CN112366506B - Miniaturized low-noise all-solid-state single-frequency continuous wave laser - Google Patents

Miniaturized low-noise all-solid-state single-frequency continuous wave laser Download PDF

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CN112366506B
CN112366506B CN202011347334.8A CN202011347334A CN112366506B CN 112366506 B CN112366506 B CN 112366506B CN 202011347334 A CN202011347334 A CN 202011347334A CN 112366506 B CN112366506 B CN 112366506B
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laser
cavity mirror
laser cavity
light
frequency
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CN112366506A (en
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苏静
卢华东
徐敏志
彭堃墀
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Shanxi University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/102—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08059—Constructional details of the reflector, e.g. shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/0813—Configuration of resonator
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/0813—Configuration of resonator
    • H01S3/0816—Configuration of resonator having 4 reflectors, e.g. Z-shaped resonators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/1066—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using a magneto-optical device
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
    • H01S3/109—Frequency multiplication, e.g. harmonic generation

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  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Nonlinear Science (AREA)
  • Lasers (AREA)

Abstract

The invention relates to a miniaturized low-noise all-solid-state single-frequency continuous wave laser, which comprises: the optical fiber coupling laser diode is used for outputting initial pump light; the laser shaping lens group is arranged on the light path of the initial pump light, and is used for shaping and focusing the initial pump light and outputting the shaped and focused pump light; the single-frequency laser is arranged on the optical path of the pumping light and used for receiving the pumping light and outputting laser; the single-frequency laser comprises two plane laser cavity mirrors, two plano-concave laser cavity mirrors and a laser gain crystal; the laser gain crystal is used for generating gain for the pump light to form gain light, and the stimulated emission cross section of the laser gain crystal is smaller than 2 multiplied by 10‑19cm2. The laser provided by the invention is simple to operate, and can realize small-sized compact low-noise laser output by utilizing the characteristic of small emission section of the laser gain crystal.

Description

Miniaturized low-noise all-solid-state single-frequency continuous wave laser
Technical Field
The invention relates to the technical field of laser, in particular to a miniaturized low-noise all-solid-state single-frequency continuous wave laser.
Background
Because of the advantages of wide and narrow line, high beam quality, low noise and the like, the all-solid-state continuous wave single-frequency laser has been widely applied to various fields such as scientific research, biomedicine, national defense construction and the like. Especially in recent years further developments in the field of quantum information have placed higher demands on the intensity noise of laser light sources. Research shows that the smaller the frequency of the intensity noise spectrum of the laser reaching the shot noise reference is, the higher compression degree of the laser with the wavelength can be realized in a wider frequency range, and further the development of quantum information is effectively promoted. The intensity noise suppression techniques that have been developed so far include photoelectric negative feedback techniques, seed light injection locking techniques, and insertion-mode cleaner techniques.
In which an electro-optical servo system in electro-optical negative feedback inevitably introduces extra electrical noise. The seed light injection locking technology needs a plurality of sets of electro-optical servo systems to realize the accurate locking of the frequencies of the driven laser and the active laser, not only increases the complexity of the system, but also inevitably introduces additional electrical noise into the system similar to photoelectric negative feedback. The technique of inserting a mode cleaner inevitably filters part of the output laser light while filtering the high-frequency band noise of the laser, and the insertion loss of this type is further increased as the fineness of the mode cleaner is further improved.
The only way recently developed to suppress the laser intensity noise by inserting a nonlinear crystal in the cavity is to have a good suppression at the relaxation oscillation frequency. In previous work (Yongguiguo, Huadong Lu, WeinaPeng, lacing Su, AND Kunchi Peng, "Intensity noise suppression of a high-power-frequency CW laser by controlling the stimulated emission rate" optical filters, Vol.44, No.24, 6033-36, (2019)), methods have been investigated to suppress laser Intensity noise by manipulating the laser cavity length to change the stimulated emission rate, but to achieve a shot noise reference at a cutoff frequency of 1MHz, the laser cavity length must be elongated to around 1m, making the overall laser system bulky.
In summary, there is a need for a new method or system for suppressing laser intensity noise, which solves the above-mentioned drawbacks.
Disclosure of Invention
The invention aims to provide a miniaturized low-noise all-solid-state single-frequency continuous wave laser, which can integrally inhibit the intensity noise of the laser in a wide range, effectively realize low-noise output, and has a compact internal structure and simple and convenient operation.
