Frequency-domain “single-shot” ultrafast transient absorption spectroscopy using chirped laser pulses

Abstract

Single-shot ultrafast absorbance spectroscopy based on the frequency encoding of the kinetics is analyzed theoretically and implemented experimentally. The kinetics are sampled in the frequency domain using linearly chirped, amplified 33 fs FWHM pulses derived from a Ti:sapphire laser. A variable length grating pair compressor is used to achieve the time resolution of 500-1000 channels per a 2-to-160 ps window with sensitivity > 5x10 -4 . In terms of the acquisition time, FDSS has an advantage over the pump-probe spectroscopy in a situation when the "noise" is dominated by amplitude variations of the signal, due to the pump and flow instabilities. The possibilities of FDSS are illustrated with the kinetics obtained in multiphoton ionization of water and aqueous iodide and one-photon excitation of polycrystalline ZnSe and thin-film amorphous Si:H. Unlike other "single-shot" techniques, FDSS can be implemented for fluid samples flowing in a high-speed jet and for thin solid samples that exhibit interference fringes; no a priori knowledge of the excitation profile of the pump across the beam is needed.Another advantage is that due to the interference of quasimonochromatic components of the chirped probe pulse, an oscillation pattern near the origin of the FDSS kinetics emerges. This pattern is unique and can be used to determine the complex dielectric function of the photogenerated species.

High-Acquisition-Rate Single-Shot Pump-Probe Measurements Using Time-Stretching Method

“…With power dependent data obtained in one second, we estimate the magnitude of the nonlinear refractive index to be 4.2×10 −13 esu, which agrees well with the previous reports on LiNbO 3 25. We note that the pulse duration of the Kerr signal was longer than that of the pump pulse, because of the signal distortions in the spectral encoding technique14, and the limited bandwidth (1 GHz) of the photodiode.…”

“…This is a variation on spectrally-encoded single-shot measurements, where the probe pulse is linearly chirped, and the temporal signal is thus encoded in the probe spectrum5914. Instead of observing the spectrum with a grating and a 2-D detector, the probe pulse and encoded temporal dynamics are further chirped to nanosecond time scales using the group velocity dispersion in the optical fiber, thus slowing down the ultrafast signal to time scales easily recorded with fast detectors and high-bandwidth electronics.…”

Plasma gelsolin levels and outcomes after aneurysmal subarachnoid hemorrhage

“…In addition to actin, plasma gelsolin binds and modulates bioactive lipids, such as endotoxin [33], lysophosphatidic acid [34], and platelet activating factor [35]. This effect may partially explain how exogenous gelsolin replacement significantly enhances survival of septic animals [8], and blunts the inflammatory response in animal models of lung injury [36] and burns [7]. Based on these data, we propose that plasma gelsolin functions as an important endogenous guard against overwhelming inflammation from tissue injuries.…”

Optical fiber-based single-shot picosecond transient absorption spectroscopy

“…When crossed with an excitation pulse in the sample, transient absorption information is imprinted across the spectrum of the "chirped" probe pulse and read out using a spectrograph and array detector. 11,12 This technique has been demonstrated with a larger time window, up to 160 ps, while presenting oscillations in the first few picoseconds that require additional analysis and which are sensitive to dynamical spectral shifts. 12 Streak cameras have also been employed in single-shot instruments 13,14 that obtained 30-50 ps rise times, but must trade off time resolution with dynamic range because of distortions due to blooming on the detector at high probe light intensities.…”