Passive mode-locked cesium diode-pumped alkali laser.

A first, to the best of our knowledge, demonstration of passive mode-locking in diode-pumped alkali laser (DPAL) is reported in this paper. An intracavity cesium vapor cell, buffered by atmospheric pressure methane, is used to passively mode lock a continuously pumped cesium DPAL with a static gain medium. A train of short pulses with duration less than 460 ps was observed using a 2.0-GHz bandwidth detector that limited the real time duration measurements. The calculated minimum duration for these pulses is 57 ps.

Narrowband diode laser pump module for pumping alkali vapors.

We describe a method of line narrowing and frequency-locking a diode laser stack to an alkali atomic line for use as a pump module for Diode Pumped Alkali Lasers. The pump module consists of a 600 W antireflection coated diode laser stack configured to lase using an external cavity. The line narrowing and frequency locking is accomplished by introducing a narrowband polarization filter based on magneto-optical Faraday effect into the external cavity, which selectively transmits only the frequencies that are in resonance with the 62S1/2 → 62P3/2 transition of Cs atoms. The resulting pump module has demonstrated that a diode laser stack, which lases with a line width of 3 THz without narrowbanding, can be narrowed to 10 GHz. The line narrowed pump module produced 518 Watts that is 80% of the power generated by the original broadband diode laser stack.

Beam quality measurement of a static-cell cesium DPAL with a stable resonator.

We performed a measurement of the beam quality of an optimized moderate power cesium Diode Pumped Alkali Laser (DPAL). The DPAL used a stable resonator and operated in continuous wave mode using a static cell filled with metallic cesium and a mixture of methane and helium at 200 and 400 torr respectively. In this work, we characterized the spatial quality of the DPAL output beam. As a result of these experiments we determined the output beam quality was excellent (M2 < 1.2) in the whole range of pump power used (up to 11.5W) and pump intensities reaching 1.5 kW/cm2. The optical conversion efficiency of this laser was 51% and the slope efficiency was 61%.

Measurements of the gain medium temperature in an operating Cs DPAL.

A Mach-Zehnder interferometer was used for contactless measurement of the temperature of the gain medium within a static cell of Cs DPAL. The maximum temperature recorded approached 700° C leading to a significant degradation of laser performance. This work also examined lasing and non-lasing heat deposition and has shown that as much as 85% of the heating in a DPAL gain medium can be attributed to quenching.

Continuous wave Cs diode pumped alkali laser pumped by single emitter narrowband laser diode.

This paper presents results of cooperative efforts on development of a continuous wave Cs diode pumped alkali laser with moderate output power, which can be considered as a prototype of the commercial device. The developed system operates at 895 nm with output power about 4 W and slope efficiency 28%. Measured turn on time of this system from the standby mode is about a minute.

In situ non-perturbative temperature measurement in a Cs alkali laser.

The two-dimensional (2D) temperature profiles of an active-gain medium in a Cs + methane diode pumped alkali laser (DPAL) have been experimentally measured. This nonperturbative technique uses a Mach-Zehnder interferometer, which is longitudinally coupled into the cavity of an operating alkali laser to probe the distortion of the optical path length in the gain medium due to heating. The resulting interferograms are analyzed using the commercial program QuickFringe to quickly and accurately measure the distortion through which the temperature profile can be determined. For a 9 W Cs + methane DPAL being pumped with 20 W of resonant D2 light, a maximum temperature rise of 58°C is observed.

Photoionization in alkali lasers.

We have calculated photoionization rates in alkali lasers. The photoionization of alkali atoms in the gain medium of alkali lasers can significantly degrade the laser performance by reducing the neutral alkali density and with it the gain. For a ten atmosphere Rb laser and a Cs exciplex laser, the photoionization induced alkali atom loss rates are greater than 10(5) sec(-1). These high loss rates will quickly deplete the neutral alkali density, reducing gain, and may require fast, possibly, supersonic flow rates to sufficiently replenish the neutral medium for CW operation.

Cs laser with unstable cavity transversely pumped by multiple diode lasers.

We have demonstrated a Cs vapor laser with an unstable resonator transversely pumped by 15 narrowband laser diode arrays. A slope efficiency of 43%, a total optical efficiency of 31% and a maximum output power 49 W were obtained with a pump power of 157 Watts.

Frequency-doubling of a high power cesium vapor laser using a PPKTP crystal.

447.3 nm blue light generation was demonstrated through direct frequency doubling a continuous-wave Cesium vapor lasers 894.6 nm output using a PPKTP nonlinear crystal. The diode-pumped Cs vapor laser has an output power as large as 10 W with a very narrow emission linewidth less than 10 GHz. The PPKTP crystal is about 30 mm long and has a moderate acceptance wavelength bandwidth. The second harmonic wave generation efficiency achieved is about 4.4 %/W. Power depletion in second harmonic pulses, which relates to the absorption related thermal effects, was observed when using high pump power, long pulse duration, or high repetition rate.

Laser diode array pumped continuous wave Rubidium vapor laser.

We have demonstrated continuous wave operation of a laser diode array pumped Rb laser with an output power of 8 Watts. A slope efficiency of 60% and a total optical efficiency of 45% were obtained with a pump power of 18 Watts. This laser can be scaled to higher powers by using multiple laser diode arrays or stacks of arrays.