Many Years Ago ( 1975) When I Got My First Laser, I Would Spend Hours Looking at the Inherent

High Power Solid State White Light Lasers… Finally a Reality

By Aron Bacs Audio Visual Imagineering, Inc.

About 27 years ago when I got my first laser, I would spend hours looking at the inherent beauty of the thin red HeNe beam of light as it passed down my upstairs hallway into my bedroom. Not since my first glance at laser light, have I been more moved than the light I viewed almost a year ago. I guess that is what got me hooked on lasers. This article hopes to describe my personal experience with one of the most color rich and newest RGB lasers on the market today, the solid-state “Showlaser” from Schneider Laser Technologies AG.

As a Design Engineer and Director of Research and Development, I get to “play” with some of the coolest new technologies around. Whenever new technology arrives, often it is unknown. That is definitely the case here. Very little technical information has been published on the Showlaser, other than a good research article from JENOPTIK Laser, Optik, Systeme GmbH (see footnote). I won’t go into details here (visit the Laserist web site for the complete article), but I would like to give you highlights, and tell you about some of my experiences with this laser system, and what to expect when and if you decide to use one for yourselves.

Showlaser Concept

Overall the Showlasers main goal is to produce very high output powers, on par with color modulated large frame ion lasers, but with much less input power, about 20 times less! Its intended design is for laser video projection, both for normal formats (4:3, 16:9, HD, etc.) and also specialty formats like the Zeiss Universal Laser Image Projector (or ZULIP) system for domed environments. Naturally vector scanning was also possible since it was “just “ an RGB laser source. The laser output is pulsed (7ps). The 80Mhz pulse rate, and pulses (details later) are too fast to be of any concern. The 7ps pulses help reduce the laser “speckle”, of utmost importance when lasers are used for video. The speckle is not completely gone however, the best way to describe it, is that most laser speckle is coarse (like 80 grit coarse sandpaper). The Showlaser speckle is very fine like 400 or 600 grit. This helps make the imagery look “cleaner”, because as you view the fine visual details in an image, you are not distracted by the relatively larger speckle.

The Showlaser contains 5 major systems. These are 1) an RGB laser, 2) 9 diode pump lasers, 3) a system control computer, 4) low voltage power supplies, and 5) a closed loop cooling system.

A Closer Look

The Showlaser produces only 3 wavelengths, 628nm, 532nm, and 446nm. Ion lasers on the other hand can lase at many different wavelengths, spreading their optical power over all (8 or more) of the lasing lines. Some of which (particularly 488nm) are undesirable for graphics systems where high color saturation is often needed to portray full color images properly. Typically the 488nm line causes a washed out look, and is often omitted or reduced. Unfortunately, the 488nm line is also one of the stronger lasing wavelengths in Ar+ and/or Ar+/Kr+ ion lasers. So when you attenuate or remove it, you can loose up to 25% or more of the lasers total output power. The Showlaser does not suffer from any of these afflictions. It is a mix of several newer solid state technologies. For example, to generate the green 532nm wavelength, it is similar to other Diode Pumped Solid State lasers. However to generate the red 628nm and blue 446nm wavelengths, some newer technologies were used. In short, these technologies include Second Harmonic Generators, Optical Parametric Oscillators and Sum Frequency Mixers, etc. All the main optical components are mounted on a series of vibration isolated optics tables within a “dry” nitrogen filled and sealed envelope. A little scary at first from a service point of view, but since I don’t go messing around inside our sealed DPSS or ion lasers glass envelopes either, it’s a moot point. Besides, alignment of the internal beam path(s) are done by motor controlled mirrors, manually or automatically.

The first “main” laser oscillator feeds a series of amplifiers. These amplifiers are needed to increase the power of the main laser oscillator which is modelocked (~7ps pulses at ~80Mhz). One reason for using pulses of high peak power, on the order of 30KW per pulse, is that nonlinear crystals (which do the frequency doubling and sum frequency mixing) operate much more efficiently at higher input powers. It may seem a little complicated at first, but this laser operates on different principles than the ion laser technology we are all used to. So accept it as you do the current 532nm DPSS (YAG) lasers that have revolutionized beam shows. Now we have solid-state white light to do graphics as well. And by the way, the green beam effects (at 532nm) now match the graphics too!

