter to convert the optical signal into an electrical signal, performing time domain signal measurement and electronic spectrum measurement, and the optical characterization includes spectrum measurement and optical power measurement.

[0041] Reference Figure 3 The feedback control circuit 10 adopts the classic Pound-Drever-Hall (PDH) technology. The output port of this circuit part includes an output RF modulation signal, which modulates the local detection laser through the electro-optical modulator 11. A feedback signal is used to control the local detection laser to perform frequency tuning to compensate for the frequency jitter of the system. The input port includes an input signal output by a laser oscillator cavity after photoelectric conversion. The signal essentially contains the signal component of the local detection light modulated by RF after passing through the fiber laser oscillator cavity.

[0042] In the embodiment, the specific operation steps of the intrinsic frequency detection method of the non-locally pumped ultrashort pulse laser system are as follows:

[0043] Step 1: Turn on the 980nm laser light source 1, control the laser power to 117mW, and inject it into the fiber laser oscillator cavity. The laser oscillator cavity can spontaneously generate a mode-locked pulse laser. The pulse laser is output through the 2×2 coupler 6. After electrical characterization, it can be known that the pulse repetition frequency is 20.22MHz, the pulse time period is about 50ns, and after optical characterization, it can be known that the laser output power is about 162μW, and the spectral center wavelength is 1565.49nm.

[0044] Step 2: Turn on the tunable continuous laser light source 5, with a power of about 23.57μW, and drive it to scan the laser frequency with a triangle wave electrical signal, with a scanning range of about 125MHz, a central wavelength of 1565.49nm, and a scanning speed of 10Hz. At this time, the output laser of the laser oscillator cavity is electrically characterized. With the help of an oscilloscope, it can be observed that multiple waveforms showing Lorentz line shapes are superimposed on the laser pulse in time (a section of the waveform is as follows Figure 4 a), the Lorentz line shape is the Resonance Peak .

[0045] Step 3: Connect the feedback control circuit 10 based on PDH technology, where the RF modulation signal frequency is set to 9MHz, and the local detection laser is modulated by an electro-optical phase modulator 11. The output feedback signal is connected to the laser as the frequency tuning drive signal of the local detection light source. By properly configuring the internal parameters of the feedback control circuit 10, the frequency of the local detection laser can always be kept at the peak of the resonance peak (frequency locking). At this time, the pulse signal amplitude of the observed laser time domain electrical signal is kept at the bottom level of the resonance peak (such as Figure 4 b).

[0046] Step 4: Couple the pulsed laser output from the laser oscillator cavity with the frequency-locked local detection light, and observe its electronic spectrum through photoelectric conversion. It can be observed that a pair of narrow-band frequency components appear in the spectrum, with frequencies of 7.45MHz and 12.77MHz respectively (such as Figure 4 c), the sum of the two frequencies is equal to the repetition frequency of the mode-locked pulse laser. This pair of frequencies is the beat frequency signal of the local detection laser and the partial frequency of the mode-locked pulse laser, indicating that there is a difference between the intrinsic resonant frequency of the laser system and the output laser frequency, that is, there is a frequency detuning amount of 7.45MHz.

[0047] For the switch control method of the non-local pump pulse laser, in an embodiment, the specific operation steps are as follows:

[0048] Step 1: Before the tunable continuous laser is injected into the laser oscillation cavity, an acousto-optic modulator 12 is connected to achieve fast frequency switching, that is, the switch signal is connected.

[0049] Step 2: According to the intrinsic frequency detection method of the non-local pump pulse laser system, the local detection light source after the acousto-optic modulator 12 is biased and locked with the system resonance frequency (keep the frequency consistent). At this time, the modulation frequency loaded in the acousto-optic modulation is 148MHz, that is, the frequency deviation. The local detection laser power is about 100μW. At this power, due to the large depth of the system resonance peak, the output of the mode-locked pulse laser is suppressed and the system is in the "off" state.

[0050] Step 3: By changing the modulation signal frequency loaded by the acousto-optic modulator 12 to 152 MHz, the offset local detection laser frequency is moved out of the resonant frequency. The mode-locked pulse laser output is restored, and the system is now in the "on" state.

[0051] Step 4: Using the frequency modulation electronic switch, the modulation signal frequency loaded into the AOM 12 can be quickly and arbitrarily switched, thereby realizing any controllable system switch.

[0052] like Figure 5 The figure shows the switching control effect of a system with double pulses at the input within a local time.

[0053] For the cutoff frequency stabilization method of the non-local pump pulse laser, in an embodiment, the specific operation steps are as follows:

[0054] Step 1: Turn on the 980nm laser light source 1, control the laser power to 117mW, and inject it into the fiber laser oscillator cavity, and the laser oscillator cavity spontaneously generates a mode-locked pulse laser. The pulse laser is output through the 2×2 coupler 6. After electrical characterization, it can be known that the pulse repetition frequency is 20.22MHz, and the pulse time period is about 50ns. After optical characterization, it can be known that the laser output power is about 162μW, and the central wavelength of the spectrum is 1565.49nm, which corresponds to a set of discrete, equally spaced frequency elements in the frequency domain;

[0055] Step 2: Connect the feedback control circuit 10 based on the PDH technology, select a frequency element in the frequency domain, and perform frequency shift through the electro-optical modulator 11, and the shift amount is controlled by the external reference signal source;

[0056] Step 3: The selected frequency element is injected into the laser oscillation cavity again as a local detection laser;

[0057] Step 4: The intensity of the 980nm laser light source 1 is regulated by the feedback control circuit 10 so that the local detection laser is always located at the intrinsic frequency of the laser system, thereby stabilizing the deviation between the selected laser frequency element and the system resonant frequency, that is, the cutoff frequency, which is equal to the external reference signal source.

