Nonlinear optics is the study of phenomena that occur as a consequence of the modification of the optical properties of a material system by the presence of light. Nonlinear optical phenomena are “nonlinear” in the sense that they occur when the response of a material system to an applied optical field depends in a nonlinear manner upon the strength of the optical field. Two additional symmetries of the nonlinear susceptibility tensor occur for the case of a lossless nonlinear medium. The condition that the nonlinear susceptibility must possess full permutation symmetry for a lossless medium can be deduced from a consideration of the form of the electromagnetic field energy within a nonlinear medium. It is also possible to describe optical nonlinearities directly in the time domain by considering the polarization P (t) that is produced by some arbitrary applied field E(t). These two methods of description are entirely equivalent; description in the time domain is more convenient for certain types of problems, such as those involving applied fields in the form of short pulses, whereas description in the frequency domain is more convenient when each input field is nearly monochromatic.

The Nonlinear Optical Susceptibility

Coherent radiation at several wavelengths in the vacuum ultraviolet (VUV) has been generated by four-wave parametric oscillation in mercury vapor. When a powerful ultraviolet pump laser of frequency ωp is tuned to a two-photon resonance, VUV signal photons at frequency ωs, as well as idler photons at frequency ωi, are generated such that ωs + ωi = 2ωp. A frequency-doubled dye laser tuned to two-photon resonance with the 6s6d1D2 level near 280.3 nm produced output at 184.9 and 143.5 nm. A tunable krypton fluoride excimer laser tuned to two-photon resonance with the 6s10s1S0 level near 248.7 nm produced output at 140.1, 130.7, 130.1, 125.9, and 125.0 nm. Approximately 1-μJ, 200-W pulses were observed at 143.5 and 125.9 nm.

Generation of high-brightness coherent radiation in the vacuum ultraviolet by four-wave parametric oscillation in mercury vapor.

http://www.rowland.harvard.edu/rjf/fischer/images/cpl_352_463.pdf

The chiral specificity of sum-frequency generation in solutions

The relationship between quantum state populations and ion signals in (2+1) resonance-enhanced multiphoton ionization (REMPI) detection of HD is investigated both experimentally, by measurements of hot-nozzle population distributions, and theoretically, by calculations of the two-photon E,F 1Σg+—X1Σg+ transition moments. The experimental and theoretical relative rotational cross-sections are in good agreement for v″ = 0 and v″ = 1, but differ for v″ = 2 and for the relative vibrational cross-sections. Arguments are presented that saturation of the E,F-X transition is the main cause of these discrepancies. In spite of the presence of saturation, this calibration gives confidence in determining the relative internal state populations of HD from its (2+1) REMPI spectrum.

Quantitative Determination of HD Internal State Distributions via (2+1) REMPI

With the two dimensional (2D) site and the three dimensional (3D) cube representations in two-photon absorption [M.T. Sun, J.N. Chen, H.X. Xu, J. Chem. Phys. 128(1–6) (2008) 064106], the charge transfer and electron–hole coherence for centrosymmetric and asymmetric fluorene derivatives have been investigated theoretically. For centrosymmetric fluorene derivative, the excitation from the ground state to intermediate excited state by the first photon is a Frenkel excitation; while the excitation by the second photon from the intermediate excited state to the final excited state is an intraband excitation, and charge transfers from one substituent to the other substituent. For asymmetric fluorene derivative in TPA, the excitations by the first and second photons are all charge transfer excited states. Theoretical visual evidence has been provided that diphenylamino-end groups do not strongly participate in pure 2PA, which confirmed the experimental assumption. We also visualize the orientation and strength of transition polarizability density (TPD) in TPA with 3D cube representation. The transition probability in TPA also was visualized with 2D site representation.

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Photoexcitation mechanisms of centrosymmetric and asymmetric fluorene derivatives in two-photon absorption

(1980). Nonlinear Optics of Free Atoms and Molecules. Optica Acta: International Journal of Optics: Vol. 27, No. 6, pp. 731-731.

D.W. Goodwin

Papers

Nonlinear Optics of Free Atoms and Molecules