Krypton fluoride laser pulse shortening by stimulated thermal scattering on a liquid surface.
Pulse shortening of the backscatter of a KrF excimer laser beam focused on the surface of n-hexane is reported. Simultaneous measurements of the backscattered beam, a Fresnel reflected beam, incoherent scattered photons from a liquid surface, and a transmitted beam are performed. The results show that the surface reflected beam disappears followed by beam expansion and the transmitted beam is reduced to form a filamentlike structure with the onset of backscatter. The pulse width of the backscattered beam shows a clear dependence on the focal position in the liquid. Incoherent scattering is sharply enhanced when the laser beam is focused at the liquid surface where the backscattered beam is especially short. The observed phenomena indicate that stimulated thermal scattering is the pulse shortening mechanism.
Phase conjugation of XeCl excimer laser radiation by excitation of various types of stimulated light scattering
Phase conjugation of XeCl excimer laser radiation (λ = 308 nm) was investigated using two different types of stimulated scattering: stimulated Brillouin scattering (STBS) and stimulated thermal scattering (STTS). It was shown that STTS may be caused by linear and multiphoton absorption, whilst STBS may be suppressed by loss of phase matching caused by absorption. The phase conjugation quality deteriorates on transition from STBS to STTS.
Pulse compression of KrF laser radiation by stimulated scattering
Pulse compression of KrF laser radiation by stimulated scattering.Sergey S.Alimpiev, Viacheslav S.Bukreev, Vladimir I.Kusakin, Sergey V.Ukhansky,Alexey Z.Obidin, Sergey K.Vartapetov, Igor A.VeselovskyGeneral Physics Inst., 1 17942 Moscow, Vavilov str. 38, USSRABSTRACTWaveform conjugation of narrowband KrF laser with linewidth 0.02 cm1 and divergence iO rad wasinvestigated. By means of Brillouin scattering in SF6 gas the 12 ns duration pump pulse was compressed up to 1.5ns with energy efficiency about 80% and the laser beam divergence retention. The waveform conjugation underthermal Raleigh scattering in hexane, heptane and hot water was also investigated. The maximum efficiency inhexane was about 10% and scattered pulse duration 2.5 ns. Waveform conjugation in a wide region of liquidsabsorption coefficients was also observed.One of the methods to decrease the laser pulse duration is the use of nonlinear optics techniques. Amongthe most prospective ones are techniques based on stimulated scattering processes. The main advantages of suchpulse compression techniques are high efficiency, low background level of amplified spontaneous emission andpossibility of waveform conjugation. A properly selected conditions of stimulated scattering in principle allow toproduce pulses much shorter than the damping mode time Td. The most widespread are the compressors basedon stimulated Brillouin and Raman scattering 1,2 Brillouincompressors possess high energy efficiency, smallfrequency shift, so the scattered radiation can be amplified in the next amplifiering stages. The minimal scatteredpulse duration can be decreased up to Ts=.O. 1 Td and for Brillouin scattering in gases this value is about somehundreds picoseconds3. Raman scattering allows to produce much shorter pulses, but because of the largefrequency shift, the further amplification Stokes pulse demands low-efficiency retransformation to antistokescomponent.In the simplest scheme of compressor laser radiation is focused in the cell with the scattering medium. Amatter of principal in this case is the choose of focusing geometry: amplification length L, beam waste length Zd