We describe our approach and latest results for Raytheon's RELI (Robust Electric Laser Initiative) program. Our
architecture leverages a slab-based, Master Oscillator / Power Amplifier (MOPA) architecture based on Raytheon's
unique planar waveguide amplifier. Technical objectives for this effort are to demonstrate > 25 kW output with
excellent beam quality and an electrical to optical efficiency > 30%. The planar waveguide architecture provides
compact packaging and is inherently scalable to 100 kW or greater in a single beam line. We report on the latest
progress and test results for the program.
We have developed and demonstrated a fiber amplifier based architecture capable of high peak power pulsed operation that is scalable to high average powers ⪆10 kW. Our approach uses a mode-locked master oscillator to provide the short pulse waveform and an array of fiber amplifiers to provide high efficiency power amplification using a coherently phased, wavelength multiplexed approach. The mode-locked oscillator input is decomposed into its individual modes using a grating, the individual wavelengths are then amplified in a CW format in the fiber amplifier array, recombined with a second grating, and phased to reproduce a high peak power, short pulsewidth, mode-locked output train. We report the initial demonstration of this architecture with an array of 4 fiber amplifiers. 4 modes of the master oscillator output were selected and amplified from 1 mW to 1 Watt each, followed by recombination and phasing. The phased output pulse train effectively reproduced the master oscillator pulse shape, providing a mode-locked output train of 50 psec pulses. The phase control is performed in parallel for each element of the amplifier array and is directly scalable to high average powers by increasing the power of the individual amplifiers and increasing the size of the amplifier array.
This paper presents the results of a recent experiment to measure the relative laser induced damage thresholds on total internal reflection (TIR) surfaces. The TIR surfaces were realized by testing the reflective surface of an undoped YAG prism at 1.06 micrometers and 12-ns pulse length. Several prisms were tested and the data from each identically processed surface combined to provide a statistically significant sample set. The lowest fluence at which damage was observed using post exposure microscopy was taken as the damage threshold for each polarization. The experimentally observed ratio of the S and P polarization damage thresholds at the TIR surface of 0.584+/- 0.081. This ratio is consistent with a mechanism of damage which is proportional to the third power of the intensity.
The Diode Array Pumped Kilowatt Laser (DAPKL) has demonstrated more than an order of magnitude increase in brightness and average power for short pulse diode-pumped solid-state lasers since its inception in 1991. Significant advances in component technology has been demonstrated, including development of a diffusion bonding process for producing large slabs of Nd:YAG laser material. Phase conjugation by stimulated Brillouin scattering has been demonstrated with high reflectivity and fidelity in a simple focused geometry with input powers of 100 W. Pulse energies at 1.06 μm of up to 10 J per pulse have been demonstrated with a beam quality of 1.25 times diffraction limited at 33 Hz. An average power of 940 Watts at 100 Hz has been obtained with two times diffraction limited beam quality. Efficient frequency doubling with an average power of 165 W has been demonstrated with 5 J per pulse at 0.53 μm. The system has been packaged in a compact brassboard for long term stability and reliability of operation.
An engineering approach for the development of laser hardware that takes advantage of the special properties of phase conjugation is reported. The principal advantages of conjugate solid-state lasers are alignment stability and passive compensation of thermal distortion in a double pass laser amplifier chain. Attention is given to the application of phase conjugation techniques to the design, fabrication, and field testing of an Nd:YAG second harmonic 0.5 Joule, 30 Hertz flashlamp pumped laser in a master oscillator power amplifier configuration. The double pass amplifier featured a phase conjugate mirror and a second harmonic crystal within the amplifier chain. The basic Nd:YAG laser produced a doubling efficiency of 75 percent from 1064 to 532 nm. This output was subsequently used as the source, and a conversion efficiency of 80 percent into six wavelengths in the visible spectrum was obtained using stimulated rotational Raman scattering.
We present three examples which serve to illustrate the way in which use of the technique of H atom photofragment translational spectroscopy can provide much new insight into the photodissociation dynamics of molecular hydrides.
This paper describes the development and implementation of MIS-36477 a Missile Specification for laser damage certification of designator optical components. This MIS is the first official government specification issued for laser damage testing of optics for military laser systems. We describe the history behind the development of laser damage testing for military systems and the gradual emergence of standards for this type of test. The necessity of a standard for laser damage testing was clearly indicated by the inability to correlate results from different test facilities1''2. The development ofde facto standards within the industry is discussed along with the rationale behind the generation of this particular specification. The MIS is described in detail and it is clear that considerably more than just a fluence level and laser parameters need to be defined to have a thorough and widely applicable specification.
In this paper we report on an empirical study of the population distributions of conditioned laser damage thresholds on antireflection (AR) coated BK-7 glass while varying the laser spot size. Two different 1.06 gm AR coating designs were tested. All damage tests were conducted at the design wavelength of 1.06 gm. To obtain the population distribution, 20 determinations of the conditioned damage threshold were performed. This procedure was repeated for each spot size on each of the samples. For control purposes, the unconditioned damage threshold was also measured for each spot size and coating design. The data was analyzed statistically by describing the population distribution and testing for differences as a function of spot size and coating design.
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