A Novel Technique for the Measurement of Polarization-Specific Ultrafast Raman Responses

Abstract

A simple time domain method for the observation of polarization-specific Raman responses in electronically nonresonant materials is demonstrated. When a cutoff filter is placed in the probe beam path before the detector in the conventional pump-probe configuration, the in-phase dichroic optical heterodyne-detected (OHD) response is enhanced as compared to the usual putative corresponding dichroic response observed when the probe is not dispersed. The ultrafast excited OHD responses of CS 2 obtained by this method are reported for parallel, perpendicular, and magic angle relative orientations of pump and probe pulse polarizations. The observed dispersed dichroic signal can be derived from the real part alone of the third-order nuclear response function. The decay of the CS 2 isotropic response is found to be dominated by a ∼500 fs decay process for times longer than ∼0.7 ps. This relaxation time scale matches the nondiffusive exponential decay seen in the birefringent and dichroic anisotropic responses of CS 2 . Calculated instantaneous normal mode (INM) isotropic and anisotropic nuclear response functions are found to exhibit exponential decays in this same 500-600 fs time scale, suggesting that this decay component may be predominantly determined by the distribution of Raman-weighted density of states.

Temporal and polarization dependence of the nonlinear optical response of solvents

“…The perpendicular polarization data are positive around zero delay, mainly due to the bound-electronic response and then rapidly become negative due to the tensor symmetry of librational and reorientational NLR, which decays at longer delays. At the magic angle, neither the librational nor the reorientational responses affect the probe, so ΔE∕E nearly follows the cross-correlation of the excitation and probe pulses, with an additional small noninstantaneous component due to the collision-induced mechanism [51][52][53].…”

Ultrafast nonresonant response of TiO2 nanostructured films

“…Equivalent measurements can be performed in a simpler experimental scheme using a cutoff filter to detect the spectrally integrated signal on the red or blue sides of the probe spectrum. 21 This technique is sensitive to the birefringent response of the medium and does not require the complicated geometrical arrangement of the SM-OKE experiment. The polarization considerations discussed for SM-OKE are also applicable here, which makes this technique particularly convenient for discerning the molecular isotropic and anisotropic contributions to the third-order response.…”

“…This technique of spatially masked OKE ͑SM-OKE͒ allows measuring different components of the third-order response tensor that are not accessible by the OHD-OKE standard technique. 12,18,19 Another approach for polarization specific measurements of the ultrafast response of transparent materials, proposed by Ziegler and co-workers, 20,21 consists in a dispersed detection of the probe pulses to enhance the signal of birefringent response of the medium through the effect of optical phase modulation. We have performed this experiment on our TiO 2 films and demonstrated its equivalence with the TL technique by calculations that retrieve the pump-probe signal with dispersed detection, starting from a TL time trace.…”

Temporal, spectral, and polarization dependence of the nonlinear optical response of carbon disulfide

“…Carbon disulfide (CS 2 ) is a widely used nonlinear optical (NLO) liquid owing to its large third-order nonlinear refraction (NLR). It has been subject to many experimental studies utilizing time-resolved techniques such as optical Kerr effect (OKE) [1][2][3][4][5][6][7][8], degenerate four-wave mixing (DFWM) [9,10], and nonlinear interferometry [11], as well as frequency domain light scattering [12][13][14], third-harmonic generation [15], and Z-scan [16][17][18][19][20][21]. It is found in a wide array of NLO applications, including liquid-core optical fibers for nonlinear photonics applications [22,23], soliton propagation [24,25], supercontinuum generation [26], slow light [27], ultrafast time-resolved imaging [28], and all-optical switching [29].…”

“…Many of the previous time-domain measurements of CS 2 have focused solely on relative magnitudes (and dynamics) of the nuclear response, and provide no information on the absolute magnitude of the nonlinearity [1,5,6,9,10,34]. Other time domain investigations have used a relative measurement technique, and compared their results to literature values of the nonlinearity of a reference material [11].…”