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Extreme ultraviolet superfluorescence from helium ions

ハリーズ　ジェームズ, James Harries

Published Jun 6, 2019• 0 citations
OpenAlex

Abstract

We report the observation of superfluorescence at wavelengths of 469 nm, 164 nm and 30.4 nm from helium ions created and excited using pulses from the EUV free-electron laser at SACLA BL1. The observations at 164 nm and 30.4 nm represent the first ever observations at such short wavelengths.

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We report the observation of superfluorescence at wavelengths of 469 nm, 164 nm and 30.4 nm from helium ions created and excited using pulses from the EUV free-electron laser at SACLA BL1. Experimental observations of intense, highly-directional emission (all 3 wavelengths) and a 1/(density) pulse delay dependence (469 nm emission), along with a detailed numerical simulation support our interpretations.

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We have studied in detail the emission of superfluorescence at a wavelength of 469 nm (4p→3s) from helium ions created and excited using free-electron laser pulses from SACLA’s BL1. In earlier work we observed superfluorescence at visible wavelengths in neutral helium [1-5]. To observe superfluorescence from helium ions we used a wavelength of 24.3 nm, resonant with the He + 1s→4p transition and sufficiently short to ionise neutral helium atoms. The density of excited He + ions created by this sequential 2-photon absorption was sufficient to allow for the development of superfluoresence.
We report the probable observation of superfluorescence at a wavelength of 164 nm from helium ions created and excited using pulses from the EUV free-electron laser at SACLA BL1. The emission is the second step of a superfluorescence cascade from excited 4p states. To our knowledge this is the shortest wavelength at which superfluoresence has ever been demonstrated. The high intensity of the emission and the narrow angular divergence strongly support the interpretation as superfluorescence, and numerical simulations will also be presented which support this.