CN114865443B - Single-frequency laser device - Google Patents

Abstract

The present invention provides a single-frequency laser device, which relates to the field of laser technology. The device includes: a laser emission source, a resonant cavity, a detector and a locking control module; the laser emission source is used to emit pump light; the resonant cavity generates self-excited oscillation to generate oscillating light and adjusts the oscillating light according to a feedback signal to generate oscillating light of a single frequency; the resonant cavity uses a modulation signal to perform light field modulation on the oscillating light of a single frequency, and outputs a signal light of a single frequency; the detector performs photoelectric conversion on the detected pump light and signal light to obtain a detection electrical signal; the locking control module mixes the demodulated signal and the detection electrical signal to obtain an error signal, and generates a feedback signal according to the demodulated signal and the error signal and transmits it to the resonant cavity to generate oscillating light of a single frequency; the locking control module also sends a modulation signal to the resonant cavity to achieve the requirement of stable single-frequency operation of the laser.

Description

A single-frequency laser device

Technical Field

The invention relates to the field of laser technology, in particular to a single-frequency laser device.

Background Art

In recent years, with the vigorous development of research fields such as quantum information and atomic physics, single-frequency continuous-wave tunable lasers have received more and more attention. They are required not only to have higher output power, but also to have higher stability, and to maintain stable single longitudinal mode operation during long-term use without any multi-mode oscillation or mode hopping.

Currently, there are very few laser companies that can provide low-intensity noise pump sources, and the cost is high. For general pump sources, their low-frequency noise is usually obvious and will dominate the noise of the laser it pumps to a certain extent. Moreover, as the pump power increases, its noise also increases further, and the impact on the laser's etalon locking cannot be ignored. The detector used in the traditional etalon locking system is a single-diode detector that only collects signal light. Once the pump power is too high and the low-frequency noise carried by the signal light is too large, the feedback system cannot extract the error signal well, which in turn affects the etalon locking.

In the experimental processes of atom capture and cooling, atomic storage, etc., the frequency of the laser output light needs to be accurately matched with the atomic transition line. This requires the laser to have a certain frequency continuous tuning capability. The transmission peak of the intracavity standard device can be locked with the resonant cavity oscillation frequency in real time, and then the cavity length of the laser can be changed to achieve continuous tuning. The existing technology cannot solve the problem of maintaining continuous and stable single longitudinal mode operation of the laser when the pump source has low-frequency intensity and high noise.

Summary of the invention

The purpose of the present invention is to provide a single-frequency laser device to meet the demand for stable single-frequency operation of the laser.

To achieve the above object, the present invention provides the following solutions:

A single-frequency laser device, comprising:

A laser emission source, used for emitting pump light;

A resonant cavity is arranged on the outgoing light path of the laser emission source, and is used to generate self-excited oscillation, generate oscillating light, and adjust the oscillating light according to the feedback signal to generate oscillating light of a single frequency; the resonant cavity is also used to perform light field modulation on the oscillating light of the single frequency using a modulation signal, and output signal light of the single frequency;

A detector, arranged on the outgoing light path of the resonant cavity, for performing photoelectric conversion on the detected pump light and the signal light to obtain a detection electrical signal;

A locking control module is connected to the resonant cavity and the detector, respectively, and is used to mix the demodulated signal and the detection electrical signal to obtain an error signal, and generate the feedback signal according to the demodulated signal and the error signal and transmit it to the resonant cavity to generate an oscillating light of a single frequency; the locking control module is also used to send the modulation signal to the resonant cavity.

Optionally, the resonant cavity specifically includes:

A first cavity mirror, arranged on an outgoing light path of the pump light, and used for transmitting the pump light;

A gain medium, arranged on the transmission light path of the first cavity mirror, for generating oscillating light under the excitation of the pump light;

A second cavity mirror is arranged on the transmission light path of the gain medium and is used to transmit the pump light;

The first cavity mirror is further used to reflect the light reflected by the fourth cavity mirror to the gain medium; the second cavity mirror is further used to reflect the oscillating light to the third cavity mirror;

a third cavity mirror, arranged on a reflection light path of the second cavity mirror, and used for reflecting the oscillating light to the etalon;

an etalon, arranged on the reflection light path of the third cavity mirror and connected to the locking control module, for receiving a feedback signal and a modulation signal sent by the locking control module, adjusting the oscillating light according to the feedback signal to generate an oscillating light of a single frequency, and performing light field modulation on the oscillating light of a single frequency according to the modulation signal to generate a signal light of a single frequency;

The fourth cavity mirror is arranged on the output optical path of the etalon, and is used for transmitting the signal light of the single frequency and reflecting the signal light of the single frequency to the first cavity mirror.

