A high-power dual-frequency laser for dual-mode optical lattice atomic clocks

Abstract

The invention discloses a dual-frequency laser applicable to a dual-mode optical lattice atomic clock, comprising a 532nm pump light source, wherein a beam splitter group, a dichroic mirror, a titanium sapphire crystal, two birefringent filters, two etalons, a birefringent crystal, an electro-optical crystal, a concave reflector and a piezoelectric ceramic PZT are sequentially arranged in the optical path of the light source emission light, wherein the dichroic mirror and the concave reflector form a resonant cavity to generate laser; the optical axis of the birefringent crystal is 45 degrees with the light incident surface, and is used to generate o-light and e-light propagation paths in the same cavity; the anti-reflection film of the birefringent filter and the high-reflection film of the concave reflector have spectral bands with overlapping edges, and are used for rough selection of laser output wavelength; the etalon and the birefringent filter are combined to perform fine mode selection; the electro-optical crystal is used to apply an electric field in a direction parallel to the o-light or e-light photoelectric vector, and independently adjust the frequency of one of the polarized lights; the PZT is combined with the electro-optical crystal to simultaneously adjust two laser frequencies.

Description

Technical Field

[0001] The present invention relates to the field of optical atomic clocks, and in particular to, but not limited to, a high-power dual-frequency laser applicable to dual-mode optical lattice atomic clocks. Background Art

[0002] Optical lattice atomic clocks are currently the atomic clocks with the highest stability and the smallest uncertainty. They play a key role in many important scientific and technological fields such as high-precision timekeeping, geoscientific measurement, and basic physics testing. The dual-mode optical lattice atomic clock based on two atomic systems, referred to as the dual-mode optical clock, can eliminate the common blackbody radiation frequency shift and DC Stark frequency shift, can perform self-comparison of the atomic clock, and can alternately perform clock transition detection to eliminate the dead time in the clock operation. Therefore, it is one of the important development directions of high-precision atomic clocks in the future. Dual-mode optical clocks can be combined using different atoms. The present invention refers to a dual-mode optical lattice atomic clock based on Sr atoms and Yb atoms. In the Sr / Yb dual-mode optical clock system, single-frequency lasers with 11 wavelengths, such as 399nm (nanometers), 461nm, 689nm, 556nm, 759nm, 813nm, 1388nm, 679nm, 707nm, 698nm, and 578nm, are involved. Therefore, how to reduce the complexity of the laser system is an important issue for the system.

[0003] Among them, the 759nm and 813nm lasers used in optical lattices have high power requirements, reaching the watt level. The existing technology generally adopts the method of tunable external cavity semiconductor laser plus external power amplification, or adopts high-power pump titanium sapphire laser, these two methods are used to achieve it. The former has large noise, while the latter has a relatively complex structure, large volume and high cost. At present, most experimental groups developing optical atomic clocks purchase lasers with independent wavelengths for experimental research. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a compact dual-frequency laser applicable to a dual-mode optical clock, aiming to generate high-power tunable dual-frequency laser in the same cavity using a common cavity technology to enhance the compactness of the light source system.

[0005] The technical solution of the embodiment of the present invention is achieved as follows:

[0006] In a first aspect, an embodiment of the present invention provides a dual-frequency laser applicable to a dual-mode optical lattice atomic clock, comprising a 532nm pump light source, wherein a beam splitter group, a dichroic mirror, a titanium sapphire crystal, two groups of birefringent filters and an etalon, a birefringent crystal, an electro-optical crystal, a concave reflector and a piezoelectric ceramic PZT are sequentially arranged in the emission light path of the pump light source, wherein the dichroic mirror and the concave reflector constitute a resonant cavity to generate laser light;

[0007] Among them, the beam splitter group is used to split the collimated pump light beam into two spatially separated beams; the optical axis of the birefringent crystal forms an angle of 45 degrees with the light incident surface, which is used to generate o-light and e-light propagation paths in the same cavity to form two intrinsic modes; the anti-reflection film of the birefringent filter and the high-reflection film of the concave reflector have spectral bands with overlapping edges, which are used for coarse selection of laser output wavelengths; the standard tool is combined with the birefringent filter for fine mode selection; the electro-optical crystal is used to apply an electric field in a direction parallel to the o-light or e-light vector to independently adjust the frequency of one of the polarized lights; the piezoelectric ceramic PZT is combined with the electro-optical crystal to simultaneously adjust the frequencies of two lasers.

