We have demonstrated stable operation of a 2-kW Yb:YAG phase-conjugate master oscillator,
power amplifier (PC-MOPA) laser system with a loop phase-conjugate mirror (LPCM). This is
the first demonstration of a CW-input LPCM MOPA operating at a power greater than 1 kW
with a nearly diffraction-limited output beam. The single-pass beam quality incident on the
LPCM varied with the specific operating conditions, but it was typically ~ 20 times diffraction-limited
(XDL). The measured beam quality with a MOPA output power of 1.65 kW was
The nonlinear optical properties of N,N-diphenyl-7-[2-(4- pyridinyl) ethenyl]-9,9-di-n-decylfluoren-2-amine [AF- 50] have been investigated. The nonlinear absorption of a saturated solution of this material in acetone was investigated with 430 femtosecond pulses at 790 nm. From these results, the two-photon absorption cross-section was determined to be 25 X 10<SUP>-50</SUP> cm<SUP>4</SUP>sec/photon molecule. This number is in agreement (within a factor of 2) with theoretical calculations. Nonlinear absorption and optical limiting measurements were also made using a Nd:YAG pumped dye laser with 4.3 ns pulses at 694 nm. These results suggest inherent differences in the performance of two-photon absorbing materials in these two different geometries.
We present new femtosecond degenerate four-wave (DFWM) measurements on a C<SUB>70</SUB> film in the wavelength range 0.9- 1.6 micrometers in conjunction with previously measured data in C<SUB>60</SUB> and C<SUB>70</SUB> in the ranges 0.74-1.7 (mu) and 0.74-0.88 micrometers , respectively. The new data reveal tow closely spaced peaks in the DFWM spectrum which we interpret as two-photon states with excitation energies of 2.41 +/- 0.05 eV and 2.64 +/- 0.03 eV. We relate these results to nonlinear optical spectra obtained by others in C<SUB>60</SUB> and C<SUB>70</SUB> films. In particular, we compare third-harmonic generation, electro-absorption and DFWM and emphasize the relative advantages of DFWM for two-photon spectroscopy.
We have extended the wavelength range of our previous study of the third order nonlinear optical susceptibility tensor (chi) <SUP>(3</SUP>)(-(omega) , (omega) , (omega) , -(omega) ) of a thin C60 film to 1.7 micrometers . We use time-resolved degenerate four-wave-mixing with femtosecond pulses to measure both the phase and magnitude of (chi) <SUB>1111</SUB>. Our data are well defined in terms of a single two-photon resonance at a fundamental wavelength of 930 nm. From our fit parameters, we predict for (chi) <SUB>1111</SUB> in the zero-frequency limit a value of (9 +/- 3) X 10<SUP>-13</SUP> esu and at the resonance maximum a value of i(3.9 +/- 0.6) X 10<SUP>-12</SUP> esu.
We use time resolved degenerate four-wave-mixing with femtosecond pulses to measure magnitude, phase, and dispersion of all nonzero components of the third order nonlinear optical susceptibility tensor (chi) <SUP>(3</SUP>)(-(omega) ; (omega) , (omega) , -(omega) ) of a polycrystalline C<SUB>70</SUB> film. Rise and fall times of the nonlinearities measured are short compared to the (112 plus or minus 5 fs) pulses employed. Accordingly, the cw symmetry relation <SUB>(chi</SUB> 1111) equals 2 <SUB>(chi</SUB> 1212) plus <SUB>(chi</SUB> 1221) is experimentally found to be satisfied. The magnitude of <SUB>(chi</SUB> 1221) is measured to be (5.04 plus or minus 0.19) 10<SUP>-13</SUP> esu relative to fused silica independent of wavelength. The ratio <SUB>(chi</SUB> 1212)/<SUB>(chi</SUB> 1221) is wavelength dependent and varies between 1.87 plus or minus 0.12 and 1.44 plus or minus 0.09. The magnitudes of phase angles for <SUB>(chi</SUB> 1111) and <SUB>(chi</SUB> 1212) are (120 plus or minus 22) degree(s) and (105 plus or minus 21) degree(s), respectively. The intensity dependence of the observed signals is cubic for intensities up to 20 GW/cm<SUP>2</SUP> at all wavelengths. Good agreement between data derived from degenerate four-wave-mixing and third-harmonic generation in C<SUB>70</SUB> as well as in C<SUB>60</SUB> films is found.
We measure the magnitude and phase of both independent components of the femtosecond (fs) third-order nonlinear optical susceptibility tensor (chi) <SUP>(3</SUP>)(-(omega) ;(omega) ,(omega) ,-(omega) ) of a C<SUB>60</SUB> film. We observe only the contribution of mechanisms whose rise and decay times are short compared to our 120 fs microjoule pulses. The value of (chi) <SUB>1111</SUB> varies between (6.39 +/- 0.35) X 10<SUP>-13</SUP> esu at 745 nm and (19.7 +/- 1.1) X 10<SUP>-13</SUP> esu at 875 nm, relative to fused silica, and rises monotonically with wavelength. Its phase angles lie between 100 and 150 degrees. Our results indicate that neither our, nor any previously published, measurements can be assumed to have approached the low frequency limit in C<SUB>60</SUB>.