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Re: barrier penetration, evanescent waves



My guess:
the seminar appears to be set up to demonstrate that if the illumination can be
monotonic, then a holographic replica can do the work of a glass optical element.

This approach can be helpful where space is at a premium, or quantities of optics are needed at attractive prices.

Brian

At 08:36 PM 9/16/02, you wrote:
Coincidence:

Thursday September 19 @ 04.pm SCI 242
* Physics Seminar * Fall 2002 *

Professor Ramen Bahuguna
Physics Department
San Jose State University

A Holographic Fingerprint Sensor

A prism fingerprint sensor based on total internal reflection has an inherent

problem: the image is aberrated and distorted. The main reason is that the
image is inclined to the camera and expensive optics is needed to correct the

aberrations.
A simple holographic optical element (a holographic diffraction grating) can
correct the above problems. A fingerprint sensor incorporating such a
grating will be demonstrated.


For more information, or to get on the Physics Seminar e>mail list,
or to enroll in Phys285 (till 9/20)
please contact Carel Boekema, Seminar Coordinator.
c•boekema 4 - 5260 boekemac@aol.com
Office Hours MWF 9.30 - 10.20 and MW 11.30 - 12.20 Sci 303




Bernard Cleyet wrote:

> "... But a finger has
> just the right combination of compliance and texture
> so that the ridges of the fingerprint absorb the
> evanescent wave (while the intervening valleys don't),
> resulting in a very-high-contrast image of the fingerprint."
>
> I forgot to mention that this is the method for fingerprinting (a digital
> camera views the ftir image and sends it to the DOJ)
>
> Before I do my demo. (semi-quantitative) for the HS Physics class, the
> instructor has passed out glass prisms for the students to see for
> themselves.
>
> bc who was finger printed this way as a requirement for a teaching
> credential.
>
> "John S. Denker" wrote:
>
> > Bernard Cleyet wrote:
> > >
> > > A model for barrier penetration is FTIR (frustrated total internal
> > > reflection). The model is exact in that the equations are of the same
> > > form (obvious, they're both described by the same wave equation).
> >
> > Yup.

cut

Brian Whatcott
Altus OK Eureka!