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A concept for laser safety glasses is demonstrated where the laser intensity itself introduces phase distortion on the transmitted laser beam and is therefore self-limiting. The absorbed light in the polycarbonate glass heats it and changes its index of refraction.
A coating on the surface produces a non-uniform intensity pattern on the transmitted laser beam. This non-uniform intensity results in a non-uniform phase distortion which destroys the coherence of the laser and does not allow the cornea to focus the laser
strongly on the retina. The absorption in the glass is the same for all laser wavelengths (the glass is sometimes referred to as a neutral density filter) and therefore the safety
glasses are good for all laser wavelengths. The amount of laser absorption required to meet the ANSI standard for max allowable exposure is a transmission of 0.1% and this is
experimentally verified by the data obtained. This attenuation is sufficient to protect the
eye from damage until the heating and phase distortion kicks in. Once this happens, the
protection is better - the higher the incident intensity. Experimental demonstration of the
effectiveness of the prototype has been obtained at 488 mm (blue light) and 514 mm
(green light) from an argon ion laser with laser duration from 0.04 seconds to 0.25
seconds. The data shows that as you increase the laser intensity beyond a certain value
the intensity at the focus of a lens actually decreases, and further increases in intensity
lowers the focal plane intensity even further. For the phase distortion safety glasses, we
can calculate the transmission which meets the ANSI standard where the phase distortion
is optimum. Thus our glasses not only meet the ANSI standard but provide protection for
any higher laser intensity. The optical quality of the prototype was very good with no
fogging, or optical distortion of transmitted laser, and after the experiment, the prototype
returned to the identical optical quality with no permanent optical distortion.
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