To improve the signal-to-noise ratio of the diode in Problem 17.1, we wish to use a semiconductor low-pass filter which has the following absorption properties at room temperature: for 9000 A...

To improve the signal-to-noise ratio of the diode in Problem 17.1, we wish to

use a semiconductor low-pass filter which has the following absorption properties at room temperature:

for 9000 A radiation ˚ α = 0.2 cm−1

for 7000 A radiation ˚ α = 103 cm−1.

How thick must the filter be to attenuate 7000 A background noise by a factor ˚

of 104?

By what factor is the signal (at 9000 A) attenuated by a filter of this thickness? ˚

Neglect reflection at the surfaces.