Scattering – Amplification – Crossed laser beams

Phys Rev E Stat Nonlin Soft Matter Phys.  2011 Aug;84(2-2):026402. Epub 2011 Aug 4.

Amplification of light in a plasma by stimulated ion acoustic waves driven by multiple crossing pump beams.

Kirkwood RK, Michel P, London RA, Callahan D, Meezan N, Williams E, Seka W, Suter L, Haynam C, Landen O.

Source

Lawrence Livermore National Laboratory, Livermore, California 94550, USA.

Abstract

Experiments demonstrate the amplification of 351 nm laser light in a hot dense plasma similar to those in inertial confinement fusion ignition experiments. A seed beam interacts with one or two counter-propagating pump beams, each with an intensity of 1.2×10^{15} W/cm^{2} at 351 nm, crossing the seed at 24.8° at the position where the flow is Mach 1, allowing resonant stimulation of ion acoustic waves. Results show that the energy and power transferred to the seed are increased with two pumps beyond the level that occurs with a single pump, demonstrating that, under conditions similar to ignition experiments where each beam has a low gain exponent, the total scatter produced by the multiple beams can be significantly larger than that of the individual beams. It is further demonstrated that the amplification is greatly reduced when the pump polarization is orthogonal to the seed, as expected from models of stimulated scatter.

Opt Express.  2006 Apr 17;14(8):3443-52.

Experimental study on seed light source coherence dependence of continuous-wave supercontinuum performance.

Lee JH, Han YG, Lee S.

Abstract

We experimentally compare output performance between laser beam (erbium fiber ring laser) and amplified spontaneous emission (ASE) beam (erbium fiber ASE) driven supercontinuums (SCs) in terms of seed beam temporal coherence. We control the degree of temporal coherence of the seed beams by using an optical filter to change their spectral linewidth. The random phase ASE driven SC is found to have better performance than the phase-correlated laser driven SC in terms of spectral smoothness and output power. Significantly high relative-intensity-noise in the output SCs is observed for both cases, i.e. the laser driven SC and the ASE driven SC irrespective of the seed beam temporal coherence due to the nonlinear amplification of quantum fluctuations both in the input pump beam and in the Raman scattering process.

Phys Rev Lett.  2003 Nov 28;91(22):225001. Epub 2003 Nov 25.

Laser-energy transfer and enhancement of plasma waves and electron beams by interfering high-intensity laser pulses.

Zhang P, Saleh N, Chen S, Sheng ZM, Umstadter D.

Source

FOCUS Center, University of Michigan, Ann Arbor, MI 48109, USA.

Abstract

The effects of interference due to crossed laser beams were studied experimentally in the high-intensity regime. Two ultrashort (400 fs), high-intensity (4 x 10(17) and 1.6 x 10(18) W/cm(2)) and 1 microm wavelength laser pulses were crossed in a plasma of density 4 x 10(19) cm(3). Energy was observed to be transferred from the higher-power to the lower-power pulse, increasing the amplitude of the plasma wave propagating in the direction of the latter. This results in increased electron self-trapping and plasma-wave acceleration gradient, which led to an increased number of hot electrons (by 300%) and hot-electron temperature (by 70%) and a decreased electron-beam divergence angle (by 45%), as compared with single-pulse illumination. Simulations reveal that increased stochastic heating of electrons may have also contributed to the electron-beam enhancement.

Phys Rev Lett.  2002 Nov 18;89(21):215003. Epub 2002 Nov 1.

Observation of saturation of energy transfer between copropagating beams in a flowing plasma.

Kirkwood RK, Moody JD, Langdon AB, Cohen BI, Williams EA, Dorr MR, Hittinger JA, Berger R, Young PE, Suter LJ, Divol L, Glenzer SH, Landen OL, Seka W.

Source

Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.

Abstract

Experiments demonstrate energy and power transfer between copropagating, same frequency, beams crossing at a small angle in a plasma with a Mach 1 flow. The process is interpreted as amplification of the low intensity probe beam by the stimulated scatter of the high intensity pump beam. The observed probe amplification increases slowly with pump intensity and decreases with probe intensity, indicative of saturation limiting the energy and power transfer due to ion-wave nonlinearities and localized pump depletion. The results are consistent with numerical modeling including ion-wave nonlinearities.