Small and Lightweight All-Solid-State Passively Q-Switched Laser for Deep-Space Exploration
Objective Deep-space exploration typically refers to the exploration of the moon and other extraterrestrial bodies.It is integral to space activities and allows humans to further understand the universe as well as explore the origin and evolution of matter and life.For deep-space detection,laser detection is used extensively as it offers good direction and strong anti-interference ability.In addition to offering high-precision detection,space lasers should be small and lightweight such that power consumption can be reduced and reliability can be increased.In deep-space exploration,the laser-detection load is limited primarily by volume,weight,and power consumption,thus necessitating micro laser devices.In this study,a small and lightweight passive Q-switched all-solid-state laser for deep-space exploration is introduced,and its prototype is developed.The laser output features a high repetition frequency,narrow pulse width,and high pulse energy.Additionally,the laser prototype is small,lightweight,and highly reliable,thus rendering it an ideal light source for deep-space exploration.Methods To achieve a small and lightweight laser structure,passive Q-switching was performed.By selecting Nd∶YAG as the gain medium and Cr∶YAG as the passive Q-switched crystal,the gain medium and passive Q-switched crystal were bonded to achieve an integrated resonator,which can not only miniaturize the laser structure but also form a short cavity structure to achieve a narrow pulse-width output.The laser was pumped using two single-tube COS(chip on submount)pulsed semiconductor lasers with a pulse repetition rate of 1 kHz and a central wavelength of 808 nm.The two semiconductor lasers were connected in series,which can significantly reduce the operating current of the pumped semiconductor laser and improve the reliability of the system.The temperature was precisely controlled via a TEC(thermo-electric cooler)to ensure the absorption efficiency of the pump light.The pumped LD(laser diode)output laser was collimated by fast-and slow-axis collimators and was focused into the laser gain medium through the focusing mirror.The fast-axis collimator is an aspherical cylindrical lens,whereas the slow-axis collimator is a flat convex cylindrical lens.The crystal was coated to form a resonator with a flat cavity structure and a physical cavity length of 11 mm.The 808 nm LD adopts the COS package and integrates the pumping LD with a laser optical-path structure,thereby affording laser integration and improving the reliability of the laser.COS packaging technology offers high integration and high reliability,thus rendering it suitable for space solid-state lasers with miniaturization and long-life requirements.Results and Discussions Under a pumping optical power of 2.16 W,a laser output with a monopulse energy of 172 μJ and a repetition frequency of 1 kHz is obtained.The laser output frequency is shown in Figure 5.Additionally,the laser was tested.Figure 6 shows the stability monitoring of the monopulse energy for a week.The mean value of the monopulse energy output by the laser is 172 μJ,and the standard deviation is 1.96 μJ.The root-mean-square of the monopulse-energy instability for one week is 1.1％.The obtained pulse waveform is shown in Figure 7.As shown,the pulse waveform is smooth and the pulse width is approximately 1.0 ns.The laser-beam quality factors are M2x=1.35 and M2y=1.27,as shown in Figure 8.The weight of the laser head,as measured using a balance,is 176.9 g(see Figure 9).Conclusions In this study,a small and lightweight passive Q-switched all-solid-state laser for deep-space exploration was introduced,and its prototype was developed.A Nd∶YAG/Cr∶YAG bonded crystal pumped using a laser diode was used to achieve a 1064 nm laser output.At the operating frequency of 1 kHz,the pulse width is 1.0 ns,the single-pulse energy is 172 μJ,and the single-pulse energy instability is 1.1％.The beam quality factors are M2x=1.35 and M2y=1.27.The COS packaging process was adopted for the machine,and the internal components and shell of the laser were welded with metal only.The size of the laser is 76.44 mm× 49.58 mm× 19.23 mm,which signifies a miniaturized laser;additionally,the weight of the laser is only 176.9 g.Thus,the laser is small,lightweight,and highly reliable,which renders it suitable as an ideal light source for deep-space exploration.
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