Chad Petersen

Efficient angular dispersion compensation in holographic generation of intense ultrashort paraxial beam modes

We experimentally demonstrate that small misalignments of the pulse stretcher or compressor of our chirped-pulse-amplification laser can precompensate for angular chirp when producing ultrashort paraxial beam modes with holographic gratings. Using this approach we can eliminate one of the two gratings needed in our 2f-2f setup [Mariyenko, Opt. Express 13, 7599 (2005)]. This allows for up to an order of magnitude more output power. We see our method as the next step in the production of intense exotic forms of ultrashort pulses, which can be used in the investigation of intense laser-matter interactions. In addition, we produce the first femtosecond (helical-)Ince-Gaussian beams.

Wavefront-correction for nearly diffraction-limited focusing of dual-color laser beams to high intensities

We demonstrate wavefront correction of terawatt-peak-power laser beams at two distinct and well-separated wavelengths. Simultaneous near diffraction-limited focusability is achieved for both the fundamental (800 nm) and second harmonic (400 nm) of Ti:sapphire-amplified laser light. By comparing the relative effectiveness of various correction loops, the optimal ones are found. Simultaneous correction of both beams of different color relies on the linear proportionality between their wavefront aberrations. This method can enable two-color experiments at relativistic intensities.

Tomographic imaging of nonsymmetric multicomponent tailored supersonic flows from structured gas nozzles.

We report experimental results on the production and characterization of asymmetric and composite supersonic gas flows, created by merging independently controllable flows from multiple nozzles. We demonstrate that the spatial profiles are adjustable over a large range of parameters, including gas density, density gradient, and atomic composition. The profiles were precisely characterized using three-dimensional tomography. The creation and measurement of complex gas flows is relevant to numerous applications, ranging from laser-produced plasmas to rocket thrusters.

Measurements of the GVD of water and methanol and laser pulse characterization using direct imaging methods

We report experimental values of the group velocity dispersion (GVD) of water and methanol at 800 nm. We find GVD800water= (25.71 ± 0.5) fs 2 mm−1 and GVD800methanol=(33.56 ±0.5) fs2 mm−1. These were measured by sending 50 fs, 800 nm pulses with various amounts of chirp through a glass cell filled with a solution of fluorescein in these solvents and recording the production of visible light from the side using a commercial digital camera. This simple setup also gives quantitative information on the duration of our pulses and lets us check independently the correct operation of our grating-based pulse compressor. Results are compared to FROG measurements.

Selective activation with all-laser-driven Thomson γ-rays

A bright, narrow band MeV γ-ray source-ray source based on Thomson scattering using a laser-driven electron accelerator has been developed. We discuss the application of this source for selective activation in regions of high particle (neutron or gamma) production, with minimal absorption in intervening materials.

Photonuclear and radiography applications of narrowband, multi-MeV all-optical Thomson x-ray source

The laser-driven Thomson scattering light source generates x-rays by the scattering of a high-energy electron beam off a high-intensity laser pulse. We have demonstrated that this source can generate collimated, narrowband x-ray beams in the energy range 0.1-12 MeV. In this work, we discuss recent results on the application of this source for radiography and photonuclear studies. The unique characteristics of the source make it possible to do this with the lowest possible dose and in a low-noise environment. We will also discuss recent experimental results that study nuclear reactions above the threshold for photodisintegration and photofission. The tunable nature of the source permits activation of specific targets while suppressing the signal from background materials.