Optionally, the locking control module specifically includes:

A signal source, used for sending a modulation signal and a demodulation signal;

A locking box, connected to the signal source, the detector and the etalon respectively, for mixing the demodulated signal and the detection electrical signal to obtain an error signal, and loading the modulation signal to the etalon;

an oscilloscope, connected to the detector and the locking box, respectively, for displaying the detection electrical signal and the error signal, and determining a phase deviation; the phase deviation being a phase value of a demodulated signal corresponding to when the error signal is zero;

The locking box is further used to generate the feedback signal according to the phase deviation, and transmit the feedback signal to the etalon to adjust the incident angle of the etalon so that the etalon outputs oscillating light of a single frequency.

Optionally, the laser emission source specifically includes:

A laser for emitting initial pump light;

The coupling module is arranged on the output light path of the laser and is used to focus the initial pump light to obtain the pump light.

Optionally, the resonant cavity comprises:

A one-way device, arranged on the reflection light path of the second cavity mirror and located between the second cavity mirror and the third cavity mirror;

The mode selection device is arranged on the reflection light path of the fourth cavity mirror and is located between the first cavity mirror and the fourth cavity mirror.

Optionally, the device further comprises:

a first light guide mirror, arranged on a transmission light path of the second cavity mirror, and used for reflecting the pump light to the detector;

The second light guide mirror is arranged on the transmission light path of the fourth cavity mirror, and is used for reflecting the signal light to the detector and transmitting the signal light out.

Optionally, the device further comprises:

A third light guide mirror is arranged on the transmission light path of the second light guide mirror, and is used to reflect the signal light to the power meter and transmit the signal light to the single frequency monitor;

A power meter, arranged on the reflected light path of the third light guide mirror, for monitoring the power of the signal light;

The single-frequency monitor is arranged on the transmission light path of the third light guide mirror and is used to monitor the mode of the signal light.

Optionally, the detector comprises:

A first photosensitive submodule, arranged on a reflection light path of the first light guide mirror, for receiving the pump light and converting the pump light into a first electrical signal;

A second photosensitive submodule, arranged on the reflection light path of the second light guide mirror, for receiving the signal light and converting the signal light into a second electrical signal;

an amplifying submodule, configured to mix and amplify the first electrical signal and the second electrical signal to obtain a mixed signal;

The filter submodule is used to filter out the low-frequency signal in the mixed signal to obtain the detection electrical signal.

Optionally, the gain medium is a broadband gain crystal or a narrowband gain crystal.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The laser emission source emits pump light, and then generates oscillation light through self-excited oscillation of the resonant cavity; the demodulation signal and the detection electrical signal obtained by the detector are mixed through the locking control module to obtain an error signal, and a feedback signal is generated according to the demodulation signal and the error signal and transmitted to the resonant cavity, and the resonant cavity adjusts the oscillation light according to the feedback signal to generate oscillation light of a single frequency; the oscillation light of a single frequency is modulated by a modulation signal through the resonant cavity, and a signal light of a single frequency is output; and the detection electrical signal obtained by the detector is obtained by photoelectric conversion of the pump light and the signal light of a single frequency; through the joint action of the resonant cavity and the locking control module, a signal light of a single frequency is obtained to meet the requirement of stable single-frequency operation of the laser.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in 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 labor.

FIG1 is a structural diagram of a single-frequency laser device with a gain medium of Ti:Sapphire provided in an embodiment of the present invention;

FIG2 is a structural diagram of a detector of a single-frequency laser device provided in an embodiment of the present invention;

FIG3 is a structural diagram of a single-frequency laser device with Nd:CYA as the gain medium provided by an embodiment of the present invention.

Explanation of symbols:

Laser-1, coupling module-2, resonant cavity-3, gain medium-4, unidirectional device-5, mode selection device-6, standard tool-7, second light guide mirror-8, first light guide mirror-9, detector-10, third light guide mirror-11, single frequency monitor-12, power meter-13, locking box-14, signal source-15, oscilloscope-16, first cavity mirror-17, second cavity mirror-18, third cavity mirror-19, fourth cavity mirror-20, laser emission source-21, locking control module-22, first photosensitizer module-23, second photosensitizer module-24, amplifier module-25, filter module-26, frequency doubling crystal-27.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.

