Diode Pumped Alkali Lasers (DPAL) are being scaled to powers of greater than 1 kW and intensities exceeding 30
kW/cm2. We have demonstrated a pulsed potassium laser with pump intensities of 1 MW/cm2 and efficiency exceeding 10%. At these higher pump intensities, nonlinear processes including two photon absorption and Stimulated Raman Scattering offer alternative wavelengths for these gas lasers. We have observed 1st and 2nd order Stokes and anti-Stokes lasing due to Stimulated Electronic Raman Scattering (SERS) in a potassium cell. When the pump is tuned about halfway between the fine structure levels of the 4 2P state, an efficient hyper-Raman process dominates. Up to 12 mW of red light is produced at a pump input of 232 mW. The threshold for the hyper-Raman process is about 60 mW. This type of laser may be useful for beam propagation experiments where a tunable probe beam spectrally close to the main beam is desired. Two-photon absorption at wavelengths near then DPAL pump transition has also been observed and used to demonstrate lasing in the blue and mid infrared. The transmission of a scanning cw ring laser through a static Rb cell reveals two-photon absorbance of greater than 10%. An absolute determination of the two-photon absorption crosssections for the Rb 5 2S – 4 2D transitions are reported. The efficiency and operationally feasible of these alternative
DPAL wavelengths is assessed.
A blue alkali laser operating by direct optical excitation of the 72P3/2 state of cesium is demonstrated. A mixture
of cesium vapor and various buffer gases (4He, CH4, C2H6) were pumped with the output of a pulsed dye laser
in a heated glass cell. The spin-orbit mixing and fluorescence quenching cross sections were calculated for each
buffer gas using the time-dependent D1 (459 nm) side fluorescence. At certain temperatures and buffer gas
pressures, a spatially coherent blue beam is produced in the forward direction. An analysis of the spectrum
shows this beam contains both D1 amplified spontaneous emission (ASE) and Stimulated Raman Scattering
A monolithic two-section quantum dot semiconductor laser is differentially pumped to form non-uniform current
injection in the gain region. We show that the nature of the spectral content in the output signal is affected by this
differential pumping; despite the fact that the separately pumped gain regions are not electrically isolated in this device.
Both negative (red-shift) and positive (blue-shift) spectral chirps were observed during mode-locked operation. It is also
demonstrated that mode locked operation is achieved with a much larger set of injection current / absorber bias voltage
pairs than was previously possible with single-pad current injection.
In this paper, two-section mode-locked lasers consisting of monolithic quantum dot gain and absorber
sections are studied as a function of absorber voltage, injected current to the gain region, and relative
section lengths. We map the regions of stable mode-locking as measured by the electrical and optical
spectra. A simple algorithm is presented that evaluates the quality of mode locking and allows automated
characterization of devices. The relative advantages of increasing the absorber length compared to
increasing the absorber reverse bias voltage are analyzed. Initial data indicate that doubling the absorber
length from 1.4 to 2.8-mm in a 5 GHz repetition rate device increases the region of stable mode-locking by
at least 25%, while increasing the absorber reverse bias can more than double the mode-locking regime.
Nonetheless, in these devices, stable mode-locking over greater than a 100 mA bias range is realized with a
grounded absorber making single bias control of a passively mode-locked semiconductor laser feasible.