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Title: An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets

Abstract

We report on the design, construction, and characterisation of a new class of in-vacuo optical levitation trap optimised for use in high-intensity, high-energy laser interaction experiments. The system uses a focused, vertically propagating continuous wave laser beam to capture and manipulate micro-targets by photon momentum transfer at much longer working distances than commonly used by optical tweezer systems. A high speed (10 kHz) optical imaging and signal acquisition system was implemented for tracking the levitated droplets position and dynamic behaviour under atmospheric and vacuum conditions, with ±5 μm spatial resolution. Optical trapping of 10 ± 4 μm oil droplets in vacuum was demonstrated, over timescales of >1 h at extended distances of ∼40 mm from the final focusing optic. The stability of the levitated droplet was such that it would stay in alignment with a ∼7 μm irradiating beam focal spot for up to 5 min without the need for re-adjustment. The performance of the trap was assessed in a series of high-intensity (10{sup 17} W cm{sup −2}) laser experiments that measured the X-ray source size and inferred free-electron temperature of a single isolated droplet target, along with a measurement of the emitted radio-frequency pulse. These initial tests demonstrated themore » use of optically levitated microdroplets as a robust target platform for further high-intensity laser interaction and point source studies.« less

Authors:
; ; ; ; ; ;  [1];  [2]; ;  [3]
  1. Blackett Laboratory, Imperial College, London SW7 2AZ (United Kingdom)
  2. Department of Physics, Harvey Mudd College, Claremont, California 91711 (United States)
  3. Radiation Physics, AWE, Aldermaston, Reading, Berkshire RG7 4PR (United Kingdom)
Publication Date:
OSTI Identifier:
22392410
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 86; Journal Issue: 3; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; DISTANCE; DROPLETS; KHZ RANGE 01-100; LASERS; LEVITATION; PHOTONS; POINT SOURCES; RADIOWAVE RADIATION; SPATIAL RESOLUTION; TRAPS; X-RAY SOURCES

Citation Formats

Price, C. J., E-mail: c.price10@imperial.ac.uk, Giltrap, S., Stuart, N. H., Parker, S., Patankar, S., Lowe, H. F., Smith, R. A., Donnelly, T. D., Drew, D., and Gumbrell, E. T. An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets. United States: N. p., 2015. Web. doi:10.1063/1.4908285.
Price, C. J., E-mail: c.price10@imperial.ac.uk, Giltrap, S., Stuart, N. H., Parker, S., Patankar, S., Lowe, H. F., Smith, R. A., Donnelly, T. D., Drew, D., & Gumbrell, E. T. An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets. United States. doi:10.1063/1.4908285.
Price, C. J., E-mail: c.price10@imperial.ac.uk, Giltrap, S., Stuart, N. H., Parker, S., Patankar, S., Lowe, H. F., Smith, R. A., Donnelly, T. D., Drew, D., and Gumbrell, E. T. Sun . "An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets". United States. doi:10.1063/1.4908285.
@article{osti_22392410,
title = {An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets},
author = {Price, C. J., E-mail: c.price10@imperial.ac.uk and Giltrap, S. and Stuart, N. H. and Parker, S. and Patankar, S. and Lowe, H. F. and Smith, R. A. and Donnelly, T. D. and Drew, D. and Gumbrell, E. T.},
abstractNote = {We report on the design, construction, and characterisation of a new class of in-vacuo optical levitation trap optimised for use in high-intensity, high-energy laser interaction experiments. The system uses a focused, vertically propagating continuous wave laser beam to capture and manipulate micro-targets by photon momentum transfer at much longer working distances than commonly used by optical tweezer systems. A high speed (10 kHz) optical imaging and signal acquisition system was implemented for tracking the levitated droplets position and dynamic behaviour under atmospheric and vacuum conditions, with ±5 μm spatial resolution. Optical trapping of 10 ± 4 μm oil droplets in vacuum was demonstrated, over timescales of >1 h at extended distances of ∼40 mm from the final focusing optic. The stability of the levitated droplet was such that it would stay in alignment with a ∼7 μm irradiating beam focal spot for up to 5 min without the need for re-adjustment. The performance of the trap was assessed in a series of high-intensity (10{sup 17} W cm{sup −2}) laser experiments that measured the X-ray source size and inferred free-electron temperature of a single isolated droplet target, along with a measurement of the emitted radio-frequency pulse. These initial tests demonstrated the use of optically levitated microdroplets as a robust target platform for further high-intensity laser interaction and point source studies.},
doi = {10.1063/1.4908285},
journal = {Review of Scientific Instruments},
number = 3,
volume = 86,
place = {United States},
year = {Sun Mar 15 00:00:00 EDT 2015},
month = {Sun Mar 15 00:00:00 EDT 2015}
}
  • The gas-dynamic program ''Zarya'' was used to analyze and interpret experimental data on the irradiation of spherical microtargets, filled with DT gas, by an iodine laser in the Iskra-IV system. Reasonable agreement was demonstrated between calculations and experiment. A yield of 10/sup 8/ neutrons per pulse is predicted by calculations based on the optimization of focusing and an increase in the laser power at the target up to the maximum of 2 TW that can be attained in the Iskra-IV system.
  • A review is presented of studies on the laser fusion problem, primarily based on experiments carried out in the Iskra-4 device. The various approaches to solving the DT-fuel ignition problem are examined, together with methods for diagnosing the properties of the laser radiation and the plasma produced when microtargets are heated and compressed. 17 refs., 8 figs., 1 tab.
  • It is shown that s-tetrazine can be deposited in an argon matrix with sufficient homogeneity that the spectral transitions due to carbon-13 and nitrogen-15 containing molecules (in natural abundance) can be clearly discerned with spectral line widths in the range of ca. 0.7 cm/sup -1/. The s-tetrazine molecules can be photolyzed with high efficiency to produce N/sub 2/ and 2HCN, and by means of a tunable laser these photolyses can be readily carried out with high isotopic selectivity. Absorption, fluorescence, and excitation spectra for the various isotopic species are presented. The modes 6a' and 6a'' are 702 and 737 cm/supmore » -1/ in argon compared with 703 and 736 cm/sup -1/ in the vapor. The HCN is formed exclusively as dimers that have spectra quite similar to those of HCN dimers formed in HCN argon mixtures at higher temperatures indicating that substantial motion occurs in the site on photolysis. A main result is that isotope separation is demonstrated for a photolabile system under matrix isolated conditions. Not only does this scheme overcome the need for specialized host lattices but renders trivial the chemical separation of photoproducts from the host, and therefore marks a more practical method of solid-state isotope separation than hitherto demonstrated.« less
  • The power of the ''Iskra IV'' iodine laser is raised to 2 TW by reducing the laser-pulse duration without loss of energy. Irradiation of spherical microtargets filled with DT gas by the iodine laser yielded for the first time 10/sup 5/ neutrons in the exploding-pusher mode.
  • The propagation of the superthermal plasma from microdisk targets irradiated with single, nanosecond CO/sub 2/ laser pulses at intensities of approx.10/sup 14/ W cm/sup -2/ is examined through the study of its effect on subsidiary passive targets. The observed propagation velocity is similar to the estimated superthermal ion acoustic speed and has an intensity dependence of I/sup 0.14-0.21/.