In order to achieve the purpose, the invention provides the following scheme:
a miniaturized, low-noise, all-solid-state, single-frequency, continuous-wave laser, comprising:
the optical fiber coupling laser diode is used for outputting initial pump light;
the laser shaping lens group is arranged on the light path of the initial pump light, and is used for shaping and focusing the initial pump light and outputting the shaped and focused pump light;
the single-frequency laser is arranged on the optical path of the pumping light and used for receiving the pumping light and outputting laser; the single-frequency laser comprises a first plane laser cavity mirror, a second plane laser cavity mirror, a first plano-concave laser cavity mirror, a second plano-concave laser cavity mirror and a laser gain crystal;
the first plane laser cavity mirror is used for receiving the pump light and reflecting the intra-cavity oscillation laser to form first emergent light;
the second planar laser cavity mirror is arranged on a light path of the first emergent light and is used for receiving and reflecting the first emergent light to form second emergent light;
the first plano-concave laser cavity mirror is arranged on a light path of the second emergent light and is used for receiving and reflecting the second emergent light to form third emergent light;
the second plano-concave laser cavity mirror is arranged on a light path of the third emergent light and used for reflecting the third emergent light to the first plane laser cavity mirror, transmitting the third emergent light and outputting laser;
the laser gain crystal is arranged on a light path between the first plane laser cavity mirror and the second plane laser cavity mirror and used for providing gain for the first emergent light; the stimulated emission cross section of the laser gain crystal is less than 2 multiplied by 10-19cm2。
Optionally, the single-frequency laser further includes:
and the frequency doubling crystal is arranged at the waist spots of the first plano-concave laser cavity mirror and the second plano-concave laser cavity mirror and is used for carrying out frequency conversion on the wavelength of the third emergent light.
Optionally, the single-frequency laser further includes:
and the optical isolator is arranged on a light path between the laser gain crystal and the second plane laser cavity mirror.
Optionally, the optical isolator includes:
the magneto-optical rotation crystal is arranged on a light path between the laser gain crystal and the second plane laser cavity mirror;
and the half-wave plate is arranged on a light path between the magneto-optically active crystal and the second plane laser cavity mirror.
Optionally, the single-frequency laser further includes:
and the optical isolator is arranged on a light path between the first plane laser cavity mirror and the second plane laser cavity mirror.
Optionally, the optical isolator includes:
the magneto-optical rotation crystal is arranged on a light path between the first plane laser cavity mirror and the second plano-concave laser cavity mirror;
and the half-wave plate is arranged on an optical path between the magneto-optically active crystal and the first plane laser cavity mirror.
Optionally, the single-frequency laser further includes: a third plane laser cavity mirror and a fourth plane laser cavity mirror;
the third planar laser cavity mirror is arranged on a light path between the second planar laser cavity mirror and the first plano-concave laser cavity mirror, and the third planar laser cavity mirror is used for reflecting the second emergent light to the first plano-concave laser cavity mirror;
the fourth plane laser cavity mirror is arranged between the first plane laser cavity mirror and the second plane laser cavity mirror, and the fourth plane laser cavity mirror is used for reflecting emergent light of the second plane laser cavity mirror to the first plane laser cavity mirror.
Optionally, the third planar laser cavity mirror is plated with a fundamental frequency light high reflection film.
Optionally, the fourth planar laser cavity mirror is plated with a fundamental frequency light high reflection film.
Optionally, the first planar laser cavity mirror is plated with a pump light high-transmittance film and a fundamental frequency light high-reflection film; the second planar laser cavity mirror is plated with a fundamental frequency light high-reflection film; the first plano-concave laser cavity mirror is plated with a fundamental frequency light high reflection film; the second plano-concave laser cavity mirror is plated with a fundamental frequency light partial transmission film and a frequency doubling light high transmission film.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the small-sized low-noise output all-solid-state single-frequency continuous wave laser is realized by utilizing the laser gain crystal with a small stimulated emission cross section, and the integral inhibition effect on the intensity noise of the laser can be realized in a wide frequency range.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic structural diagram of a four-mirror ring resonator according to the present invention;
FIG. 2 is a schematic structural diagram of a six-mirror ring resonator according to the present invention;
FIG. 3 is a diagram of a theoretical calculated relationship between a cut-off frequency (SNL cutoff frequency) of a single frequency continuous wave laser output noise and a stimulated emission cross-section (SECS of the laser crystal) of a laser gain crystal;
FIG. 4 shows the measured Nd CaYAlO4Intensity noise plot of single frequency laser as laser gain crystal.
