A compact long-cavity-path multi-pumping alkali laser

Abstract

The application discloses a compact long-cavity-path multi-path pumped alkali laser, which comprises a cross-flow alkali metal vapor cell, an alkali laser resonant cavity mirror, at least two 45-degree dichroic mirrors and a semiconductor laser pumping source, the cross-flow alkali metal vapor cell is used for providing a gain medium for the alkali laser, the alkali laser resonant cavity mirror is used for forming a laser resonant cavity and selecting a mode, the 45-degree dichroic mirror is used for folding and separating a pumping beam and a laser beam, and the semiconductor laser pumping source is a narrow-wavelength semiconductor laser adopting a line width compression technology, which is used for exciting alkali metal vapor atoms, forming population inversion and being one of three elements of laser. The compact long-cavity-path multi-path pumped alkali laser scheme disclosed by the application can select a proper number of pumping modules according to power level, volume and weight requirements of a laser system.

Description

Technical Field

[0001] This invention belongs to the field of alkali metal laser technology and relates to a compact long cavity path multi-pumped alkali metal laser. Background Technology

[0002] Currently, the laser gain medium and optical windows of rare-earth ion-doped solid-state or fiber lasers and gas lasers have low laser damage resistance thresholds, making them highly susceptible to damage during high-power laser pumping. This limits the single-tube output power of the laser to some extent. To obtain higher-power laser sources, multiple gain medium schemes, such as beam combining and laser master oscillation amplification, are typically employed.

[0003] The seed stage and amplification stage of a high-power laser master oscillator amplification system typically use separate solid or optical fibers as gain media. The optical path of the system is difficult to assemble and adjust, and the heat dissipation equipment is required to be high and complex. The system generates a lot of heat. As the output power increases, the more heat dissipation equipment the amplification system has and the higher the heat dissipation power, resulting in a large system size and weight, a low system energy-to-weight ratio, and difficulty in mounting it on a mobile platform for engineering applications.

[0004] Alkali metal lasers are three-level lasers that utilize alkali metal vapor as the gain medium and narrow-linewidth semiconductor lasers as the pump source. They are also often referred to as semiconductor laser-pumped alkali lasers (DPAL). Due to a series of outstanding advantages, including high Stokes efficiency, low heat generation, good beam quality, compact structure, non-toxic laser medium, low cost and high reusability of the vapor pool, high system reliability, and laser wavelengths (potassium (K): 770.11 nm; rubidium (Rb): 794.98 nm; cesium (Cs): 894.95 nm) falling within the atmospheric window, alkali metal lasers are considered a reliable, high energy-to-weight ratio, compact, high average power (≥1 MW) laser source.

[0005] However, due to the low thermal conductivity of the mixed gas (composed of alkali metal vapor and buffer gas) within the alkali metal vapor cell, high-power laser pumping easily leads to the formation of localized high temperatures within the cell. This causes a rapid increase in the alkali metal vapor concentration, primarily manifested as a high particle number concentration in the third energy level (relaxation level) of alkali metal atoms. This directly reduces the absorption rate of the pump light by the vapor cell, further decreasing the optical-to-optical efficiency of the alkali metal laser. Simultaneously, high temperatures also cause thermal phenomena such as alkali metal consumption within the vapor cell, decreased laser power or even cessation of oscillation, contamination and damage to the vapor cell's optical window. Therefore, timely removal of the heat generated within the alkali metal vapor cell during high-power laser pumping, preventing photochemical reactions, alkali metal consumption, thermal effects, and vapor cell damage caused by localized high temperatures, is one of the main problems urgently needing to be solved in high-power alkali metal laser development. Summary of the Invention

[0006] (I) Purpose of the Invention

[0007] The purpose of this invention is to address the current situation where high-power laser sources have low energy-to-weight ratios and large size and weight, making them difficult to mount on mobile platforms for engineering applications. This invention proposes a compact long-cavity multi-pump alkali metal laser, aiming to solve the problems of complex structure, difficult optical assembly and adjustment, large size, low energy-to-weight ratio, and difficulty in mounting on mobile platforms for engineering applications in high-power laser systems using discrete gain media.

[0008] (II) Technical Solution

[0009] To address the aforementioned technical problems, this invention provides a compact long-cavity multi-channel pumped alkali metal laser.

