A high spatio-temporal resolution optical pyrometer at the ORION laser facility

A streaked pyrometer has been designed to measure the temperature of ≈100 µm diameter heated targets in the warm dense matter region. The diagnostic has picosecond time resolution. Spatial resolution is limited by the streak camera to 4 µm in one dimension; the imaging system has superior resolution of 1 µm. High light collection efficiency means that the diagnostic can transmit a measurable quantity of thermal emission at temperatures as low as 1 eV to the detector. This is achieved through the use of an f/1.4 objective, and a minimum number of reflecting and refracting surfaces to relay the image over 8 m with no vignetting over a 0.4 mm field of view with 12.5× magnification. All the system optics are highly corrected, to allow imaging with minimal aberrations over a broad spectral range. The detector is a highly sensitive Axis Photonique streak camera with a P820PSU streak tube. For the first time, two of these cameras have been absolutely calibrated at 1 ns and 2 ns sweep speeds under full operational conditions and over 8 spectral bands between 425 nm and 650 nm using a high-stability picosecond white light source. Over this range the cameras had a response which varied between 47 ± 8 and 14 ± 4 photons/count. The calibration of the optical imaging system makes absolute temperature measurements possible. Color temperature measurements are also possible due to the wide spectral range over which the system is calibrated; two different spectral bands can be imaged onto different parts of the photocathode of the same streak camera

Studying radiative shocks using laser driven blast waves in clustered gases

We report on the creation of radiative blast waves by irradiating gases of atomic clusters with intense short pulse laser light. The efficient absorption of the cluster medium leads to high energy deposition and development into a cylindrical shock. These non-equilibrium, optically thin shocks have great potential for hydrodynamic scaling with astrophysical relevance, particularly for supernova remnants. We discuss how cluster blast waves may become susceptible to spatial and temporal instabilities and the application of the RAPCAL atomic physics code to determine our plasma conditions. © 2010 Elsevier B.V

Observation of a velocity domain cooling instability in a radiative shock.

We report on experimental investigations into strong, laser-driven, radiative shocks in cluster media. Cylindrical shocks launched with several joules of deposited energy exhibit strong radiative effects including rapid deceleration, radiative preheat, and shell thinning. Using time-resolved propagation data from single-shot streaked Schlieren measurements, we have observed temporal modulations on the shock velocity, which we attribute to the thermal cooling instability, a process which is believed to occur in supernova remnants but until now has not been observed experimentally