Description of the symbols:
1-fiber coupled laser diode, 2-laser shaping lens group, 3-single frequency laser, 4-first plane laser cavity mirror, 5-second plane laser cavity mirror, 6-first plano-concave laser cavity mirror, 7-second plano-concave laser cavity mirror, 8-laser gain crystal, 9-frequency doubling crystal, 10-magneto-rotation crystal, 11-half wave plate, 12-third plane laser cavity mirror and 13-fourth plane laser cavity mirror.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a miniaturized low-noise all-solid-state single-frequency continuous wave laser, which realizes small-size low-noise output by using a laser gain crystal with a small stimulated emission section and can perform the integral inhibition effect on the intensity noise of the laser in a wide frequency range.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
As shown in fig. 1 and fig. 2, the miniaturized low-noise all-solid-state single-frequency continuous wave laser provided by the present invention includes: the laser comprises a fiber coupling laser diode 1, a laser shaping lens group 2, a single-frequency laser 3 and a laser gain crystal 8.
The fiber coupled laser diode 1 is used for outputting initial pump light;
specifically, the pumping mode of the fiber-coupled laser diode 1 is end pumping or side pumping. The pumping mode of the fiber coupled laser diode 1 is single-end pumping or double-end pumping.
Further, the center wavelength of the fiber-coupled laser diode 1 is 808nm, the diameter of the fiber core is 400 μm, the numerical aperture is 0.22, and the maximum output power is 15W.
The laser shaping lens group 2 is arranged on a light path of the initial pump light, and the laser shaping lens group 2 is used for shaping and focusing the initial pump light and outputting the shaped and focused pump light.
Specifically, the laser shaping lens group 2 includes a lens having a focal length of 30mm and a lens having a focal length of 80 mm.
And focusing the pump light after shaping and focusing on the laser gain crystal 8 by the shaping action of the lens with the focal length of 30mm and the focusing action of the lens with the focal length of 80 mm.
The single-frequency laser 3 is arranged on the optical path of the pump light, and the single-frequency laser 3 is used for receiving the pump light and outputting laser; the cavity of the single-frequency laser 3 is a ring resonant cavity running in one direction.
Specifically, the single-frequency laser 3 includes: a first plane laser cavity mirror 4, a second plane laser cavity mirror 5, a first plano-concave laser cavity mirror 6, a second plano-concave laser cavity mirror 7 and a laser gain crystal 8.
The first plane laser cavity mirror 4 is used for receiving the pump light and reflecting the intra-cavity oscillation laser to form first emergent light;
the second planar laser cavity mirror 5 is arranged on a light path of the first emergent light, and the second planar laser cavity mirror 5 is used for receiving and reflecting the first emergent light to form second emergent light;
the first plano-concave laser cavity mirror 6 is arranged on a light path of the second emergent light, and the first plano-concave laser cavity mirror 6 is used for receiving and reflecting the second emergent light to form third emergent light;
the second plano-concave laser cavity mirror 7 is arranged on a light path of the third emergent light, and the second plano-concave laser cavity mirror 7 is used for reflecting the third emergent light to the first plane laser cavity mirror 4, transmitting the third emergent light and outputting laser;
the laser gain crystal 8 is arranged on a light path between the first plane laser cavity mirror 4 and the second plane laser cavity mirror 5, and the laser gain crystal 8 is used for providing gain for the first emergent light; the stimulated emission cross section of the laser gain crystal 8 is less than 2 multiplied by 10-19cm2。
Specifically, the laser gain crystal having a small stimulated emission cross section has Nd: CaYAlO4、Yb:CaYAlO4、Er:CaYAlO4、Yb:CaGdAlO4、Yb:Y3Al5O12、Yb:Sr3Y(BO3)3And the like. In the invention, the laser gain crystal 8 adopts Nd CaYAlO4A crystal; the doping concentration of the laser gain crystal 8 is 1 at.%, and the dimension is 3 multiplied by 6mm3And 808/1080nm antireflection films are plated at two ends of the laser gain crystal 8.
