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Using Two-Photon Photoemission for Auto Correlation Measurement

IP.com Disclosure Number: IPCOM000059958D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 27K

Publishing Venue

IBM

Related People

Heinz, TF: AUTHOR

Abstract

Lasers are capable of producing pulses of such short duration that their intensity as a function of time cannot be measured directly by usual electronic devices. The technique of determining the autocorrelation of the laser pulse by means of nonlinear mixing of the pulse with a delayed replica of itself can overcome that problem. Presently, the most widely used method for this purpose is second-harmonic generation in a nonlinear crystal. In this scheme, the energy of the second-harmonic radiation is recorded as a function of the delay time between the two copies of the laser pulse. The phenomenon of two- photon photoemission has been frequently observed, as first presented by H. Sonnenberg, H. Heffner, and W. Spicer (Appl Phys . Lett . 5, 95 (1964)).

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Using Two-Photon Photoemission for Auto Correlation Measurement

Lasers are capable of producing pulses of such short duration that their intensity as a function of time cannot be measured directly by usual electronic devices. The technique of determining the autocorrelation of the laser pulse by means of nonlinear mixing of the pulse with a delayed replica of itself can overcome that problem. Presently, the most widely used method for this purpose is second-harmonic generation in a nonlinear crystal. In this scheme, the energy of the second-harmonic radiation is recorded as a function of the delay time between the two copies of the laser pulse. The phenomenon of two- photon photoemission has been frequently observed, as first presented by H. Sonnenberg, H. Heffner, and W. Spicer (Appl Phys . Lett . 5, 95 (1964)). That effect is applied to autocorrelation measurements in the device shown above. This autocorrelation device splits a pulsed laser beam into two parts and recombines the parts on a photocathode responding with two- photon photoemission. The total emitted charge is detected as a function of the relative delay between the two pulses, which can be easily adjusted by changes in the optical path length. This method can be most conveniently realized by measuring the charge induced in a vacuum photodiode or in a photomultiplier. When the two-step photoemission process occurs through a virtual intermediate state, the time resolution of this technique will be very high (<<psec). This situation will prevail in materials not having an appreciable linear absorption at the laser frequency. A possible implementation of this idea is indicated schematically in the figure. The incoming pulsed laser beam 10 is divided into two parts by a beam splitter (BS) and recombined by the same beam splitter after reflections from mirrors M1 and M2. Mirror M2 can be adjusted to effect a change in the path length, i.e., in the relative delay between the two pulses. A quarter- wave plate QWP may be a...