Vol. 16, No. 3, Oct-December 2005 

Tech Tips for Practicing Laserists

I am a big fan of diffraction gratings. I consider the use of gratings to be one
of the great frontiers of laser show exploration. With a graphics or a beam show setup, we can be pretty sure of what we are going to see: beams hitting mirrors or being scanned around on a screen. But introduce the element of diffraction gratings, and we are in the great unknown. It is possible to combine the various forms of gratings in so many ways that the results are unpredictable. Best of all, gratings are easy-to-use and inexpensive.

What is a diffraction grating? Without going into technical details, a grating is an optical element that multiplies a laser beam. One beam going into a grating will come out as many beams. One beam may be transformed into five, nine, 25, 81, or thousands of individual beams!

Diffraction gratings are a great way for laserists to increase the number of different “looks” in their shows. Gratings allow laserists to instantly multiply the number of beams, regardless of the number of beams a projector can produce or the number of bounce mirrors available. Combinations of reflection gratings can create huge beam grid patterns over the audience; even a small fraction of a beam passing through a rotating grating can create an effective and interesting background for laser graphics. It is easy to multiply the single laser beams so many times that it is impossible for an audience member to visually take in the whole show at one glance.

believe that a show that uses a healthy dose of diffraction gratings is far more exciting to the audience than one without gratings. I will discuss gratings that I like to use in my own shows. I am hoping this will give readers a place to start, because the selection can be overwhelming.
	This high-density grid pattern (GWR-2) produces a "burst" effect when you are looking toward the grating.

For years, I used plastic sheets of grating material made by Rosco. But Rosco stopped selling them (around 1990, I believe) leaving me without a source. Fortunately, I had plenty of plastic sheets in stock. I used these sheets by taping the material onto a mirror that would reflect the laser beam. This technique was barely satisfactory, because 1) the mirror got sticky with the tape, and 2) the grating rarely lay flat against the mirror, leading to a distorted effect.

In 1994, I traveled to Germany and met Peter Mayer of Creative Laser Production. I wanted to meet Peter because of some small programs I had written and offered for sale for the Pangolin LD400 system. Out of the whole world, Peter was the only one who bought these programs. I figured that we were kindred spirits, and I was determined to meet this guy.

What I remember of that meeting was that he had an air-cooled argon and he bounced the beam onto a little piece of glass and immediately laser dots were everywhere. I mean everywhere! It was a prototype wide-angle diffraction grating with a 180° pattern. I had never seen anything like it. Then, Peter asked if I would like to represent this product for him and I accepted his offer.

Peter was working on a method of making gratings using holography. He used this method because it offered a way to create a less expensive, mass-produced grating specifically suited to the laser light show marketplace. By using a photosensitive film and exposing the film to a carefully created pattern of light, tiny slits are created in the film. The slits diffract the light into different patterns. To create a reflection grating (the beam bounces off the grating instead of going through it), reflective aluminum is deposited on a transmissive grating using a vacuum chamber.

Peter’s first production runs had some flaws, but he kept working on the process until he developed a series of high quality products called Lightworld gratings. Over the years he has consistently pushed the envelope of grating manufacturing, giving us such unique pieces as the Poly-6 Track (a multiple grating with bands like a phonograph record), the Poly-4 Sector (a multiple grating with quadrants like a pizza pie), and the Poly-20 Sector (with tiny grating windows just big enough for a beam to pass through). Part of the fun of ILDA’s Advanced Technology Workshop is waiting to see what Peter has come up with this year!

For myself, one of Peter’s biggest contributions was the creation of a nomenclature to describe these gratings. With so many combinations possible, much time can be wasted in trying to describe the effect that one is looking for. Most laserists, when they want gratings, ask for a “starburst” or a “burst.” I lost a few customers when I insisted they study the nomenclature to see what was available and then place their order using the correct description. We are not mind readers, and it is possible to very accurately describe gratings using this system!

Most gratings are described with series of letter and numbers. The letters refer to the following properties: L, line; G, grid, W, wide; T, transmission; R, reflection; C, circle; and S, square. Numbers are used after the initial letter designation to denote two things: The density of the grating effect (the higher the number, the more dots/meter), and then the size of the grating in millimeters. For example, LWR-1-100C refers to a “Line Wide Reflective”, density 1 (low density), 100-millimeter diameter circle grating.
The gratings that I have used consistently are: LWR-1-100C, LWR-2-100C,GWR-1-100C, GWR-2-100C, GWT-2-50C and the Poly-4 Sector 50C.

How do I use them? Let’s start with the flat beam patterns, the LWR effects. These are used just like bounce mirrors. When the laser beam hits the grating, a line of dots is produced. I created special mounts that allow me to quickly rotate the lines until they are in a level plane above the audience.The mount also allows some right to left movement to get the effect centered.
	This GWR-2 grating seen again, but with "dots" visible where the beam terminates on a surface.

I like to place the LWR-2 effect in a pair as low over the audience as possible. This is a very wide effect, so usually everyone in the audience sees a beam (or 10) passing right overhead from these gratings. The LWR-1 grating produces fewer lines, therefore each line is a little brighter. I usually move these up above the LWR-2 effect to create a different angle of interest. If there is a balcony in the venue, the LWR-1 goes over the heads of the audience in the balcony (see photo of LWR-2 on top of p. 16).

Here’s a money saving tip: the bounce from a grating is much more intense and “crisp” if the grating is used fairly close to the laser projector, within about 6 meters. Most projectors can hit a target fairly accurately within 6 meters. By using the smaller size Lightworld gratings, you can save half the cost!
Here’s another trick: if you wish to use the reflection from an LWR grating to produce a row of dots in a straight line, the beam must strike the grating at a right angle. If the beam strikes the grating from below, the line of dots will curve upwards at each end; if the beam strikes the grating from above, the line will curve downwards at each end. The same is true for transmission gratings.
Nowadays, I enjoy using gratings to spray laser dots all over the venues where I perform. This is where the GWR effects are useful. I mount these on a rotating motor shaft, and use as many motor-mounted gratings as possible. Screens, walls and ceilings are covered with laser patterns. Wow! Everything is spinning! You better sit down when you look at these effects.

Money-saving tip #2: for these “dot” effects, I sometimes mount a tiny GWR-2-20S grating right in front of the projector to bounce back up onto the graphics screen. This is a real money saver because the 20mm size is only around $10! Why buy larger gratings than you need? The laser beam is often tiny, and the effect is the same!

I always want at least one dual crossed grid grating dot effect on the main graphics screen in my shows. This is where I use the combination of Poly-4-Sector underneath a GWR-2-50C. The GWR effect is always slowly rotating, and I can rotate the Poly-4-Sector under DMX control, stopping it at any one of 4 patterns. This allows me to give variety to the patterns and to “bump” the pattern in time to the beat.

I hope that the laserists of the world will take advantage of the great advances that Peter Mayer has made in diffraction grating design and production. When I see a show, I believe that it will be a better and more interesting show because of the use of diffraction gratings.

Laser Spectacles: (+1) 512-392-4600; www.laserspectacles.com
Creative Laser: (+49) 89-470-5611; www.creativelaser.de