A potential new light source for nuclear fusion

Rose, CS; McDonald, GS; Christian, JM

Abstract

Lasers typically emit light of one or two, well-defined, frequencies (or ‘colours’). However, numerous applications arise if such light can be converted into a broad, multi-frequency (e.g. ‘multi-colour’) comb of laser beams. Applications range from meteorology, sensing and measurements to those potentially in the domain of
the emerging research field of attosecond science. We report on detailed investigations of a novel self-organisational effect that can convert laser light into an extremely broad comb of multi-colour beams. The
importance of this new effect is that it spontaneously gives rise to an extreme enhancement of the output comb
bandwidth, and that constituent frequencies may self-synchronize.

The bandwidth generated may extend across the entire visible spectrum, resulting in white light laser output. But, the breadth of new frequencies actually extends well beyond this – into the invisible infra-red and ultra-violet
regions of the electromagnetic spectrum. The synchronization of so many frequencies can result in attosecond pulses. During the last decade, there have been several reports of contexts [1-3] where efficient broadband
frequency comb generation may be possible. We will demonstrate distinctiveness with regard to these known
contexts, and summarise results from an exhaustive exploration of this new effect. Moreover, we will compare
modelling results with two new analytical models, developed to lend insight into the underlying physics
involved.

A specific potential application of our results arises in the area of Inertial Confinement Fusion (ICF), where high
gain targets require collisional absorption to be the dominant process in the laser-target coupling. Experiments
have shown that reducing the coherence of the incident light can suppress laser-driven plasma instabilities [4,5].
However, a simple increase in the bandwidth of the incident light can also increase thresholds and lower growth
rates for such instabilities [6-8]. Thus, instability-free transmission of high energy light can be attained by
dividing this energy into very many, separate frequency channels. However, absorption of the energy of this
comb of multi-colour beams at the fusion target can remain relatively unaffected by such frequency division.
This approach, as an alternative to or in combination with the use of incoherent sources, has therefore been
suggested for ICF [9,10].

Citation

Rose, C., McDonald, G., & Christian, J. (2010, November). A potential new light source for nuclear fusion. Presented at 1st CSE Doctoral School Postgraduate Research Conference, University of Salford, Greater Manchester

• Presentation Conference Type: Lecture
• Conference Name: 1st CSE Doctoral School Postgraduate Research Conference
• Conference Location: University of Salford, Greater Manchester
• Start Date: Nov 17, 2010
• Deposit Date: Oct 17, 2011
• Publicly Available Date: Apr 5, 2016
• Additional Information: Event Type : Conference; References : [1] Spillane S M, Kippenberg T J and Vahala K J, Nature 415, 621 (2002) [2] Del’Haye P et al, Nature 450, 1214 (2007) [3] Pollinger M et al, Phys. Rev. Lett. 103, 053901 (2009) [4] Obenschain SP et al, Phys. Rev. Lett 62, 768 (1989) [5] Coe SE et al, Europhys. Lett. 10, 31 (1989) [6] Thomson JJ and Karush JI, Phys. Fluids 17, 1608 (1974) [7] Thomson JJ, Nucl. Fusion 15, 237 (1975) [8] Guzdar PN, Liu CS and Lehmberg RH, Phys. Fluids B 3, 2882 (1991) [9] Eimerl D, Hargrove RS and Paisner JA, Phys. Rev Lett. 46, 651 (1981) [10] Eimerl D, Kruer WL and Campbell EM, Comments Plasma Phys. 15, 85 (1992)