Helmholtz T.F. II

Remeasurement on DVC-1500M


PSD of the vibration


Oscilloscope trace 5ms/div


K resolution element of the projection lens in the eye resolution cell.

Adjustment/setup condition

Magnet tine parallelism/Wood spacer 60μm ampl/17Vampl
Conic frusta2 -> black flock paper for better beam dump

Sine wave distortion (measured by a piezoelectric sensor on the tine)
0dB @100Hz
-24dB @200Hz 0.4%
-30dB @300Hz,400Hz

Results: Speckle contrast was observed to decrease with the exposure time (T) as inverse square root of T, approximately.
Speculation 1: Best plausible function form as M=aT in

seems to fail in approximation of the observed characteristic against T.
Speculation 2:
At that very low average intensity as shown below, however, the shot noise on the CCD is not negligible, which is also reduced with the exposure time.

Speckle patterns at 10s and 40s exposure time, shown with 20dB and 10dB gain,respectively.

Average intensity with the moving diffuser is 80 gray scale, which is 40% of 200 gray scale in case for without the diffuser, while transmission at 700nm on the #1000 frost glass diffuser is specified to 39%.

Speculation_2 is confirmed by the speckle contrast (triangle) observed at 10s exposure time and twice laser power (10mW), which is equivalent to one at 14s exposure time and 5mW laser power.

Oxide Corporation

Speckle contrast Measurement System