Single-shot Supercontinuum Spectral Interferometry Research Articles

Transient-grating single-shot supercontinuum spectral interferometry (TG-SSSI).

We present a technique for the single-shot measurement of the spatiotemporal (1D space+time) amplitude and phase of an ultrashort laser pulse. The method, transient grating single-shot supercontinuum spectral interferometry (TG-SSSI), is demonstrated by the space-time imaging of short pulses carrying spatiotemporal optical vortices. TG-SSSI is well suited for characterizing ultrashort laser pulses that contain singularities associated with spin/orbital angular momentum or polarization.

Simplified single-shot supercontinuum spectral interferometry.

We have experimentally demonstrated a simplified method for performing single-shot supercontinuum spectral interferometry (SSSI) that does not require pre-characterization of the probe pulse. The method, originally proposed by D. T. Vu, D. Jang, and K. Y. Kim, uses a genetic algorithm (GA) and as few as two time-delayed pump-probe shots to retrieve the pump-induced phase shift on the probe [Opt. Express26, 20572 (2018)]. We show that the GA is able to successfully retrieve the transient modulations on the probe, and that the error in the retrieved modulation decreases dramatically with the number of shots used. In addition, we propose and demonstrate a practical method that allows SSSI to be done with a single pump-probe shot (again, without the need for pre-characterization of the probe). This simplified method can prove to be immensely useful when performing SSSI with a low-repetition-rate laser source.

Simplified chirp characterization in single-shot supercontinuum spectral interferometry.

Single-shot supercontinuum spectral interferometry (SSSI) is an optical technique that can measure ultrafast transients in the complex index of refraction. This method uses chirped supercontinuum reference/probe pulses that need to be pre-characterized prior to use. Conventionally, the spectral phase (or chirp) of those pulses can be determined from a series of phase or spectral measurements taken at various time delays with respect to a pump-induced modulation. Here we propose a novel method to simplify this process and characterize reference/probe pulses up to the third order dispersion from a minimum of 2 snapshots taken at different pump-probe delays. Alternatively, without any pre-characterization, our method can retrieve both unperturbed and perturbed reference/probe phases, including the pump-induced modulation, from 2 time-delayed snapshots. From numerical simulations, we show that our retrieval algorithm is robust and can achieve high accuracy even with 2 snapshots. Without any apparatus modification, our method can be easily applied to any experiment that uses SSSI.

Optimizing the time resolution of supercontinuum spectral interferometry

Single-shot supercontinuum spectral interferometry is a powerful technique for measuring transient refractive index changes. In principle, its time resolution is limited only by the available probe bandwidth. However, this assumes that the phase extraction has sufficient spectral resolution and that the probe spectral phase is exactly known. Using an analytical model for the spectral phase and amplitude modulation of a chirped probe pulse by a weak transient phase perturbation, we show how the probe chirp and spectral resolution determine the achievable time resolution. A simple, practical technique for precise in situ measurement of the probe spectral phase is described in detail, and the sensitivity of the extracted temporal phase profile to uncertainty in the probe spectral phase is demonstrated in numerical simulations.

Direct measurements of the nonlinear index of refraction of water at 815 and 407 nm using single-shot supercontinuum spectral interferometry

Single-shot supercontinuum spectral interferometry was used to measure the nonlinear index of refraction due to the optical Kerr effect in water at both 815 and 407 nm, with pump pulse lengths of ∼90 and ∼250 fs, respectively. Knowledge of the nonlinear index at 407 nm allows pulse tailoring to achieve remote underwater pulse compression and self-focusing.

Space- and time-resolved measurement of rotational wave packet revivals of linear gas molecules using single-shot supercontinuum spectral interferometry

Femtosecond laser-induced alignment and its periodic quantum revivals are measured in a range of linear gas molecules using an improved version of single-shot supercontinuum spectral interferometry. In particular, room temperature alignment revivals of hydrogen and deuterium molecules are measured for the first time, to the best of our knowledge, in a single shot. Wave packet collisional dephasing rates are also measured.

Single-shot, space- and time-resolved measurement of rotational wavepacket revivals in H_2, D_2, N_2, O_2, and N_2O

Femtosecond laser-induced alignment and periodic recurrences in hydrogen and deuterium are measured in a single shot for the first time, in a room temperature gas cell. Single-shot Supercontinuum Spectral Interferometry (SSSI) is employed, with measurements also performed in room temperature samples of nitrogen, oxygen, and nitrous oxide. Unlike previous optical techniques for probing molecular alignment in gases or liquids, SSSI quantitatively and directly measures the degree of molecular alignment without reliance on model fits, and it can do so with spatial resolution transverse to the pump beam. In addition, wavepacket collisional dephasing rates can be directly measured in gas samples at useful densities.

Measurement of ultrafast dynamics in the interaction of intense laser pulses with gases, clusters, and plasma waveguides

Femtosecond time-resolved dynamics in the interaction of high intensity, ultrashort laser pulses with various targets—gases, nanometer-size clusters, and plasma waveguides—was studied using a new ultrafast optical diagnostic: Single-shot supercontinuum spectral interferometry (SSSI). The diagnostic measures ultrarapid transients induced by an intense laser pulse in the complex refractive index of the evolving target medium, providing a direct view of how the laser-produced disturbances, such as plasma densities, evolve in time and space. Using the SSSI diagnostic (i) the laser-induced double step ionization of helium, (ii) time-resolved explosion dynamics of intense-laser-heated clusters, and (iii) the coupling and guiding of intense laser pulses injected into a plasma waveguide were examined.

Single-shot measurement of laser-induced double step ionization of helium

The spatio-temporal evolution of the free electron density induced in a helium gas jet by an intense femtosecond pulse is measured with ~10 fs resolution in a ~1 ps temporal window. The double-stepionization feature is observed. In these measurements, we use the technique of single-shot supercontinuum spectral interferometry. It is demonstrated that finite laser-gas interaction lengths can strongly affect the interpretation of such measurements.