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Title: CaF{sub 2} ablation plumes as a source of CaF molecules for harmonic generation

Generation of low-order harmonics (third and fifth) of the fundamental radiation of a Q-switched Nd:YAG laser (1064 nm, pulse 15 ns) was observed in a CaF{sub 2} laser ablation plume. The ablation process is triggered by a second Q-switched Nd:YAG laser operating at 532 or 266 nm. In the scheme employed, the fundamental laser beam propagates parallel to the target surface at controllable distance and temporal delay, allowing to the probing of different regions of the freely expanding plume. The intensity of the harmonics is shown to decrease rapidly as the distance to the target is increased, and for each distance, an optimum time delay between the ablating laser pulse and the fundamental beam is found. In situ diagnosis of the plume by optical emission spectroscopy and laser-induced fluorescence serves to correlate the observed harmonic behavior with the temporally and spatially resolved composition and velocity of flight of species in the plume. It is concluded that harmonics are selectively generated by CaF species through a two-photon resonantly enhanced sum-mixing process exploiting the (B {sup 2{Sigma}+}-X {sup 2{Sigma}+}, {Delta}{nu}=0) transition of the molecule in the region of 530 nm. In this work polar molecules have been shown to be the dominatingmore » species for harmonic generation in an ablation plume. Implications of these results for the generation of high harmonics in strongly polar molecules which can be aligned in the ablation plasma are discussed.« less
Authors:
; ;  [1] ;  [1] ;  [2] ; ;  [3]
  1. Instituto de Quimica Fisica Rocasolano, CSIC, Serrano 119, 28006 Madrid (Spain)
  2. (Spain) and Instituto de Estructura de la Materia, CSIC, Serrano 123, 28006 Madrid (Spain)
  3. Blackett Laboratory, Imperial College London, SW7 2 BW London (United Kingdom)
Publication Date:
OSTI Identifier:
21408735
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 81; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevA.81.043841; (c) 2010 The American Physical Society
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ABLATION; BEAMS; CALCIUM FLUORIDES; EMISSION SPECTROSCOPY; FLUORESCENCE; HARMONIC GENERATION; HARMONICS; MOLECULES; NEODYMIUM LASERS; PLASMA; PLUMES; PULSES; TIME DELAY ALKALINE EARTH METAL COMPOUNDS; CALCIUM COMPOUNDS; CALCIUM HALIDES; EMISSION; FLUORIDES; FLUORINE COMPOUNDS; FREQUENCY MIXING; HALIDES; HALOGEN COMPOUNDS; LASERS; LUMINESCENCE; OSCILLATIONS; PHOTON EMISSION; SOLID STATE LASERS; SPECTROSCOPY