Cooled CCD camera

Outline


Fully developed speckle
image shown at 0 dB gain

Here, use of the speckle standard
as screen is assumed.
You could use a white paper
with higher diffuse reflectivity
at risk of volumetric scattering
and polarization diversity


Histogram representing nearly
negative exponential function
type PDF.


Offset Gamma density function fit

DVC-1500M ΔT=25K   DVC company

Wide dynamic range :4096 gray scale

Sensitivity calibration at 8s exposure:

1gray scale=3.2×10-3 cd/m2 @F/500

Which corresponds to 0.8mm pin hole

       Ref: 1×10-6 cd/m2 @ F/8

Dark current @exposure 1-9s: 11.3 gray scale

 

Measurement condition guideline

Laser source power: 5mW (~3.4 lm @532nm)

Screen incident illuminance: 200lx  

Ave scattered light illuminance: 2 lx (1% of incident)

Ave luminance at 8s exposure: 200 gray scale

=0.64 cd/m2

FS 4096 gray scale=20σ, where Iav=s=200 gray scale.  

The probability density function (PDF) of speckle intensity can be displayed as the histogram of the measured intensity.

 

In the fully developed speckle case, since its PDF is the negative exponential type function, the speckle contrast may be calculated from logarithmic fitting the higher intensity side slope of the histogram.

Oxide Corporation

Speckle contrast Measurement System