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Photoresist Strongly Absorbent in Optical Spectrum

IP.com Disclosure Number: IPCOM000046323D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Brown, KH: AUTHOR [+2]

Abstract

This photoresist can be exposed in the customary manner with ultraviolet radiation, but it remains strongly absorbent to visible radiation. It is useful for producing acoustic holograms with laser excitation.

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Photoresist Strongly Absorbent in Optical Spectrum

This photoresist can be exposed in the customary manner with ultraviolet radiation, but it remains strongly absorbent to visible radiation. It is useful for producing acoustic holograms with laser excitation.

In effect, these acoustic holograms focus laser-generated thermoelastic energy produced over a large area to a small area, resulting in a large value of thermoelastic power density. The focused beam is useful for nondestructive testing purposes.

In the past, experimentation was done with a metal mask consisting of evaporated silver with a rubber membrane cemented over the evaporated silver. The rubber membrane acted as an absorber in the optical spectrum which overcame the fact that the silver would have reflected most of the incident light. Work was done with the focussing effect using a frequency-doubled Nd-YAG pulsed laser shining onto the absorber. The mask was designed originally to focus thermoelastic energy at 10 MHz.

Here, the photoresist substitutes for the rubber and the silver film to act as the optical absorber, providing efficient optical-to- thermoelastic conversion while submerged in a water tank or in a water environment. At the same time, the photoresist serves as the medium which can be exposed to produce the desired hologram upon its development. In this way, large patterns can be fabricated readily using lasers or other masks to form the desired hologram. No evaporations are required. Experimental work shows that the conversion efficiency of the material is quite high. Efficiency is considerably higher than for the rubber membrane and is higher than that for metal films in water.

To achieve a photoresist with the stated properties, it is necessary to modify normal resist so that while it remains active in the region of exposure (300-400 nm), an additional absorption is created at longer wavelengths which renders th...