CN108110596B

CN108110596B - Alkali metal laser

Info

Publication number: CN108110596B
Application number: CN201711453483.0A
Authority: CN
Inventors: 王玉洁; 李志永; 谭荣清
Original assignee: Institute of Electronics of CAS
Current assignee: Institute of Electronics of CAS
Priority date: 2017-12-27
Filing date: 2017-12-27
Publication date: 2020-02-04
Anticipated expiration: 2037-12-27
Also published as: CN108110596A

Abstract

The present disclosure provides an alkali metal laser comprising: a semiconductor laser for outputting pump light; an alkali metal vapor cell comprising two parallel window sheets; and highly reflecting mirrors for reflecting alkali metal atoms²P_1/2→²S_1/2Transitioning the optical oscillation of the corresponding wavelength; wherein, the etalon effect between the two parallel window sheets is used as the laser output coupling element of the alkali metal laser to output alkali metal atoms²P_1/2→²S_1/2The transition corresponds to the wavelength of the laser light. The alkali metal laser disclosed by the invention utilizes the vapor chamber as the output coupling mirror, effectively avoids the insertion loss caused by the fact that the window sheet is not coated with a film, reduces the total loss of the resonant cavity, has no parasitic oscillation, overcomes the influence of no coating of the window on the power and efficiency of the DPAL, and can realize the DPAL with long service life.

Description

Alkali metal laser

Technical Field

The disclosure relates to the technical field of laser, in particular to an alkali metal laser with an uncoated inner surface of a vapor chamber as an output coupling surface.

Background

A semiconductor laser pumped alkali metal laser (DPAL) is a novel optical pumping gas laser, the gain medium of which is vapor alkali metal atoms, mainly potassium (K), rubidium (Rb) and cesium (Cs) vapor, the corresponding pumping light wavelengths are 766nm, 780nm and 852nm, and the output laser wavelengths are 770nm, 795nm and 895nm, respectively. The DPAL has high quantum efficiency, combines the advantages of a gas laser and a solid laser, and has the potential of good beam quality and ultrahigh power laser output.

The gain medium of DPAL is an alkali metal atom in the vapor state, located in group IA of the periodic table of elements, and is very chemically active. The laser wavelength of DPAL is in near infrared band, and the antireflection film material usually adopts fluoride and oxide, so under the action of high-temperature and high-power density laser, alkali metal atoms are easy to generate chemical reaction with the film material on the inner surface of the vapor chamber, which causes film failure and window pollution. At present, one of the methods for solving the problem is to make the inner surface of the vapor chamber not coated with a film and to make the pump light and the laser light incident normally.

At present, a DPAL resonant cavity generally consists of a plurality of lenses, laser feedback is realized according to the resonant cavity design theory of a laser, and the laser output power is improved. However, the existing DPAL still has the following technical drawbacks: an etalon of low sharpness is formed between the uncoated inner surfaces of the alkali metal vapor chambers, and parasitic oscillation is accompanied, thereby reducing the power of the main oscillation and the optical efficiency.

Disclosure of Invention

Technical problem to be solved

In view of the above technical problems, the present disclosure provides an alkali metal vapor laser using an uncoated inner surface of a vapor chamber as an output coupling surface, which is referred to as an alkali metal laser hereinafter, and the vapor chamber is used as an output coupling mirror, thereby effectively avoiding insertion loss caused by uncoated window pieces, reducing total loss of a resonant cavity, avoiding parasitic oscillation, overcoming the influence of uncoated window on DPAL power and efficiency, and realizing a long-life DPAL.

(II) technical scheme

According to an aspect of the present disclosure, there is provided an alkali metal laser including: a semiconductor laser for outputting pump light; an alkali metal vapor cell comprising two parallel window sheets; and highly reflecting mirrors for reflecting alkali metal atoms²P_1/2→²S_1/2Transitioning the optical oscillation of the corresponding wavelength; wherein, the etalon effect between the two parallel window sheets is used as the laser output coupling element of the alkali metal laser to output alkali metal atoms²P_1/2→²S_1/2The transition corresponds to the wavelength of the laser light.

In some embodiments, the alkali metal laser further includes a focusing lens for focusing the pump light such that a beam waist position of the focused pump light is located at a central position of the alkali metal vapor chamber.

In some embodiments, the alkali metal vapor chamber contains an alkali metal simple substance and a buffer gas, and the particle number reversal of the upper and lower energy levels of the alkali metal atom laser is realized after the focused laser pumping.

In some embodiments, the temperature of the alkali metal vapor chamber is from 100 ℃ to 200 ℃; the buffer gas is methane, ethane or helium.

