Distinguishing bulk and interface modulation of optical third harmonic generation due to coherent optical phonon excitation

Low frequency coherent Raman spectroscopy

We revisit low frequency coherent Raman spectroscopy (LF-CRS) and present a unified theoretical background that provides consistent physical pictures of LF-CRS signal generation. Our general framework allows to compute the signal to noise ratio in the multitude of possible LF-CRS, and more generally CRS, experimental implementations both in the spectral and time domain.

Elucidating low-frequency vibrational dynamics in calcite and water with time-resolved third-harmonic generation spectroscopy

Coherent low-frequency vibrational dynamics in condensed phase from crystal, water, to aqueous electrolyte are elucidated by time-resolved third-harmonic-generation (TRTHG) spectroscopy.

Time-resolved coherent Raman spectroscopy by high-speed pump-probe delay scanning

Using a spinning window pump-probe delay scanner, we demonstrate a means of acquiring time-resolved vibrational spectra at rates up to 700 Hz. The time-dependent phase shift accumulated by the probe pulse in the presence of a coherently vibrating sample gives rise to a Raman-induced frequency shifting readily detectable in a balanced detector. This rapid delay scanning system represents a 23-fold increase in averaging speed and is >10× faster than state-of-the-art voice coil delay lines. These advancements make pump-probe spectroscopy a more practical means of imaging complex media.

Distinct broadband third-harmonic generation on a thin amorphous medium-air interface

We achieve a series of distinct broadband third-harmonic generation (THG) signals at the amorphous glass-air interface attributed to third-order and cascaded third-order nonlinear processes. A novel THG laser sideband arises from cascaded interaction between fundamental pulses and the cascaded four-wave mixing signals. The spatially separated THG sidebands with distinct spectral profiles manifest femtosecond quantum beats. Using a versatile setup with two crossing near-IR pulses temporally delayed to each other, we design an incident pulse polarization control method on the THG sideband lasers and also acquire the low-frequency surface Raman spectrum of the amorphous medium.

Coherent nonlinear optical studies of elementary processes in biological complexes: diagrammatic techniques based on the wave function versus the density matrix

Two types of diagrammatic approaches for the design and simulation of nonlinear optical experiments (closed-time path loops based on the wave function and double-sided Feynman diagrams for the density matrix) are presented and compared. We give guidelines for the assignment of relevant pathways and provide rules for the interpretation of existing nonlinear experiments in carotenoids.

Communication: Comment on the effective temporal and spectral resolution of impulsive stimulated Raman signals

A compact correlation-function expression for time-resolved stimulated Raman signals, generated by combining a spectrally narrow (picosecond) with a broad (femtosecond) pulse, is derived using a closed time path loop diagrammatic technique that represents forward and backward time evolution of the vibrational wave function. We show that even though the external spectral and temporal parameters of the pulses may be independently controlled, the effective temporal and spectral resolution of the experiment may not exceed the fundamental bandwidth limitation.