Thermal effects in phase-conjugation in saturable absorbers with picosecond pulses

Abstract

Phase conjugation reflcction with efficiencies o f 400% for microsecond pulses and ~50% Tur picosecond pulses has been obtained in saturable absorber dye Solutions. The effect o f difTcrcnt solvcnls on thc gencration o f the thermal pitase grating involved was investigated.We ltave recently reported [1] phase-conjugation [2] with conversión efficiences of up to 50% in DODCI and other saturable absorbers obtained with picosecond pulses from a mode-locked dye láser. Phase-conjugation reflection with lower efficiency, has also been measured [3] in an intra-cavity saturable absorber dye cell in the experimental arrangement conunonly used for passive mode-locking of pulsed and CW dye lasers [4,5], Photoisomer effeets [6] in the saturable absorber dye were found [3] to be important in the phase-conjugation process, particularly when the láser was tuned to longer wavelengths. Martin and Hellwarth [7] have shown that thermally induced refractive Índex changes [8][9][10][11] were the dominant mechanism in a variety of liquids employed in a four-wave mixing process for image conversión from infrared to visible and more recently the influence of the thermal grating in phase conjugation was discussed by Heilweil et al. [12]. We have investigated the role played by thermal effeets in phase conjuga tion reflection of picosecond pulses from saturable absorbers. In particular, the influence of solvents with very different thermal properties have been investigat ed together with the time behaviour of the conjugated wave.The experimental set up (fíg. 1) is similar to that reported previously [1]. The essential improvement is the use of a fast electro-optic Pockels' cell shutter between the láser and the sample cell to select out a well defined portion of the dye láser pulse train. A fast piloto diode (ITL type FD 125), PD1, was used to trigger the Pockels' cell and similar photodiodes (PD2 and PD3) monitored the probe beam intensity (¡2) and the conjúgate wave intensity (/4). A flashlamp pumped passively mode-locked dye láser [4] generated ~1 .2 ps pulses of ~100 mJ energy. In both cases, the láser was tuned by an intra-cavity etalon. The láser beam was focussed into the dye cell by lens L (f= 40 cm) and divided by a glass beam splitter 0 030-4018/81/0000-0000/$ 02.50 ©North-Holland Publishing Company 67

Laser analytical spectrometry based on optical phase conjugation by degenerate four-wave mixing in a flowing liquid analyte cell

“…Degenerate four-wave mixing (D4WM) is one of the most versatile techniques for the generation of optical phase conjugation in a nonlinear medium (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). The D4WM method utilizes two exactly counterpropagating forward pump, Ef, and backward pump, Ej,, beams.…”

Self-Action Effects and Degenerate Four-Wave Mixing

“…The analysis of D F W M has been extended to include arbitrary polarization combinations (Steel et al, 63 ZePdovich and S h k u n o v , 64 Martin et al, 65 and Bol'shov et al 66 ), the effects of nonlinear phase shifts (Marburger and L a m 6 7 ) , pump depletion (Marburger and L a m , 6 8 H s u , 6 9 and Lazaruk and R u b a n o v 7 0 ) , saturable absorbers (Abrams and L i n d , 71 Apanasevich et al, 12 Watkins et al, 13 and B r o w n 7 4 ) , Doppler broadening and atomic motion ( W a n d z u r a , 75 Nilsen and Yariv, 76 and Humphrey et al 11 ), thermal effects (Key et al, 18 Eichler et al, 19 Heilweil et al, 80 Andrews and Hochstrasser, 81 and Tocho et al 82,83 ), frequency offsets and spectral bandpass (Pepper and A b r a m s , 84 F u and Sargent, 85 W a n d z u r a , 75 Nilsen and Y a r i v , 76 and Pilipetsky and S h k u n o v 8 6 ) , two-photon resonant media (Fu and S a r g e n t 8 7 ) , transient responses (Rigrod et al 88 ), and D F W M in plasmas (Steel and L a m 8 9 ) . Phase conjugation in optical waveguides has been discussed by Yariv et al, 90 Jensen and Hellwarth,91 AuYeung et al, 92 and Hellwarth.…”

“…Tocho et al 82, 83 have reported D F W M reflectivity measurements in the saturable dye D O D C I in several solvents using light from a frequencydoubled N d : Y A G laser at 532 nm. Reflectivity was measured for both picosecondand microsecond-duration pulses.…”

Trace-concentration detection of cobalt in a liquid flow cell by degenerate four-wave mixing using low-power off-resonant laser excitation

“…The nonlinear effect induced by these input beams produces the phase conjugate signal beam that is a time-reversed replica of the incident probe beam. Many types of material, including metal vapors (6), semiconductors (7), liquid crystals (8), thin dye films (9,10), absorbing dye solutions (11,12), suspension solutions (13), and ruby crystals (14) have been used as the nonlinear medium to generate optical phase conjugation. To produce a measurable phase conjugate signal, some of the D4WM experiments mentioned above used high-energy pulsed lasers (e.g., 10® W/cm2).…”