In some embodiments, the outer surfaces of the two parallel window pieces are coated with antireflection coatings.

In some embodiments, the non-parallelism between the opposing inner surfaces of the two parallel window pieces is less than 1 mrad.

In some embodiments, the window sheet is made of quartz glass or sapphire.

In some embodiments, the high reflector has a reflectivity of greater than 99% at the laser wavelength of the DPAL for forming a resonant cavity of an alkali metal laser with an inner surface of a window piece of the vapor chamber.

In some embodiments, the semiconductor laser has a wavelength aligned with the wavelength of the alkali metal D2 line of the DPAL working substance and a linewidth of less than 0.1 nm.

In some embodiments, the alkali metal laser is an end-pumped DPAL or a side-pumped DPAL.

(III) advantageous effects

According to the technical scheme, the alkali metal laser with the uncoated inner surface of the vapor chamber as the output coupling surface has at least one of the following beneficial effects:

(1) the vapor chamber is used as an output coupling mirror, so that the insertion loss caused by the fact that the window sheet is not coated is effectively avoided, and the total loss of the resonant cavity is reduced.

(2) The lasing mode is selected by a single resonator, with no parasitic oscillation.

(3) The present disclosure overcomes the impact of window no-coating on DPAL power and efficiency, and can achieve a long-lived DPAL.

Drawings

The above and other objects, features and advantages of the present disclosure will become more apparent from the accompanying drawings. Like reference numerals refer to like parts throughout the drawings, which are not intended to be drawn to scale, emphasis instead being placed upon illustrating the principles of the disclosure.

Fig. 1 is a schematic diagram of an overall device of an end-pumped alkali metal laser according to an embodiment of the disclosure.

Fig. 2 is a graph showing the transmittance of a vapor cell in the rubidium laser region as a function of wavelength, in accordance with an embodiment of the present disclosure.

Fig. 3 is a schematic diagram of a side pumped vapor cell etalon effect based alkali metal laser according to an embodiment of the present disclosure.

< description of symbols >

1-semiconductor laser, 2-focusing lens, 3-high reflector, 4, alkali metal vapor chamber, 5-laser.

Detailed Description

For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.

It should be noted that in the drawings or description, the same drawing reference numerals are used for similar or identical parts. Implementations not depicted or described in the drawings are of a form known to those of ordinary skill in the art. Additionally, while exemplifications of parameters including particular values may be provided herein, it is to be understood that the parameters need not be exactly equal to the respective values, but may be approximated to the respective values within acceptable error margins or design constraints. Directional phrases used in the embodiments, such as "upper," "lower," "front," "rear," "left," "right," and the like, refer only to the orientation of the figure. Accordingly, the directional terminology used is intended to be in the nature of words of description rather than of limitation.

The etalon effect generated by two window sheets with uncoated inner surfaces of the vapor chamber is utilized, the window sheets of the vapor chamber are used as a laser output device and an output coupling mirror of the laser, the laser device is simplified, and the adverse effect of the uncoated inner surfaces of the vapor chamber is eliminated.

In an embodiment of the present disclosure, as shown in fig. 1, the alkali metal vapor laser includes: a narrow linewidth semiconductor laser 1, a focusing lens 2, a high reflection mirror 3, and an alkali metal vapor chamber 4. Specifically, a focusing lens, a high reflection mirror and an alkali metal vapor chamber are sequentially arranged behind the semiconductor laser by taking the propagation direction of the semiconductor laser beam as an optical axis.

The semiconductor laser outputs semiconductor laser, namely pump light, and the semiconductor laser is used as a DPAL (dual pumped laser) pump source after beam shaping, so that the population inversion between the upper energy level and the lower energy level of the alkali metal working substance laser is realized. Laser light output from the semiconductor laser is incident on the focusing lens. The wavelength of the semiconductor laser is aligned with the wavelength of the alkali metal D2 line of the DPAL working substance (i.e., the wavelength is the same), and the line width is typically less than 0.1 nm.

The focusing lens focuses the pump light for increasing the power density of the pump light. The light beam focused by the focusing lens is incident into the alkali metal vapor chamber, and the beam waist position where the focusing lens focuses the pump light is located near the center position of the alkali metal vapor chamber.

The alkali metal vapor chamber is filled with an alkali metal simple substance and buffer gas, is a working substance of the alkali metal vapor laser, and can realize the population inversion of the upper and lower energy levels of the alkali metal atom laser after the focused semiconductor laser pumping. The temperature of the alkali metal vapor chamber is typically 100 ℃ to 200 ℃ to provide the temperature and corresponding population concentration required for the operation of the alkali metal laser gain medium. The gas inside the alkali metal vapor chamber may be either flowing or static.

