Tony DCG wrote:Here I hope is is a photo of the ring
Sorry if the photo is of poor quality
The rings start in the almost center and are about an half inch apart
The Laser is a Melos Griot 457nm 200mw elipitcal beam
Ah, would it be this one?
A very nice laser looking at the specs.
I did a couple of plates some months ago that had similar banding, but my stripes were straight lines.
I don't have a photo to show as they were not capped with a cover plate, so I will have to reprocess.
However, I shot three holograms of the same scene, two came out stripped and one was perfect.
I initially thought that the problem was caused by insufficient settling time to allow the plate to get to ambient temperature,
but all three plates had the same length of settling time.
The fact that the stripes are not equally spaced tells us something important.
It's not the sort of result I would expect to see from a mode hop.
It looks like the sort of result you could get from plate movement, or expansion/contraction of the plate.
Having said that, I did set my 315M-100 on the table with a makeshift interferometer and spent many hours sitting in the dark
watching fringes over a two week period. It turns out that my laser needs quite a bit of time to settle down.
I didn't observe any mode hops, but just a very slow drift in the fringes. It seems to take my laser a couple of hours
to stabilize enough for my exposures, that can be 20 - 40 minutes long.
Could a slow drift in laser wavelength produce the results we are seeing???
I have not had time to shoot any holograms since running tests on my laser,
but I plan to extended my laser warm up time before attempting to make an exposure.
How much time to you leave your laser on before making an exposure?
Steven.