Posts: 12

I record a speckle pattern using off axis digital holography. However if I take consecutive shots with nothing being changed, I see that the correlation of the Hologram intensity reduces with that of the first shot. Due to which my reconstruction gives different recobstructed field at different times. My laser is stable. I dont see the speckle pattern changing visually in the camera. However the noise seems degrading my signal. Can you please help me with it.

Posts: 49

Hi Sanjiv,

What do you mean that your laser is stable? Because it can be stable in intensity but have phase fluctuations or frequency drift. If the drift in frequency is larger than the spectral correlation width of your medium that means that the speckle will change (as for example a scattering medium gives rise to different speckles for frequencies separated than more than the spectral correlation width).

Another factor is the interferometric stability, the arms should be of the same length, isolated from vibrations, temperature changes and without airflow (so inside a box) to prevent phase fluctuations between the two arms.

The fact that the speckle does not change visually is irrelevant, I guess you measured the decorrelation as a function of the time, what does it look like? If you did not do it, you should start there to quantify the decorrelation.