Laser Diodes

On: Sun, Sep 16, 01 01:44:19 AM

Mike Chiu wrote:

I have just started reading about holograms after not paying attention to them for several years. Learning about the success with laser diodes has inspired me to want to pursue the holography bug I once had. How does one know what laser diode will work and what will not? Also, is the advantage of a 35mW diode substantially dramatic that it's worth the money? Now that I'm a college graduate, I can afford to spend money compared to when I was just thinking about it in college. lastly, is there a chance that the box of Agfa film I bought 5+ years ago is still usable? I bought the film but never once opened the box. Everyone speaks highly of the old agfa film, and it'd be nice to know that they were still usable. However, I'm not holding my breath. Mike Chiu yoyoman@insync.net
RESPONSES

Colin Kaminski - Sun, Sep 16, 01 03:46:17 AM

I really like the simplicity of making a single beam reflection hologram with the 5 mw diode from Integraf. But if you want to do split beam set-ups it is really nice to have more power. I am very happy with my D&S laser for bigger set ups. You will just have to try the film but don't hold your breath. 64.167.151.72

Brian Greenstone - Sun, Sep 16, 01 03:19:01 PM

Well, last night I made my first hologram with a 35mw diode. I did a simply single-beam test and I only exposed it for 1 second which ended up being too long! My Laser Power Meter told me the exposure should be about .3 to .5 seconds, but I didn't believe it, so I did 1 full second. The hologram went to 80% dark in only about 20-30 seconds during development, so I guess my meter was right. An exposure of less than a half-second is pretty impressive and quite an advantage. I may have to upgrade to the 50mw diodes once the 645nm ones come down in price. -Brian 66.69.244.199

Colin - Sun, Sep 16, 01 03:53:49 PM

Brian, What laser power meter are you using? Also I know the diodes are advancing quickly, a year ago I was told the diodes shorter than 658 nm are very prone to mode hopping. 64.167.151.72

Brian - Sat, Sep 22, 01 10:45:38 AM

Colin- I'm using one of those $300 hand-held gizmo's that Coherent makes. Others sell the same thing under different names. I got mine from Edmund for $295 I think. It's a great thing to have. Very handy, and very accurate. No need to guess at exposure times. The formula I use for the Slavich plates is 100 micro-watts per second. So, if the meter tells me 50 micro-watts then I know it's a 2 second exposure. Or, as in my first test, it said it was about 360 micro-watts, so I knew it was about 1/3 second. However, since the Slavich plates are less sensitive to the 658nm diodes, I like to add 20% to the time, but I need to run more tests on that this week. -Brian 66.69.244.199

Tom B. - Tue, Sep 25, 01 01:15:54 AM

I recently got one of those LaserChecks myself. Something it took me a while to realize (and that I keep forgetting) is that when measuring energy density (watts per square cm) of the spread beam at the plate, you need to double the reading because the area of the detector is only 1/2 square cm (8 mm diameter). For example 100 microwatts per square cm would read as 50 microwatts since light from only 1/2 sq. cm is being collected. 24.67.253.203

Brian - Tue, Sep 25, 01 02:47:48 PM

Tom- Are you sure about that? I'd think the thing would be calibrated to report mw per cm and not per 1/2 cm. Plus, the aperature on my LaserCheck is about .9cm or so, not .5cm. The 7 holograms I've made so far by using the readings from the LaserCheck have all come out perfectly. -Brian 66.69.244.199

Tom B. - Tue, Sep 25, 01 10:00:28 PM

Well, the thing is designed for use with a collimated beam smaller than the aperture, in which case the power reading is just total power collected, with no area involved. When measuring power density, (watts per sq. cm) of a spread beam, then you need to know the area of the detector. If you spread a 5 mW beam to cover 1 cm^2, then the power density is 5 mW per cm^2. But if you only collect 1/2 cm^2 of the spread light, you only see half the power, or 2.5 mW. The 8 mm aperture of the detector came from the Coherent specs - it could be that the active area of the detector is smaller than the apparent size. Given the number of things which determine the optimum exposure (including film, processing, brightness of the object etc.) I think the meter readings are only a guideline, useful mostly as an aid to repeating a setup that works, which you seem to have found. 24.67.253.203

Use this form to add your comments to the current forum entry above
Your Name:
The Text...

in
HTML, or
Plain text
Action or
| Main Index | Reload | Help? |