The purpose of the present invention is to provide a single-frequency laser device, which emits pump light through a laser emission source, and then generates oscillation light through self-excited oscillation of a resonant cavity; a demodulated signal and a detection electrical signal obtained by a detector are mixed through a locking control module to obtain an error signal, and a feedback signal is generated according to the demodulated signal and the error signal and transmitted to the resonant cavity, and the resonant cavity adjusts the oscillation light according to the feedback signal to generate oscillation light of a single frequency; a modulation signal is used to perform light field modulation on the oscillation light of the single frequency through the resonant cavity, and a signal light of a single frequency is output; and the detection electrical signal obtained by the detector is obtained by photoelectric conversion of the pump light and the signal light of the single frequency; through the joint action of the resonant cavity and the locking control module, a signal light of a single frequency is obtained to meet the requirement of stable single-frequency operation of the laser.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1 , the single-frequency laser device of this embodiment includes: a laser emission source 21 , a resonant cavity 3 , a detector 10 and a locking control module 22 .

The laser emission source 21 is used to emit pump light; the laser emission source 21 specifically includes: a laser 1 and a coupling module 2; the laser 1 is used to emit initial pump light; the coupling module 2 is arranged on the output light path of the laser 1, and is used to focus the initial pump light to obtain pump light.

The laser 1 can be any pump source that can provide excitation to the gain medium 4, such as a solid laser, a gas laser, a liquid laser, a fiber laser, a semiconductor laser, etc.

The resonant cavity 3 is arranged on the outgoing light path of the laser emission source 21. The resonant cavity 3 is used to generate self-excited oscillation, generate oscillating light, and adjust the oscillating light according to the feedback signal to generate oscillating light of a single frequency. The resonant cavity 3 is also used to use a modulation signal to modulate the light field of the oscillating light of a single frequency and output a signal light of a single frequency.

Specifically, the resonant cavity 3 includes: a first cavity mirror 17 , a gain medium 4 , a second cavity mirror 18 , a third cavity mirror 19 , an etalon 7 and a fourth cavity mirror 20 .

The first cavity mirror 17 is arranged on the output light path of the pump light, the gain medium 4 is arranged on the transmission light path of the first cavity mirror 17, the second cavity mirror 18 is arranged on the transmission light path of the gain medium 4, the third cavity mirror 19 is arranged on the reflection light path of the second cavity mirror 18, the standard tool 7 is arranged on the reflection light path of the third cavity mirror 19 and is connected to the locking control module 22, and the fourth cavity mirror 20 is arranged on the output light path of the standard tool 7.

The first cavity mirror 17 is arranged on the outgoing optical path of the pump light, and is used to transmit the pump light; the gain medium 4 is used to generate oscillating light under the excitation of the pump light, that is, to generate stimulated radiation; the second cavity mirror 18 is arranged on the transmission optical path of the gain medium 4, and is used to transmit the pump light out; the pump light is in the resonant cavity 3, and not all the pump light undergoes self-excited oscillation, and a part of the pump light that has not undergone self-excited oscillation is directly transmitted out through the second cavity mirror 18. The first cavity mirror 17 is also used to reflect the light reflected by the fourth cavity mirror 20 to the gain medium 4, forming a closed optical path; the second cavity mirror 18 is also used to reflect the oscillating light to the third cavity mirror 19.

The third cavity mirror 19 is arranged on the reflection light path of the second cavity mirror 18, and is used for reflecting the oscillating light to the standard tool 7; the standard tool 7 is arranged on the reflection light path of the third cavity mirror 19, and is connected to the locking control module 22, and is used for receiving the feedback signal and the modulation signal sent by the locking control module 22, adjusting the oscillating light according to the feedback signal to generate the oscillating light of a single frequency, and performing light field modulation on the oscillating light of a single frequency according to the modulation signal to generate the signal light of a single frequency; the standard tool 7 is installed on the scanning galvanometer motor.

The fourth cavity mirror 20 is disposed on the output optical path of the etalon 7 , and is used for transmitting the signal light of a single frequency and reflecting the signal light of a single frequency to the first cavity mirror 17 .

Specifically, the resonant cavity 3 further includes a unidirectional device 5 and a mode selection device 6; the unidirectional device 5 is arranged on the reflected light path of the second cavity mirror 18 and between the second cavity mirror 18 and the third cavity mirror 19, and is used to make the pump light unidirectionally run inside the resonant cavity 3. The mode selection device 6 is arranged on the reflected light path of the fourth cavity mirror 20 and between the first cavity mirror 17 and the fourth cavity mirror 20, and is used to select the frequency mode of the pump light. The mode selection device 6 can be used, for example, to perform rough mode selection by a birefringent filter, and the unidirectional device 5 can also be used by self-injection or seed light injection.

The resonant cavity 3 can be any cavity type such as a ring cavity, a standing wave cavity, a three-mirror cavity, a four-mirror cavity, a six-mirror cavity, etc.; and the pumping mode of the device can be end pumping, side pumping, single-end pumping, double-end pumping, etc.

The detector 10 is arranged on the outgoing light path of the resonant cavity 3 and is used to perform photoelectric conversion on the detected pump light and signal light to obtain a detection electrical signal.

