Testing power laser, and why is paper not affected...

On Sun, 28 Feb 2016 14:30:18 GMT, Jan Panteltje Gave us:

Pretty lame. Very doubtful that it produces 5 watts. Maybe the supply consumes 5 Watts, but I doubt the laser even makes 2.

Yes, all diode lasers emit a pretty wide, elliptical fan beam. It is because the resonant cavity is so short. There are VCSEL lasers where the cavity is a bit longer, these are supposed to have a narrower angle.

Don't ever point this thing at anything outside, especially airplanes.

Jon

Are all those shiny bits functional?

Or inside, especially where there might be reflections and innocent bystanders might be walking by.

"Never look into the laser beam with your remaining eye"

On a sunny day (Sun, 28 Feb 2016 11:34:59 -0600) it happened Jon Elson wrote in :

Thank you, yes that makes sense, I think I get it now.

Been reading about that lately, decided to get his one before they are impounded just like those airboards. Last year kids where shining on my curtains with a green power laser.

For me it is mainly curiosity and doing some physics.

There was a project some years ago to kill mosquitos by using a laser, sensing the reflection, from the reflection they could find if it was a mosquito or say a bird or something else, and then for a moment increased power and burned the beast, found it:

Laser soldering, I think it is not enough power, and too many problems with the tin reflecting the beam everywhere. But an electronically controlled mirror setup could do interesting things, easy to make.

Playing with this stuff adds a lot to your experience and understanding, great fun.

Does making it look bad-ass count as functional?

--sp

Retroreflectors immediately come to mind...

For some real fun, you could whip up your own phase-conjugate mirror, a sort of below-threshold laser that dumps all of its stored energy back along a pump beam's incoming direction.

Mark L. Fergerson

On a sunny day (Sun, 28 Feb 2016 12:14:18 -0800 (PST)) it happened " snipped-for-privacy@bid.nes" wrote in :

I found this:

Nice! But I notice it doesn't state the current draw. I have a green one that's rated at 50mW output and that draws 370mA so it's a bit of a hog. IIRC green is the most dangerous colour and I'm always very wary about catching a flash of it accidentally. I'd be downright scared to death with this one of yours, though. Might be pretty good for home defence for people who aren't allowed to own guns. So, how many amps it draw?

There are acres of paper on the topic. Start here for an overview and fol low the references:

Been a while.

I'd like to go with with ADP or KDP (ammonium or potassium dihydrogen pho sphate) because they're cheap and relatively easy to grow in big (pop-can-s ize or better) single crystals, though ADP shouldn't be allowed to get abov e 200F or so. However I can't recall their efficiency at given wavelengths, so I'd download this (again):

and start with reasonable performance parameters like say dumping several KW of green light back at pointer-wielders. ;>)

Anyway, choose a crystal and cut it (or buy it cut), build a cavity, arra nge to illuminate it with appropriate pump light, and park it in the window .

Mark L. Fergerson

On a sunny day (Sun, 28 Feb 2016 20:22:36 -0800 (PST)) it happened " snipped-for-privacy@bid.nes" wrote in :

Ah, nice, hologram, now I am with it again. Many many years ago, at some exibition about lasers, I bought some holograms and a book on practical holography, how to make those, in those days film was still used, no digital cameras... I had a helium neon laser, and played a bit with those holograms, quite big ones actually. Not sure I still have that book, will have to search...

Looks like I have some reading to do, thank you for the pointing me in the right direction.

mm looks complicated, electronics already is a life time learning curve, photonics likely the same. Bottle of barium titanate on ebay is about 46 $

Potassium dihydrogen phosphate 100 grams is only 2$ !!!!

Ammonium dihydrogen phosphate monobasic - 99%

kW... that will get me arrested I think. Maybe some alu foil.., return the beam.

:-)

Modern single colour LEDs are quite good at playing back basic holograms made with a He-Ne laser. Some are better than others.

I have a selection of them that we made in the second year. Our group included someone with a very steady hand who did the optical bench work and myself as an experienced darkroom worker. The lab techs couldn't believe how many plates we got through that afternoon. I even made a hologram of a reference mirror as a diffraction grating.

Modern white light holograms are impressive (usually playback as green). For a while they were used as anticopy devices but the fakers rapidly caught up and now the fake holgrams are as good as originals.

BTW The paper will burn if you put black marker pen or graphite on it.

On a sunny day (Mon, 29 Feb 2016 10:55:54 +0000) it happened Martin Brown wrote in :

I just found an old 35 mm slide that came with that book, that you could put in your slide projector and use as light source. The book is gone... Found a hologram of a seashell.

Nice, yes in those days I developed and enlarged and did the whole photo thing, I stopped at color, was to much of a hassle all those bath. Anyways by then I already had build a video camera.

Yes, actually white paper, the type we normally use for printers. has some special properties. I don't know if you have an UV light, like for checking bank notes, say euro bills, if you put the UV light on these white paper sheets, then the paper will light up brightly! The paper is extremely reflective and maybe luminescent? not only in the blue, but also in the deeper blue to UV. UV lights for couterfeit checking also emit some visual light, great stuff to play with, many plastics light up, London Tonic (quinine) lights up under UV. so that made me wonder if I could make a mirror for blue from printer paper, a simple U parabolic line, will try that some day. UV light can also be used to verify if old documents (the chart to the gold treasure etc) are authentic. The paper of old days did not have that reflective luminescent property. So if the 'old' document lights up then it is likely fake. I am not sure how much effect the 450 nm laser has...

Does the speckle-y light have anything to do with it? I notice that the bright NE-2 orange JL likes is particularly speckle-y.

The narrower the bandwidth it has the better. But even a basic red LED is a much better approximation to monochromatic than a red filter. And modern ones are plenty bright enough from a small point like emitter.

Low pressure sodium streetlamps were the other common playback light source (and available back when we made the holograms).

Green is perceptually the brightest matching the eyes response but in the cheap and nasty Chinese high power ones the thing you have to worry about is the NdYAG 1064nm line that is doubled to 532nm (or for UV laser ablation quadrupled to 266nm). The cheap nasty stuff can omit the high pass filter to save money and have an insane amount of the invisible IR pump beam mixed in with the visible light.

There always seems to be a bit of 532nm in with the UV beam too.

Same applies to the ~400nm blue from an 800nm IR pump laser.

If you want to measure the optical power, its fairly easily for lasers abov e 50 mW. Get a small Peltier cooler element, preferably with say 10-12 junc tions. Paint one side black with carbon based spray paint. That means a fla t black paint such as Krylon engine paint. That forms your optical absorber . Professional units use a carbon disk or a very specialized paint from 3M. ..

Heatsink the other side of the Peltier.

Use an op-amp to level shift the output voltage of the Peltier to something a meter can read.

Calibrate with a metal cased power resistor pressed against the absorber an d a variable PSU.

Professional laser Watt meters use a highly customized Peltier element with a built in calibration coil made of resistance wire, but that is beyond th e scope of a simple device.

Steve

You most likely have a two watt Nichia 445 nanometer laser diode. Probably what is known as a "M140" to laser hobbyists. The M140 is the model number of the Casio video projector that contains 22 of them. The Chinese Ebay sel lers used to buy the projectors and "harvest" the diodes for resale...

Steve

On a sunny day (Mon, 29 Feb 2016 08:52:32 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

Cool, I have a big Peltier somewhere for an air-dehumifier. Black paint too.