C. Rolland

Line‐tunable oscillation of a cw NH3 laser from 10.7 to 13.3 μm

A cw CO2 laser operating on the R(30) 9‐μm transition is down shifted by 180 MHz in a pair of acousto‐optic modulators, and used to optically pump sR(5,0) transition of NH3 at line center. Vibrational inversion is created in the ν2 mode, and cw oscillation is observed on 20 different NH3 lines, spanning the region between 10.7 and 13.3 μm. Single line output powers as high as 760 mW were measured in a waveguide cavity. The operation of this laser is explained using a simple thermalization model, and several potential applications are discussed.

cw optically pumped 12‐μm NH3 laser

A 30‐W cw CO2 laser operating on the R(30) 9‐μm transition is used to pump a ring laser cavity containing NH3. Emission at 12.08 μm is observed with cw output power of 180 mW. A Raman process is shown to be responsible for the gain at 12.08 μm.

10-W cw optically pumped 12-μm NH3 laser

A 37‐W cw CO2 laser operating on the R(30) 9‐μm transition is used to pump a linear waveguide cavity containing NH3. Raman emission at 12.08 μm is observed with a cw output power of 10.2 W. This performance represents a photon conversion efficiency of >40%, the highest yet reported for a cw optically pumped infrared laser.

Investigation of cw optically pumped 12-μm NH 3 lasers using a tunable diode laser

The small-signal gain of a cw optically pumped 12-μm NH3 system is investigated as a function of pump intensity, pressure, pump offset, and polarization using a tunable diode laser as a probe. In general, the experiment is found to be in good agreement with calculations based on the theory of two laser fields interacting with a three-level molecular system. Raman gains in excess of 3%/cm are obtained using a waveguide configuration. The significance of these findings is discussed in terms of designing an efficient and powerful cw 12-μm laser.

Tunable-diode-laser measurements of gain in optically pumped NH(3).

A tunable-diode laser is used for the first reported time to make gain measurements in a cw optically pumped 12-microm NH(3) amplifier. The tunability of the diode laser enables us to demonstrate that no inversion exists in the 12-microm laser and that Raman processes are responsible for the gain. High-sensitivity techniques allow gain coefficients as low as 0.001%/cm to be detected, and the experimental measurements are found to be in good agreement with theory.

Dynamics of the line-tunable 12-μm continuous-wave NH 3 laser as measured with a tunable-diode laser

A cw CO2 laser operating on the R(30) 9-μm transition is downshifted by 180 MHz in a pair of acousto-optic modulators to give an exact coincidence with the sR (5, 0) transition in NH3. The downshifted radiation optically pumps mixtures of NH3 in N2 and creates vibrational inversion in the ν2 mode of NH3. This inversion is monitored with a tunable-diode laser operating in the 11–12-μm region. Gain coefficients as large as 3.4%/cm are measured in the P branch of the ν2 band, and the measured gain coefficients are found to be in good agreement with a rate-equation model based on rotational thermalization. Detailed measurements of gain coefficients are presented as a function of NH3 transition, pump power, and gas mixture and pressure. These results will aid in the optimization of cw NH3 lasers operating in the 11–13-μm region.

Gain saturation in cw 12-μm NH 3 Raman lasers

An oscillator–amplifier technique is used to study gain saturation in cw 12.08-μm waveguide NH3 lasers. Population transfer in the NH3 ground state, rather than pump depletion, is shown to be the dominant mechanism for reduction of the Raman gain in this laser system. A model based on the density matrix formalism accounts for the main features of the experimental results and allows an effective rate to be determined for rotational relaxation in the ground state of NH3.