Long range, combined UV-IR LIDAR system was built and tested. The system was developed to
operate as a multi-wavelength DIAL in the IR (8-11 μm), dual exciting wavelengths LIF LIDAR in the
UV, and aerosol map and track at 1.5 μm. The IR transmitter is a continuous tunable solid-state
Tandem Optical Parametric Oscillator (OPO) [1]. The first OPO stage generates the 1.5 μm beam and
the second OPO stage pumped by the first, generates the IR band. In the UV the transmitter generates
and transmits either the 266 nm or the 355 nm wavelengths sequentially. All the outgoing laser beams
are prealigned to ensure geometric overlap over the measured paths. Energy references are measured
for each beam on every pulse. The receiver is based on a single reflective telescope with coatings
optimized for both the UV and the IR. The optical signal is routed between the different detection
packages by means of a computerized optical scanner mirror. The receiver-transmitter layout is
based on periscope geometry and is equipped with a large θ-φ scanner. Computer control enables fast
switching between the different measurements and wavelengths, data acquisition and spatial scan as
well.
The system was built inside a mobile trailer and was field tested to descriminate aerosol types in a
complex enviroment [2].
The threshold fluence for laser induced damage in wide band gap dielectric materials, such as fused silica and MgF2, is observed to be lower by up to 20% for negatively (down) chirped pulses than for positively (up) chirped, at pulse durations ranging from 60 fs to 1 ps. This behavior of the threshold fluence for damage on the chirp direction was not observed in semiconductors, such as silicon and GaAs. Based on a model describing electron generation in the conduction band and Joule heating, it is suggested that the decrease in the damage threshold for negatively chirped pulse is related to the role of multiphoton ionization in wide gap materials.
We present a theoretical and experimental investigation of the efficiency, beam quality and signal bandwidth of a confocal, unstable OPO resonator. Reduction by more than 20 times of the divergence as well as bandwidth narrowing by factor of ~5 of the signal beam, in comparison to the plane-parallel resonator, are obtained. Resonator configurations have been found where the beam quality of the signal exceeds the beam quality of the pump.
A compact IR transmitter for the 8-12 micrometers atmospheric window is presented. The transmitter consists of two optical parametric oscillators (OPOs) in series, pumped by a 1.064 micrometers Nd:YAG laser. The first conversion stage is a double-pass non-critically phase-matched KTP OPO. A singly resonant configuration is used - the signal at 1.574 micrometers is resonated and coupled out with a 73 percent reflectivity output mirror. The first OPO's signal serves as a pump for a double-pass type I phase-matched AgGaSe2 OPO. This second OPO resonates the signal and couples out the idler at 8-11 micrometers . We eliminate high oscillating intensities inside the cavity by means of a low feedback. The low feedback causes a high threshold level, but have a minor influence on the total efficiency. Pumped by 6.5mJ at 1.574 micrometers , the AgGaSe2 OPO produced up to 0.5mJ at 8.5 micrometers , with beam quality of M2 equals 4-5 and spectral width of 4-5cm-1. Small physical dimensions, simplicity, and fairly good stability, makes this tandem OPO system usable for remote sensing applications. The described system is currently used for laboratory aerosol backscatter measurements.
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