If you search the wiki for multicoherence volumes you will find a post on this.Jeffrey Weil wrote:Hey Everyone,
I decided to come back and confuse everyone more! How about multi coherence volume lighting!
Use more than one beam to light up your object front to back and adjust each beam path so things are sill within the coherence distance of the laser when the light gets to the recording plate. This way, split beam of course, you could light up an object of any depth only limited by your laser power and table size, not your coherence length.
Jeffrey Weil
NorthBeach Holography Inc.
hologram depth
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Colin Kaminski
hologram depth
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Konrad
hologram depth
I'd like to add my few cents. I have Melles Griot HeNe LHP-121 (rated 2mW, real output 3mW) which has guaranted coherence about 40cm - I made 20cm depth Denisyuk with it. Also I tried to find maximum coherence of this laser and I setup Michelson interferometer with path length difference 50, 100, 150, 200, 250cm... end of the table - still high contrast fringes on all length! I must make more precise tests in the future.
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JohnFP
hologram depth
Konrad, take note, that's why I loved Jeffrey Weil's suggestion and Colin's response.
If you look at this link on the Wiki, it explains how your coherence length can go in and out due to two or more modes oscillating at the same time. You may have a continuous coherence length of 20cm and then it may fuzz out, then come back in. So your way of testing coherence length maximum is the common way but flawed unless you step the one leg of the interferometer every few mm or so.
Review the section "Longitudinal Modes and Coherence Length" at this link
http://www.holowiki.com/index.php/Laser
The beauty with Jeffrey's suggestion is that it is definitive and a one step process (you do need to burn a plate though).
If you look at this link on the Wiki, it explains how your coherence length can go in and out due to two or more modes oscillating at the same time. You may have a continuous coherence length of 20cm and then it may fuzz out, then come back in. So your way of testing coherence length maximum is the common way but flawed unless you step the one leg of the interferometer every few mm or so.
Review the section "Longitudinal Modes and Coherence Length" at this link
http://www.holowiki.com/index.php/Laser
The beauty with Jeffrey's suggestion is that it is definitive and a one step process (you do need to burn a plate though).