RF CO<SUB>2</SUB> slab lasers with waveguide-unstable resonators demonstrated last years to be an effective tool for many applications. Increase of the total power using technique of phase locking of lasers can be achieved without deterioration of beam quality. Till now, no attempt was made to develop such technique for slab-laser arrays. Authors propose to arrange optical coupling between individual resonators using beams diffracting over the edge of convex mirror in asymmetric unstable resonator. 3-dimensional diffraction code was applied taking into account refractive index gradients and gain saturation effects in combination with diffraction and waveguiding effects in a whole optical tract including the coupling channel. In-phase and out-of-phase mode competition was studied in dependence on parameters of resonators and active medium, assuming the lasers were identical. Key parameters for phase locking are defined: optical coupling channel length and position of the resonator optical axis relative to the nearest edge of the convex mirror. The numerical simulations evaluate tolerances for the length of optical coupling channel. A range of the key parameters providing in-phase mode stable operation at high above threshold conditions is found for a particular laser construction. An option to generalize optical coupling method to N-slab-laser array is discussed.
We present results of computer simulations of the launch through the atmosphere of a cone-shaped flyer which demonstrate that laser ablation rockets, using a 1MW ground-based laser, can lift 6kg payloads into low earth orbit. We discuss optimization of delivered mass, mass ratio and energy cost.
Approximately ideal flight paths to low-Earth orbit (LEO) are illustrated for laser-driven flights using a 1-MW Earth-based laser, as well as sensitivity to variations from the optima. Different optima for ablation plasma exhaust velocity V<SUB>E</SUB>, specific ablation energy Q*, and related quantities such as momentum coupling coefficient C<SUB>m</SUB> and the pulsed or CW laser intensity are found depending upon whether it is desired to maximize mass m delivered to LEO, maximize the ratio m/M of orbit to ground mass, or minimize cost in energy per gram delivered. A notional, cone-shaped flyer is illustrated to provide a substrate for the discussion and flight simulations. Our flyer design conceptually and physically separates functions of light collection, light concentration on the ablator, and steering. All flights begin from an elevated platform. Flight simulations use a detailed model of the atmosphere and appropriate drag coefficients for sub- and supersonic flight in the continuum and molecular flow regimes. A 6.2-kg payload is delivered to LEO from an initial altitude of 35 km with launch efficiencies approaching vacuum values of about 100 kJ/g.
In this paper, we summarize the electron pumping and molecular transfer kinetics of pulsed CO lasers, as to their influence, as well as the influence of gas pressure and temperature, on pulsed laser emission line structure, pulse duration and energy output per unit gain volume. Correspondence with existing experimental laser data is shown and compared to these factors. Implications for pulsed laser applications are explored.
The operational characteristics of a 135 kW continuous wave carbon dioxide laser system are described. A brief description of the fast-flowing electrical discharge coaxial laser system is presented followed by a detailed discussion of the operational and output characteristics of the device. Diagnostics systems configured to measure electrical discharge voltage and current, mass flow, laser cavity pressure, laser output power, output spatial intensity distribution and output temporal stability are described. The data collected with these systems are summarized with subsequent analyses presented and compared with theory. The 135 kW carbon dioxide laser is located at the Laser Hardened Materials Evaluation Laboratory (LHMEL) at Wright-Patterson Air Force Base, Ohio, USA. The device was developed and is currently operated for the purpose of characterizing the thermal response of materials.
Nearly 200,000 pieces of debris in the 1 - 20 cm range in low- Earth orbit (LEO), a legacy of 35 years of spaceflight now threaten long-term space missions. An economical solution to the problem is to use a ground-based laser to create a photoablation jet on the objects and cause them to re-enter the atmosphere and burn up. A sensitive optical detector is required to locate objects as small as 1 cm at 1500 km range. Applied when the object is rising and between about 45 and 15- degree zenith angle, the necessary (Delta) v is of order 100 m/s. A laser of 30 kW average power at 5-ns pulsewidth and a 4 - 6 m mirror with adaptive optics can clear near-Earth space of the 1-20-cm debris in 2 years of operation. A high altitude site minimizes turbulence correction, interference from nonlinear optical effects, and absorption. We discuss the effect of nonlinear optical processes in the atmosphere as boundaries on propagation, and how to choose system parameters to guarantee optimum conversion of laser energy to target momentum. The laser might be Nd:glass (1.06 micrometer/530 nm), or iodine (1.3 micrometer).
