Home / Journals / Optics / Stimulated Scattering and Phase Conjugation for Near Ultraviolet Spectral Region
Stimulated Scattering and Phase Conjugation for Near Ultraviolet Spectral Region
Lead Guest Editor:
Vladimir B. Karpov
Electrical-Electronics Engineering Department, Trakya University,
Stimulated scattering (SS) is widely used in scientific research and practical applications. This motivates studies of the physical mechanisms responsible for SS in various spectral regions. An important application is phase conjugation (PC) via stimulated backscattering (PC via SS). Various SS mechanisms have specific characteristics (frequency shift, decay time, etc.) that manifest themselves in the PC mirrors properties.
Detailed experimental studies of SS have been conducted only in the near-infrared (near-IR) region. For such experiments the pump radiation must have both high power and narrow bandwidth. The first sources of this kind were Q-switched single-mode ruby (λ=0.69µm) and Nd:glass (λ=1.06µm) lasers. For weak linear absorption, stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) were usually observed, for stronger linear absorption - stimulated thermal scattering (STS) caused by the heating due to linear absorption (linear STS-2).
In the first experimental studies of SBS for the near-IR pump radiation the unshifted spectral components were supposed to be the pump spectral lines. But under this experimental conditions the pump spectral lines could not be distinguished from slightly-shifted components corresponding, for instance, to linear STS-2. Multiphoton absorption could not influence the experiments because 5÷10 near-IR photons with energies 1÷2eV would be required to obtain the nearest electron resonance with an energy about 10eV.
Theoretical studies of SS have mostly relied on experimental results obtained for the near-IR region, and the modern SS theory applies only to linearly absorbing media.
Reliable near-ultraviolet (near-UV) radiation sources (discharge XeF, XeCl, KrF, and ArF excimer lasers) became available considerably later than the solid-state near-IR lasers. When experimentalists in 1980-s had to deal with the PC via SS driven by excimer laser beams, the SS theory developed for the near-IR was applied to the near-UV spectral region. Part of the experimental measurements of the frequency shift and the PC fidelity gained from previous studies of SS of nanosecond (5÷10ns) near-UV (λ=193÷351nm) laser pulses in liquids (hexane, heptane, and others) are found to disagree with the theory of SS, which takes into account only the linear (single-photon) light absorption.