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Forums
4hv.org :: Forums :: Electromagnetic Radiation
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Laser Pointer

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Tetris
Fri Apr 06 2012, 01:42AM Print
Tetris Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660
I got this laser pointer from China (that is, physically in China, not just made there). It is about 100mW. At the time I bought it, I had no idea that it was. I intentionally bought it to tease my cats, but after finding out about its power, I don't want to hurt my sweet kittehs. It isn't strong enough to burn things. It kinda makes black things barely warm. I have virtually no experience with lasers. I don't want to have wasted 13 dollars on nothing. What can I do with this laser?
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Forty
Fri Apr 06 2012, 02:57AM
Forty Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
If you can focus it to a pinpoint it will probably burn stuff, which is amusing enough to try it.

you can always use it to point at things from afar...

If it's green, they're great for pointing out constellations and whatnot, just be careful around airports.

13 bucks isn't that much of a waste. People spend 10 times that for less powerful laser pointers.

I wouldn't shine it around people, animals, or reflective/white surfaces though.
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jnbrex
Fri Apr 06 2012, 05:43AM
jnbrex Registered Member #3950 Joined: Wed Jun 15 2011, 12:45AM
Location:
Posts: 51
Throw it out... seriously, if you shine it into someone else's eyes or bounce it off a reflective surface into your eyes, you risk instant blindness.
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Steve Conner
Fri Apr 06 2012, 07:46AM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The power could be somewhat exaggerated if you bought it in a Chinese street market. But it's probably not eye safe for people or animals.

Maybe you can do an Instructable on making laser safety goggles for cats. tongue
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klugesmith
Sat Apr 07 2012, 01:54AM
klugesmith Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1715
Not to scare people, but another forum has a contemporary thread about a young laser enthusiast who just got a permanent blind spot from a freak accident. Link2

HVC:
From this rank amateur in photometry, here are some ideas for measuring your pointer's absolute power within perhaps a factor of two, without buying a >$200 thermopile-based laser power meter.
Always beware of specular reflections of your pointer beam. You can get safety glasses appropriate for your laser wavelength, but they'll cost more than the laser.

1. Use a good lux-meter, or photographer's incident light meter with a lux or footcandle scale.
Key challenges: matching beam area to sensor area, and (for red pointers) having the meter's spectral filter match the standard visibility roll-off curve at the specific wavelength.

2. Much more basic: illuminate a Si photovoltaic cell bigger than the beam, and measure its short-circuit output current. Look at the amps per watt spectral curve in sensor datasheet.

3. Simple calorimetry: carefully measure the heating rate of some little thing with good absorbance. I'm imagining some Al sheet folded or rolled into a steep, hollow cone or V-shape, with blackened internal surfaces. Small thermocouple or thermistor attached to the outside. For thermal insulation, drill a deep hole in a large block of styrofoam and put the thermal test mass at the bottom (after weighing it, to determine its heat capacity).
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Tetris
Sat Apr 07 2012, 02:56PM
Tetris Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660
klugesmith wrote ...

Not to scare people, but another forum has a contemporary thread about a young laser enthusiast who just got a permanent blind spot from a freak accident. Link2

HVC:
From this rank amateur in photometry, here are some ideas for measuring your pointer's absolute power within perhaps a factor of two, without buying a >$200 thermopile-based laser power meter.
Always beware of specular reflections of your pointer beam. You can get safety glasses appropriate for your laser wavelength, but they'll cost more than the laser.

1. Use a good lux-meter, or photographer's incident light meter with a lux or footcandle scale.
Key challenges: matching beam area to sensor area, and (for red pointers) having the meter's spectral filter match the standard visibility roll-off curve at the specific wavelength.

2. Much more basic: illuminate a Si photovoltaic cell bigger than the beam, and measure its short-circuit output current. Look at the amps per watt spectral curve in sensor datasheet.

3. Simple calorimetry: carefully measure the heating rate of some little thing with good absorbance. I'm imagining some Al sheet folded or rolled into a steep, hollow cone or V-shape, with blackened internal surfaces. Small thermocouple or thermistor attached to the outside. For thermal insulation, drill a deep hole in a large block of styrofoam and put the thermal test mass at the bottom (after weighing it, to determine its heat capacity).

Number 2 would be the simplest for my case. Unfortunately, all the photocells I get are from the classroom, and they always seem to dissapear from my box. The next time I go to that one store, I will buy it (its too far away to just get one thing)
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testtest
Mon Apr 09 2012, 08:33PM
testtest Registered Member #3271 Joined: Mon Oct 04 2010, 02:29AM
Location: Canada
Posts: 159
HighVoltageChick wrote ...

I got this laser pointer from China (that is, physically in China, not just made there). It is about 100mW. At the time I bought it, I had no idea that it was. I intentionally bought it to tease my cats, but after finding out about its power, I don't want to hurt my sweet kittehs. It isn't strong enough to burn things. It kinda makes black things barely warm. I have virtually no experience with lasers. I don't want to have wasted 13 dollars on nothing. What can I do with this laser?

i would be careful with these lasers. Unlike the red that emit light directly from the inversion junction the green ones are quite different. The Optical Society of America had an article in their OPN monthly magazine for members about those about a year ago. This prompted me to "look" at a few that I have here, look at the spectrometer emissions wavelength as well as use a power meter. I have several from 400mW to small laser pointers. All emit detectable light at the three wavelength. The cheapest one however I would consider dangerous.

