Advanced Diagnostic Development

The Plasma & Ultrafast Physics Group (PUPG) develops advanced diagnostic for laser-plasma experiments. These diagnostics are often the basics for new physics understanding and provide an opportunity for hands-on experimental learning. The group utilizes state-of-the-art computational design tools, including FRED, OSLO, SIMION, to help understand the subtleties of the diagnostic performance. Many of the diagnostic projects have undergraduate and graduate student participation. Below are a few of the PUPG advanced diagnostic projects that have been fielded at the University of Rochester’s Laboratory for Laser Energetics.

Grating Efficiency Calculator

As a summer undergraduate project, Jeremy Hassett developed a grating efficiency calculator. The Plane Reflectance Diffraction Grating Efficiency Calculator is available for download. It is an application structured for use in optical system design and analysis. The application allows the user to calculate diffracted efficiency for optical diffraction gratings for a wide range of wavelengths, diffracted orders, and nearly arbitrary groove shapes. The efficiency data can then be saved and exported for use in system analysis. A number of default gratings and setups have been provided along with the application. The installation package also contains several helpful documents demonstrating how the application is used.

Optical Thomson Scattering

Thomson scattering is a valuable technique for measuring the plasma conditions in laser-produced plasmas [1]. Simultaneous measurements of the ion-acoustic and electron plasma wave spectrum provide the first-principle measurements of electron temperature, ion temperature, electron density, and plasma flow velocity [8]. Thomson-scattering measurements on OMEGA use a 2ω (527-nm) or 4ω (263-nm) optical laser as a source that is scattered by electron density fluctuations in the plasma [9]. The Thomson-scattering diagnostic is routinely used on the OMEGA Laser System to measure the collective Thomson-scattering spectrum [2]. The development of a fully reflective system allows measurements to be made over a wide spectral range (190 nm to 700 nm) [3].

The script to calculate the collisionless Thomson scattering spectrum from Appendix D in Reference [1] can be downloaded here.

4ω Probe Development

A 10-ps, 263-nm (4ω) laser and a suite of optical diagnostics (schlieren, interferometry, and angular filter refractometry [3] was being built to probe plasmas produced on the OMEGA EP Laser System [4]. Light scattered by the probe beam is collected by an f/4 catadioptric telescope (figure below) and a transport system images with a near-diffraction-limited resolution (~3-µm full width at half maximum) over a 5-mm field of view to a diagnostic table. The transport system provides a contrast greater than 1:104 with respect to all wavelengths outside of the 263±2-nm measurement range.