Around the Lab

Phoebe Rounds

April, 2003

Recently, Phoebe Robeson Rounds was selected as a finalist in the Intel Science Talent Search for research she performed while participating in LLE’s 2002 Summer High School Research Program. Phoebe developed a systematic method for generating new tripler designs for use on OMEGA or any other high-power ICF laser system. Her method involves the optimization of thickness, tilt, and spacing of the frequency-conversion crystals. Phoebe is the second student from the LLE program to advance to the finals in this nationwide competition.

Many of LLE’s Summer High School Program participants go on to submit their research findings to various scientific competitions. Of these competitions, the Intel Science Talent Search is generally considered the most prestigious. This year Phoebe Robeson Rounds was selected as a finalist in this competition for research she performed while participating in LLE’s 2002 Summer High School Research Program. As a finalist in the national Intel Science Talent Search, Phoebe was awarded a $5000 scholarship, a high-performance computer, and an all-expenses paid trip to Washington, DC to compete against 39 other finalists for additional scholarships up to $100,000. Irondequoit High School will also receive $1000 to support its math and science programs as a result of Phoebe’s nomination. Phoebe is the second student from the LLE program to advance to the finals in this nationwide competition.

OMEGA uses neodymium (Nd)-doped glass to generate its laser pulses. Nd-glass lasers emit beams in the infrared range of the spectrum. These beams are ineffective for inertial confinement fusion (ICF) research because a large fraction of the energy absorbed by the targets is converted to fast electrons which detrimentally preheat the target. Therefore, all Nd-doped glass laser systems utilized for ICF research employ some method of frequency conversion to convert the beams to the more-efficient UV wavelength. OMEGA’s beams are passed through at least two potassium dihydrogen phosphate (KDP) crystals “doubler” and a “tripler” to perform the conversion to UV. The original frequency-conversion crystal design for OMEGA involved only one tripler crystal. While this design was efficient, a wider bandwidth of laser light was desired to improve the effectiveness of smoothing by spectral dispersion (SSD), a technique developed by LLE and implemented on OMEGA for the creation of smoothly focused laser beams. A second tripler was added to each beamline of the system in 2000 to increase the bandwidth from 0.3 to 1.0 THz in the UV (4 Å to 12 Å in the IR).

Two frequency-conversion crystals mounted in the OMEGA laser system. The optic sits in a gimbal allowing the tilt to be adjusted so that optimum frequency conversion can be achieved.

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