Optically pumped rare gas lasers are being investigated as potential high-energy, high beam quality systems. The lasing medium consists of rare gas atoms (Rg=Ne, Ar, Kr, or Xe) that have been electric discharge excited to the metastable np5(n+1)s P32 state. Following optical excitation, helium (He) at pressures of 200-1000 Torr is used as the energy transfer agent to create a population inversion. The primary technical difficulty for this scheme is the discharge production of sufficient Rg* metastables in the presence of >200  Torr of He. In this Letter, we describe a pulsed discharge that yields >1013  cm-3Ar* in the presence of He at total pressures up to 750 Torr. Using this discharge, a diode-pumped Ar* laser providing 4.1 W has been demonstrated.

Three plasma discharge systems operating at pressures between 450 and 760 Torr are used to excite rare gas atoms and of particular interest to this work the metastable 6 s [ 3 2 ] 2 (Racah notation) state of xenon. This metastable state of rare gas atoms is of interest of due to its ability to operate as a ground level for a lasing scheme operating in the near infrared with the potential to be scaled to higher power. Spectroscopic measurements of the metastable xenon population densities and the spectral broadening of the 904.545 nm transition are presented.

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 10(11) 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.

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.

Pressure induced broadening and spectral shift rates have been resolved for the two ground state hyperfine lines in the 5(2)S(1/2) -> 6(2)P(1/2) and 5(2)S(1/2) -> 6(2)P(3/2) of Rb-85 and Rb-87 in the presence of 5-50 Tort of helium, argon, methane, and ethane. Broadening rates averaged over the hyperfine components, for the P-1/2 transition for He, Ar, CH4, and C2H6 are 60.2, 45.2, 63.8, and 60.4 MHz/Torr, respectively and 50.4, 42.4, 62.0, and 60.4 MHz/Torr for the P-3/2 transition. Average spectral shift rates for the P-1/2 transition were found to be 15.7, -11.5, -18.1, and -19.9 MHz/Tort for He, Ar, CH4, and C2H6, respectively, and 3.1, - 12.6,-21..8, and -19.9 MHz/Torr for the P-3/2 transition. Deviation in broadening and shift rates between hyperfine lines was found to be as high as 16 and 7.6 MHz/Torr respectively. Published by Elsevier Ltd.

Pressure induced broadening and spectral shift rates have been resolved for the two ground state hyperfine lines in the 52S1/2→62P1/2 and 52S1/2→62P3/2 of 85Rb and 87Rb in the presence of 5–50 Torr of helium, argon, methane, and ethane. Broadening rates averaged over the hyperfine components, for the P1/2 transition for He, Ar, CH4, and C2H6 are 60.2, 45.2, 63.8, and 60.4 MHz/Torr, respectively and 50.4, 42.4, 62.0, and 60.4 MHz/Torr for the P3/2 transition. Average spectral shift rates for the P1/2 transition were found to be 15.7, −11.5, −18.1, and −19.9 MHz/Torr for He, Ar, CH4, and C2H6, respectively, and 3.1, −12.6,−21.8, and −19.9 MHz/Torr for the P3/2 transition. Deviation in broadening and shift rates between hyperfine lines was found to be as high as 16 and 7.6 MHz/Torr respectively.

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.

Optical delays are observed for a pulse propagating through hot cesium vapor in the vicinity of peak absorption features. By tuning the pulse frequency across the absorption spectrum +/-20 GHz, delays up to 66 ns have been observed. In this experiment pulse delays are captured using a gated imaging camera system across the cesium D(2) spectrum and compared to delay predictions.