Construction of a Tabletop Michelson Interferometer
Estimating Camera Sensitivity
It is critical to understand the sensitivity of the camera to light from the interferometer, given the high intended image acquisition speed. The camera purchased for this setup, Casio EX-F1, has a movie frame rate capability of 1200 Hz. The following information allows an order of magnitude estimate of the sensitivity. (The camera uses a CMOS sensor. Note that lx=lm·m2)
- a sample CMOS chip, Micron's MT9P401, has sensitivity of 1.4 V/lx·s and supply voltage of 2.8 V yielding 2 lx·s of light energy to saturation.
- Light intensity conversion - 320 lm/W given:
- a 100 W incandescent light bulb is measured to have the perceived intensity of about 1600 lm
- a rough figure of efficiency for a 100 W is 5%
Using these conversions, the sensor pixels saturate at 6.3×10-3 W·m2·s. At 1200 Hz acquisition rate, assuming 100% duty cycle, the saturation figure is 5.2×10-6 W·m.
Now, let us assume that only about 5% of 1 mW laser light reaches the sensor due to cleanup in the beam expander and the light transmitted through the diamond. If the light is expanded to a 2 cm diameter beam, the beam at the sensor is rated at 1.6×10-8 W·m2
The two order of magnitude shortfall means that very little of the dynamic range of the sensor will be used, leading to a low signal to noise ratio. Increasing the specification of the laser to 5 mW may be called for as a result.