[0008] In some possible embodiments, the angle of the wedge-shaped prism is adjusted to match the two pump light beams with the oscillation mode in the cavity, thereby obtaining two orthogonally polarized intrinsic oscillation modes.

[0009] In some possible embodiments, the vibration modes in the cavity are roughly filtered by coating the optical interface in the cavity with overlapping spectral band edges, and the modes are finely selected using a set of birefringent filters and an etalon, so that the resonant cavity outputs dual-frequency lasers of specific wavelengths; wherein the anti-reflection films of the two birefringent filters respectively overlap with the spectral band edges of the high-reflection film of the concave reflector, so as to realize single-frequency operation of a specific wavelength in one polarization direction.

[0010] In some possible embodiments, the two birefringent filters are a first birefringent filter and a second birefringent filter; wherein the first birefringent filter is coated with a 600nm to 770nm anti-reflection film, the second birefringent filter is coated with an 800nm ​​to 1000nm anti-reflection film, and the concave reflector is coated with a 740nm to 830nm high-reflection film; the laser frequency is finely adjusted by the voltage between the piezoelectric ceramic PZT and the electro-optical crystal, so that the resonant cavity outputs dual-frequency lasers of 759nm and 813nm.

[0011] In some possible embodiments, the laser further comprises another resonant cavity, the optical elements contained in the two resonant cavities are consistent and share the same pump light source; wherein the third birefringent filter in the other resonant cavity is coated with a 600nm to 810nm anti-reflection film, the fourth birefringent filter is coated with a 910nm to 1000nm anti-reflection film, and the concave reflector is coated with a 790nm to 930nm high-reflection film, and the mode is finely selected by adjusting the two birefringent filters and the two standards in the other resonant cavity, so that the other resonant cavity outputs a dual-frequency laser of 798nm and 922nm.

[0012] In some possible embodiments, the power ratio between two pump light beams separated in the same resonant cavity and the power ratio between the corresponding dual-frequency lasers outputted therefrom are adjusted by adjusting the insertion depth of the wedge-shaped prism in the pump light path.

[0013] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0014] In the embodiments of the present invention, firstly, the complexity of the system is reduced by the method of common cavity and common pumping; secondly, tunable dual-frequency output is realized by using independent birefringent filters and etalons; and frequency locking of the dual-frequency laser is realized by using intracavity electro-optical crystals and cavity mirror PZT, thereby meeting the requirements of atomic cooling and optical lattice for frequency certainty and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0016] Figure 1 A schematic diagram of the basic structure of a dual-frequency laser applicable to a dual-mode optical lattice atomic clock provided by an embodiment of the present invention;

[0017] Figure 2 A schematic diagram of wavelength screening through dual-frequency laser coating provided by an embodiment of the present invention;

[0018] Figure 3 A schematic diagram of an extended structure of a dual-frequency laser applicable to a dual-mode optical lattice atomic clock provided by an embodiment of the present invention;

[0019] Reference numerals in the figure: 1-532nm pump source; 2-first beam splitter group; 3-first dichroic mirror; 4-first titanium sapphire crystal; 5-first birefringent filter; 6-first etalon; 7-second birefringent filter; 8-second etalon; 9-first birefringent crystal; 10-first electro-optic crystal; 11-first concave reflector; 12-first piezoelectric ceramic PZT; 13-second beam splitter group; 14-second dichroic mirror; 15-second titanium sapphire crystal; 16-third birefringent filter; 17-third etalon; 18-fourth birefringent filter; 19-fourth etalon; 20-second birefringent crystal; 21-second electro-optic crystal; 22-second concave reflector; 23-second piezoelectric ceramic PZT. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] In the following description, reference is made to “some embodiments”, which describe a subset of all possible embodiments, but it will be understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0022] It should be pointed out that the terms "first\second\third" involved in the embodiments of the present invention are only used to distinguish similar objects and do not represent a specific ordering of the objects. It can be understood that "first\second\third" can be interchanged in a specific order or sequence where permitted, so that the embodiments of the present invention described here can be implemented in an order other than that illustrated or described here.