[0010] This invention employs a single cross-flow alkali metal vapor cell to provide multi-stage independently pumpable gain media, reducing the pump pressure of high-power alkali metal laser systems, increasing single-tube output power, avoiding the large size disadvantage of traditional discrete gain media layouts in high-power laser systems, and greatly improving the energy-to-weight ratio of high-power alkali metal laser systems. It is very suitable for engineering applications mounted on mobile platforms. At the same time, the use of a cross-flow alkali metal vapor cell allows the mixed gas inside the cell to flow, avoiding local high-temperature phenomena and improving the stability of the alkali metal laser.

[0011] The compact long-cavity multi-pumped alkali metal laser of the present invention includes: a semiconductor laser pump source 1, a pump laser beam 2, a laser total reflection mirror 3, an optical window 4, a 45° dichroic mirror 5, a laser beam 6, a laser output coupling mirror 7, and a transverse flow alkali metal vapor cell 8.

[0012] Among them, the semiconductor laser pump source 1 uses linewidth narrowing technology to obtain a pump laser with a narrower frequency linewidth, so as to improve the utilization rate of pump light. In addition, multiple pump modules are provided according to the number of optical windows 4 set on the cross-flow vapor pool 8 to excite alkali metal vapor in the corresponding optical window group, thereby improving the single tube pump limit.

[0013] The pump laser beam 2 is generated by the semiconductor laser pump source 1 and transmitted to the transverse alkali metal vapor pool 8 through a beam shaping system composed of optical lenses. The pump alkali metal vapor atoms form stimulated radiation and generate alkali metal laser.

[0014] Among them, the laser total reflection mirror 3 and the output coupling mirror 7 constitute the laser resonant cavity mirror, which is one of the three essential elements for generating alkali metal lasers. Depending on the power level and pumping requirements of the alkali metal laser system, the two end surfaces of the laser total reflection mirror can be coated in two ways: The first is to coat one end surface with an anti-reflection coating with a center wavelength equal to the pump light wavelength, and the other end surface with both an anti-reflection coating with the pump light wavelength and a total reflection coating with a center wavelength equal to the laser wavelength. This method can be used to construct a laser resonant cavity and also to transmit pump lasers, suitable for higher power laser systems. The second method is to coat only one end surface of the mirror with a total reflection coating with a center wavelength equal to the laser wavelength, used only for constructing a laser resonant cavity.

[0015] The optical windows 4 are located at both end faces of the transverse flow alkali metal vapor cell 8, and at least two sets are included, for pumping and laser beam transmission. The central axis of any optical window 4 is parallel to the central axis of the transverse flow alkali metal vapor cell 8, and two optical windows 4 whose center-to-center line is parallel to the central axis of the transverse flow vapor cell 8 form an optical window group. The alkali metal vapor between each group of optical windows 4 constitutes the gain medium of the alkali metal laser system. By setting multiple sets of optical windows 4 in the transverse flow alkali metal vapor cell 8, the purpose of forming multiple gain media in a single vapor cell is achieved to enable multi-path pumping and improve gain and injected energy.

[0016] Among them, one end of the 45° dichroic mirror 5 is coated with a 45° incident total reflection film with a center wavelength of the laser wavelength and a 45° incident antireflection film with a center wavelength of the pump laser wavelength, and the other end is coated with a 45° incident antireflection film with a center wavelength of the pump laser wavelength, which is used to deflect the laser light path.

[0017] The laser beam 6 is provided by an alkali metal vapor pool 8 as a gain medium, a pump laser beam 2 provided by a semiconductor laser pump source as an excitation source, and a laser resonant cavity composed of a laser total reflection mirror 3 and a laser output coupling mirror 7, which ultimately produces an alkali metal laser with good beam quality and a narrow frequency linewidth.

[0018] The laser output coupling mirror 7 and the laser total reflection mirror 3 together constitute an alkali metal laser resonant cavity mirror, used for mode selection of alkali metal lasers. The end surface near the transverse flow alkali metal vapor cell 8 is coated with a reflective film with a center wavelength of the laser wavelength, and the other end surface is coated with an antireflective film with a center wavelength of the laser wavelength.

[0019] Among them, the cross-flow alkali metal vapor pool 8 is a container for containing alkali metal laser gain medium (composed of alkali metal vapor and buffer gas). It adopts a metal-glass composite structure. An internal fan drives the mixed gas in the vapor pool to flow in a cross-flow manner, avoiding the photochemical reaction, alkali metal consumption, laser power reduction, laser oscillation stoppage, and optical window damage caused by local high temperature in the vapor pool during high-power pumping. At least two sets of optical windows 4 are provided on its end face for pumping and laser beam transmission, and to increase the single tube injection power.