Specifically, in the experiment, the laser gain crystal 8 is wrapped by indium foil, vacuum indium welding is carried out in a red copper furnace with good heat conductivity, a thermoelectric cooler (TEC) and cooling circulating water are matched to refrigerate red copper heat sink, the temperature of the laser gain crystal 8 is accurately controlled, and the control precision is 0.01 ℃.
Further, the single-frequency laser 3 further comprises a frequency doubling crystal 9. The frequency doubling crystal 9 is arranged at the waist spots of the first plano-concave laser cavity mirror 6 and the second plano-concave laser cavity mirror 7 and is used for carrying out frequency conversion on the wavelength of the third emergent light. Specifically, the frequency doubling crystal 9 is arranged at the waist spots of the first plano-concave laser cavity mirror 6 and the second plano-concave laser cavity mirror 7, so that the maximum nonlinear effect of the frequency doubling crystal 9 is ensured.
Specifically, the frequency doubling crystal 9 is made of a lithium triborate crystal, a bismuth borate crystal, a barium metaborate crystal, a periodically poled potassium titanyl phosphate crystal, or a periodically poled lithium tantalate crystal.
Further, in this embodiment, the frequency doubling crystal 9 is a type i noncritical phase-matched lithium triborate crystal; in the experiment, the frequency doubling crystal 9 is placed in a red copper heat preservation furnace, the phase matching temperature is 136.9 ℃, and the crystal temperature control precision is 0.1 ℃.
Further, the single-frequency laser 3 further includes an optical isolator. The optical isolator is arranged on a light path between the laser gain crystal 8 and the second plane laser cavity mirror 5.
Specifically, the optical isolator includes: a magneto-optically active crystal 10 and a half-wave plate 11.
The magneto-optically active crystal 10 is arranged on a light path between the laser gain crystal 8 and the second plane laser cavity mirror 5;
the half-wave plate 11 is arranged on the optical path between the magneto-optically active crystal 10 and the second planar laser cavity mirror 5.
In addition, the present invention provides another embodiment of an optical isolator position; specifically, the optical isolator is arranged on the optical path between the first plane laser cavity mirror 4 and the second plane laser cavity mirror 7;
the optical isolator includes: a magneto-optically active crystal 10 and a half-wave plate 11. The magneto-optically active crystal 10 is arranged on a light path between the first plane laser cavity mirror 4 and the second plano-concave laser cavity mirror 7; the half-wave plate 11 is arranged on the optical path between the magneto-optically active crystal 10 and the first plane laser cavity mirror 4.
Specifically, the magneto-optical rotation crystal 10 of the external magnetic field and the half-wave plate 11 corresponding to the oscillation laser wavelength form an optical isolator, so that the spatial hole burning effect can be eliminated, and the stable unidirectional running of the intracavity oscillation laser in the annular resonant cavity of the laser can be ensured.
Further, the single-frequency laser 3 further includes: a third plane laser cavity mirror 12 and a fourth plane laser cavity mirror 13.
The third planar laser cavity mirror 12 is disposed on the light path between the second planar laser cavity mirror 5 and the first plano-concave laser cavity mirror 6, and the third planar laser cavity mirror 12 is configured to reflect the second outgoing light to the first plano-concave laser cavity mirror 6;
the fourth planar laser cavity mirror 13 is disposed between the first planar laser cavity mirror 4 and the second planar laser cavity mirror 7, and the fourth planar laser cavity mirror 13 is configured to reflect the emergent light of the second planar laser cavity mirror 7 to the first planar laser cavity mirror 4.
Specifically, the third plane laser cavity mirror 12 is plated with a fundamental frequency light high reflection film. And the fourth plane laser cavity mirror 13 is plated with a fundamental frequency light high reflection film.
Further, the first plane laser cavity mirror 4 is plated with a pump light high-transmittance film and a fundamental frequency light high-reflection film; the second planar laser cavity mirror 5 is plated with a fundamental frequency light high reflection film; the first plano-concave laser cavity mirror 6 is plated with a fundamental frequency light high reflection film; the second plano-concave laser cavity mirror 7 is plated with a fundamental frequency light partial transmission film and a frequency doubling light high transmission film.