[0023] Those skilled in the art will appreciate that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the field to which the embodiments of the present invention belong. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as here.

[0024] The pump source is the part that provides energy to the laser system. Examples of pump sources include electrical discharges, flash lamps, arc lamps, light from other lasers, chemical reactions, or even explosive devices. The type of pump source used depends primarily on the gain medium, which also determines how the energy is transferred to the medium.

[0025] The gain medium is the main determinant of the operating wavelength and other characteristics of the laser. Gain media in different materials have either linear spectra or broad spectra. Gain media with broad spectra allow tuning of the laser frequency. There are hundreds of different gain media that enable laser operation (see the list of laser types for a list of the most important ones). The gain medium is excited by the pump source to produce a population inversion, and spontaneous and stimulated emission of photons occurs in the gain medium, resulting in optical gain or amplification.

[0026] Birefringent filters are made of crystal materials and have birefringence and filtering functions. In terms of filtering performance, birefringent filters can select light with a specific wavelength to pass as needed, while other wavelengths of light are clamped or eliminated.

[0027] An etalon is a tool used for measurement and calibration, and is commonly used in industrial production and scientific research. The principle of an etalon is based on precise dimensions and specifications to ensure the accuracy and reliability of the measurement results. For example, the Fabry-Perot etalon, or FP etalon. The main function of the FP etalon is to control the wavelength and frequency of the laser. Due to the interference phenomenon of the FP etalon, only photons of a specific wavelength and frequency can form a stable oscillation in the resonant cavity, thereby achieving laser output.

[0028] When a beam of monochromatic light enters a birefringent crystal at a certain angle, it will be decomposed into two beams refracted in different directions except for special angles. They are linearly polarized light with mutually perpendicular vibration directions. This is the phenomenon of birefringence. These two beams of linearly polarized light with mutually perpendicular polarization directions are o-light (ordinary light) and e-light (extraordinary light). The propagation path of o-light in a birefringent crystal is consistent with the propagation path of light in an isotropic medium (such as glass), while the propagation path of e-light is deflected relative to the propagation path of light in an isotropic medium. For birefringent crystal YVO4 whose cutting direction is at a 45-degree angle to the optical axis, e-light has a larger refraction angle, so the propagation distance of e-light is greater when it is incident at an angle close to vertical incidence in a flat birefringent crystal.

[0029] Figure 1 A schematic diagram of the basic structure of a dual-frequency laser applicable to a dual-mode optical lattice atomic clock provided by an embodiment of the present invention is shown in FIG. Figure 1As shown, it includes a 532nm pump light source 1, and in the emission light path of the pump light source, a first beam splitter group 2, a first dichroic mirror 3, a first titanium sapphire crystal 4, two groups of birefringent filters and etalons (i.e., a first birefringent filter 5 and a first etalon 6 are a group, and a second birefringent filter 7 and a second etalon 8 are another group), a first birefringent crystal 9, a first electro-optical crystal 10, a first concave reflector 11 and a first piezoelectric ceramic PZT are sequentially arranged. 12, wherein the first dichroic mirror 3 and the first concave reflector 11 form a resonant cavity to generate laser; wherein the first beam splitter group 2 is used to split the collimated pump light beam into two spatially separated beams; the optical axis of the first birefringent crystal 9 forms an angle of 45 degrees with the light incident surface, and is used to generate o-light and e-light propagation paths in the same cavity to form two intrinsic modes; the anti-reflection film of the first birefringent filter 5 and the second birefringent filter 7 respectively have spectral bands with overlapping edges with the high-reflection film of the first concave reflector 11, which are used for rough selection of laser output wavelength; each group of etalons is combined with the corresponding birefringent filter for fine mode selection; the first electro-optical crystal 10 is used to apply an electric field in a direction parallel to the o-light or e-light photoelectric vector to independently adjust the frequency of one of the polarized lights; the first piezoelectric ceramic PZT 12 is combined with the first electro-optical crystal 10 to simultaneously adjust the two laser frequencies.