[0020] (III) Beneficial Effects

[0021] The compact, long-cavity, multi-channel pumped alkali metal laser provided by the above technical solution has the following beneficial effects:

[0022] (1) In this invention, the method of setting multiple optical windows in a single alkali metal vapor cell for multi-channel pumping is adopted, which improves the single-tube pumping capability of the alkali metal laser and can greatly improve the output power of the alkali metal laser.

[0023] (2) In this invention, the cross-flow alkali metal vapor pool adopts a flow heat dissipation layout, which can better homogenize the local temperature distribution of the laser field, reduce the thermal load pressure of the alkali metal laser, and improve the laser damage resistance threshold of the alkali metal laser.

[0024] (3) In this invention, a single alkali metal vapor cell can be used to achieve multi-channel pumping, making the structure of the alkali metal laser compact and giving it a high energy-to-weight ratio advantage.

[0025] (4) In this invention, potassium, rubidium, cesium and other gases can be injected into the alkali metal vapor pool at the same time to realize at least three different wavelengths of high-power alkali metal laser. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a compact, long-cavity, multi-pumped alkali metal laser (suitable for high-power alkali metal laser systems).

[0027] Figure 2 This is a schematic diagram of a compact, long-cavity, multi-pumped alkali metal laser (suitable for lower power alkali metal laser systems). Detailed Implementation

[0028] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0029] To address the issues of complex optical path assembly, large size and weight, low energy-to-weight ratio, and localized high temperature phenomena in the vapor pool of alkali metal vapor laser systems during high-power pumping in current solid-state or fiber laser master oscillator amplification systems, which suffer from the separate layout of gain media, a compact long-cavity multi-pumped alkali metal laser scheme is proposed, taking into account the high efficiency and low heat generation of alkali metal Stokes lasers. Figure 1 This is a schematic diagram of a compact, long-cavity, multi-pumped alkali metal laser suitable for higher power levels, related to embodiments of the present invention. Figure 2 This is a schematic diagram of a compact, long-cavity, multi-pumped alkali metal laser suitable for lower power levels, related to embodiments of the present invention.

[0030] This embodiment of a compact long-cavity multi-pumped alkali metal laser includes: a semiconductor laser pump source 1, a pump laser beam 2, a laser total reflection mirror 3, an optical window 4, a 45° dichroic mirror 5, a laser beam 6, a laser output coupling mirror 7, and a transverse flow alkali metal vapor cell 8. Two sets of opposing optical windows 4 are provided on the transverse flow alkali metal vapor cell 8. On the outer sides of one set of optical windows 4, a laser total reflection mirror 3 and a 45° dichroic mirror 5 are respectively arranged. A semiconductor laser pump source 1 is arranged outside the laser total reflection mirror 3, and another semiconductor laser pump source 1 is arranged outside the 45° dichroic mirror 5. On the outer sides of the other set of optical windows 4, a laser output coupling mirror 7 and another 45° dichroic mirror 5 are respectively arranged. A semiconductor laser pump source 1 is arranged outside the 45° dichroic mirror 5.

[0031] The semiconductor laser pump source 1 serves as the pump source for an alkali metal vapor laser, used to generate alkali metal lasers. Generally, semiconductor lasers have a wide wavelength linewidth, requiring additional linewidth narrowing techniques to match the wavelength linewidth of the semiconductor laser pump source with the linewidth of the D2 line broadened by the buffer gas in the vapor cell, thereby improving the utilization rate of the pump laser.

[0032] The pump laser beam 2 is generated by the semiconductor laser source 1. The beam spot in its geometric space should be subjected to beam shaping processing to improve the mode matching efficiency of the pump light and the laser, and increase the optical-optical efficiency of the laser system.

[0033] The laser total reflection mirror 3 serves as a laser resonant cavity mirror for generating alkali metal lasers. Its surface near the pump laser source is coated with an anti-reflection film with a center wavelength equal to the pump laser wavelength, while the other end is coated with both an anti-reflection film with the pump laser wavelength and a total reflection film with a center wavelength equal to the laser wavelength. Its usage is as follows: Figure 1As shown, this is suitable for alkali metal laser systems with higher power levels. Alternatively, systems such as... Figure 2 The method shown requires only one end face to be coated with a broadband total reflection film with a center wavelength equal to the pump light and laser wavelength, making it suitable for alkali metal laser systems with lower power levels.