The locking control module 22 is connected to the resonant cavity 3 and the detector 10 respectively. The locking control module 22 is used to mix the demodulated signal and the detection electrical signal to obtain an error signal, and generate a feedback signal based on the demodulated signal and the error signal and transmit it to the resonant cavity 3 to generate an oscillating light of a single frequency; the locking control module 22 is also used to send the modulation signal to the resonant cavity 3.

Specifically, the locking control module 22 specifically includes: a signal source 15, a locking box 14 and an oscilloscope 16; the locking box 14 is connected to the signal source 15, the detector 10 and the standard tool 7 respectively, and the oscilloscope 16 is connected to the detector 10 and the locking box 14 respectively. The signal source 15 is used to send a modulation signal and a demodulation signal; the locking box 14 is used to mix the demodulation signal and the detection electrical signal to obtain an error signal, and load the modulation signal to the standard tool 7; the modulation signal is loaded onto the standard tool 7, that is, the scanning galvanometer motor where the standard tool 7 is located, so that the angle of the standard tool 7 is deflected, and the light field in the resonant cavity 3 is modulated. The electro-optical effect of the crystal is independent of the frequency of the modulation signal, so the frequency of the modulation signal can be arbitrarily selected. The modulation signal is used as a carrier to enable the detector 10 to detect the light signal.

The oscilloscope 16 is used to display the detection electrical signal and the error signal, and to determine the phase deviation; the phase deviation is the phase value of the demodulated signal corresponding to the error signal being zero; the locking box 14 is also used to generate a feedback signal according to the phase deviation, and transmit the feedback signal to the standard tool 7 to adjust the incident angle of the standard tool, that is, to control the angle of the standard tool 7 by controlling the rotating shaft of the rotating galvanometer motor, so that the transmission peak of the standard tool 7 is locked on the single-frequency mode, so that the standard tool 7 outputs an oscillating light of a single frequency.

In order to achieve real-time locking of the etalon, the device often uses photoelectric negative feedback regulation. When the transmission peak of the etalon 7 deviates from the laser oscillation mode, the locking control module 22 will generate a correction signal, i.e., a feedback signal, to control the incident angle of the etalon 7 and pull its transmission peak back to the laser oscillation mode. The most important thing is the extraction of the error signal, which is generally done by a modulation and demodulation method. The function generator, i.e., the signal source 15, generates two sinusoidal signals S1 and S2 of the same frequency, wherein the S1 signal is loaded onto the motor of the etalon 7 as a modulation signal to control the incident angle of the etalon 7, that is, the etalon 7 performs an initial deflection according to the modulation signal, and the wavelength corresponding to its transmission peak is also periodically modulated, and the detector 10 (photodiode structure) is used to detect this light intensity modulation signal. After S2 is mixed with the signal detected by the detector 10 as a demodulation signal, the deviation signal between the transmission peak of the etalon 7 and the oscillation mode of the resonant cavity 3, i.e., the error signal, is extracted after filtering by a low-pass filter. The error signal is processed by a proportional amplification integral circuit to generate a control signal. The generated control signal is added to the DC bias signal by an adder to obtain a feedback signal, which is then loaded onto the control board of the galvanometer motor, that is, onto the etalon 7, for feedback control of the incident angle of the etalon 7. Therefore, the extraction of the error signal is crucial. Since the operating frequency of the scanning galvanometer motor used to fix the etalon 7 is 1kHz, the low-frequency noise of the pump source will be transmitted to the signal light generated by the laser along with the pump light, affecting the locking of the etalon.

In the locking process of the etalon 7, assuming that the low-frequency intensity noise of the laser 1 is Δ(t), after being transmitted to the detector 10, the signal measured by the detector 10 is

Apply a modulation signal with a frequency of ω to the etalon 7

Bsin(ωt+ε);

The local oscillator signal with the same frequency as the modulation signal is the demodulated signal:

Csin(ωt+δ);

After mixing the detection signal and the local oscillation signal, we get

Among them, A, B, and C are the amplitude strengths of each signal. ε and δ are the phases of each signal, and f(t) is the high-frequency term. After filtering out the high-frequency term using a low-pass filter, the error signal D ₁ is obtained:

To achieve etalon locking, the laser oscillation mode and the etalon transmission peak must coincide, that is, D ₁ = 0. However, at this time, Δ(t) interferes with the error signal, making it not always zero.

D ₁ is mainly determined by the noise Δ(t). When the detector is immune to the noise transmitted by the pump source in the signal light, the measured detection signal is

The resulting error signal is

D ₂ is a constant. At this time, as long as the relative phase difference between the detection signal and the demodulation signal is set to 0, the etalon 7 can be locked.

