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(17) W cm(-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.
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: C J
authors.initials: CJ
authors.lastname: Price
authors.affiliation: Department of Physics, Harvey Mudd College, Claremont, California 91711, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Donnelly
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Giltrap
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: N H
authors.initials: NH
authors.lastname: Stuart
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Parker
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Patankar
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: H F
authors.initials: HF
authors.lastname: Lowe
authors.affiliation: Radiation Physics, AWE, Aldermaston, Reading, Berkshire RG7 4PR, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Drew
authors.affiliation: Radiation Physics, AWE, Aldermaston, Reading, Berkshire RG7 4PR, United Kingdom.
authors.forename: E T
authors.initials: ET
authors.lastname: Gumbrell
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: R A
authors.initials: RA
authors.lastname: Smith