[(a)–(c)] Time-domain representation of the BB SFG process with the narrow-band nonresonant (visible) pulse (shown in green) arriving (a) before , (b) simultaneously with , and (c) after the BB resonant (IR) pulse (shown in purple). Only envelopes of and are shown. The first-order polarization induced in the sample by the IR pulse (orange lines) is the same in all cases, but the upconverted second-order nonlinear polarization , which emits the BB-SFG signal (red lines), is different and asymmetric for positive and negative delays . [(d)–(f)] Frequency-resolved BB-SFG signals for negative, zero, and positive IR-visible pulse delays , showing different amplitude, width, and asymmetry of the spectral peak, and nonresonant background level (teal dotted line). See text for discussion.
Temporal profiles [(a) and (c)] and spectra [(b) and (d)] of the narrow-band visible pulses produced by the 4-f stretcher and used for the BB-SFG measurements. [(a) and (b)] Pulse with bandwidth. [(c) and (d)] pulse with bandwidth. Solid black lines—model fit (see Sec. V).
Temporal profile (a) and spectrum (b) of a narrow-band visible pulse produced by an air-spaced etalon . Solid black lines show fit to the model described in Sec. V.
BB-SFG spectra of the stretch of PA measured using (a) broad and (b) broad visible pulse produced by the 4-f stretcher, recorded at different time delays between the resonant IR and nonresonant visible pulses. The IR-visible time delays are indicated for each spectrum. Solid black lines show model fits (see Sec. V).
Intensity (top), FWHM (middle), and central frequency (bottom) of the measured BB-SFG line shape using stretcher-produced narrow-band visible pulses, as a function of the IR-visible time delay. Black squares: visible pulse; red circles: visible pulse. The peak intensity for the visible pulse has been multiplied by 2. The lines through points are to guide the eye only.
Intensity, FWHM, and central frequency of the BB-SFG line shape measured using etalon-produced narrow-band visible pulses (FWHM of ) as a function of the IR-visible time delay.
Contributions to the homodyne-detected SFG spectrum for a single Lorentzian line with nonresonant background. (a) Real and imaginary parts (solid and dashed lines, respectively) of the resonant (blue) and nonresonant (red) contributions. (b) Squared real and imaginary parts (solid and dashed lines, respectively) of the resonant contribution (blue) and total susceptibility , showing the asymmetry and broadening of the real part of the total susceptibility (solid red line) due to the addition of the nonresonant contribution. (c) Homodyne-detected SFG spectra of the resonant contribution alone (blue) and total susceptibility (red) showing the asymmetry and broadening due to the nonresonant contribution.
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