The alkali metal vapor chamber comprises two parallel window sheets which are sequentially arranged along the optical axis direction of the pump light, the outer surface and the inner surface of each window sheet are vertical to the optical axis direction of the pump light, the outer surface of each window sheet is plated with an antireflection film corresponding to the wavelength of the pump light and the wavelength of the laser light (the antireflection film has high transmittance for the wavelength band corresponding to the wavelength of the pump light and the wavelength of the laser light in the laser), and the inner surface of each window sheet is not plated with a film; and the parallelism between the inner surfaces is high, and the non-parallelism should be less than 1 mrad. The material of the window sheet can be quartz glass, sapphire and the like.

Another function of the alkali metal vapor cell is to output the DPAL laser as an output coupling mirror. The two window sheets of the alkali metal vapor chamber form an etalon with low sharpness, the reflectivity of the vapor chamber to laser is improved, a resonant cavity is formed by the etalon and the high reflection mirror, and DPAL laser is output, namely the etalon is used as an output coupling mirror. The vapor chamber is used as an output coupling mirror, so that the insertion loss caused by the fact that the window sheet is not coated with a film can be effectively avoided, and the total loss of the resonant cavity is reduced.

The high-reflectivity mirror has high reflectivity at DPAL laser wavelength, the reflectivity is generally more than 99%, and the high-reflectivity mirror is used for forming a resonant cavity of alkali metal laser with the inner surface of the vapor chamber and reflecting alkali metal atoms²P_1/2→²S_1/2The transition corresponds to the optical oscillation of the wavelength. The laser mode of the present disclosure is selected by a single resonant cavity, with no parasitic oscillation. In the laser device shown in fig. 1, the external dimension is smaller than the size of the pump light at the position of the lens, and is generally smaller than 1/5 of the spot diameter of the pump light. Under the size proportion, the pump light can be ensured to have higher utilization rate.

The alkali metal vapor chamber outputs alkali metal atoms by using etalon effect between two parallel window sheets as a laser output coupling element²P_1/2→²S_1/2The transition corresponds to the wavelength of the laser light 5.

The alkali metal laser of this embodiment will be described in detail below by taking a rubidium vapor chamber as an example.

The semiconductor laser outputs semiconductor laser with the wavelength of 780.02nm and the line width of 0.12nm in the air, and the semiconductor laser is used for pumping a rubidium vapor chamber to realize the population inversion between the upper energy level and the lower energy level of the rubidium laser. The light beam output from the semiconductor laser is incident on the focusing lens.

The focusing lens focuses the pump light, the focal length is 75mm, the clear aperture is 50mm, the semiconductor laser beam is focused, the power density of the pump light is improved, and the diameter of a focused focal point is 0.75 mm. The light beam focused by the focusing lens is incident into the rubidium vapor chamber, and the focus is near the center of the rubidium vapor chamber.

The rubidium vapor chamber is filled with rubidium and methane, and is the working substance of the rubidium laser. The methane pressure was 80 kPa. After being pumped by the focused semiconductor laser, the population inversion of the upper and lower energy levels of the rubidium DPAL laser can be realized. The temperature of the Rb vapor chamber was 165 ℃ to provide the temperature and corresponding population concentration required for Rb-DPAL operation. The outer surface of the rubidium vapor chamber is plated with an anti-reflection film with the thickness of 795nm, and the transmittance of the outer surface through single permeation is higher than 99%. The wedge angle between the inner surfaces of the rubidium steam chamber is 1mrad, and the rubidium steam chamber has higher parallelism. The window material is quartz glass. The length between the inner surfaces of the rubidium steam chamber is 8mm, and the diameter of the window sheet is 20 mm.

The case of a rubidium vapor chamber with an uncoated inner surface as a DPAL output mirror is as follows. The change in transmittance caused by the etalon formed between the uncoated inner surfaces can be represented by the following equation:

in the formula (1), R is the single reflectivity of the inner surface to the laser light. For quartz glass, R is 5%. λ is the laser wavelength. d is the distance between the inner surfaces of the vapor chamber and is 8 mm. F is the sharpness of the etalon, 0.22, i.e., the etalon formed between the two internal surfaces has a low sharpness characteristic.

The transmittance of the vapor chamber having no inner surface coating film in the wavelength range of λ around 795nm is shown in FIG. 2 by the above equation (1).