[0030] Here, titanium sapphire crystal is used as the gain medium, which can generate sufficiently high gain at 759 nm and 813 nm at the same time. Piezoelectric ceramic PZT (Lead Zirconate Titanate) and electro-optical crystal are used as frequency adjustment actuators to lock two laser frequencies simultaneously. PZT is lead zirconate titanate piezoelectric ceramic, where P is the abbreviation of lead element Pb, Z is the abbreviation of zirconium element Zr, and T is the abbreviation of titanium element Ti. PZT is a solid solution of PbZrO3 and PbTiO3, with a perovskite structure. PZT is a polycrystalline material formed by sintering lead dioxide, lead zirconate, and lead titanate at a high temperature of 1200 degrees, and has positive and negative piezoelectric effects. The cavity mirror is fixed on the PZT piezoelectric ceramic. When PZT expands and contracts, micro-conversion occurs, which changes the cavity length of the laser cavity, thereby increasing its output power or stabilizing the output frequency.

[0031] The working principle of the dual-frequency laser applicable to the dual-mode optical lattice atomic clock provided by the embodiment of the present invention is as follows: to achieve dual-wavelength output, a birefringent crystal whose optical axis is at an angle of 45 degrees to the light incident surface is placed in the cavity, so that ordinary light (o light) and extraordinary light (e light) propagation paths are generated in the same cavity, forming two eigenmodes. Since the e light has a lateral walk-off relative to the o light in the gain crystal optical path, the gains of the two eigenmodes are spatially separated to avoid mode competition, thereby obtaining stable dual-wavelength oscillations. In addition, the polarizations of the o light and the e light are perpendicular to each other, so an electro-optical crystal can be inserted into the cavity, and the frequency of one of the polarized lights can be independently adjusted by applying an electric field in a direction parallel to the o light or the e photoelectric vector, and then combined with the piezoelectric ceramic PZT, the frequencies of the two lasers can be locked simultaneously.

[0032] Traditional optical lattice atomic clocks use independent single-wavelength lasers to achieve laser cooling of atoms and optical lattice trapping. The system is relatively complex and large, and the cost is high. Dual-mode optical lattice atomic clocks involve more complex laser systems. The present invention reduces the complexity of the system through the method of co-cavity and co-pumping.

[0033] In some possible embodiments, the beam splitter assembly includes two focusing lenses and a wedge-shaped prism. The wedge-shaped prism is inserted into the optical path of the pump light and generates a double light beam that shares the same lens imaging system by refracting half the cross-sectional area of ​​the collimated light.

[0034] Here, the present invention uses a high-power 532nm dual-beam laser for pumping, wherein the dual beams are generated by a wedge-shaped prism refracting half the cross-sectional area of ​​the collimated light, so that the two beams are generated by the same laser and share the same lens imaging system. By adjusting the angle of insertion of the wedge-shaped prism, the two pump beams are matched with the oscillation mode in the cavity, and two orthogonally polarized intrinsic oscillation modes are obtained.

[0035] In some possible embodiments, the vibration modes in the cavity are roughly filtered by coating the optical interface in the cavity with overlapping spectral band edges, and the modes are finely selected using a set of birefringent filters and an etalon, so that the resonant cavity outputs dual-frequency lasers of specific wavelengths; wherein the anti-reflection films of the two birefringent filters respectively overlap with the spectral band edges of the high-reflection film of the concave reflector, so as to realize single-frequency operation of a specific wavelength in one polarization direction.