It can be seen that as long as the detector 10 is immune to the noise of the laser 1, the etalon 7 can achieve stable locking. Currently, there are very few laser companies that can provide low-noise lasers 1 (pump sources), and the cost is high. For general lasers 1 (pump sources), their low-frequency noise is usually obvious and will dominate the noise of the laser 1 it pumps to a certain extent. Moreover, as the pump power increases, its noise also increases further, and the impact on the locking of the etalon 7 cannot be ignored. The detector 10 used in the traditional etalon 7 locking control module 22 is a single diode detector that only collects signal light. Once the pump power is too high and the low-frequency noise carried by the signal light is too large, the feedback system, that is, the locking control module 22, cannot extract the error signal well, thereby affecting the locking of the etalon 7.

The present invention provides a single-frequency continuous wave laser device which is simple to operate and is immune to the noise of the laser 1 (pump source). When the low-frequency noise of the laser 1 (pump source) is too large, the etalon 7 can still be stably locked.

As an optional implementation, the first cavity mirror 17 and the second cavity mirror 18 are concave mirrors; the third cavity mirror 19 and the fourth cavity mirror 20 are plane mirrors.

In one embodiment, as shown in FIG1 , the single-frequency laser device further includes: a first light guide mirror 9 and a second light guide mirror 8; the first light guide mirror 9 is arranged on the transmission light path of the second cavity mirror 18, and the second light guide mirror 8 is arranged on the transmission light path of the fourth cavity mirror 20; the first light guide mirror 9 is used to reflect the pump light to the detector 10; the second light guide mirror 8 is used to reflect the signal light to the detector 10 and transmit the signal light out.

Specifically, the device also includes: a third light guide mirror 11, a power meter 13 and a single-frequency monitor 12; the third light guide mirror 11 is arranged on the transmitted light path of the second light guide mirror 8, the power meter 13 is arranged on the reflected light path of the third light guide mirror 11, and the single-frequency monitor 12 is arranged on the transmitted light path of the third light guide mirror 11; the third light guide mirror 11 is used to reflect the signal light to the power meter 13, and transmit the signal light to the single-frequency monitor 12; the power meter 13 is used to monitor the power of the signal light; the single-frequency monitor 12 is used to monitor the mode of the signal light.

As an optional implementation, the gain medium 4 is a broadband gain crystal or a narrowband gain crystal; the gain medium 4 can be a broadband or narrowband gain crystal such as Ti:sapphire, Nd:CYA, Nd:YAG, Nd:YVO ₄ , etc.

There are two types of connection relationships between the components shown in FIG1 . The components connected by solid lines are realized through optical paths, while the components connected by dotted lines are realized through electrical connections.

In one embodiment, as shown in Figure 2, the detector 10 includes: a first photosensor module 23, a second photosensor module 24, an amplifier module 25 and a filter module 26; the first photosensor module 23 is arranged on the reflected light path of the first light guide mirror 9, and the second photosensor module 24 is arranged on the reflected light path of the second light guide mirror 8; the first photosensitive submodule 23 is used to receive pump light and convert the pump light into a first electrical signal; the second photosensitive submodule 24 is arranged on the reflected light path of the second light guide mirror 8, and is used to receive signal light and convert the signal light into a second electrical signal; the amplifier module 25 is used to mix and amplify the first electrical signal and the second electrical signal to obtain a mixed signal; the filter module 26 is used to filter out the low-frequency signal in the mixed signal to obtain a detection electrical signal.

The detector 10 is a dual-diode structure and includes a subtraction circuit inside, which can filter out the pump light component carrying noise in the signal light, so that the locking is not affected by the noise.

The first photosensitive submodule 23 and the second photosensitive submodule 24 are both composed of photosensitive diodes, and the model of the photosensitive diode selected is 5973; the amplifying submodule 25 is composed of an amplifier, and the filtering submodule 26 is composed of an RC oscillating circuit; the RC oscillating circuit is composed of a capacitor C2 and a resistor R4; in addition, the detector 10 is also composed of a peripheral circuit, and the peripheral circuit includes resistors R1, R2, R3 and capacitor C1 connected by lines.

After the subtraction processing of the detector 10, only the signal light component required for locking remains. The AC signal is output from the AC end through the amplifier module 25 and enters the locking box 14 for mixing with the demodulated signal to extract the error signal. After the DC signal is attenuated, it is connected to the oscilloscope 16 through the DC end. The power of the pump light and the signal light received by the detector 10 is judged by the same amplitude of the electrical signal elevation.

