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Optical Delay Modulator for Ultrafast Measurements

IP.com Disclosure Number: IPCOM000034814D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Grischkowsky, DR: AUTHOR [+3]

Abstract

A technique is described whereby optical delay modulation is implemented in pumping or probing beam ultrafast measurement applications, so as to eliminate undesirable side effects of conventional beam chopping. Also discussed is a retro-reflector used to stabilize the angles of reflection. The delay modulation technique is compatible with standard lock-in techniques. In many optical ultrafast measurement applications, the standard method of increasing the signal-to-noise ratio is to chop the repetitively pulsed pumping beam at a fixed rate and to use a lock-in amplifier to detect changes in the probing beam, as the time delay between the pumping and probing pulses is varied. However, in some applications, chopping of the pumping beam produces undesirable false signals at the lock-in amplifier.

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Optical Delay Modulator for Ultrafast Measurements

A technique is described whereby optical delay modulation is implemented in pumping or probing beam ultrafast measurement applications, so as to eliminate undesirable side effects of conventional beam chopping. Also discussed is a retro-reflector used to stabilize the angles of reflection. The delay modulation technique is compatible with standard lock-in techniques. In many optical ultrafast measurement applications, the standard method of increasing the signal-to-noise ratio is to chop the repetitively pulsed pumping beam at a fixed rate and to use a lock-in amplifier to detect changes in the probing beam, as the time delay between the pumping and probing pulses is varied. However, in some applications, chopping of the pumping beam produces undesirable false signals at the lock-in amplifier. The concept described herein provides a method of eliminating the undesirable side effect by modulating the delay between the pump and probe beam, instead of amplitude chopping the pumping beam. The delay modulation concept involves the use of a spinning transparent disc, on which a precise pattern of alternating reflecting and transparent stripes have been fabricated, as shown in Fig. 1. The stripes alternately reflect and transmit the beam. The pattern is created through the use of lithography by using a precision chopping wheel as a mask on a transparent plastic substrate. The resulting disc is spun by the same motor and...