Frequency Domain Holography Research Articles

Comparative study of optical nonlinearities of CO[formula omitted] and N[formula omitted]O via single-shot spatio-temporally-resolved visualization

We investigate the electronic and rotational Raman optical nonlinearities as well as ionization of CO2, which is one of the frequently-used molecules in nonlinear optics, using single-shot spatio-temporally-resolved frequency-domain holography (FDH). As a reference, we also perform FDH measurements using N2O whose optical nonlinearities have been studied with single-shot methods previously. Our FDH experiments show that CO2 exhibits overall smaller optical nonlinearities than N2O but has a higher ionization threshold. Furthermore, the FDH results on the delayed rotational Raman response of the molecules are supported by spectral broadening experiments in a gas cell. Our study shows that CO2 is a highly-nonlinear molecule which is comparable to N2O due to a combination of high Raman nonlinearities and high ionization threshold.

Iterative Frequency-Domain Interferometry Technology for Ultrafast Phase Measurement

This paper presents an original design of the single-shot iterative frequency-domain interferometry (IFDI) technology to measure the ultrafast phase. Unlike frequency domain holography (FDH), in which the reference pulse interferes with the phase-modulated probe pulse, in IFDI two linearly chirped probe pulses co-propagate and are both phasemodulated by the measured ultrafast phase, and then the phase can be reconstructed with the iterative algorithm. Compared with two types of FDH, the IFDI technology has better accuracy and stability.

Single-shot ultrafast visualization and measurement of laser-matter interactions in flexible glass using frequency domain holography.

We perform single-shot frequency domain holography to measure the ultrafast spatio-temporal phase change induced by the optical Kerr effect and plasma in flexible Corning Willow Glass during femtosecond laser-matter interactions. We measure the nonlinear index of refraction ($ {n_2} $n2) to be $(3.6 \pm 0.1) \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $(3.6±0.1)×10-16cm2/W and visualize the plasma formation and recombination on femtosecond time scales in a single shot. To compare with the experiment, we carry out numerical simulations by solving the nonlinear envelope equation.

Wakefields in a cluster plasma

We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma.

Single-shot measurement of the free-space time domain terahertz (THz) waveforms by iterative frequency-domain interferometry technology

In this paper, a design of single-shot iterative frequency-domain interferometry (IFDI) technology is presented to measure ultrafast phase. Compared with frequency domain holography (FDH), IFDI technology has better accuracy and stability in some situations. Besides, combined with electro-optic sampling, comparative experiments on the free-space time domain terahertz waveforms measurement using FDH, IFDI, and femtosecond pump-probe technology are conducted, and the results confirm the feasibility and accuracy of the IFDI.

Spatio-temporal profiling of cluster mass fraction in a pulsed supersonic gas jet by frequency-domain holography

We present an in-depth study of a rapid, noninvasive, single-shot optical method of determining cluster mass fraction fc(r, t) at specified positions r within, and at time t after opening the valve of, a pulsed high-pressure pulsed supersonic gas jet. A ∼2 mJ, 40 fs pump pulse ionizes the monomers, causing an immediate drop in the jet's refractive index njet proportional to monomer density, while simultaneously initiating hydrodynamic expansion of the clusters. The latter leads to a second drop in njet that is proportional to cluster density and is delayed by ∼1 ps. A temporally stretched probe pulse measures the 2-step index evolution in a single shot by frequency-domain holography, enabling recovery of fc. We present a model for recovering fc from fs-time-resolved phase shifts. We also present extensive measurements of spatio-temporal profiles fc(r,t) of cluster mass fraction in a high-pressure supersonic argon jet for various values of backing pressure P0 and reservoir temperature T0.

Characterization of cluster/monomer ratio in pulsed supersonic gas jets

We determine cluster mass fraction fc(r,t) at position r within, and time t after firing, a pulsed supersonic gas jet by measuring femtosecond evolution of the jet’s refractive index by single-shot frequency domain holography. A fs pump pulse singly ionizes monomers, while quasi-statically ionizing and heating clusters to a level at which recombination remains negligible as clusters expand. Under these conditions, index evolves in two simple steps corresponding to monomer and cluster contributions, allowing recovery of fc without detailed cluster dynamic modeling. Variations of fc with t are measured.