Further, as shown in fig. 1, the miniaturized low-noise all-solid-state single-frequency continuous wave laser is an all-solid-state single-frequency continuous wave laser that realizes low-noise output for a four-mirror ring resonator. Specifically. The all-solid-state single-frequency continuous wave laser for realizing low-noise output by the four-mirror ring-shaped resonant cavity comprises an optical fiber coupling laser diode 1, a laser shaping lens group 2 and a single-frequency laser 3. The single-frequency laser 3 comprises a first plane laser cavity mirror 4, a second plane laser cavity mirror 5, a first plano-concave laser cavity mirror 6, a second plano-concave laser cavity mirror 7, a laser gain crystal 8 with a small stimulated emission section, a frequency doubling crystal 9, a magneto-optical rotation crystal 10 with an external magnetic field and a half-wave plate 11 corresponding to the oscillation laser wavelength. The central wavelength of the fiber coupled laser diode 1 is 808nm, the core diameter and the numerical aperture of the fiber are 400 μm and 0.22 respectively, and the maximum output power is 15W. The pump light coupled out by the optical fiber is focused on the laser gain crystal 8 through the shaping action of the lens with the focal length of 30mm and the focusing action of the lens with the focal length of 80 mm. The optical resonant cavity in this embodiment is a four-mirror ring cavity, wherein the first planar laser cavity mirror 4 is plated with a pump light high-transmittance film and a fundamental frequency light high-reflectance film; the second plane laser cavity mirror 5 is plated with a fundamental frequency light high reflection film; the first plano-concave laser cavity mirror 6 is plated with a fundamental frequency light high reflection film; the second plano-concave laser cavity mirror 7 is plated with a fundamental frequency light partial transmission film and a frequency doubling light high transmission film. The laser gain crystal 8 is Nd: CaYAlO with small stimulated emission cross section4Crystal with doping concentration of 1 at.% and crystal size of 3X 6mm3And the two ends of the crystal are coated with 808/1080nm antireflection films. In the experiment, the crystal is wrapped by indium foil, the crystal is placed in a red copper furnace with good heat conduction performance by vacuum indium welding, and the temperature of the crystal is accurately controlled by a red copper heat sink which is refrigerated by matching a thermoelectric cooler (TEC) and cooling circulating water, and the control precision is 0.01 ℃. The magneto-optical rotation crystal 10 of the external magnetic field and the half-wave plate 11 corresponding to the oscillation laser wavelength form the optical isolator 3, which can eliminate the space hole burning effect and ensure the stable unidirectional operation of the laser in the laser. The frequency doubling crystal 9 is I-type noncritical phase matched triboronLithium crystal, the frequency doubling crystal is placed in a red copper heat preservation furnace, the phase matching temperature is 136.9 ℃, and the crystal temperature control precision is 0.1 ℃. And the frequency doubling crystal is placed at the waist spot between the first plano-concave laser cavity mirror 6 and the second plano-concave laser cavity mirror 7 to ensure that the optimal nonlinear conversion efficiency is obtained.
Further, another embodiment of the miniaturized low-noise all-solid-state single-frequency continuous wave laser provided by the present invention is, as shown in fig. 2, an all-solid-state single-frequency continuous wave laser that realizes low-noise output for a six-mirror ring resonator. Specifically, the all-solid-state single-frequency continuous wave laser for realizing low-noise output by the six-mirror ring-shaped resonant cavity comprises an optical fiber coupling laser diode 1, a laser shaping lens group 2 and a single-frequency laser 3. The single-frequency laser comprises a first plane laser cavity mirror 4, a second plane laser cavity mirror 5, a third plane laser cavity mirror 12, a fourth plane laser cavity mirror 13, a first plano-concave laser cavity mirror 6, a second plano-concave laser cavity mirror 7, a laser gain crystal 8 with a small stimulated emission cross section, a frequency doubling crystal 9, a magneto-optical crystal 10 with an external magnetic field and a half-wave plate 11 corresponding to the oscillation laser wavelength. The center wavelength of the fiber-coupled laser diode 1 is 808nm, the fiber core diameter and the numerical aperture are 400 μm and 0.22, respectively, and the maximum output power is 15W. The pump light coupled out by the optical fiber is focused at the laser gain crystal 8 by the shaping action of the lens with the focal length of 30mm and the focusing action of the lens with the focal length of 80 mm. The optical resonant cavity designed in this embodiment is a six-mirror ring cavity, wherein the first planar laser cavity mirror 4 is plated with a pump light high-transmittance film and a fundamental frequency light high-reflectance film; the second plane laser cavity mirror 5 is plated with a fundamental frequency light high reflection film; the third plane laser cavity mirror 12 is plated with a fundamental frequency light high reflection film; the fourth plane laser cavity mirror 13 is plated with a fundamental frequency light high reflection film; the first plano-concave laser cavity mirror 6 is plated with a fundamental frequency light high reflection film; the second plano-concave laser cavity mirror 7 is plated with a fundamental frequency light partial transmission film and a frequency doubling light high transmission film. The laser gain crystal 8 is Nd: CaYAlO with small stimulated emission cross section4Crystal with doping concentration of 1 at.