Obituary of John Murray (1943-2013)

John Roberts Murray passed away at age 70 on 2 June 2013, in Danville, California. Murray is best known for his work on Raman effect in gasses.

At Lawrence Livermore Laboratory (LLNL), Murray developed RAPIER (an acronym for Raman amplifier pumped by intensified excimer radiation) technology to study techniques for compressing rare-gas-halide laser pulses efficiently by combining the Raman effect with pulse stacking. The RAPIER Laser was successfully deployed and tested at the kilojoule energy level by Murray and Julius Goldhar in 1983 at LLNL. Murray also developed a krypton fluoride (KrF) excimer laser, and the resulting publication is still often cited by KrF laser enthusiasts.

Murray was born in Medford, Oregon, on 8 August 1943, while his father was at an army camp training for World War II. He received BS and PhD degrees in Physics from the Massachusetts Institute of Technology in 1965 and 1970. He became involved in scientific research in the early days of lasers as an undergraduate student. His first published paper was “Test of Special Relativity or of the Isotropy of Space by Use of Infrared Masers” with Jaseja, Javan, and Townes, (Phys. Rev., 133 (1964) A1221). His Ph.D. thesis, entitled, “Design and operating parameters of an ionized argon laser, and its use in measuring the absolute intensity and dispersion of Raman lines,” was supervised by Ali Javan, co-inventor of the gas laser.

Murray was the first to observe the Dicke narrowing of forward spontaneous Raman emission from molecular hydrogen at low pressure in the Doppler regime, an extremely challenging physics experiment given the finicky nature of lasers at the time. After two years in the US Army, he joined LLNL in Livermore, California, where he was employed by the laser fusion program until he retired in 2003. His work focused on KrF and neodymium glass laser technology.

Murray was also instrumental in the design of the laser system for the National Ignition Facility at Livermore with colleagues John Hunt, Ken Manes, John Holzrichter, Jack Campbell, John Trenholme and the Livermore laser science team. Both the Beamlet test bed and the NIF were the first large aperture, high-energy and high peak power lasers to use a multi-pass solid-state amplifier scheme with a fast large aperture plasma electrode optical switch and high-efficiency large aperture single-crystal Type I/ Type I phase-matched third harmonic converters. In his early days at Livermore, Murray worked with H.T. Powell and C. K. Rhodes on high-power gas lasers excited by relativistic electron beams. Murray contended that these lasers operating in the visible-to-ultraviolet spectral range showed great promise for scaling up to the average powers and pulse repetition rates required for an inertial confinement fusion reactor. However, these lasers, he noted, function efficiently only when they are delivering pulses about 30 times too long for imploding a fusion fuel capsule.

To adapt these lasers to the needs of inertial confinement fusion, Murray sought to perfect a method of pulse compression to concentrate the energy of long laser pulses into a brief, intense burst. Raman amplification had already been observed at that time; however, there was a common misperception that it was always associated with uncontrolled self focusing and thus could not be used to generate good quality, high-energy optical beams. Murray showed theoretically that Raman gain in a gas, such as methane, could be well controlled, and the beam quality of the output Stokes beam could be even better than that of the original pump beams.The RAPIER project showed that it was possible to operate a large excimer laser in a pulse stacking mode where the energy was extracted from an amplifier by a train of pulses in series, and then, with appropriate delays, combined to form a pump for a large aperture atmospheric pressure gas Raman amplifier.

A backward travelling Stokes beam was used to further compress the optical energy in time. When stimulated scattering became an issue in LLNL’s Nova laser studies, Murray was called upon to figure out how to understand and overcome this limitation. Murray served as lead scientist for the Beamlet test-bed. As chief scientist, Murray was a key member of the NIF laser design team from its conception through its successful commissioning. He led the beam smoothing working group with colleagues Sham Dixit and Mark Henesian and guided many NIF design efforts. Murray and Henesian at LLNL were the first to observe and quantify the effects of stimulated rotational Raman scattering (SRRS) from molecular nitrogen in long air paths and the extreme beam filamentation from this effect in atmospheric propagation.

Murray was the lead member of a team with Henesian and Jeff Paisner in the study of atmospheric SRRS for the Star Wars Program at LLNL. Murray correctly identified transverse stimulated Brillouin scattering at the third harmonic as the cause of optical damage in the NOVA large aperture fused silica focusing optics and suggested using a small amount of bandwidth on the laser pulse to mitigate the damage.

Several of Murray’s publications remain highly cited to this day, including “Raman Pulse-Compression of Excimer Lasers for Application to Laser Fusion,” published in IEE Journal of Quantum Electronics (Vol 15, Issue 5, 1979) and co-authored by J. Goldhar and D. Eimerl et al; and “National Ignition Facility Laser Performance Status,” in Applied Optics (Volume 46 Issue 16, 2007) and co-authored by C. A. Haynam, P. Wegner, and J. Auerbach. Murray began his association with Optical Society of America (OSA) publications in 1984 as a topical editor for JOSA B. In 1991 he became a divisional editor for Applied Optics, and he served as editor-in-chief from 1993-1999. He was chairman of the OSA Publications Council from 2000-2002. He was elected a Fellow of OSA in 1993.

Murray enjoyed his family, photography, woodworking, and carpentry. In addition to his many accomplishments, he will be especially remembered for his great vision and mentoring and encouragement of young scientists, and as a kind and empathetic friend to all. He will be sincerely missed by his family, many friends, and many past colleagues.