[0036] Here, since the gain bandwidth of the titanium sapphire crystal is very wide, how to achieve the required dual-frequency laser output of a specific wavelength is one of the technical difficulties. To this end, the embodiment of the present invention adopts a coating method of overlapping the spectral band edges on the intracavity optical interface to roughly filter the intracavity vibration mode, and uses a birefringent filter and an etalon to finely select the mode, such as Figure 2As shown in the figure, the spectral band of the anti-reflection film coated on the first birefringent filter overlaps with the spectral band of the high-reflection film coated on the first concave reflector, so that the loss in the narrow band centered at 759 nm is small, thereby achieving intracavity mode selection in the narrow band; at the same time, the first birefringent filter and the corresponding etalon are used to finely select the mode to achieve single-frequency operation of 795 nm wavelength in the polarization direction. Similarly, the edges of the anti-reflection film coated on the second birefringent filter and the high-reflection film coated on the first concave reflector overlap with each other, so that the loss in the narrow band centered at 813 nm is small. Combined with the second birefringent filter and the corresponding etalon, single-frequency operation of 813 nm in the polarization direction is achieved. Finally, the laser achieves dual-frequency output without mode hopping at 759 nm and 813 nm.

[0037] It is worth noting that titanium sapphire crystal has a very wide gain bandwidth and is prone to mode hopping. Therefore, it is difficult for the existing dual-frequency laser structure to achieve mode-hop-free tunable dual-frequency output using titanium sapphire as the gain crystal. The present invention uses independent birefringent filters and etalons, combined with a coating method that overlaps the spectral band edges, to achieve frequency-tunable dual-frequency output without mode hopping.

[0038] In some possible embodiments, the two birefringent filters are a first birefringent filter and a second birefringent filter; wherein the first birefringent filter is coated with a 600nm to 770nm anti-reflection film, the second birefringent filter is coated with an 800nm ​​to 1000nm anti-reflection film, and the concave reflector is coated with a 740nm to 830nm high-reflection film; the laser frequency is finely adjusted by the voltage between the piezoelectric ceramic PZT and the electro-optical crystal, so that the resonant cavity outputs dual-frequency lasers of 759nm and 813nm.

[0039] Here, the embodiment of the present invention uses independent birefringent filters and etalons, combined with a coating method that overlaps the spectral band edges, to achieve frequency-tunable dual-frequency output without mode hopping; on the basis of the above, the frequency locking of the dual-frequency laser is achieved by using an electro-optical crystal and piezoelectric ceramic PZT in the cavity, thereby meeting the requirements of atomic cooling and optical lattices for frequency certainty and stability. In this way, combined with the common cavity technology, high-power tunable 759nm and 813nm dual-frequency lasers are generated in the same cavity to enhance the compactness of the light source system.

[0040] In some possible embodiments, the laser further comprises another resonant cavity, the optical elements contained in the two resonant cavities are consistent and share the same pump light source; wherein the third birefringent filter in the other resonant cavity is coated with a 600nm to 810nm anti-reflection film, the fourth birefringent filter is coated with a 910nm to 1000nm anti-reflection film, and the concave reflector is coated with a 790nm to 930nm high-reflection film, and the mode is finely selected by adjusting the two birefringent filters and the two standards in the other resonant cavity, so that the other resonant cavity outputs a dual-frequency laser of 798nm and 922nm.

[0041] Here, on the basis of using one resonant cavity to output dual-frequency lasers of 759nm and 813nm, the second resonant cavity can be expanded to further generate dual-frequency lasers of 798nm and 922nm, which can be used for primary cooling, transverse cooling and Zeeman deceleration after frequency doubling. Therefore, four high-power lasers can be generated simultaneously using a single technology platform, such as Figure 3 As shown, it includes a 532nm pump light source 1, and a first beam splitter group 2, a first dichroic mirror 3, a first titanium sapphire crystal 4, a first birefringent filter 5 and a second birefringent filter 7, a first etalon 6 and a second etalon 8, a first birefringent crystal 9, a first electro-optical crystal 10, a first concave reflector 11 and a first piezoelectric ceramic PZT 12, wherein the first dichroic mirror 3 and the first concave reflector 11 form a resonant cavity, and another resonant cavity composed of the 532nm pump light source 1, a second beam splitter group 13, a second dichroic mirror 14, a second titanium sapphire crystal 15, a fourth birefringent filter 6 and a fourth birefringent filter 18, a third etalon 17 and a fourth etalon 19, a second birefringent crystal 20, a second electro-optical crystal 21, a second concave reflector 22 and a second piezoelectric ceramic PZT 23, thereby forming a "one pump, two cavities, four wavelengths" laser system, so as to significantly improve the compactness of the laser system.

