C. Duzy

The effect of weak dispersion on stimulated Raman scattering

The Raman gain of an undepleted plane-wave multimode pump laser is calculated. The Stokes and pump fields are represented as vector states in a Hilbert space, and the Dirac bracket notation is introduced to simplify the form of the equations. It is shown that in the absence of dispersion the Stokes vector component correlated with the pump grows exponentially with the monochromatic-pump gain, while all other Stokes components experience zero growth. Perturbation theory is used to second order to determine the gain decrease resulting from relative dispersion between pump and Stokes, and the results are compared with previous works.

Kinetic issues for short-pulse KrF laser operation

Various kinetic issues that are important for modeling the performance of large-scale-size krypton fluoride lasers have been investigated. These kinetic issues include: electron quenching, photoionization from excited rare gas atoms, fuel burn-up, and the accessibility of higher lying levels of KrF* to be effectively stimulated by the laser cavity flux. The results of these studies have been incorporated into a laser kinetics code. Absorption and gain measurements have been carried out over a broad range of conditions to provide a data base to test the codes accuracy and to make subsequent refinements. The code projections for short-pulse operating conditions important for laser-fusion applications are presented.

Stimulated Raman scattering of XeF* laser radiation in H 2 - Part II

Stimulated Raman scattering (SRS) experiments in hydrogen have been performed with a collimated beam from ane-beam pumped XeF laser operating at 353 nm. An unstable resonator provided good beam quality at energies of about 1.2 J and pulse lengths of about 320 ns. A folded-path Raman cell allowed cell lengths to be continuously varied up to 11 m at a hydrogen pressure of 10 atm. Energy conversion efficiencies of >45 percent to first Stokes (S1) at 414 nm and >40 percent to second Stokes (S2) at 500 nm were observed with no indication of significant four-wave processes.

Raman conversion using crossed broadband pump beams and bisecting Stokes

The effects of stimulated Raman conversion under the conditions of crossed pump beams and a bisecting injected Stokes are examined. It is found that the beam quality of the emerging Stokes wave and the effective gain can be characterized by the following two parameters: the temporal coherence of the crossed pump beams and the angle between the pumps.

Shallow angle beam combining using a broad-band XeF laser

Experiments in which two xenon fluoride laser pump beams (353 nm) were crossed at an angle of 2.5 mrad in a 565-cm-long Raman amplifier containing high-pressure (10-atm) hydrogen are described. Bisecting the angle made by these two pump beams was a seed beam at the vibrational Stokes shifted wavelength of 414 nm. This seed beam was generated from a portion of the pump beam that was split off and brought to focus in a separate Raman seed generator. All three beam paths were adjusted so they arrived in the main Raman amplifier at the same time. For the 1.4-AA (FWHM) xenon fluoride pump radiation this required path offset precision to within 0.2 mm over many meters of optical path. The beam quality of the resulting amplified Stokes beam was determined through shearing interferometry techniques to be near the diffraction limit, whereas the pump beams had significant optical distortion. >

Stokes wavefront preservation in broad-band forward raman amplification

The theory of broad-band forward Raman amplification is presented. An exact solution for the pump and Stokes fields is derived in the limit of negligible population transfer, negligible linear dispersion, an arbitrary number of axial modes with mode spacing much larger than the Raman linewidth, collimated-beam ray optics, and arbitrary Raman conversion. It is shown that if the incident pump and Stokes fields are factorable into two factors, one of which is time dependent while the other depends on transverse displacement, then the Stokes field is amplified with no alteration in its wavefront.

Stokes phase preservation during Raman amplification

Experiments have been performed to measure the degree to which the phase information on an input Stokes beam can be preserved in a hydrogen Raman amplifier in the presence of phase and intensity nonuniformities on the pump beam. The experiments were conducted at Fresnel numbers of about 40 and at amplified Stokes fluences of up to 3.4 J cm−2. Astigmatism and focus on the pump did not transfer to the Stokes, and astigmatism on the input Stokes was maintained during amplification. Strong, ordered intensity nonuniformities on the pump beam resulted in large wave-front errors on the amplified Stokes, possibly due to a self-focusing effect. A more uniform pump resulted in an amplified Stokes beam quality of 1.2 times the diffraction limit.