The design and performance of a laser diode pumped ruby laser is reported. The laser consists of a 5 mm long 0.05% doped ruby crystal placed within a hemispherical laser resonator. A single mode gallium nitride laser diode, operating at 405 nm provided up to 320 mW of pump power. Beam shaping optics were used to circularize the pump beam and a 150 mm focal length lens produced a ~20 μm waist in the crystal. The laser produced up to 44 mW of output power with a slope efficiency of 17%.
A frequency tripled, Nd:Glass laser has been constructed and installed at the Dynamic Compression Sector located at the Advanced Photon Source. This 100-J laser will be used to drive shocks in condensed matter which will then be interrogated by the facility x-ray beam. The laser is designed for reliable operation, utilizing proven designs for all major subsystems. A fiber front-end provides arbitrarily shaped pulses to the amplifier chain. A diode-pumped Nd:glass regenerative amplifier is followed by a four-pass, flashlamp- pumped rod amplifier. The regenerative amplifier produces up to 20 mJ with better than 1% RMS stability. The passively multiplexed four-pass amplifier produces up to 2 J. The final amplifier uses a 15-cm Nd:glass disk amplifier in a six-pass configuration. Over 200 J of infrared energy is produced by the disk amplifier. A KDP Type-II/Type-II frequency tripler configuration, utilizing a dual tripler, converts the 1053-nm laser output to a wavelength of 351 nm and the ultraviolet beam is image relayed to the target chamber. Output energy stability is better than 3%. Smoothing by Spectral Dispersion and polarization smoothing have been optimized to produce a highly uniform focal spot. A distributed phase plate and aspheric lens produce a farfield spot with a measured uniformity of 8.2% RMS. Custom control software collects all data and provides the operator an intuitive interface to operate and maintain the laser.
A 100-J, 351-nm laser has been developed for the Dynamic Compression Sector located at the Advanced Photon Source. This laser will drive shocks in solid-state materials which will be probed by picosecond x-ray pulses available from the synchrotron source. The laser utilizes a state-of-the-art fiber front end providing pulse lengths up to 20 ns with pulse shapes tailored to optimize shock trajectories. A diode-pumped Nd:glass regenerative amplifier is followed by a four-pass, flash-lamp-pumped rod amplifier. The regenerative amplifier is designed to produce up to 20 mJ with high stability. The final amplifier uses a six-pass, 15-cm, Nd:glass disk amplifier based on an OMEGA laser design. A KDP Type-II/Type-II frequency tripler configuration converts the 1053-nm laser output to a wavelength of 351 nm and the ultraviolet beam is image relayed to the target chamber. Smoothing by Spectral Dispersion and polarization smoothing have been optimized to produce uniform shocks in the materials to be tested. Custom control software collects all diagnostic information and provides a central location for all aspects of laser operation.
We report on the results from our transversely pumped alkali laser. This system uses an Alexandrite laser to pump a
stainless steel laser head. The system uses methane and helium as buffer gasses. Using rubidium, the system produced
up to 40 mJ of output energy when pumped with 63 mJ. Slope efficiency was 75%. Using potassium as the lasing
species the system produced 32 mJ and a 53% slope efficiency.
We report on the results from several of our alkali laser systems. We show highly efficient performance from an
alexandrite-pumped rubidium laser. Using a laser diode stack as a pump source, we demonstrate up to 145 W of
average power from a CW system. We present a design for a transversely pumped demonstration system that will show
all of the required laser physics for a high power system.
Diode pumped alkali lasers (DPAL) offer the potential for high power and efficient operation. The extremely low
quantum defect of the alkali system minimizes thermal management requirements. At the same time DPALs keep
advantages of gas lasers (no thermal stresses, high intrinsic beam quality). Side pumped geometry simplifies system
design, separating laser and pump light and providing physical space for a large number of diode stacks needed for
power scaling. The three-level nature of these lasers complicates modeling, making numerical simulation the most viable
option for system studies in this geometry.
We have built a simplified numerical code for simulation of CW laser performance in different side pumped geometries
and studied performance of a rubidium DPAL with helium and methane buffer gases at high pump power. We observed
dramatic differences in pump absorption with the laser turned off compared to an operating laser. Cell temperature is a
key parameter that controls effective absorption length. If pump density is sufficiently high, we can find an operating
point with optical to optical efficiency above 60% with reasonably homogenous spatial laser output profile even for a
single side pumped laser cell.
We report on the results of our diode pumped alkali laser experiments. Using volume bragg gratings, we have produced
a 1.28 kW diode stack with a 0.35 nm bandwidth and ~70% of the power contained in the peak. We use two of these stacks to pump a 23 mm rubidium cell. We achieve 29 W of average output power at a 14% duty factor.
Diode pumped alkali lasers have developed rapidly since their first demonstration. These lasers offer a path to convert highly efficient, but relatively low brightness, laser diodes into a single high power, high brightness beam. General Atomics has been engaged in the development of DPALs with scalable architectures. We have examined different species and pump characteristics. We show that high absorption can be achieved even when the pump source bandwidth is several times the absorption bandwidth. In addition, we present experimental results for both potassium and rubidium systems pumped with a 0.2 nm bandwidth alexandrite laser. These data show slope efficiencies of 67% and 72% respectively.
General Atomics has been engaged in the development of diode pumped alkali vapor lasers. We have been examining
the design space looking for designs that are both efficient and easily scalable to high powers. Computationally, we
have looked at the effect of pump bandwidth on laser performance. We have also looked at different lasing species. We
have used an alexandrite laser to study the relative merits of different designs. We report on the results of our
experimental and computational studies.
We have examined the interaction of deuterium clusters with high intensity, ultrafast laser radiation. Upon irradiation a hot plasma is created with a sufficient temperature to produce nuclear fusion. We have seen that larger clusters produce more fusion neutrons than small er clusters, consistent with a Coulomb explosion model. Fusion yields is currently limited by propagation effects. Using interferometric imaging we have examined the laser propagation and found that the laser energy is absorbed before it penetrates to the center of the gas jet.