Dear Lindsey

If the illumination laser beams have been expended and collimated, both object wave and reference wave will become spherical waves after MO unless you used infinity MO.

You should understand why adding a MO into the reference arm. In most of cases, it used to compensate the inherent phase aberration which is introduced by the MO and other lenses in the object arm. The position of MO in the reference arm requires high precision adjustments in practice. You can find some reference papers or books on phase aberration compensation in digital holography. Many works on the successful compensation of such phase aberrations have already been reported. I think this will be helpful.

Junwei

Thank you very much for your answer Junwei!

I will look into the inherent phase aberration 

I am inclined to take out the MO in the reference arm to start with the simplest form of off axis configuration. However without the MO the light intensity is very strong. I already have a ND filter, does it mean i should apply another one?

Another question I have is on how to find the right equation for the reference wave. The set up is not perfect and off axis but experimentally it is hard to determine the angle tilted.., I am wondering if there is an common way for experimenters to find the angle, whether it is through algorithm or experimental measurement.

Thank you again for your help I really appreciate it!

What is the power of your laser? Usually, you should expended and collimated the laser beam before the BS. Then, the light intenstity should not very strong. One ND filter should be enough.

In practice, it hard to measure the angle between the object wave and reference wave directly. In usually, you can determine this angle by analyzing the position of spectrum. You can find the relevant formula in off-axis chapter of any of the holographic books.

You might also want to take a look on "phase-shifting" technique for the case of on-axis recording scheme. This is when no angle is being introduced between an object and reference arms. (Modified Linnik interferometer is often adjusted for this purpose.) This method enables to suppress the background, leaving the image of the object only. There are a lot more benefits, I have just pointed on the method. Cheers

George Sergeevich Kalenkov

Thank you for the reply!

For the background case, couldn't i just subtract a background picture that i take with no object in the paths from the hologram to get rid of the backgrounds

Also after some reading I pressumed the set up I have (with the beams divided to two arms) I can have an off axis hologram as long as the  two source of light does not superimpose on each other?

i have read alittle bit phase shifting and it seems to require a controllable mirror to adjust the angles. Is this method with on axis an better alternative  than off axis configuration?

Thank you!!