% and crystal size of 3X 6mm3And the two ends of the crystal are coated with 808/1080nm antireflection films. In the experiment, the laser gain crystal 8 is made of indiumThe foil is wrapped, the copper foil is placed in a red copper furnace with good heat conduction performance in a vacuum indium welding mode, a thermoelectric cooler (TEC) and cooling circulating water are matched for refrigeration, the red copper heat sink is used for accurately controlling the crystal temperature, and the control accuracy is 0.01 ℃. The magneto-optical rotation crystal 10 of the external magnetic field and the half-wave plate 11 corresponding to the wavelength of the oscillation laser form the optical isolator 3, which can eliminate the space hole burning effect and ensure the stable unidirectional operation of the laser. The frequency doubling crystal 9 is a type I noncritical phase matching lithium triborate crystal, the crystal is placed in a red copper heat preservation furnace, the phase matching temperature is 136.9 ℃, and the temperature control precision of the crystal is 0.1 ℃. And the frequency doubling crystal 9 is placed at the waist spot between the first plano-concave laser cavity mirror 6 and the second plano-concave laser cavity mirror 7 to ensure that the optimal nonlinear conversion efficiency is obtained.
In the invention, when the laser cavity parameters and the pumping conditions are fixed, the problem that the existing all-solid-state continuous wave laser has higher intensity noise in a broadband range can be improved by only utilizing the characteristic of the small emission section of the laser gain crystal 8, and when the stimulated emission section of the laser gain crystal 8 is smaller than 2 multiplied by 10-19cm2In the process, the miniaturized low-noise all-solid-state single-frequency continuous wave laser output can be realized without adding a complicated locking system or introducing an additional mode cleaner.
The invention provides a miniaturized low-noise all-solid-state single-frequency continuous wave laser, which has the following principle:
the intensity noise spectral function of a single frequency continuous wave laser can be expressed as:
Vf＝k1(ωf,γf)Vvac+k2(ωf,γf)Vp+k3(ωf,γf)Vspont+k4(ωf,γf)Vdipole+k5(ωf,γf)Vlosses；
wherein k is1，k2，k3，k4，k5Respectively expressed as vacuum noise VvacPumping noise VpSpontaneous emission noise VspontDipole fluctuation noise VdipoleAnd damage of cavityLoss induced noise VlossesThe coefficient of (a). Relaxation oscillation frequency omega of laserfAnd damping rate of relaxation oscillations gammafCan be expressed as:
Figure BDA0002800310610000101
γf＝Gα2+Γ+γt；
wherein alpha is2Is the number of photons in the cavity, k is the cavity decay rate (sum of the loss of the output coupling mirror and the loss in the cavity), Γ is the pump rate, γtG is the coupled radiation rate between the atomic transition and the laser cavity mode, expressed as:
Figure BDA0002800310610000102
wherein σsThe laser stimulated emission cross section is shown as the specification, rho is the density of atoms doped in a gain medium, c is the speed of light, L and L are the length of the gain medium and the length of a laser resonant cavity respectively, and n is the refractive index of a crystal.
From the above formula of the intensity noise spectrum function, it can be seen that the intensity noise of the laser is proportional to the frequency of the relaxation oscillation and the damping rate of the relaxation oscillation. Noise spectrum V of intensityfNormalized to shot noise reference, V f1 means that the intensity noise of the laser reaches the quantum noise limit. At this time Vvoc＝Vspont＝Vdipole＝V losses1, and pumping noise VpIs the actual pump field noise. Under the condition that the doping density and length of the laser gain crystal, the cavity parameters of the laser and the pumping conditions are the same, namely the doping atom density rho in the gain medium, the length l of the gain medium, the attenuation rate k in the cavity, the pumping rate gamma and the pumping noise VpAnd the laser cavity length L is kept consistent by omegafAnd gammafThe expression shows that the relaxation frequency and the damping rate of the relaxation oscillation of the continuous single-frequency laser are proportional to the stimulated emission section sigma of the laser gain crystals. Simultaneous dependent on intensity noise spectral functionTheoretical numerical simulation shows that the cutoff frequency of the noise spectrum of the continuous single-frequency laser is in direct proportion to the G parameter, namely the smaller the stimulated emission cross section of the laser gain medium is, the smaller the G parameter is, and further the strength of the mutual coupling effect between the number of particles in the gain medium in the cavity and photons in the resonant cavity is weakened, so that the smaller the cutoff frequency of the noise spectrum of the continuous single-frequency laser is, the effect of inhibiting the strength noise of the laser by controlling the stimulated emission cross section of the laser gain crystal is finally achieved, and an effective way is provided for realizing the miniaturized low-noise all-solid-state continuous wave single-frequency laser.
