445nm beam correction optic

This is a forum to share experiences and ideas about holography.
Joe Farina

445nm beam correction optic

Post by Joe Farina » Sun Aug 29, 2010 5:47 pm

Someone has built an interesting beam correction device for the 445nm diode, in reflection mode:

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... K:MEWAX:IT

DJ Mathson

445nm beam correction optic

Post by DJ Mathson » Sun Aug 29, 2010 10:03 pm

More about it at PL.

JohnFP

445nm beam correction optic

Post by JohnFP » Mon Aug 30, 2010 11:23 am

Mine is seated in a heat sink in which the fins are in front of the beam. Well, I tried to make a hologram and got great colors that looks like a hologram of a mirror. I could barely see the object. What I suspect is happening is the raw beam out of the diode has some quickly diverging light off to the sides that must be hitting the fins and thus interfering with main part of the beam.

I will flip the diode around such that the fins are in the back and again use the raw beam exiting out of the laser. I do have a prism and may put that in just to correct the beam a little more, but it seems I am only in the 2 - 2 1/2 minute exposure time even throw away most of the beam. And with SBR, not a problem.

Joe Farina

445nm beam correction optic

Post by Joe Farina » Mon Aug 30, 2010 12:24 pm

Hello John, congratulations on getting the diode up and running so quickly.

I was planning to use a large block of aluminum for the heatsink on mine, but after telling Ahmet the dimensions of the block, he informed me that my heatsink would probably not be adequate (which was surprising to me). So I bought a much larger one with fins, it's 6 X 10 inches X about 2 inches deep (the finned portion). He said that should be OK. Also, he told me to be very careful to maximize the contact between the diode base and the heat sink assembly, particularly around the rim of the diode base, so that there would be adequate heat transfer. I'm not used to dealing with high-power diodes generating so much heat, so I'm glad Ahmet was abe to spot those problems.

By the way, were you using any kind of method to determine whether or not the diode was running single mode?

JohnFP

445nm beam correction optic

Post by JohnFP » Mon Aug 30, 2010 1:00 pm

No, just gave it a whirl making a hologram. :wink:

Thieu

445nm beam correction optic

Post by Thieu » Mon Aug 30, 2010 3:24 pm

John, at what current were you operating the diode? Cause higher than about 250 mA it becomes severely multimode. At really high currents, a couple of hundreds of mA, the mode structure even gets 'fuzzy', the modes aren't spaced apart evenly anymore. I think this is because the cavity gets distorted by the filamentation of the gain. I would expect the coherence length at that current level to decrease to a millimeter at most, with the object disappearing instead of becoming breadsliced. Just speculating here, but this may explain the mirror effect.

Thieu

445nm beam correction optic

Post by Thieu » Mon Aug 30, 2010 3:33 pm

Joe, you probably were going to do this already, but just in case: it's also a good idea to use a tiny drop of heat conductive paste between diode and heatsink. Just make sure you don't get any on the facet cause it will be very hard to get it off.

Joe Farina

445nm beam correction optic

Post by Joe Farina » Mon Aug 30, 2010 7:59 pm

Thieu wrote:Joe, you probably were going to do this already, but just in case: it's also a good idea to use a tiny drop of heat conductive paste between diode and heatsink. Just make sure you don't get any on the facet cause it will be very hard to get it off.
Hi Thieu, yes thermal compound is part of the plan, I will be sure to keep it off the facet or window. By the way, I was wondering what you think of noise-detection methods for the 445nm diode. Do you think sampling the light output with a photodiode (and having an audible indicator, like with Wolfgang's noise-detector) is good, or would it be better to use something which generates fringes? Or maybe both? I have the feeling that the key to success with this diode will be in knowing when it's single-mode or not.

dave battin

445nm beam correction optic

Post by dave battin » Mon Aug 30, 2010 11:05 pm

JohnFP wrote:No, just gave it a whirl making a hologram. :wink:
If it works! That's really all that counts for display holography.............
John have you set the diode up in a Michelson interferometer yet ? By watching the fringes and and adjusting the power, you will quickly see where to set it to get nice steady fringes! watch them to drift for a good long while, give it a try please.

i had my laser in a set up where i could quickly transfer the laser from the setup, to the interferometer. Then, if your hologram does not come out, transfer the laser to the interferometer and see what’s going on (fringe wise), Now go on and make a New power adjustment.

Initially use the best fringe contrast possible and lowest power setting possible ,keep it thermally constant (wrap in insulation blanket),and you can be sure it will be stable operating at such a low power.

Colin Kaminski

445nm beam correction optic

Post by Colin Kaminski » Tue Aug 31, 2010 1:09 am

When I was making 10 gallon TEC cooled beer fermentors I found Arctic Silver. I would not make a thermal assembly without it or one of its analogs.

http://www.arcticsilver.com/as5.htm

Thermal Resistance:
<0.0045°C-in2/Watt (0.001 inch layer)

Keeping gaps to less than .001" helps as well. I lapped all assemblies to 600 grit.

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