[0034] The optical windows 4 are located at both ends of the cross-flow alkali metal vapor cell 8 and are used for the transmission of pump light and laser light. At least two sets are included for multi-channel pumping to improve the injection power of a single tube. Special attention should be paid to sealing the optical windows to the cross-flow alkali metal vapor cell to prevent impurities such as oxygen and water vapor from entering the cavity and to prevent leakage of the mixed gas inside the cavity, which could lead to oxidation of the alkali metal and affect the performance of the laser system. Generally, the ultimate vacuum at the sealed optical window should be <10⁻³ Pa.

[0035] The 45° dichroic mirror 5 is used to fold the pump light and laser light path. One end of its surface is coated with a 45° incident antireflection film with a center wavelength of the pump laser wavelength, and the other end of its surface is coated with a 45° antireflection film with a center wavelength of the pump laser wavelength and a 45° incident total reflection film with a center wavelength of the laser wavelength.

[0036] The laser beam 6 is generated by the semiconductor laser pump source 1 exciting the gain medium in the transverse flow alkali metal vapor pool 8, and then selecting the laser mode through the laser resonant cavity composed of the laser total reflection mirror 3 and the laser output coupling mirror 7.

[0037] The laser output coupling mirror 7 serves as a laser resonant cavity mirror for generating alkali metal lasers. One end of the mirror, which is close to the transverse flow alkali metal vapor pool 8, is coated with a reflective film with a center wavelength equal to the laser wavelength and a high reflective film with a pump laser wavelength. The other end is coated with an anti-reflective film with a center wavelength equal to the laser wavelength.

[0038] The cross-flow alkali metal vapor cell 8 adopts a metal-glass composite structure. An internal fan drives the mixed gas within the vapor cell to flow in a cross-flow manner, homogenizing the internal temperature field, reducing temperature differences, lowering the maximum temperature, and preventing thermal phenomena such as photochemical reactions, alkali metal consumption, laser power reduction or even oscillation cessation, optical window contamination or damage, and low beam quality that may occur during high-power pumping. The vapor cell cavity should avoid using components that release oil fumes. The sealing performance of all seals should be considered in light of the impact of high-temperature corrosive environments, with particular attention to the sealing performance of the internal fan. It should be ensured that under high-temperature, high-speed operation, there will be no gas leakage or oil fumes affecting the cavity's airtightness and the laser system's performance.

[0039] The mixed gas consists of alkali metal vapor and a buffer gas. The alkali metal vapor is usually potassium vapor, rubidium vapor, cesium vapor, or the above-mentioned mixed gas. The buffer gas can be methane, ethane, helium, argon, or a mixture of the above-mentioned gases.

[0040] In this embodiment, the pump laser beam emitted by a module of the semiconductor laser pump source 1, which has undergone linewidth narrowing, is beam shaped to form a pump laser beam 2. The beam is then transmitted through a laser total reflection mirror 3 or a 45° dichroic mirror 5, and reaches and passes through the optical window 4 of the transverse flow alkali metal vapor pool 8, pumping the alkali metal vapor atoms in the transverse flow alkali metal vapor pool 8 to form a population inversion.

[0041] After population inversion, the alkali metal vapor atoms emit photons, which are amplified by the laser resonant cavity composed of the laser total reflection mirror 3 and the laser output coupling mirror 7, and finally form the laser beam 6. Depending on the laser output power level, the single-tube output power of the laser system can be increased by appropriately increasing the number of optical windows 4 on the transverse flow alkali metal vapor cell 8, combined with the 45° dichroic mirror 5, to increase the number of pump lasers and improve the single-tube output power of the laser system.

[0042] As can be seen from the above technical solution, the present invention has the following significant features:

[0043] 1. The compact long cavity path multi-pumped alkali metal laser proposed in this invention improves the single-tube pump power of the laser system by setting multiple optical windows on a cross-flow alkali metal vapor cell, avoiding the use of a separate gain medium layout, and has the characteristics of simple optical path assembly and adjustment, compact structure and high energy-to-weight ratio.

[0044] 2. The cross-flow alkali metal vapor cell of the compact long cavity multi-channel pumped alkali metal laser proposed in this invention adopts a metal-glass composite structure, which can arbitrarily change the type and proportion of atmosphere in the vapor cell, and the system optimization has low cost and short time consumption.