Referring to fig. 3, a theoretical relationship between the cut-off frequency (SNL cutoff frequency) of the output noise of the monochromatic continuous wave laser and the stimulated emission cross-section (SECS of the laser crystal) of the laser gain crystal indicates that the cut-off frequency of the output intensity noise of the monochromatic continuous wave laser is in direct proportion to the stimulated emission cross-section of the laser gain crystal, when Nd is greater than the threshold value3+When the ion doping concentration is 1 at.%, for Nd CaYAlO4A crystal having a stimulated emission cross-section at 1080nm of 1.04X 10-19cm2This value is only about Nd: YAlO3One fourth of the stimulated emission cross section of the crystal (Nd: YAlO)3The stimulated emission cross section of the crystal at 1080nm is 4.6 multiplied by 10-19cm2) The theoretical calculation shows that the Nd is CaYAlO4The cut-off frequency of the output noise of the single-frequency laser as the laser gain crystal is 1.53MHz and is lower than that of Nd: YAlO3The cut-off frequency of the output noise of the single-frequency laser as the laser gain crystal is 2.1 MHz.
CaYAlO as shown in FIG. 44FIG. 4 shows the intensity noise plot of a single frequency laser as a laser gain crystal in Nd: CaYAlO4The cut-off frequency of the output noise of the single-frequency laser used as the laser gain crystal is 1.5MHz, and the experimental result is consistent with the theoretical calculation.
When the low-noise all-solid-state single-frequency continuous wave laser is output, the method is simple and convenient to operate, a photoelectric servo system is not required to be additionally arranged, so that extra electric noise is not introduced, the sensitivity of a locking system to the environment is not increased, a device for filtering the noise of the laser is not required to be additionally inserted, and the method is not required to be additionally providedThe power of the laser is additionally consumed and noise is introduced, when the laser cavity parameters and the pumping conditions are fixed, the problem that the existing all-solid-state continuous wave laser has high intensity noise in a broadband range can be solved by only utilizing the characteristic of the small emission section of the laser gain crystal, the integral inhibition effect on the intensity noise of the laser is carried out in the broadband range, and when the stimulated emission section of the laser gain crystal is smaller than 2 multiplied by 10-19cm2In the process, the miniaturized low-noise all-solid-state single-frequency continuous wave laser output can be realized without adding a complicated locking system or introducing an additional mode cleaner.
The core of the invention is the all-solid-state single-frequency continuous wave laser which utilizes the laser gain crystal with small stimulated emission section to realize low-noise output, and all-solid-state single-frequency continuous wave laser output is realized by reducing G parameter (coupling radiation rate between atomic transition and laser cavity mode) by using the characteristic of small stimulated emission section of the laser gain crystal, which belongs to the protection scope of the invention. The above embodiments are only exemplary of a few configurations. There are many types of laser gain crystals with small emission cross-sections, and thus there are many more specific embodiments.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. The utility model provides a miniaturized low-noise all-solid-state single-frequency continuous wave laser which characterized in that, miniaturized low-noise all-solid-state single-frequency continuous wave laser includes:
the optical fiber coupling laser diode is used for outputting initial pump light;
the laser shaping lens group is arranged on the light path of the initial pump light, and is used for shaping and focusing the initial pump light and outputting the shaped and focused pump light;
the single-frequency laser is arranged on the optical path of the pumping light and used for receiving the pumping light and outputting laser; the single-frequency laser comprises a first plane laser cavity mirror, a second plane laser cavity mirror, a first plano-concave laser cavity mirror, a second plano-concave laser cavity mirror and a laser gain crystal;
the first plane laser cavity mirror is used for receiving the pump light and reflecting the oscillation light in the cavity to form first emergent light;
the second planar laser cavity mirror is arranged on a light path of the first emergent light and is used for receiving and reflecting the first emergent light to form second emergent light;
the first plano-concave laser cavity mirror is arranged on a light path of the second emergent light and is used for receiving and reflecting the second emergent light to form third emergent light;
the second plano-concave laser cavity mirror is arranged on a light path of the third emergent light and used for reflecting the third emergent light to the first plane laser cavity mirror, transmitting the third emergent light and outputting laser;
the laser gain crystal is arranged on a light path between the first plane laser cavity mirror and the second plane laser cavity mirror and used for providing gain for the first emergent light; the stimulated emission cross section of the laser gain crystal is less than 2 multiplied by 10-19cm2(ii) a The laser gain crystal adopts Nd CaYAlO4A crystal, the laser gain crystal having a doping concentration of 1 at.% and a size of 3 × 3 × 6mm3And the two ends of the laser gain crystal are coated with 808/1080nm antireflection films.
2. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 1, further comprising:
and the frequency doubling crystal is arranged at the waist spots of the first plano-concave laser cavity mirror and the second plano-concave laser cavity mirror and is used for carrying out frequency conversion on the wavelength of the third emergent light.
3. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 1, further comprising:
and the optical isolator is arranged on a light path between the laser gain crystal and the second plane laser cavity mirror.
4. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 3, wherein the optical isolator comprises:
the magneto-optical rotation crystal is arranged on a light path between the laser gain crystal and the second plane laser cavity mirror;
and the half-wave plate is arranged on a light path between the magneto-optically active crystal and the second plane laser cavity mirror.
5. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 1, further comprising:
and the optical isolator is arranged on a light path between the first plane laser cavity mirror and the second plane laser cavity mirror.
6. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 5, wherein the optical isolator comprises:
the magneto-optical rotation crystal is arranged on a light path between the first plane laser cavity mirror and the second plano-concave laser cavity mirror;
and the half-wave plate is arranged on an optical path between the magneto-optically active crystal and the first plane laser cavity mirror.
7. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 1, further comprising: a third plane laser cavity mirror and a fourth plane laser cavity mirror;
the third planar laser cavity mirror is arranged on a light path between the second planar laser cavity mirror and the first plano-concave laser cavity mirror, and the third planar laser cavity mirror is used for reflecting the second emergent light to the first plano-concave laser cavity mirror;
the fourth plane laser cavity mirror is arranged between the first plane laser cavity mirror and the second plane laser cavity mirror, and the fourth plane laser cavity mirror is used for reflecting emergent light of the second plane laser cavity mirror to the first plane laser cavity mirror.
8. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 7, wherein the third planar laser cavity mirror is plated with a fundamental-frequency light high-reflection film.
9. The miniaturized, low-noise, all-solid-state, single-frequency continuous wave laser of claim 7, wherein the fourth planar laser cavity mirror is plated with a fundamental-frequency light high-reflectivity film.
10. The miniaturized low-noise all-solid-state single-frequency continuous wave laser device according to claim 1, wherein the first planar laser cavity mirror is plated with a pump light high-transmittance film and a fundamental frequency light high-reflection film; the second planar laser cavity mirror is plated with a fundamental frequency light high-reflection film; the first plano-concave laser cavity mirror is plated with a fundamental frequency light high reflection film; the second plano-concave laser cavity mirror is plated with a fundamental frequency light partial transmission film and a frequency doubling light high transmission film.
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WO2014007900A2 (en) * 2012-05-11 2014-01-09 Massachusetts Institute Of Technology Methods, systems, and apparatus for high energy optical-pulse amplification at high average power
CN105390929A (en) * 2015-12-22 2016-03-09 南京先进激光技术研究院 All-solid-state laser capable of obtaining single-frequency output at wavelength of 558nm
CN111313216A (en) * 2019-11-19 2020-06-19 山西大学 Method for suppressing intensity noise of high-power continuous wave single-frequency laser

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CN105390929A (en) * 2015-12-22 2016-03-09 南京先进激光技术研究院 All-solid-state laser capable of obtaining single-frequency output at wavelength of 558nm
CN111313216A (en) * 2019-11-19 2020-06-19 山西大学 Method for suppressing intensity noise of high-power continuous wave single-frequency laser

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