A concept combining the advantages of solid-state and gas-laser technologies is being developed to realize a scalable, efficient 4-micron laser. A Nd:YAG laser is tuned to 1.3391 microns by temperature-tuning and cavity selection. The addition of diode seeding permits excitation of a specific v = 3 rotational state of HBr. Lasing can potentially occur in three subsequent steps to the ground state, emitting numerous lines in the 4-micron region, which enhances efficiency and spectral coverage. Using up to 25-mJ pump energy, two elements of the possible three-level cascade have been observed. We have observed emission selectivity due to intracavity carbon dioxide and inferred the presence and contributory influence of pure-rotational stimulated emission, which may have importance to the overall behavior of other similar molecular pulsed lasers (and even continuous-wave HX lasers). We present theoretical and experimental results demonstrating the operational principle and utility of this laser system.
We demonstrate the use of an Nd:YAG laser to optically pump an HBr gas laser, a concept combining the advanctages of solid-state and gas-laser technologies. A Q-switched Nd:YAG laser, tuned to 1.34 μm and frequency-stabilized, excites the v=3, J=5 state of HBr in a third-overtone transition. A diode laser locked to the HBr transition provides the seed signal for the Nd:YAG laser. Higher efficiencies than previously obtained for similar systems are expected in this concept because of the possibility of cascade lasing, which we have observed in our experiments and predicted in our simulations. Pump pulses of approximately 400-ns duration and 20-mJ energy are directed along the axis of a 1-m containing 15-torr HBr. In the currently unoptimized configuration, approximately 6 laser lines at about 4 μm are observed. The observed laser spectrum suggests collisional pumping for some lines and that intracavity atmospheric CO2 is a factor. We have developed and used a kinetic model, which shows good agreement with the experimental results. There is evidence of pure rotatioal lasing. Amplifiers are being added to increase the pump energy to 1 J.
Due to a narrow window of high atmospheric transmission near 4 microns, there is a great deal of interest for a scalable laser energy source in this spectral region. We propose a concept that combines the advantages of solid-state and gas laser technology. A Nd:YAG laser is tuned to 1.3391 microns by inserting an intracavity etalon and raising the operating temperature of the laser rod to 85 degree(s)C. This allows us to excite the v (0 →3), J (4 → 5) vibrational-rotational transition of HBr. To stabilize the frequency, a diode laser locked to this HBr transition seeds the Nd:YAG laser. Once excited, HBr can potentially lase in three subsequent steps to the ground state, emitting three photons in the 4-micron region. We present theoretical and experimental results demonstrating the operational principle of this laser system.
Laser-pumped molecular lasers can be the source of laser wavelengths that are otherwise unavailable. In these laser sources a gas cell containing selected molecules is optically pumped with an available laser to generate output at a wavelength longer than that of the pump. For example, the CO2 laser has long been used to generate far-infrared coherent radiation from optically pumped gases exemplified by methanol and heavy water. Indeed, laser-pumped molecular lasers have generated thousands of laser lines from the vacuum ultraviolet to the millimeterwave region since their inception in the early seventies. While these lasers are useful for specified wavelengths, they also offer the advantage of very good beam quality. The pump laser is not required to have good beam quality in order to achieve this performance. Interest in laser-pumped molecular lasers is expected to increase in the near future because of the needs of various users. Examples may be found in the mid-infrared region where compact sources are largely unavailable. The use of improved solid-state lasers or diode lasers as pump sources for molecular lasers will result in useful sources for remote sensing, ladar, and other applications.
We describe the results of an analytical and experimental program that is investigating the feasibility of developing mid-IR lasers based upon laser pumped gas phase molecules. We present results for lasing on overtone pumped HF, HCl, and DF. In addition, describe several possible excitation sources including diode lasers and alexandrite lasers.
High-explosive charges were used in the early 1980's at Los Alamos National Laboratory to pump high-energy atomic-iodine lasers. Laser outputs at the kilojoule level were measured in a series of experiments. Two techniques were used to convert the high-explosive (HE) energy release to optical radiation for the photolysis of the perfluoroalkyliodide fuel. One technique used strong shockwaves propagating through argon gas and driven by the detonation as an intense optical pump source. The second approach used exploding metal films driven by megampere-level current pulses from explosive-driven magnetic flux compression generators. The optical extraction system for both types of single-pulse lasers was a power oscillator configuration using a stable resonator. The purpose of these experiments was to evaluate the scaling potential of HE-driven lasers for a number of applications including inertial confinement fusion. The HE field experiments were supported by a number of laboratory laser experiments. Exploding wires were used to pump 100-J atomic-iodine lasers (and 20-J molecular iodine lasers). Atomic-iodine lasers were also pumped with exploding metal films. In support of this work, several types of optical pump sources were characterized. These included HE-driven shockwaves in a variety of rare gases, exploding metal wires and films, surface discharges, ablating-wall flashlamps, and xenon flashlamps. Equivalent blackbody temperatures as a function of various parameters were measured for each source using absolutely calibrated photodetectors equipped with optical bandpass filters.
The H/NF2/BiF system is one of the most promising concepts for high-power short wavelength chemical lasers (SWCL). The preferred approach uses the H + NF2 reaction to efficiently generate NF(a) energy-carrier molecules. These latter species interact with Bi compounds to produce excited BiF. The potential lasing transition is BiF(A-X) emitting near 460 nm. We report in this paper one-dimensional (1-D) reactive-flow modeling of the H/NF2/BiF system. This work supports design of an experimental demonstration of continuous-wave lasing in a supersonic-flow, purely chemical system. The model treats the subsonic plenum, transonic throat, and supersonic expansion regions.