Measurement of third-order nonlinear susceptibilities by non-phase matched third-harmonic generation

Abstract

liquids, solids and air are determined by third-harmonic generation. The samples are placed behind the focal region of a laser beam in an evacuated environment to avoid third-harmonic generation of the surroundings. For fluid media the sample cell is made out of two thin fused quartz plates and oriented to an angle of zero net third-harmonic production in each window (minimum Maker fringe position). PACS: 42.65The measurement of third-order nonlinear susceptibilities x (3) ( -co 3 ; co v co v coJ responsible for thirdharmonic generation is aggravated by disturbing light production in surrounding media (sample cell, air). Avoiding the influence of the surrounding substances in the light path by tight focussing (sample length longer than confocal parameter) results in zero thirdharmonic generation under phase-matched condition and for positive phase-mismatch Ak = k 3 -3k x >0 (normal dispersive media). Only in anomalous dispersive matter light generation at frequency co 3 occurs [1,2]. In a collimated pump beam (frequency coj the third-harmonic light is periodically generated and annihilated for Ak + 0 and efficient light generation requires Ak = 0. Circularly polarized laser light does not generate third-harmonic light in transparent media at all [6].Third-order nonlinear susceptibility values # (3) ( -co 3 ; co v co 1 ,co 1 )of gases were obtained by putting a gas cell with its entrance window (absorbing at co 3 ) in the focal plane of a laser [1], The susceptibilities of some solids were measured in reflection [3]. A comparison of third-harmonic generation with cascading secondorder processes was used to derive x In this paper we report on an accurate method to determine the third-order nonlinear susceptibilities X (3) ( -co 3 ; co v co v co t ) of solids, liquids and gases. Third-harmonic generation in a slightly diverging beam (thin sample behind focal plane of a lens) is studied. Third-harmonic generation in air along the path of the laser beam is avoided by putting the sample into a vacuum chamber. The entrance and exit windows of the sample cell for liquids and gases are made out of thin plane fused silica plates (thickness: «0.2 mm). By tilting the cell to a Maker fringe minimum position for each window [11] no thirdharmonic light is produced in each of the windows. The cell is slightly wedged in order to record a Maker fringe curve when the filled cell is laterally shifted relative to the light path.

Nonresonant third order hyperpolarizability of rare gases and N2 determined by third harmonic generation

“…[4]. Two gas cells of length / = 4.52 cm (He, Ne) and /= 1.18 cm (all other gases) were constructed.…”

“…According to the anharmonic oscillator model the third order hyperpolarizability is related to the linear polarizability by [4,7] 7 (3) (-co 3 ; oj h oj h co!) = mhf 2 e A )y { Ph^\ (16) where | is the anharmonic coupling constant, m the electron mass,/the oscillator strength and e the electron charge.…”

“…Experimental determinations of nonresonant third order hyperpolarizabilities of gases are scarce [1][2][3][4]. Their measurement by third harmonic generation or collinear four-photon frequency mixing [1][2][3] is complicated by the fact that these processes occur in all media along the path of the laser beams and that tight focusing of laser light into a normal dispersive sample results in no third harmonic or frequency mixing output at all [2,3,5,6].…”

“…The problem of third harmonic generation along the light path outside the sample is avoided by putting the gas cells into a vacuum chamber behind the focal region of the slightly focused laser beam and using cell windows of thickness equal to an even integer of the coherence length ir/Ak of the interaction [4,7] (Maker fringe minima [8]). …”

Phase-matched third-harmonic generation of Nd: Glass-laser picosecond pulses in a new cyanine-dye solution

“…In this low-intensity regime the nonlinear refractive-index effects are negligible. Without the n 2 terms, (1) and (2) are analytically solvable and the expression for the third-harmonic energy-conversion efficiency of Gaussian input pump pulses given by [19,42] _ 47r 2 4.3.1 Pump Laser Reduction. In 5 mm samples a reduction of pump-pulse transmission occurs at peak pulse intensities above 4 x 10 11 W/cm 2 for TFE and above 6 x 10 11 W/cm 2 for HFIP.…”