Stable single-frequency all-solid state laser plays an important role in resonance fluorescence lidar.Owing to the advantages of compact and stable structure,all-solid single-frequency lasers have been developed rapidly in lidar vehicle-borne and airborne applications.Recently,a scheme for tripling 1 116 nm laser to obtain the light source for iron resonance fluorescence lidar has been developed.There is a neodymium-doped yttrium aluminum(Nd∶YAG)garnet emission line lies at 1 116 nm,which is within only a few gigahertz(GHz)of the tripled wavelength of the absorption line of iron at 372 nm.Therefore,the design of 1 116 nm single-frequency laser and the measurement of frequency characteristics is essential for iron lidar.We demonstrated a stable single-frequency 1 116 nm Nd∶YAG laser in this paper.An optimized ramp-fire scheme is applied to realize the seed injection and frequency jitter control.This single-frequency laser has a compact all-solid structure and a good stability to be as fundamental frequency applied in iron lidar.The 1 116 nm single-frequency laser system mainly includes three parts:a distributed feedback fiber laser as the 1 116 nm seed,a side-pumped Nd∶YAG straight-cavity slave laser and a detection-control system module.The fiber laser provides a stable 1 116 nm continuous laser with a spectral signal-to-noise ratio at 79 dB.A set of wave plates is placed between seed and slave cavity to adjust the polarization before entering slave cavity.The total cavity length is set to 54 cm with two piezoelectric transducers placed on two cavity mirrors.The detection-control system module detects the match degree between seed laser and slave cavity longitudinal mode while one piezoelectric transducer vibrating.When the interference between seed and the light reflected through the cavity reaches a maximum,detection-control system turns on the Q-switch and applies a direct current voltage to the other piezoelectric transducer to compensate for the nonlinear vibration.Then the 1 116 nm single-frequency pulse is established.The realization of 1 116 nm single-frequency laser is shown.The laser produces 6.48 mJ energy at 60 Hz repetition with a pulse width of 75.7 ns.The envelop of the pulse waveform becomes smooth after seed injection because only one longitudinal mode is established.After 24 hours' measurement,the mean energy is 6.48 mJ with a standard deviation of 0.25 mJ.The wavelength is measured by a WS-7 wavelength meter and the output wavelength is stable around 1 116.297 9 nm.In lidar detection,the frequency jitter of light source directly affects the systematic error in lidar detection.So the frequency characteristics are measured in detail by heterodyne beat frequency.The full width at half maximum of spectrum is 33.2 MHz and the center frequency stability(root mean square)is 818.3 kHz,corresponding less than 1 m/s error in wind speed measurement.In this study,a 1 116 nm single-frequency pulsed laser is designed and developed based on the seed injection technology,in which the Nd∶YAG laser is side-pumped by 808 nm LD array.The obtained pulse energy is 6.48 mJ at a repetition rate of 60 Hz,and the corresponding pulse duration is 75.7 ns.The standard deviation of the energy jitter is 0.25 mJ and the center frequency stability(root mean square)is 818.3 kHz.The laser's working stability meets the requirements of lidar detection.The 372 nm iron resonance fluorescence lidar light source can be obtained by frequency tripling 1 116 nm single-frequency laser.
Solid state laserSingle-frequency laserSeed injectionFrequency stabilityDoppler radar
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