Characterization of thin metal films by ultrafast laser induced ultrasound

Hao Zhang, Alessandro Antoncecchi, Stephen Edward, Paul Planken, Stefan Witte

Research output: Chapter in Book / Report / Conference proceedingConference contributionAcademicpeer-review

Abstract

Ultrafast laser pulses incident on metals can lead to the generation of coherent phonon wave packets with frequencies in the gigahertz to terahertz range [1,2]. Material characterization using such ultrafast laser-induced ultrasound pulses provides access to a frequency range that is inaccessible by any other means. Our objective is to study the optical and acoustic properties of materials by generating and detecting ultrasound waves with ultrafast laser pulses. To generate high frequency acoustic waves in a way that also optimizes their detection, we use a pair of crossed 40 fs femtosecond pump pulses at 400 nm wavelength to project interference fringes on the surface of thin metal films. Because ultrasound is only generated in the interference maxima, this approach produces a spatially periodic array of acoustic pulses. The acoustic pulses propagate through the film and are reflected at the back surface. A delayed probe pulse (30 fs, 800 nm) then detects the returning acoustic echo by detecting a change in the optical response that occurs every time an acoustic echo returns to the surface. Because a periodic array of ultrasound waves was produced, we can detect the first order diffraction of the probe beam by this 'acoustic grating'. By performing these measurements in thin free-standing metal membranes, the influence of substrate interfaces is eliminated, and acoustic attenuation is only caused by propagation in the metal, providing clean measurements of the metal parameters without external factors.

Original languageEnglish
Title of host publication2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019
PublisherInstitute of Electrical and Electronics Engineers Inc.
ISBN (Electronic)9781728104690
DOIs
Publication statusPublished - 17 Oct 2019
Event2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019 - Munich, Germany
Duration: 23 Jun 201927 Jun 2019

Publication series

Name2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019

Conference

Conference2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019
CountryGermany
CityMunich
Period23/06/1927/06/19

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