Transforming characteristic of phase-shift from frequency-domain to time-domain in frequency-domain holography

Two phase-shift transformation modes from frequency-domain to time-domain in frequency-domain holography (FDH) are theoretically investigated for single-shot transient measurement. One mode is the directly mapping mode, in which restrictive conditions and time resolution for the general perturbation profile are analytically derived. Another is the full Fourier transform mode, in which analytical expressions characterizing the accuracy of the phase-shift transformation are clearly given. Theoretical and simulated results show that in mapping mode, at a fixed bandwidth, the accuracy of retrieved temporal phase-shifts is clearly affected by the relative perturbation and chirp amount of the probe pulse, and in transform mode, the inaccuracy of phase value in the frequency-domain is transferred into time-domain with reduced magnitude.

Holographic visualization of laser wakefields

We report ‘snapshots’ of laser-generated plasma accelerator structures acquired by frequency domain holography (FDH) and frequency domain shadowgraphy (FDS), techniques for visualizing quasi-static objects propagating near the speed of light. FDH captures images of sinusoidal wakes in mm-length plasmas of density 1<ne <5×1018 cm−3 from phase modulations they imprint on co-propagating probe pulses. Changes in the wake structure (such as the curvature of the wavefront), caused by the laser and plasma parameter variations from shot to shot, were observed. FDS visualizes laser-generated electron density bubbles in mm-length plasmas of density ne⩾1019 cm−3 using amplitude modulations they imprint on co-propagating probe pulses. Variations in the spatio-temporal structure of bubbles are inferred from corresponding variations in the shape of ‘bullets’ of probe light trapped inside them and correlated with mono-energetic electron generation. Both FDH and FDS average over structural variations that occur during propagation through the plasma medium. We explore via simulations a generalization of FDH/FDS (termed frequency domain tomography (FDT)) that can potentially record a time sequence of quasi-static snapshots, like the frames of a movie, of the wake structure as it propagates through the plasma. FDT utilizes several probe–reference pulse pairs that propagate obliquely to the wake, along with tomographic reconstruction algorithms similar to those used in medical CAT scans.

Visualization of plasma bubble accelerators using Frequency-Domain Shadowgraphy

We report on generation of relativistic electron beams in the wake of a relativistically intense laser pulse traversing a 1.7 mm long atmospheric density helium gas jet. The plasma wake structure is recovered using a Frequency-Domain Holography (FDH) and Frequency-Domain Shadowgraphy (FDS). As the gas density changes, the accelerated electron beams show variations in cross-section area, divergence, total charge, and peak energy. FDH phase reconstruction shows discontinuities and large phase jumps due to plasma electrons blown out by the pump pulse, probe pulse refraction, and nonlinear propagation in plasma. However, FDS amplitude reconstruction shows bright spots that yield information about bubble formation and evolution.

Studies of laser wakefield structures and electron acceleration in underdense plasmas

Experiments on electron acceleration and optical diagnostics of laser wakes were performed on the HERCULES facility in a wide range of laser and plasma parameters. Using frequency domain holography we demonstrated single shot visualization of individual plasma waves, produced by 40TW, 30fs laser pulses focused to the intensity of 1019W∕cm2 onto a supersonic He gas jet with plasma densities ne&amp;lt;1019cm−3. These holographic “snapshots” capture the variation in shape of the plasma wave with distance behind the driver, and resolve wave front curvature seen previously only in simulations. High-energy quasimonoenergetic electron beams were generated using plasma density in the range 1.5×1019≤ne≤3.5×1019cm−3. These experiments demonstrated that the energy, charge, divergence, and pointing stability of the beam can be controlled by changing ne, and that higher electron energies and more stable beams are produced for lower densities. An optimized quasimonoenergetic beam of over 300MeV and 10mrad angular divergence is demonstrated at a plasma density of ne≃1.5×1019cm−3. The resultant relativistic electron beams have been used to perform photo-fission of U238 with a record high reaction yields of ∼3×105∕J. The results of initial experiments on electron acceleration at 70TW are discussed.

Single-shot measurement of temporal phase shifts by frequency-domain holography

Frequency-domain holography is used to measure ultrafast phase shifts induced either by the nonlinear susceptibility ?(3) of fused silica or by ionization fronts in air over a temporal region of 1 ps with 70-fs resolution in a single shot. The use of an imaging spectrometer adds one-dimensional spatial resolution to the single-shot temporal measurements.

Time domain antenna holography

Time domain holography from direct time domain far field measurements is presented as a novel, fast approach to antenna diagnostics, which offers a greater insight into the electrical properties of antennas than that possible using standard frequency domain holography. Experimental results from one array antenna measured in a compact range are presented which illustrate the effectiveness of the new approach.