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 three level analytic model for optically pumped alkali metal vapor lasers is developed by considering the steady state rate equations for the longitudinally averaged number densities of the ground 2S 1/2 and first excited 2P3/2, and 2P1/2 states. The threshold pump intensity includes both the requirements to fully bleach the pump transition and exceed optical losses, typically about 200 Watts/cm2. Slope efficiency depends critically on the fraction of incident photons absorbed. For efficient operation, the collisional relaxation between the two upper levels should be fast to prevent bottle-necking. By assuming a statistical distribution between the upper two levels, the limiting analytic solution for the quasi-two level system is achieved. The highly saturated pump limit of the recently developed three-level model for Diode Pumped Alkali Lasers (DPAL) is also developed. The model is anchored to several recent laser demonstrations. A rubidium laser pumped on the 5 2S1/2 – 5 2P3/2 D2 transition by a pulsed dye laser at pump intensities exceeding 3.5 MW/cm2 (< 1000 times threshold) has been demonstrated. Output energies as high as 12 μJ/pulse are limited by the rate for collision relaxation of the pumped 2P3/2 state to the upper laser 2P1/2 state. More than 250 photons are available for every rubidium atom in the pumped volume during each pulse. For modest alkali atom and ethane spin-orbit relaxer concentrations, the gain medium can only process about 50 photons/atom during the 2 – 8 ns pump pulse. At 110° C and 550 Torr of ethane, the system is bottlenecked. The system efficiency based on absorbed photons approaches 36% even for these extreme pump conditions. Furthermore, at 320°C with 2500 torr of helium, a pulsed potassium laser with 1.15 MW/cm2 peak intensity and 9.3% slope efficiency has been demonstrated.
Course Instructor
NON-SPIE: SYS 282 - Managing the Systems Engineering Process
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.