Researchers from the United States and Russia conducted laser-material interaction tests at the LOK Company, St. Petersburg, Russia. These tests were conducted using a one-of-a-kind, continuous wave, supersonic, e-beam-sustained carbon monoxide (CO) laser. The purpose of these tests were to characterize the laser while performing collaborative research between scientists from Russia and the United States. Additionally, the testing verified previously- reported laser characteristics. All planned laser-material interaction tests were successfully conducted. Several material samples were irradiated by the CO laser to allow calculation of the laser energy and power levels. Statistical errors were reduced by testing materials with different characteristics at varying laser energy and power levels. Laser-material interaction tests were also conducted at varying distances from the laser output window to assess beam quality and divergence.
Under ideal conditions photoconductive switches utilizing ohmic contacts can be made to conduct high currents that scale directly with input optical trigger power. In practice, however,
ohmic contacts can only be approximated by using heavily-doped contact/metallization regions, so that photoswitch structures employing intrinsic substrate layers to support switch voltage can
be viewed as n-i-n, p-i-n, or p-i-n, depending on the contact doping. Under bias, these contacts preferentially inject majority carriers (either holes or electrons) into the substrate that can form
high local space charge electric fields at elevated current densities. In this paper we show both experimentally and analytically that contact space charge formation in a cryogenic silicon n-i-n
photoswitch structure ultimately limits its on-state current capability.
This paper deals with the analytical and experimental determination of the morphology of debris plumes in hypersonic low pressure aerodynamic flowfields. These debris plumes are composed of both gas and solid particulate matter ablated from composite materials by repetitive pulse high energy laser beams. The repetition rate of these individual clouds is determined by that of the incident laser beam. Repetition rates covered in the study range from 10 Hz to 100,000 Hz, and are compared to the steady vapor plume from a CW laser/material interaction situation. Extensive modeling of the coupled gasfrarticulate plume and its expansion into the hypersonic flowfield has been accomplished, and compared to pertinent experiments. These experiments were performed in a large scale hypersonic test facility using high stagnation temperature and stagnation pressure flowfields to produce test conditions with static temperatures in the range 200-300 Kelvin, static pressures in the range 10-4 to 10-1 atmospheres, and freestream test section Mach numbers in the range of two to five. Data will be presented on the behavior of vapor only, particulate only, and combined vapor/particulate plumes injected into such flowfields.
The application of laser systems to the investigation of the properties of materials has become an important part of materials research in recent years. The demand for laser systems capable of supplying high-energy, high-quality output beams on a reliable basis has sparked increased activity in the area of research and prototyping of such devices. Accordingly, the design and construction methods used to produce a 65 kdowatt Carton Dioxide Electric Discharge Coaxial Laser (EDCL) device are discussed. Specific design criteria are identified in accordance to the critical performance requirements for the laser device. Furthermore, the unique construction methods and support system requirements essential to EDCL technology are described along with test results. The 65 kilowatt C02 EDCL laser was constructed for the Laser Hardened Materials Evaluation Laboratory of the Air Force Materials Laboratory located at Wright-Patterson Air Force Base, Ohio under contract F33615-84-C-5086.
Experiments involving the adsorption of gas phase molecules onto thin metal films and the subsequent desorption and ionization of these species are described. The observed ion yield displays a rather striking laser pulse repetition rate dependence that can be interpreted using a simple model that quantitatively analyzes the competition between collisional adsorption and laser induced desorption.