Figure 1 is a structural diagram of a single-frequency laser device with a gain crystal of Ti:Sapphire. The complete implementation process is as follows: Laser 1 is a 20W 532nm continuous wave single-frequency all-solid-state laser. Resonant cavity 3 adopts a four-mirror ring cavity structure, and the pumping method is end-face pumping. The cavity mirrors of the resonant cavity 3 are: M1 (the first cavity mirror 17) is a concave-convex mirror with a curvature radius of 100 mm, and the concave surface is coated with a 532nm anti-reflection film and a 740-890nm high-reflection film; M2 (the second cavity mirror 18) is a plano-concave mirror with a curvature radius of 100 mm, and the concave surface is coated with a 532nm anti-reflection film and a 740-890nm high-reflection film; M3 (the third cavity mirror 19) and M4 (the fourth cavity mirror 20) are both plane mirrors, M3 (the third cavity mirror 19) is coated with a 740-890nm high-reflection film, and the output coupling mirror M4 (the fourth cavity mirror 20) is coated with a partially transmissive film with a transmittance of 5.5% for 740-890nm laser. After the 20W532nm high-power all-solid-state continuous wave pump light passes through the coupling module 2 composed of f=200mm and f=120mm lenses, the waist spot is 48μm, and it is focused on the titanium sapphire crystal cut by the Brewster angle between M1 (first cavity mirror 17) and M2 (second cavity mirror 18) of the resonant cavity 3, the center of the gain medium 4. The generated signal light passes through the unidirectional device 5 composed of TGG and compensation plate placed in the magnet between M2 (second cavity mirror 18) and M3 (third cavity mirror 19) to realize the unidirectional operation of the laser, and passes through the birefringent filter between the cavity mirror M1 (first cavity mirror 17) and M4 (fourth cavity mirror 20), that is, the mode selection device 6 for mode rough selection. The standard tool 7 is fixed on the rotating shaft of the scanning galvanometer, placed between M3 (third cavity mirror 19) and M4 (fourth cavity mirror 20), and its rotation angle is controlled by locking the control box and the LabVIEW program.

The pump light passes through the crystal once, and the pump light transmitted by M2 (the second cavity mirror 18) enters the first photosensitive submodule 23 of the detector 10 under the reflection of the first light guide mirror 9. A small part of the signal light output by M4 (the fourth cavity mirror 20) is reflected by the second light guide mirror 8 and enters the second photosensitive submodule 24 of the detector 10. The two signals are filtered by the subtraction circuit inside the detector 10. One of the output signals of the detector 10 is connected to the oscilloscope 16 for two-way optical power monitoring, and the power of the two beams of light is adjusted by adjusting the second light guide mirror 8 to make them the same. The other signal is connected to the locking box 14 after passing through the filter. Combined with the standard tool 7 locking device, the modulation signal is given by the signal source 15, and the parameters in the LabVIEW program are adjusted to lock. After locking, the single-frequency monitor 12 is used to monitor that there is no multi-mode oscillation and mode hopping phenomenon, which means that the locking is successful.

The implementation of the device provided by the present invention mainly includes the following contents:

The initial pump light generated by the laser 1 is injected into the gain medium 4 in the resonant cavity 3 through the coupling module 2. The pump light that passes through the gain medium 4 once enters the first photosensitive submodule 23 of the detector 10 under the reflection of the first light guide mirror 9. The signal light output by the fourth cavity mirror 20 of the resonant cavity 3 is reflected by the second light guide mirror 8 and enters the second photosensitive submodule 24 of the detector 10. The two signals are filtered by the subtraction circuit inside the detector 10, that is, the filter submodule 26. The DC end of the output signal of the detector 10 is connected to the oscilloscope 16 for two-way optical power monitoring. The power of the two beams of light is adjusted by adjusting the second light guide mirror 8 to make them the same. The AC end is connected to the locking box 14 after passing through the filter. Combined with the locking device of the standard tool 7, that is, the locking control module 22, the modulation signal is given through the signal source 15, and the parameters in the LabVIEW program are adjusted to lock. After locking, the single-frequency monitor 12 is used to monitor that there is no multi-mode oscillation and mode hopping phenomenon, which means that the locking is successful.

As an optional implementation, as shown in FIG3 , the implementation process of a single-frequency laser device using Nd:CYA as a gain medium is as follows:

The resonant cavity 3 adopts a four-mirror ring resonant cavity, and the pumping mode is end-face pumping. The resonant cavity 3 includes a first cavity mirror 17, a gain medium 4, a second cavity mirror 18, a third cavity mirror 19, an etalon 7, a fourth cavity mirror 20, a one-way device 5 and a frequency doubling crystal 27; the first cavity mirror 17 is arranged on the output light path of the pump light, the gain medium 4 is arranged on the transmission light path of the first cavity mirror 17, the second cavity mirror 18 is arranged on the transmission light path of the gain medium 4, the third cavity mirror 19 is arranged on the reflection light path of the second cavity mirror 18, the etalon 7 is arranged on the transmission light path of the gain medium 4 and between the gain medium 4 and the second cavity mirror 18, and the etalon 7 is also connected to the locking box 14. The fourth cavity mirror 20 is arranged on the reflection light path of the third cavity mirror 19. The one-way device 5 is arranged on the transmission light path of the gain medium 4 and between the gain medium 4 and the etalon 7.