[0058] The above is a detailed introduction to the switch control method, eigenfrequency detection method and cutoff frequency stabilization method of a non-locally pumped ultrashort pulse laser system provided by the present invention. This article uses specific examples to illustrate the structure and working principle of the present invention. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. The laser system is a non-locally pumped ultrashort pulse laser system, characterized by: It includes a non-local pump light source, a laser oscillator cavity, an optoelectronic detection component, a feedback control circuit and a local detection light source, wherein both the local detection light source and the non-local pump light source are injected into the laser oscillator cavity; The frequency or wavelength of the non-local pump light source is outside the frequency or wavelength range of the output pulse laser; the frequency or wavelength of the local detection light source is within the frequency or wavelength range of the output pulse laser and is a single-frequency laser component that emits continuous light, which can achieve frequency or wavelength tuning, or can achieve frequency tuning and frequency scanning functions through an external optical modulator, the optical modulator includes an electro-optical or acousto-optic modulator, and the tuning method is an analog or digital electronic control method.

2. The non-locally pumped ultrashort pulse laser system according to claim 1, characterized in that: The laser oscillator cavity includes a gain medium, an active or passive light intensity modulation device, and an optical reflection device, and is suitable for a free space laser cavity, an optical fiber laser cavity, an optical body medium, and a micro-nano optical waveguide resonant cavity.

3. The non-locally pumped ultrashort pulse laser system according to claim 1, characterized in that: The photoelectric detection component includes an optical detection component and an electrical detection component, wherein the optical detection component includes a spectrometer, a spectrum analyzer, an optical power meter, and an optical autocorrelator, and the electrical detection component includes a photoelectric converter, a splitter, a filter, an oscilloscope, and an electronic spectrometer.

4. An eigenfrequency detection method for a non-locally pumped ultrashort pulse laser system according to any one of claims 1 to 3, characterized in that: The eigenfrequency detection method comprises the following steps: Step 1: Turn on the non-local pump light source and inject it into the laser oscillator cavity. By adjusting the intensity of the pump light source, the laser oscillator cavity generates a pulsed laser output, that is, mode-locked pulse laser generation is achieved; Step 2: While the pulsed laser is outputting normally, turn on the local detection light source and start the laser frequency scan; Step 3: Electrically detect the output pulse laser. After the laser passes through the photoelectric converter and low-pass filter, one or more "resonance peak" waveforms are observed on the oscilloscope. The waveform presents a Lorentz line shape, which is the inherent characteristic of the laser system. Step 4: Read the frequency or wavelength information of the local detection laser, obtain the frequency at the peak of the resonance peak in step 3, and measure the intrinsic frequency of the laser system.

5. The eigenfrequency detection method according to claim 4, characterized in that: The mode-locked pulse laser is output by a classic mode-locked pulse laser system composed of a non-local pump light source and a laser oscillator cavity.

6. A laser system switch control method, used in the non-locally pumped ultrashort pulse laser system according to any one of claims 1 to 3, characterized in that: Based on the fact that the local detection light at the resonant frequency has an inhibitory effect on the generation of ultrashort pulses in the laser oscillator cavity, the switch control operation of the output laser pulse can be achieved by controlling the frequency or power of the detection laser. The switch control includes the following steps: Step 1: Based on the eigenfrequency detection method described in claim 4, measure the eigenresonance peak; Step 2: Stop the frequency scanning of the local detection laser, and set the frequency or wavelength of the local detection laser to the peak value of the resonance peak, or control the frequency tuning state of the laser through a feedback circuit so that the laser frequency or wavelength is always at the peak value of the resonance peak; Step 3: Adjust the power of the local detection laser to a high level until the pulsed laser of the laser oscillator cavity stops outputting, which corresponds to the laser "off" state; Step 4: Turn off the local detection laser, or move the laser frequency or wavelength out of the peak of the resonance peak, and the laser oscillator cavity resumes the pulsed laser output, which corresponds to the laser "on" state.

7. The switch control method according to claim 6, characterized in that: The electronically controlled frequency tuning function contained in the local detection laser source can be used in combination with a feedback control circuit to quickly and arbitrarily switch the above switching state.

8. A cutoff frequency stabilization method for the non-locally pumped ultrashort pulse laser system according to any one of claims 1 to 3, characterized in that: The local detection light source is controlled to always be located at the resonant frequency of the laser oscillator cavity through a feedback control circuit, and a stable frequency deviation is always maintained between the output frequency of the laser and the resonant frequency. The cutoff frequency stabilization method includes the following steps: Step 1: The pulsed laser output by the laser oscillator corresponds to a set of discrete, equally spaced frequency elements in the frequency domain; Step 2: Select one of the frequency elements and perform frequency shift through an electro-optical modulator, where the shift amount is controlled by an external reference signal source; Step 3: The selected frequency element is injected into the laser oscillation cavity again as the local detection laser; Step 4: The intensity of the non-local pump light source is regulated by a feedback control circuit so that the local detection laser is always located at the intrinsic frequency of the laser system, thereby stabilizing the deviation between the selected laser frequency element and the system resonant frequency, i.e., the cutoff frequency, which is equal to the external reference signal source.

9. The cut-off frequency stabilization method according to claim 8, characterized in that: The offset is derived from a standard low-noise ultra-stable radio frequency signal source, or an atomic clock; the frequency tuning of the local detection light source is achieved by current control of a non-local pump light source.

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