Question

d) Provided a recording medium (film) with sensitivity of 100uJ/cm2 and a power detector with 10mm of diameter, background measured optical power of 8uW and measured optical power from the laser source of 50uW, determine the exposure time of the recording medium.

Answer 1

We are given with:
Sensitivity: 100uJ/cm2
Diameter: 10mm
Background Optical Power: 8uW
Source Optical Power: 50uW

Required: exposure time

Solution:
Exposure time =  sensitivity x area / (background power - source power)
= 100uJ/cm2 (π/4) (1 cm)² / (80 uW - 50 uW)
= 2.62 s

The exposure time is 2.62 seconds.