[0042] In some possible embodiments, the power ratio between two pump light beams separated in the same resonant cavity and the power ratio between the corresponding dual-frequency lasers outputted therefrom are adjusted by adjusting the insertion depth of the wedge-shaped prism in the pump light path.

[0043] The dual-frequency laser applicable to the dual-mode optical lattice atomic clock is described below in conjunction with a specific embodiment. However, it should be noted that this specific embodiment is only for better illustrating the present invention and does not constitute an improper limitation to the present invention.

[0044] The embodiment of the present invention intends to use the common cavity technology to generate high-power tunable 759nm and 813nm dual-frequency lasers in the same cavity to enhance the compactness of the light source system. The structure is as follows Figure 1As shown. A high-power 532nm green laser is transmitted to the focusing lens group through an optical fiber, and a wedge prism is used to divide the beam into two spatially separated beams; through the calibration value, a single-mode oscillation is formed in the cavity; a YVO4 birefringent crystal is inserted into the cavity (the light-passing surface is at a 45-degree angle to the optical axis), and the angle of the wedge prism is adjusted to match the pump double beam with the oscillation mode in the cavity, and two orthogonally polarized intrinsic oscillation modes are obtained by pumping; birefringent filters and etalons are used for mode selection, the first birefringent filter is coated with a 600nm to 770nm anti-reflection film, the second birefringent filter is coated with an 800nm ​​to 1000nm anti-reflection film, and the first concave reflector is coated with a 740nm to 830nm high-reflection film; the laser frequency is finely adjusted by the voltage of the first piezoelectric ceramic PZT and the first electro-optical crystal, and a dual-frequency laser of 759nm and 813nm is output; finally, the first piezoelectric ceramic PZT and the first electro-optical crystal are used as frequency adjustment actuators for frequency locking.

[0045] Change the coating configuration: the first birefringent filter is coated with a 600nm to 810nm anti-reflection film, the second birefringent filter is coated with a 910nm to 1000nm anti-reflection film, the first concave reflector is coated with a 790nm to 930nm high-reflection film, and the birefringent filter is adjusted to output dual-frequency lasers of 798nm and 922nm.

[0046] Finally, the insertion depth of the wedge prism in the pump light path is adjusted to adjust the power ratio of the two pump light beams, thereby adjusting the power ratio in the output dual-frequency laser.

[0047] The key points of the dual-frequency laser provided by the embodiment of the present invention that can be applied to the dual-mode optical lattice atomic clock include but are not limited to: 1) The traditional optical lattice atomic clock uses an independent single-wavelength laser to achieve laser cooling and optical lattice trapping of atoms. The system is relatively complex and large, and the cost is high. The dual-mode optical lattice atomic clock involves more and more complex laser systems. The present invention reduces the complexity of the system through the method of common cavity and common pumping. 2) Since the titanium sapphire crystal has a very wide gain bandwidth, mode hopping is prone to occur. Therefore, it is difficult for the existing dual-frequency laser structure to achieve mode-hop-free tunable dual-frequency output with titanium sapphire as the gain crystal. The present invention uses independent birefringent filters and etalons, combined with a coating method with overlapping spectral band edges, to achieve frequency tunable and mode-hop-free dual-frequency output. 3) Based on the previous point, the frequency locking of the dual-frequency laser is achieved by using an intracavity electro-optical crystal and a piezoelectric ceramic PZT, thereby meeting the requirements of atomic cooling and optical lattice for frequency certainty and stability.

