Ruby Laser
The ruby laser was the very first laser device in history. Ruby lasers produce powerful pulses of visible, red, laser light. The fluorescence life of ruby is in the millisecond range, which permits easy storage of large quantanties of energy. This relatively long fluorescence life also causes ruby to become an ideal candadite for q-switching, which can yield huge peak powers in the mega-watt range! Unlike the output from common yag-based devices, the long pulse from a ruby laser makes it capable of drilling and boring through hard materials with a dramatic display of sparks and vapor. In terms of photographic portreyal of laser power, ruby is perhaps one of the most interesting examples. The visible output makes ruby somewhat unique when compared with other high power sources among classic laser types.
My experience with this laser has been a journey. I conducted experiments with a variety of different flashlamps, reflector configurations, and resonator mirrors. What originated as a complicated device eventually progressed to a simple design with excellent performance. Before covering my history with the development of this device, I would like to direct attention to the display below. Here are some action shots, showing some of the more interesting examples of laser performance.
Laser Beam on Razor Blade Target:
Shooting Hole Through a Spoon:
Hole Through Stainless Steel Ruler:
Hole Through Saw Blade: 
Hole in Pocket Knife:
Hole through screwdriver: 
Shooting Hole Through Quarter
Dremel Wheel Cutting Tool
Cigarette Lighter Flint
The following three photos (L-R) show the result of three laser pulses in a row, without any repositioning of the lens or target between shots. The first photo shows a ruby laser beam focused onto a small piece of cigarette lighter flint. With the second pulse, the focused beam strikes below the surface of this target (because now a small pit has been made). Less white light intensity during the second shot permits a better view of the sparks. On the third shot, energy density is reduced because the part of the beam that strikes the target (inside the pit that has been made from the two previous shots) is past the focal point of the lens.
This example somewhat illustrates a limit I have encountered with laser drilling. In order to drill through something like steel, the laser beam has to be tightly focused. If the target is positioned in front of, or past this focal point; the energy density is not high enough to vaporize target materials like metal. This is a problem when attempting to drill through anything more than a few millimeters thick: as the drill hole becomes progressively deeper with each laser pulse, the remaining metal eventually falls past the focal point of the focusing lens. In an effort to overcome this problem, I tried mounting the lens onto a rail-mounted sled from inside an old CD/DVD reader/burner. It was actually a very clever idea suggested to me by Milan Karakas. After doing so however, I discovered an entirely new situation: as the cone shaped beam was moved closer into the target with successive pulses, the sides of the 'cone' began to become blocked by the front surface of the target, which surrounded the outer circumference of the hole. As the lens was moved closer to the target, an increasingly larger percentage of the beam profile was blocked from entering the tunnel which had been created by preceding pulses. Eventually the advantages of moving the focal point into the target had all but completely disappeared.
Charred Wood
Carbon absorbs most of the light that falls upon it's surface, and reflects very little of it. At the wavelength of a ruby laser, no lens is necessary to heat carbon to the point of incandescence. The resulting plume of fire is projected away from the target with some force: sometimes moving small target samples due to the thrust that is created. It is quite a spectacular display. The photos below show what happens when the beam strikes a piece of wood that has been pre-charred (burned). An unfocused beam was used in the top picture, and the plume in the bottom picture is a result of the focused laser output. Without pre-charring, the laser beam would have very little effect on a piece of lightly colored wood. The pulse does not last long enough to effect a lightly colored surface - at least not with an unfocused beam.
Charcoal is one of my favourite targets. Below are a few examples I like. The picture below shows an interesting plume made with charred wood. Directly below this picture is one which illustrates the results obtained with artist's charcoal. It is followed by another 'charred wood' shot. The bottom four photos (L-R) show artist's charcoal, followed by three photos which display laser fire on BBQ charcoal.
Here are some pictures of the laser device firing, shortly after it was completed. The cherry red beam is visible in my smoke filled room. My eyes are shut tightly, and I am looking down (away from the laser device) as it is firing. There are no second chances with this type of laser: even a stray reflection or glare from the laser beam will result in a very serious and permanent eye injury. The flashlamps are also very dangerous. They put out enough light to be an eye hazard, as well as being a burn hazard to exposed skin at close range.