At the wavelength of the rubidium D1 line (DPAL laser), the transmittance was 87.8%. Thus, the vapor cell with the inner surface uncoated increases the reflectivity to the laser wavelength under the etalon effect. In the present disclosure, the output coupling mirror is used.

The high-reflection mirror has high reflectivity at 795nm, the reflectivity is more than 99%, and the high-reflection mirror is used for forming a resonant cavity of the alkali metal laser with the inner surface of the vapor chamber. In the device shown in FIG. 1, the spot size of the pump light is 20X 20mm at the position of the high reflection mirror²The diameter of the high reflector is 2 mm. The diameter of the high reflector is about 1/10 of the pump light spot, and 1/5, 99% of the pump light which is smaller than the diameter of the pump light spot is incident into the rubidium vapor chamber through the high reflector.

In another embodiment of the present disclosure, the difference from the previous embodiment is that the alkali metal laser in the previous embodiment is an end-pumped DPAL, while the alkali metal laser in the present embodiment is a side-pumped DPAL, and the incident directions of the pump lights are different, and the device structure is shown in fig. 3. Specifically, the semiconductor laser side pumping may be from a single direction or may be from multiple directions. The vapor chamber acts as an output coupling mirror for the laser.

In summary, the alkali metal laser disclosed by the invention overcomes the influence of no film coating of the window on the power and efficiency of the DPAL, and can realize the DPAL with long service life.

So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. From the above description, those skilled in the art should clearly recognize that the alkali metal laser of the present disclosure is applicable.

It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. In addition, the above definitions of the various elements are not limited to the specific structures, shapes or modes mentioned in the embodiments, and those skilled in the art may easily modify or replace them:

(1) the focusing lens of the present disclosure may also have other focal lengths and sizes that enable focusing of the semiconductor laser, for increasing the power density of the semiconductor laser.

(2) In the case of side-pumped DPAL, the pump light can also be directly guided into the alkali metal vapor chamber without a focusing lens, and the laser light is output on the inner surface of the vapor chamber without coating.

(3) The alkali metal vapor cell of the present disclosure may also be a potassium vapor cell or a cesium vapor cell. The high-reflection mirror is plated with high-reflection films at 770nm or 895nm respectively, and the reflectivity is higher than 99%.

(4) The gas in the alkali metal vapor chamber can also flow, and the gain medium flows to effectively reduce thermal deposition without influencing the output of laser on the inner surface of the vapor chamber without coating.

(5) The buffer gas of the alkali metal vapor chamber can also be alkane gases such as methane, ethane and the like, the gas pressure of the buffer gas can also be other values, and only the etalon formed by the vapor chamber needs to be ensured to have higher reflectivity to the buffer gas and the fluorescence spectrum under the proportion, so that the laser output can be realized.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims

1. An alkali metal laser comprising:

a semiconductor laser for outputting pump light;

the alkali metal vapor chamber comprises two parallel window sheets, wherein the outer surfaces of the two parallel window sheets are plated with antireflection films; and

highly reflecting mirrors for reflecting alkali metal atoms²P_1/2→²S_1/2The reflection rate of the high reflector at the laser wavelength of DPAL is more than 99%, and the high reflector and the inner surface of the window sheet of the vapor chamber form a resonant cavity of an alkali metal laser;

wherein, the etalon effect between the two parallel window sheets is used as the laser output coupling element of the alkali metal laser to output alkali metal atoms²P_1/2→²S_1/2The transition corresponds to the wavelength of the laser light.

2. The alkali metal laser as claimed in claim 1, further comprising a focusing lens for focusing the pump light such that a beam waist position of the focused pump light is located at a central position of the alkali metal vapor cell.

3. The alkali metal laser as claimed in claim 2, wherein the alkali metal vapor chamber contains an alkali metal simple substance and a buffer gas, and the particle count inversion of the upper and lower levels of the alkali metal atom laser is realized after the focused laser pumping.

4. The alkali metal laser according to claim 3, wherein the temperature of the alkali metal vapor chamber is 100 ℃ to 200 ℃; the buffer gas is methane, ethane or helium.

5. The alkali laser of claim 1, wherein the non-parallelism between the opposing inner surfaces of the two parallel window pieces is less than 1 mrad.

6. The alkali metal laser of claim 1, wherein the window piece is made of quartz glass or sapphire.

7. The alkali metal laser of claim 1, wherein the wavelength of the semiconductor laser is aligned to the alkali metal D2 line wavelength of the DPAL working substance with a line width of less than 0.1 nm.

8. The alkali metal laser of claim 1, wherein the alkali metal laser is an end-pumped DPAL or a side-pumped DPAL.