Multiple variants of the Diode Pumped Alkali Laser (DPAL) have recently been demonstrated at the Air Force Research Laboratory (AFRL). Highlights of this ongoing research effort include: a) a 571W rubidium (Rb) based Master Oscillator Power Amplifier (MOPA) with a gain (2α) of 0.48 cm-1, b) a rubidium-cesium (Cs) Multi-Alkali Multi-Line (MAML) laser that simultaneously lases at both 795 nm and 895 nm, and c) a 1.5 kW resonantly pumped potassium (K) DPAL with a slope efficiency of 50%. The common factor among these experiments is the use of a flowing alkali test bed.
A metastable argon laser operating at 912 nm has been demonstrated by optically pumping with a pulsed titanium sapphire laser to investigate the temporal dynamics of an Advanced Noble Gas Laser (ANGL). Metastable argon concentrations on the order of 1011 cm-3 were maintained with the use of a radio frequency (RF) capacitively coupled discharge. The end-pumped laser produced output powers under 2 mW of average power with pulse lengths on the order of 100 ns. A comparison between empirical results and a four level laser model using longitudinally average pump and inter-cavity intensities is made. An alternative, highly-efficient method of argon metastable production for ANGL was explored using carbon nanotube (CNT) fibers.
High energy laser pulses were fired into a 365μm diameter fiber optic cable constrained in small radii of curvature
bends, resulting in a catastrophic failure. Q-switched laser pulses from a flashlamp pumped, Nd:YAG laser were injected
into the cables, and the spatial intensity profile at the exit face of the fiber was observed using an infrared camera. The
transmission of the radiation through the tight radii resulted in an asymmetric intensity profile with one half of the fiber
core having a higher peak-to-average energy distribution. Prior to testing, the cables were thermally conditioned while
constrained in the small radii of curvature bends. Single-bend, double-bend, and U-shaped geometries were tested to
characterize various cable routing scenarios.
Optically tunable pulse delays in cesium vapor were demonstrated by pumping several D2 transitions and burning holes
in the D1 absorption spectrum. A modified sub-Doppler absorption spectroscopy setup was used with counter
propagating beams with a Gaussian 7-ns full-width at half-maximum probe pulse is scanned across the D1 absorption
spectrum. Probe laser optical delays followed Kramers-Kronig model prediction for Cs D1 without D2 pump laser. Optical control of pulse delay was demonstrated by varying pump intensity. Localized delay effects in agreement with
model predictions were observed in the neighborhood of a burnt hole.
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