An onboard computer/controller oversees the proper operation of the laser system. Such as the start sequence (which now takes about 30 minutes), the temperature control of the nonlinear crystals and pump diodes (via the on board closed loop refrigeration system), and the low voltage power supplies which provide power for the diodes, sensors, etc. The start sequence time of ~30 minutes (more on this later) is needed to stabilize the temperature and currents of all the crystals and associated components within the system including the vibration isolated optical tables. I believe as more data is collected, this time may be shortened. This is like other DPSS laser units approx. 25 startup time, so again this technology is similar to ones some of us already use on a day to day basis. And since the Showlaser has a computer on board, it is possible to upload new software/firmware, as well as diagnose the system should there be a problem. I wish my ion lasers could tell me how its color balance, power, temperature, alignment, etc. were doing.

The RGB beams then bounce off a set of computer controlled mirrors, through specially designed high efficiency Acousto Optic Modulators, to another set of computer controlled mirrors, an then to the fiber input coupler. The output from the Showlaser is an FC style fiber optic connector. We use the 25 fiber cable supplied by Schneider (really good fiber). Through careful optical design of the collimator and projection optics, I have developed methods to project 30K images, with a spot size of less than 50mm (2”) diameter with a screen distance of over 100m (325’) at our premier HersheyPark, PA venue. The output is much better than most direct fed ion laser systems!

Setting Up the Showlaser

The Showlaser ships in a reusable shipping container (made of a lightweight, fiber composite material) complete with an unloading ramp with stainless steel skids, not a wooden crate. The container has shock mounted feet and a foamed out interior. It takes at least two people to uncrate the unit mostly due to the size of the container (approx. 3.5’ W x 5’ L x 4’ H) and weight of the laser itself. We took great care in rolling the laser down the containers ramp to the floor. The laser itself comes complete with heavy duty casters. Two large handles, on the unit’s ends, are lift/handling points for personnel. We take the same care when unpacking our ion lasers, but I must say handling the ion lasers is a bit more precarious due to their length, weight, umbilical cable, and shear dead lift required by personnel. Once on the floor, a single person can move the laser to its final destination with relative ease.

A laptop (or desktop) computer with parallel and/or a serial port is needed to access the laser operations, both in simple and diagnostic modes. There is a control box for laser operation in the works. This will eliminate the need for a computer to operate the Showlaser in the near future. The Showlaser has front controls which are operable from both the laser unit as well as from software. Turn the key to the on position, press start and the startup sequence is underway. Computer operation is great for when the laser (or lasers) are in remote locations!

Shutting down the laser system is very simple, whether using software and/or the front panel controls, push stop, and turn the key to off. You can pack up the laser immediately after use, so you actually get the ~30 minute startup time back at the end of the show. Other than topping of the de-ionized cooling water and periodic cooling filter changes, that’s about it. Again, like ion lasers, changing the inline filters is nothing new. You do use water filters don’t you?

There is so much detail on the complete operation of the unit, but I hope I have given you a basic rundown of the system. To use it, is to appreciate the engineering effort that was undertaken to make this both a visually amazing laser system as well as one that’s easy and informative to operate.

Basic specifications for the Showlaser:

18W average (35KW peak) internal power from the main RGB laser crystals, at a minimum of 13W color balanced RGB light into the FC style fiber. We typically have been getting over 10.5W out of the fiber. A weight of 660lb. Expected lifetimes are 10Khrs. Input power ranges from 220-240VAC (50/60Hz ) at less than 3KW (that’s two hair dryers). As I write this article new AOM units, ones specially designed for vector scanning, i.e. higher extinction ratios than required by the video system, are being tested by tarm Showlaser GmbH. I hope to have more information by the time you read this and can then answer even more questions. Also I should have at least one system at ILDA 2001 for everyone to see, enjoy, and ask further questions. See you in November!

More info Notes: http://www.avilasers.com (US Representatives) http://www.jenoptik-los.de/lasergeraete/deutsch/products/vortrag_e.pdf (JENOPTIK paper) http://www.tarm.de (Europe Representatives)