[0048] The dual-frequency laser applicable to a dual-mode optical lattice atomic clock provided by the embodiment of the present invention has the advantages of reduced system complexity and reduced system cost. In particular, the proposed "one pump, two cavities, four wavelengths" laser system significantly improves the compactness of the laser system.

[0049] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the present invention, the size of the serial number of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention. The serial numbers of the above-mentioned embodiments of the present invention are only for description and do not represent the advantages and disadvantages of the embodiments.

[0050] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0051] The above is only an embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A dual-frequency laser applicable to a dual-mode optical lattice atomic clock, characterized in that: It includes a 532nm pump light source, in which a beam splitter group, a dichroic mirror, a titanium sapphire crystal, a birefringent crystal, an electro-optical crystal, a concave reflector and a piezoelectric ceramic PZT are sequentially arranged in the emission light path of the pump light source, wherein the dichroic mirror and the concave reflector form a first resonant cavity to generate laser; Among them, the beam splitter group is used to split the collimated pump light beam into two spatially separated beams; the optical axis of the birefringent crystal forms an angle of 45 degrees with the light incident surface, which is used to generate o-light and e-light propagation paths in the same cavity to form two intrinsic modes; a group of birefringent filters and an etalon are respectively arranged on the o-light and e-light propagation paths, the anti-reflection film of the birefringent filter and the high-reflection film of the concave reflector have spectral bands with overlapping edges, which are used for coarse selection of laser output wavelengths; the etalon and the birefringent filter are combined to perform fine mode selection; the electro-optical crystal is used to apply an electric field in a direction parallel to the o-light or e-light photoelectric vector to independently adjust the frequency of one of the polarized lights; the piezoelectric ceramic PZT is combined with the electro-optical crystal to simultaneously adjust the frequencies of two lasers.

2. The dual frequency laser according to claim 1, characterized in that: The beam splitter group includes two focusing lenses and a wedge-shaped prism. The wedge-shaped prism is inserted into the optical path of the pump light and generates a double light beam that shares the same lens imaging system by refracting half the cross-sectional area of ​​the collimated light.

3. The dual frequency laser according to claim 1, characterized in that: The vibration mode in the cavity is roughly selected and filtered by coating the optical interface in the cavity with the spectral band edges overlapped, and the mode is finely selected by using the set of birefringent filters and the standard tool, so that the first resonant cavity outputs a dual-frequency laser of a specific wavelength; wherein the anti-reflection films of each of the two birefringent filters overlap with the spectral band edges of the high-reflection film of the concave reflector, respectively, to realize single-frequency operation of a specific wavelength in one polarization direction.

4. The dual frequency laser according to claim 3, characterized in that: The two birefringent filters are a first birefringent filter and a second birefringent filter; wherein, the first birefringent filter is coated with a 600nm to 770nm anti-reflection film, the second birefringent filter is coated with an 800nm ​​to 1000nm anti-reflection film, and the concave reflector is coated with a 740nm to 830nm high-reflection film; the laser frequency is finely adjusted by the voltage between the piezoelectric ceramic PZT and the electro-optical crystal, so that the first resonant cavity outputs a dual-frequency laser of 759nm and 813nm.

5. The dual frequency laser according to claim 4, characterized in that: The laser further comprises a second resonant cavity, the optical element contained in the second resonant cavity is consistent with that in the first resonant cavity, and the two resonant cavities share the same pump light source; The third birefringent filter in the second resonant cavity is coated with a 600nm to 810nm anti-reflection film, the fourth birefringent filter is coated with a 910nm to 1000nm anti-reflection film, and the concave reflector is coated with a 790nm to 930nm high-reflection film. The mode is finely selected by adjusting the two birefringent filters and the two standards in the second resonant cavity, so that the second resonant cavity outputs dual-frequency lasers of 798nm and 922nm.

6. The dual frequency laser according to claim 2, characterized in that: By adjusting the insertion depth of the wedge-shaped prism in the pump light path, the power ratio between the two pump light beams separated in each resonant cavity and the power ratio between the corresponding output dual-frequency lasers are adjusted.

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