Lasers

Traditional gas lasers that most are familiar with have almost been buried by the number of solid state (semiconductor) lasers now flooding the market.

The prices of these are plummeting, and combined with the fact that it isn't at all hard to extract free lasers from broken cd and dvd players, experimenting with lasers has never been more feasible.

A typical laser pointer

When people think of lasers, they think of one of two things - laser pointers or big lasers that burn clean holes through steel.

Lasers come in a variety of sizes, ranging from tiny pin-head sized tracking lasers to lasing units larger than a house. What's different is generally their power output.

Laser optical power output is usually specified in watts (W) and milliwatts (mW).

To put this into perspective... the typical laser pointer you will find on the shelves at your local department store would have an output of around 1mW. On the other hand, lasers which burn holes through steel typically have power outputs of a few thousand watts.

In Australia, the maximum legal power output for a laser pointer is restricted to less than 1mW. In the USA, the limit is 5mW.

Optical Power Output	Class	Precautions
<0.1mW	I	No real danger
0.1mW - 1mW	II	Avoid direct eye exposure
1mW - 5mW	IIIa	Avoid direct eye exposure
5mW - 500mW	IIIb	Avoid direct skin and eye exposure
>500mW	IV	Avoid eye and skin exposure to direct and scattered laser radiation

International standards on laser power classification

Sensitivity of the human eye by wavelength
(Image courtesy of www.tedmontgomery.com)

The wavelength of a laser is also another important factor in classifying a laser. The wavelength for a typical red laser pointer is 670nm.

The eye has different sensitivities to different wavelengths, so a 635nm laser would appear about four times as bright as a 670nm laser of similar power output. In fact, the eye is most sensitive to green/yellow light - you can try this experiment with various colour LEDs of the same power.

A few years ago , I managed to get a 5mW red laser diode, at 635nm. Since this wavelength appeared 4 times as bright as the normal laser pointer, and also 5 times the power, all in all it appeared about 20 times as bright as a normal laser pointer.

Red 635nm laser diode

Here the laser beam from the 635nm diode is being reflected several times off two front surface mirrors (mirrors with the silver coating at the front).

Its fun to experiment with lasers! This time the laser beam is reflected off a mirror into a CD, where the the beam is refracted before it comes out, where it is again refracted.

The 50mW DPSS laser head and driver circuitry mounted in a custom case.

The two previous pictures might look pretty awesome, but I have to admit I cheated. The laser beam is visible because it is grazing the surface of the table. In fact, just like a normal laser pointer, it is very difficult to see the beam in the air.

The same is not true with my newer 50mW DPSS (diode pumped solid state) laser. This one is also just powerful enough to burn some holes through things...

Here is the resultant laser beam at night - the bright green beam is visible in midair. The wavelength from this diode is 532nm, which appears 20 times as bright as a standard red laser pointer, and 50 times the power output. So, in perspective this would appear about 1000 times brighter than a red laser.

This I am playing with some homebrew optics. Although this isn't a focused beam. I've put a diverging lens (scrounged from a scanner) in front of the output so I don't over-saturate the camera. Here the beam is being split by a prism (window pane) and reflected off a back surface mirror (bathroom mirror) so that the two beams are parallel.

Ever seen those Hong Kong laser light shows at night? Well stuff that, here's the Penguin's Lab version!

The camera is mounted behind the laser unit, which is why the beam seems to start out of nowhere. A friend located a tad over 2km away reported sighting this beam clearly in the night sky.

Be warned that this is not the safest thing to do with any laser. As with anything which could affect aviation - please check with your local area to ensure you won't cause a freak accident.

This image was taken in Jan 2008 during Cyclone Helen's raid on Darwin. Some pretty fresh gales are evident from the blurred palm leaves in the photo. This is a long exposure - the laser was shone for a few seconds in three separate points, with the beam quickly moving between to draw a nice pretty triangle on the trees. Where the beam has shone in one position for more than a second or two, a beam line is visible in the photo.

Here is a (very neatly) hand written laser trail on palm trees. You can get pretty proficient at writing like this. This was a long exposure of 6 seconds.

So far I have also used this laser to burn through black electrical tape, light matches, and blast pits into hard black plastics. When it burns through tape, the cut is precise and clean. Not bad for a fairly modest 50mW!

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