A diode-pumped Cr:LiSAF laser for UAV-based water vapor differential absorption lidar (DIAL)

Abstract

An autonomous, compact, high-energy, injection seeded, diode-pumped, tunable Cr:LiSAF laser for a water vapor differential absorption lidar (DIAL) system deployed on a highaltitude Unpiloted Airborne Vehicle (UAV) has been developed. A unique laser resonator, consisting of a Cr:LiSAF slab pumped by 8 high-power diode bar stacks in a total internal reflection configuration, provides high extraction efficiency and good laser beam quality. Output pulse energies of >35 mJ at 834 nm and 25 mJ at 816 nm, with pulse widths of -90 ns at 6 Hz pulse repetition rate, were obtained. A linewidth of less than 0.01 cm-' was achieved by injection seeding with an 816 nm DFB diode laser. Using a photo-acoustic cell (PAC), an innovative seeding system was utilized to lock the DFB laser wavelength to a water vapor absorption line and to consistently seed the slave laser at a desired wavelength within the absorption line. A high spectral purity (>99%) and excellent tuning performance were demonstrated. Water vapor profiles measured with a DIAL system utilizing this laser compare well with radiosonde data taken before and after the measurements.

Development of a widely tunable amplified diode laser differential absorption lidar for profiling atmospheric water vapor

“…They showed on-and off-line water vapor absorption profiles from the ground up to approximately 3 km, but the long time delay (~1 hour) between measurements prevented the retrieval of a DIAL profile. Prasad et al [31] describe a Cr:LiSAF laser for DIAL operation on a Unpiloted Airborne Vehicle (UAV), and show measurements from a breadboard system that have loose agreement with a regional radiosonde profile up to approximately 1.4 km.…”

“…Differential absorption lidar (DIAL) [7,[26][27][28] systems also are moving toward smaller size and lower-cost, which may someday allow deployment in unattended networks [5,[29][30][31][32][33][34]. DIAL measurements require measuring backscattered light at wavelengths on and off an absorption line, with wavelengths sufficiently close to each other that aerosol scattering and other systematic features of the measurement cancel in a ratio.…”

“…One promising avenue of research toward compact water vapor DIAL instruments is to use semiconductor laser transmitters [5,[29][30][31][32][33][34][35]. Diode lasers are compact, inexpensive, can be tuned readily, and have good spectral coverage in the near infrared spectral region where appropriate water vapor absorption lines exist.…”

Progress toward a water-vapor differential absorption lidar (DIAL) using a widely tunable amplified diode laser source

“…4,[23][24][25][26][27][28][29] Diode lasers are compact, inexpensive, can be tuned readily, and have good spectral coverage in the near infrared spectral region where appropriate water vapor absorption lines exist. In the early 1990s, the increased availability of high-power diode lasers and photon-counting avalanche photodiode detectors led to the proposal of diode DIAL systems for boundary layer water vapor profiling.…”

Mode referencing of an external cavity diode laser for continuous frequency stabilization

“…[1][2][3][4] However, depending on the type of device involved, control of the frequency-stabilizing mechanism may vary in complexity. For example, some widely tuneable sources with multisection architectures, such as the sampled-grating distributed Bragg reflector ͑SG-DBR͒ laser, require several current sources to drive the device, and very precise manipulation of these is required to control and stabilize the output emission wavelength.…”