Vacuum-ultraviolet frequency-modulation spectroscopy

Frequency-modulation (FM) spectroscopy has been extended to the vacuum-ultraviolet (VUV) range of the electromagnetic spectrum. Coherent VUV laser radiation is produced by resonance-enhanced sum-frequency mixing ($\nu_{\mathrm{VUV}}=2\nu_{\mathrm{UV}}+\nu_2$) in Kr and Xe using two near-Fourier-transform-limited laser pulses of frequencies $\nu_{\mathrm{UV}}$ and $\nu_2$. Sidebands generated in the output of the second laser ($\nu_2$) using an electro-optical modulator operating at the frequency $\nu_{\mathrm{mod}}$ are directly transfered to the VUV and used to record FM spectra. Demodulation is demonstrated both at $\nu_{\mathrm{mod}}$ and $2\nu_{\mathrm{mod}}$. The main advantages of the method are that its sensitivity is not reduced by pulse-to-pulse fluctuations of the VUV laser intensity, compared to VUV absorption spectroscopy is its background-free nature, the fact that its implementation using table-top laser equipment is straightforward and that it can be used to record VUV absorption spectra of cold samples in skimmed supersonic beams simultaneously with laser-induced-fluorescence and photoionization spectra. To illustrate these advantages we present VUV FM spectra of Ar, Kr, and N$_2$ in selected regions between 105000cm$^{-1}$ and 122000cm$^{-1}$.Comment: 23 pages, 10 figure

Experimental determination of DT ion temperatures in laser fusion targets

Using the time-of-flight technique, energy distribution measurements were made of the fusion produced $alpha$ particles emitted from laser implosions of DT gas contained in glass microshells. The number of nuclear reactions was determined by an absolute measurement of both the number of $alpha$ particles and the number of neutrons. From the FWHM of the $alpha$ particle energy distributions, upper limits of the plasmas ion temperature have been inferred. By applying corrections for the broadening of the distribution due to the fuel and the pusher, ion temperatures of 2-3 keV have been calculated. These measurements constitute significant evidence that the implosions produced thermonuclear burn of the DT fuel. (auth

The Beam Line X NdFe-steel hybrid wiggler for SSRL

A wiggler magnet with 15 periods, each 12.85 cm long, which achieves 1.40 T at a 2.1 cm gap (2.26T at 0.8 cm) has been designed and is now in fabrication at LBL. This wiggler will be the radiation source of the high intensity synchrotron radiation beam line for the Beam Line X PRT facility at SSRL. The magnet utilizes Neodymium-Iron (NdFe) material and Vanadium Permendur (steel) in the hybrid configuration to achieve simultaneously a high magnetic field and short period. Magnetic field adjustment is with a driven chain and ball screw drive system. The magnetic structure is external to an s.s. vacuum chamber which has thin walls, 0.76 mm thickness, at each pole tip for higher field operation. Magnetic design, construction details and magnetic measurements are presented

Development of a NdFe-steel hybrid wiggler for SSRL

A NdFe-steel hybrid configured permanent magnet wiggler, is being developed for insertion in the SPEAR ring at the Stanford Synchrotron Radiation Laboratory, SSRL. Featuring 15 complete periods, a 12.9-cm magnetic period length, and a peak magnetic field range of 0.01 to 1.4 Tesla, the wiggler, was designed to provide an intense radiation source for the National Laboratory/University of California participating research team (PRT) facility on Beam Line VIII-W. A new permenent magnet material, neodymium-iron (NdFe), is being used in the magnetic structure instead of rare-earth cobalt, REC, used previously in the 27-period wiggler now on Beam Line VI. NdFe advantages include a 16% higher coercive force (10.6-kOe vs 9.0-kOe) and lower cost. The wiggler design features a thin walled, rigid vacuum chamber with pole pockets on opposing surfaces allowing a 2.1-cm minimum magnetic gap with a 1.8-cm beam vertical aperture. At 3 GeV the wiggler at peak field is expected to radiate approximately two kilowatts in a 5-mrad horizontal fan with a 7.8 keV critical energy. Calculations are in progress to model the wiggler radiation spatial and spectral radiation emission

Flat-response x-ray-diode-detector development

In this report we discuss the design of an improved sub-nanosecond flat response x-ray diode detector needed for ICF diagnostics. This device consists of a high Z cathode and a complex filter tailored to flatten the response so that the total x-ray energy below 1.5 keV can be measured using a single detector. Three major problems have become evident as a result of our work with the original LLNL design including deviation from flatness due to a peak in the response below 200 eV, saturation at relatively low x-ray fluences, and long term gold cathode instability. We are investigating grazing incidence reflection to reduce the response below 200 eV, new high Z cathode materials for long term stability, and a new complex filter for improved flatness. Better saturation performance will require a modified XRD detector under development with reduced anode to cathode spacing and increased anode bias voltage

Filtered detector arrays for single pulsed photon measurements above 100 keV

We discuss the design of filtered detector arrays for single pulsed, 100 keV photon spectral and angular distribution measurements at the Lawrence Livermore Laboratory Argus laser facility