Time-resolved nonlinear optical spectroscopy of perovskites.

Ultrafast decay of optical phonons has been studied in wide-bandgap BaSnO3 and SrTiO3 perovskites using nonlinear spectroscopy with 120 femtosecond time resolution. The coherent Raman mode excitations have been selected and traced with tunable optical pulses. Decay of symmetry forbidden modes of vibrations have been detected directly in time. Phonon decay rates for the main LO- and TO- phonon modes have been found to be within 1.36-1.78 ps-1 and are explained in terms of parametric phonon interactions and pure dephasing mechanisms in the materials that are of interest in microelectronic applications.

Femtosecond coherent Raman system with >75†dB dynamic range for probing vibration modes across 250-2400†cm-1.

We report on the design and performance of a time-resolved Coherent Raman spectroscopy system with time resolution of better than 120 fs. The coherent transients can be traced with more than 75 dB dynamic range while accessing and probing Raman active modes across a 250-2400 cm-1 frequency. The system delivers an equivalent spectral resolution of better than 0.1 cm-1 regarding line bandwidth parameters for probed Raman resonances.

High spectral resolution second harmonic generation microspectroscopy at thin layer interfaces with broadband continuum pulses.

We demonstrate an effective microspectroscopy technique by tracing the dispersion of second order nonlinear optical susceptibility χ (2) in single atomic layer materials. The experimental method relies on the detection of single-shot second harmonic (SH) spectra from the materials and the subsequent data normalization. The key point in our study is that we used a broadband (˜350 nm) near-infrared femtosecond continuum pulses generated at high repetition rates in a photonic crystal fiber with superior spatial quality and stable spectral power density. This is opposite to the point-by-point laser tuning method in SH generation spectroscopy that was applied extensively in the past and has shown limited precision in obtaining χ (2) dispersion. The continuum pulse technique produces spectral resolution better than 2 meV (<0.3 nm at 450 nm) and shows low (<5-6% rms) signal detection noise allowing the detection of subtle features in the χ (2) spectrum at room temperatures. Fine sub-structure features within the main peak of χ (2) spectra indicate the impact of broadened resonances due to exciton transitions in the single layer materials. • Tailored continuum pulses are used to generate second harmonic signal in non-centrosymmetric semiconductors. • SHG spectrum carries fingerprints of the bandstructure around the direct gap states. • The technique produces fine spectral resolution and much better signal-to-noise ratio compared to point-by-point wavelength tuning methods.

ZnGeP2 optical parametric oscillator with 3.8-12.4-mum tunability.

A ZnGeP>(2) (ZGP) optical parametric oscillator (OPO) with wide mid-IR tunability has been demonstrated. The singly resonant angle-tuned ZGP OPO was pumped by 100-ns erbium laser pulses at lambda =2.93mum and yielded output that was continuously tunable from 3.8 to 12.4 mum (type I phase matching) and from 4 to 10 mum (type II phase matching). An OPO pump threshold was less than 1 mJ in the whole 4-12 mum range of the output, and the quantum conversion efficiency reached 35%. An OPO linewidth was typically a few wave numbers; however, with a single intracavity etalon (uncoated Si plate) in a type II OPO it was narrowed to <0.5cm(-1). We demonstrate the sensitive detection of N(2)O gas with the narrow-linewidth OPO.

Time-domain polarization coherent anti-Stokes Raman spectroscopy of Tl atoms: dephasing measurements of separate multipole moments.

Polarization nondegenerate nonstationary coherent anti-Stokes Raman spectroscopy was used in measurements of pulse responses for separate electronic multipole moments. The 6P(1/2)-6P(3/2) transition of Tl atoms was investigated. Doppler dephasing conditions, quantum beats of the hyperfine components of this transition are clearly seen when pure anisotropic scattering is registered, but they are small in the case of purely antisymmetric scattering. Under collisional dephasing conditions the relaxation rates of anisotropic and antisymmetric scattering agree with existing theory within +/-5%.