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.

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).

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?

richnormand wrote ...


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.