[0045] 3. The compact long cavity multi-pump alkali metal laser proposed in this invention can simultaneously achieve high-power alkali metal laser output of multiple wavelengths. The cross-flow alkali metal vapor pool can be simultaneously injected with mixed alkali metal vapors containing potassium, rubidium, cesium, etc., and can achieve high-power alkali metal lasers of at least three wavelengths.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A compact long-cavity multi-pump alkali metal laser, characterized in that, include: The system comprises a semiconductor laser pump source, a pump laser beam, a laser total reflection mirror, an optical window, a 45° dichroic mirror, a laser output coupler, and a transverse flow alkali metal vapor cell. At least two sets of optical windows are provided on the transverse flow alkali metal vapor cell. One set of optical windows has a 45° dichroic mirror and a laser output coupler arranged on both sides of its two sides, while the other set of optical windows has a laser total reflection mirror and a 45° dichroic mirror arranged on both sides of its two sides. All 45° dichroic mirrors are located on the same side of the transverse flow alkali metal vapor cell, and a semiconductor laser pump source is arranged on the outside of each 45° dichroic mirror. A semiconductor laser pump source is arranged on the outer side of the laser total reflection mirror corresponding to the other optical window sides. The pump laser beam emitted by one module of the semiconductor laser pump source is shaped into a pump laser beam, which is transmitted through a laser total reflection mirror (3) or a 45° dichroic mirror, and reaches and passes through the optical window of the transverse flow alkali metal vapor pool to pump the alkali metal vapor atoms in the transverse flow alkali metal vapor pool, thereby forming a population inversion. After the alkali metal vapor atoms form population inversion, they emit photons, which are amplified by a laser resonant cavity composed of a laser total reflection mirror and a laser output coupling mirror, and finally form a laser beam.

2. The compact long-cavity multi-pump alkali metal laser as described in claim 1, characterized in that, The semiconductor laser pump source generates a pump laser beam, which is then transmitted to a transverse flow alkali metal vapor cell by a beam shaping system composed of optical lenses. This pumps alkali metal vapor atoms, resulting in stimulated emission and the generation of alkali metal laser.

3. The compact long-cavity multi-pump alkali metal laser as described in claim 2, characterized in that, The laser total reflection mirror and the output coupling mirror form a laser resonant cavity mirror, which generates alkali metal laser.

4. The compact long-cavity multi-pump alkali metal laser as described in claim 1, characterized in that, The surface of the laser total reflection mirror is coated with a total reflection film with a center wavelength of the laser wavelength, which is used to form a laser resonant cavity.

5. The compact long-cavity multi-pump alkali metal laser as described in claim 1, characterized in that, The laser total reflection mirror has an antireflection coating with a center wavelength of the pump light wavelength deposited on one side surface, and an antireflection coating with a center wavelength of the pump light wavelength and a total reflection coating with a center wavelength of the laser wavelength deposited on the other side surface.

6. The compact long-cavity multi-pump alkali metal laser as described in claim 4 or 5, characterized in that, The central axis of the optical window is parallel to the central axis of the cross-flow alkali metal vapor cell, and two optical windows whose center lines are parallel to the central axis of the cross-flow vapor cell form a group of optical windows. The alkali metal vapor between each group of optical windows constitutes the gain medium of the alkali metal laser system. By setting multiple groups of optical windows in the cross-flow alkali metal vapor cell, multiple gain media can be formed in a single vapor cell for multi-channel pumping.

7. The compact long-cavity multi-pump alkali metal laser as described in claim 6, characterized in that, The 45° dichroic mirror has a 45° incident total reflection film with a center wavelength of the laser wavelength and a 45° incident antireflection film with a center wavelength of the pump laser wavelength on one side surface, and a 45° incident antireflection film with a center wavelength of the pump laser wavelength on the other end surface, which is used to deflect the laser light path.

8. The compact long-cavity multi-pump alkali metal laser as described in claim 7, characterized in that, The laser output coupling mirror has a reflective film with a center wavelength of the laser wavelength deposited on the side surface near the cross-flow alkali metal vapor cell, and an anti-reflective film with a center wavelength of the laser wavelength deposited on the other end surface.

9. The compact long-cavity multi-pump alkali metal laser as described in claim 8, characterized in that, The cross-flow alkali metal vapor pool contains the alkali metal laser gain medium and adopts a metal-glass composite structure. An internal fan drives the mixed gas in the vapor pool to flow in a cross-flow manner.

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