The laser 1 is used to emit the initial pump light; the coupling module 2 focuses the initial pump light to obtain the pump light. The pump light enters the resonant cavity 3 to generate self-excited oscillation to generate oscillating light. That is, the gain medium 4 generates stimulated radiation under the excitation of the pump light.

The pump light will not be completely converted into oscillation light by the gain medium 4 in the resonant cavity 3. After the pump light passes through the first cavity mirror 17, the gain medium 4, the one-way device 5, the etalon 7 and the second cavity mirror 18, a part of the pump light that has not been converted into oscillation light will be directly transmitted from the second cavity mirror 18. In this embodiment, the second cavity mirror 18 is also the output mirror of the signal light. The pump light is reflected to the detector 10 by the first light guide mirror 9 (high reflection of the pump light and high transmission of the signal light). The transmitted signal light is reflected into the detector 10 by the second light guide mirror 8 in a small part, and most of it is transmitted by the second light guide mirror 8.

In this embodiment, frequency-doubled light is also generated, which is equivalent to a dual-wavelength laser device. Under the action of the frequency-doubled crystal 27, the light transmitted by the fourth cavity mirror 20 is the frequency-doubled light of the signal light.

The first cavity mirror 17 and the second cavity mirror 18 of the resonant cavity 3 are plane mirrors, the third cavity mirror 19 and the fourth cavity mirror 20 are plano-concave mirrors with a curvature radius of 50 mm, the first cavity mirror 17 is coated with an 808nm high-transmittance film and a 1080nm high-reflection film, the second cavity mirror 18 is coated with a partially transparent film with a 1080nm transmittance of 4%, the third cavity mirror 19 is coated with a 1080nm high-reflection film, and the fourth cavity mirror 20 is coated with a 1080nm high-reflection film and a high-transmittance film with a 540nm transmittance of 95%.

Laser 1 is a 15W 808nm semiconductor laser, which is focused to the gain medium 4, that is, the center of the gain crystal Nd:CYA, through a coupling module 2 composed of lenses of f=30mm and f=50mm, to generate fundamental frequency light of 1080nm. A one-way device 5 placed in a magnet is inserted into the optical path to ensure unidirectional operation of the laser. The one-way device 5 is composed of TSAG and a half-wave plate. A frequency doubling crystal 27 is added between the third cavity mirror 19 and the fourth cavity mirror 20 to generate a frequency doubling light of 540nm. The standard tool 7 is inserted into the optical path, and its scanning galvanometer motor is connected to the locking box 14. After the pump light and the fundamental frequency light are outputted by the second cavity mirror 18, they are split by the first light guide mirror 9, and the pump light 808nm is reflected to the first photosensitive submodule 23 of the detector 10. The transmitted fundamental frequency light 1080nm passes through the second light guide mirror 8, and a small part is reflected to enter the second photosensitive submodule 24 of the detector 10. The transmitted fundamental frequency light is split into a small part for the monitoring mode of the single frequency monitor 12 by the third light guide mirror 11, and the rest is used to monitor the power change by the power meter 13. The fundamental frequency light is frequency-doubled by the frequency-doubled crystal to generate the frequency-doubled light 540nm, which is outputted from the fourth cavity mirror 20.

The advantages of the present invention are as follows:

The low-frequency noise in the signal light used for locking can be filtered out by the subtraction circuit of the detector 10, so that the extracted error signal is a constant value, effectively avoiding the influence of the low-frequency noise in the laser 1 (pump source) on the locking of the standard tool 7, so that the laser device can achieve a more stable single-frequency tuning process. The device is simple in design, easy to operate and easy to implement; the generated laser single-frequency stability is high, and it has high practical value in the fields of quantum optics.

It is applicable when the low-frequency noise of the laser 1 (pump source) is too high, affecting the stable locking of the etalon 7 of the single-frequency continuous-wave laser device.

It is suitable for a type of single-frequency continuous wave laser device that needs to be locked with an etalon 7 but is affected by the noise of the laser 1 (pump source).