The DPSS green lasers use a pump diode laser around 808nm (near IR) to pump a nonlinear crystal. That xtal has highly reflective facets and contain the 1062nm lasing that happens from the 808nm pumping. The nonlinearity then creates the 532nm (1/2 the wavelength) green light that you see. All good if designed properly. However, to save money, the cheap ones will very often not filter out the IR light. I have one in particular that has a small grating to make prtty pattern of dot and line. However the straylight gets diffracted at a different angle, but you do not see it. If you use an IR viewer you see the 1.06um light in between the green dots! Using a power meter, the 1.06 um (1060nm) IR light accounts for almost HALF the power reading.

Although you cannot see the 808 and 1060nm they do get somewhat focussed on your retina and the 532 and 1060nm are usually nearly colinear. You dont see 1060 nm it so there is no blink reflex while it damages your eye. I can give you much more info if you are interested.

So please do not use the green pointer with kitty. A small low power red is much safer. I know my cat likes it!

Keep in mind that any laser more than 4-5 mW in the visible can be dangerous. In the IR even more so and all are classed as such until you reach the eye safe wavelenths (not the case here)
Cheers and be safe.
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Tetris
Tue Apr 10 2012, 04:22PM
Tetris Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660
richnormand wrote ...

HighVoltageChick wrote ...

I got this laser pointer from China (that is, physically in China, not just made there). It is about 100mW. At the time I bought it, I had no idea that it was. I intentionally bought it to tease my cats, but after finding out about its power, I don't want to hurt my sweet kittehs. It isn't strong enough to burn things. It kinda makes black things barely warm. I have virtually no experience with lasers. I don't want to have wasted 13 dollars on nothing. What can I do with this laser?

i would be careful with these lasers. Unlike the red that emit light directly from the inversion junction the green ones are quite different. The Optical Scociety of America had an article in their OPN monthly magazine for members about those about a year ago. This prompted me to "look" at a few that I have here, look at the spectrometer emissions wavelength as well as use a power meter. I have several from 400mW to small laser pointers. All emit detectable light at the three wavelength. The cheapest one however I would consider dangerous.

The DPSS green lasers use a pump diode laser around 808nm (near IR) to pump a nonlinear crystal. That xtal has highly reflective facets and contain the 1062nm lasing that happens from the 808nm pumping. The nonlinearity then creates the 532nm (1/2 the wavelength) green light that you see. All good if designed properly. However, to save money, the cheap ones will very often not filter out the IR light. I have one in particular that has a small grating to make prtty pattern of dot and line. However the straylight gets diffracted at a different angle, but you do not see it. If you use an IR viewer you see the 1.06um light in between the green dots! Using a power meter, the 1.06 um (1060nm) IR light accounts for almost HALF the power reading.

Although you cannot see the 808 and 1060nm they do get somewhat focussed on your retina and the 532 and 1060nm are usually nearly colinear. You dont see 1060 nm it so there is no blink reflex while it damages your eye. I can give you much more info if you are interested.

So please do not use the green pointer with kitty. A small low power red is much safer. I know my cat likes it!

Keep in mind that any leser more than 4-5 mW in the visible can be dangerous. In the IR even more so and all are classed as such until you reach the eye safe wavelenths (not the case here)
Cheers and be safe.
oh god... hm I know my laptop's webcam lacks an IR filter, and you can somewhat see IR on it as white dots. I will most certainly try that when I get home from school.
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testtest
Tue Apr 10 2012, 09:59PM
testtest Registered Member #3271 Joined: Mon Oct 04 2010, 02:29AM
Location: Canada
Posts: 159
@HighVoltageChick

May I suggest reading this before exploring further,
Link2
In particular the note about IR leakage from DPSS lasers (what you have here) later in the article they comment on how to separate the IR from the visible. Considering that in some cases the IR could account to close to half the output power it is generous to call that leakage!

Another link you should explore is;
Link2

and

Link2

Happy reading and keep safe. These small units can roll or topple and the beam can hit your eye. It takes only a fraction of a second to result in a retinal burn or worse. To give you an idea at that power level (100mW) in my lab we have a door interlock and all personnel have laser google.
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testtest
Tue Apr 10 2012, 10:16PM
testtest Registered Member #3271 Joined: Mon Oct 04 2010, 02:29AM
Location: Canada
Posts: 159
hm I know my laptop's webcam lacks an IR filter, and you can somewhat see IR on it as white dots. I will most certainly try that when I get home from school.

----------------------------------------- ---------------------------------------
If that is so just aim a TV remote control at the camera. The 800nm LEDs in the control should then be crearly visible to the camera. The filter in the camera is there to prevent reading a part of the spectrum where your eye is not sensitive and therefore present a better gradation of perceived intensity. These silicon CCDs will respond all the way to the bandgap. You can see 1000nm wavelength easily if you remove the IR bloking filter. I got a cheap ccd camera on e-bay, removed the filter and affixed it to a cheap ($20, all plastic) astronomy grating spectrometer. Very useful to check remotes for dead batteries and check LEDs, opto-interrupters, garage door safety beams, and lots of stuff around the house and lab.
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