Photochemically-induced acousto-optics in gases

Acousto-optics consists of launching acoustic waves in a medium (usually a crystal) in order to modulate its refractive index and create a tunable optical grating. In this article, we present the theoretical basis of a new scheme to generate acousto-optics in a gas, where the acoustic waves are init...

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Bibliographic Details
Published inarXiv.org
Main Authors Michel, Pierre, Lancia, Livia, Oudin, Albertine, Kur, Eugene, Riconda, Caterina, Ou, Ke, Perez-Ramirez, Victor M, Lee, Jin, Edwards, Matthew R
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 16.06.2024
Subjects
Absorption
Acoustic waves
Acoustics
Acousto-optics
Chemical reactions
Diffraction
Diffraction efficiency
Gas composition
Gas heating
Gases
High power lasers
Mathematical analysis
Optical components
Optics
Ozone
Photodissociation
Refractivity
Room temperature
Ultraviolet radiation
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Summary:Acousto-optics consists of launching acoustic waves in a medium (usually a crystal) in order to modulate its refractive index and create a tunable optical grating. In this article, we present the theoretical basis of a new scheme to generate acousto-optics in a gas, where the acoustic waves are initiated by the localized absorption (and thus gas heating) of spatially-modulated UV light, as was demonstrated in Y. Michine and H. Yoneda, Commun. Phys. 3, 24 (2020). We identify the chemical reactions initiated by the absorption of UV light via the photodissociation of ozone molecules present in the gas, and calculate the resulting temperature increase in the gas as a function of space and time. Solving the Euler fluid equations shows that the modulated, isochoric heating initiates a mixed acoustic/entropy wave in the gas, whose high-amplitude density (and thus refractive index) modulation can be used to manipulate a high-power laser. We calculate that diffraction efficiencies near 100% can be obtained using only a few millimeters of gas containing a few percent ozone fraction at room temperature, with UV fluences of less than 100 mJ/cm2, consistent with the experimental measurements. Our analysis suggests possible ways to optimize the diffraction efficiency by changing the buffer gas composition. Gases have optics damage thresholds two to three orders of magnitude beyond those of solids; these optical elements should therefore be able to manipulate kJ-class lasers.
ISSN:2331-8422