In conclusion, the present invention can effectively make the single-frequency continuous wave laser device immune to the noise of the laser 1 (pump source), and the device is simple and easy to operate.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims (6)

1. A single frequency laser device, the device comprising:

the laser emission source is used for emitting pump light;

The resonant cavity is arranged on an emergent light path of the laser emission source and is used for generating self-oscillation, generating oscillation light, and adjusting the oscillation light according to a feedback signal to generate oscillation light with single frequency; the resonant cavity is also used for carrying out optical field modulation on the oscillating light with the single frequency by adopting a modulation signal to output signal light with the single frequency;

the detector is arranged on the emergent light path of the resonant cavity and is used for carrying out photoelectric conversion on the detected pump light and the detected signal light to obtain a detection electric signal;

The locking control module is respectively connected with the resonant cavity and the detector and is used for mixing a demodulation signal and the detection electric signal to obtain an error signal, generating the feedback signal according to the demodulation signal and the error signal and transmitting the feedback signal to the resonant cavity so as to generate oscillating light with single frequency; the locking control module is also used for sending the modulation signal to the resonant cavity;

The resonant cavity specifically comprises:

The first cavity mirror is arranged on an emergent light path of the pump light and is used for transmitting the pump light;

The gain medium is arranged on the transmission optical path of the first cavity mirror and is used for generating oscillation light under the excitation of the pumping light;

the second cavity mirror is arranged on the transmission optical path of the gain medium and is used for transmitting the pumping light;

the first cavity mirror is also used for reflecting light reflected by the fourth cavity mirror to the gain medium; the second cavity mirror is also used for reflecting the oscillation light to a third cavity mirror;

the third cavity mirror is arranged on a reflection light path of the second cavity mirror and is used for reflecting the oscillation light to the etalon;

The etalon is arranged on the reflection light path of the third cavity mirror, is connected with the locking control module, and is used for receiving a feedback signal and a modulation signal sent by the locking control module, adjusting the oscillating light according to the feedback signal to generate oscillating light with a single frequency, and performing light field modulation on the oscillating light with the single frequency according to the modulation signal to generate signal light with the single frequency;

the fourth cavity mirror is arranged on the output light path of the etalon and is used for transmitting out the signal light with the single frequency and reflecting the signal light with the single frequency to the first cavity mirror;

The locking control module specifically comprises:

the signal source is used for sending out modulation signals and demodulation signals;

the locking box is respectively connected with the signal source, the detector and the etalon and is used for mixing the demodulation signal and the detection electric signal to obtain an error signal and loading the modulation signal to the etalon;

The oscilloscope is respectively connected with the detector and the locking box and is used for displaying the detection electric signal and the error signal and determining phase deviation; the phase deviation is the phase value of the demodulation signal corresponding to zero of the error signal;

The locking box is further used for generating the feedback signal according to the phase deviation and transmitting the feedback signal to the etalon so as to adjust the incidence angle of the etalon, so that the etalon outputs oscillating light with single frequency;

the resonant cavity includes:

the unidirectional device is arranged on the reflection light path of the second cavity mirror and is positioned between the second cavity mirror and the third cavity mirror;

the mode selecting device is arranged on the reflection light path of the fourth cavity mirror and is positioned between the first cavity mirror and the fourth cavity mirror.

2. The single frequency laser device of claim 1, wherein the laser emission source specifically comprises:

a laser for emitting an initial pump light;

The coupling module is arranged on the emergent light path of the laser and used for focusing the initial pump light to obtain the pump light.

3. The single frequency laser device of claim 1, wherein the device further comprises:

the first light guide mirror is arranged on a transmission light path of the second cavity mirror and used for reflecting the pump light to the detector;

the second light guide lens is arranged on the transmission light path of the fourth cavity lens and used for reflecting the signal light to the detector and transmitting the signal light out.

4. A single frequency laser device as claimed in claim 3, wherein the device further comprises:

the third light guide lens is arranged on a transmission light path of the second light guide lens and is used for reflecting the signal light to the power meter and transmitting the signal light to the single-frequency monitor;

The power meter is arranged on the reflection light path of the third light guide lens and is used for monitoring the power of the signal light;

And the single-frequency monitor is arranged on the transmission light path of the third light guide lens and is used for monitoring the mode of the signal light.

5. A single frequency laser device as claimed in claim 3 wherein the detector comprises:

The first photosensitive submodule is arranged on a reflection light path of the first light guide mirror and is used for receiving the pump light and converting the pump light into a first electric signal;

the second photosensitive submodule is arranged on a reflection light path of the second light guide mirror and is used for receiving the signal light and converting the signal light into a second electric signal;

The amplifying submodule is used for mixing and amplifying the first electric signal and the second electric signal to obtain a mixed signal;

and the filtering sub-module is used for filtering the low-frequency signals in the mixed signals to obtain detection electric signals.

6. The single frequency laser device of claim 1, wherein the gain medium is a broadband gain crystal or a narrowband gain crystal.