<==== Sam's Laser FAQ ====>

Safety, Info, Links, Parts, Types, Drive, Construction

A Practical Guide to Lasers for Experimenters and Hobbyists

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Table of Contents

PART I - Basics, Safety, General Information, Print/Web Resources, Parts, Manufacturers

PART II - Lasers Based on Commercial Components - Diode, HeNe, Ar/Kr Ion, CO2

PART III - Lasers Constructed from Basic Materials, Hardware, Optics, and Electronic Parts

Laser Equipment Gallery

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Author and Copyright

Author: Samuel M. Goldwasser

Corrections/suggestions: sam@stdavids.picker.com

Copyright (c) 1994,1995,1996,1997,1998
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

1.This notice is included in its entirety at the beginning.
2.There is no charge except to cover the costs of copying.

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This document is still under development and will probably continue to be in this state until will beyond the time when the Sun turns into a red giant or Hell freezes over, though the Engineers may be able to prevent the latter, at least :-).

Many of the circuits have been reverse engineered - traced from various schematics or actual hardware. There may be errors in transcription, interpretation, analysis, or voltage or current values listed. They are provided solely as the basis for your own designs and are not guaranteed to be 'plans' that will work for your needs without some tweaking.

Many power supplies and other laser components operate at extremely lethal voltage and current levels. The optical output from even modest power lasers can result in instant and irreversible damage to vision. No one ever should attempt to operate, troubleshoot, repair, or modify such equipment without understanding and following ALL of the relevant safety guidelines for lasers and high voltage and/or line connected electrical and electronic systems.

We will not be responsible for damage to equipment, your ego, county wide power outages, spontaneously generated mini (or larger) black holes, planetary disruptions, or personal injury or worse that may result from the use of this material.

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Thanks to Don Klipstein (Email: don@misty.com) for his comments and additions to this document. His Web site (http://www.misty.com/~don/) is a valuable resource for information relating to lighting and related technology in general.

Thanks to Steve Roberts (osteven@akrobiz.com for much of the material in the chapters on Argon/Krypton Ion Lasers including direct contribution of text and photos and via email discussions.

Thanks to Chris Chagaris (Email: pyro@grolen.com) for his comments and additions to this document. His first-hand experience in constructing several lasers from scratch has been extremely valuable in polishing and enhancing the chapters on Amateur Laser Construction.

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Please don't scrap your unwanted or broken laser related equipment or parts!

I am interested in obtaining dead or partially dead lasers and laser parts of all types and sizes including but not limited to: laser diodes, HeNe and Ar/Kr or other tubes, laser diode drivers, HeNe and other power supplies or power supply components, optics, modulators, deflectors, sensors, other types of circuits, etc.

Obviously I would be interested in working units as well but since this is strictly for non-profit use to expand knowledge, all I can really pay is slug mail shipping and maybe a wee bit more for something of sufficient entertainment value (mine).

Any information found during my dissection or repairs would would eventually find its way into this continually evolving document.

In addition to hardware, schematics for laser diode drivers, HeNe, Ar/Kr, and other laser power supplies, as well as other laser related circuits are also of particular interest. Where permitted, these would be added to this document or made available at the web sites as well (i.e., they are not proprietary or in violation of copyright restrictions if made public).

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Scope and Purpose of This Document

Many types of lasers are used in conjunction with popular hobbyist projects, basement experimentation, and just plain old late night tinkering. Diode and helium-neon (HeNe) lasers in particular are very common due to several factors including the wide availability of inexpensive components and systems (new and surplus) and the relative ease of constructing working devices. A greater number of argon (and krypton) ion lasers will be turning up on the surplus market at very affordable prices as they are replaced with more modern (but still very expensive) solid state alternatives. There is often interest in carbon dioxide lasers because of their higher power capability.

However, on-line and print resources with detailed information on driving laser diodes and powering helium-neon lasers seem to be scarce. Some of those that do exist are incorrect and potentially dangerous (or at least destructive). There appears to be virtually nothing at all on argon/krypton ion and CO2 lasers. And, even less on the nitty-gritty of amateur laser construction.

This document was written in the hopes of rectifying this situation.

Contributions in almost any form are always welcome and will be acknowledged appropriately.

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Organization of This Document

For the most part, we assume that you are at least familiar with the basic concept of what a laser is and have an idea of your intended application - be it for optics experimentation, communications, ranging, simple curiosity, or just being able to say you have a working laser in the house :-).

PART I includes some general information on lasers and laser related topics. In addition to essential laser safety information, there are extensive lists of references and Web links to laser safety sites, tutorials on lasers and laser related topics, and laser and optics organizations and manufacturers.

There isn't much in the way of laser physics and other theoretical topics. (You can now breath a sigh of relief!) Nor will there be much in the way of the design of laser shows, holography experiments, interferometers, or other laser applications - though a bit is provided just to stimulate your interest. I leave these to the many excellent books and articles that have been published over the years.

Our major emphasis is on the practical aspects of the types of diode, HeNe, and argon/krypton ion lasers (with CO2 lasers under development), that may be found outside of a well funded research lab - those available at reasonable cost on the used or surplus market, for example.

If you are interested in detailed information on other types of lasers, laser applications, laser physics, laser experiments, or laser research, consult the chapter: Laser Information Resources for a list of books, magazine articles, and Web links covering everything laser related from basic questions like "What is a laser" or "How do lasers work" to "Spectra in stimulated emission of rare gases" and "Dissociative excitation transfer and laser oscillation in RF discharges" - and everything in between. A quick check of some of the educational web sites may provide everything you need.

PART II deals with the care and feeding of lasers constructed from readily available components like helium-neon tubes and laser diodes. There is also extensive information on the design and construction of power supply, driver, and other circuits.

The chapters on specific types of lasers includes *8* circuits for driving laser diodes, *16* complete schematics for helium-neon laser power supplies, as well as simple modulators and other useful goodies. Most of these have been tested and/or came from working commercial designs and can be constructed using readily available inexpensive parts.

The material on argon/krypton ion lasers includes extensive information on the general characteristics and features, power supply requirements and design considerations including circuit descriptions, and maintenance and alignment of these highly prized devices. There are even complete ion laser power schematics of varying levels of sophistication which can be replicated using readily available parts or used as the basis for a custom design of your own!

There is even some coverage of CO2 lasers including a discussion of sealed CO2 tubes which are powered in a very similar way to helium-neon lasers.

To the best of my knowledge, no other resource in the explored universe (or elsewhere) currently comes close to providing as much practical information on these topics in a form which is both easy to read and readily accessible in one place - if at all.

PART III is for the true basement experimenter and provides information on actually constructing entire lasers from basic materials like beach sand and copper ore :-). Well, maybe not quite that basic but: glass tubing, mirrors, hardware, gasses, chemicals, and electronic components like transformers, resistors, capacitors, diodes, and high voltage warning signs!

Where you really think constructing a laser from scratch would be a challenge, fun, and educational, first keep in mind that such an endeavor is generally a LOT of work and depending on the type of laser, may require access to fairly sophisticated facilities and equipment (at least compared to the average kitchen sink - and that, too, may be needed!). These may include the need for glass blowing, a high vacuum system, access to a machine shop, and sources for assorted lab supplies, chemicals, pure gases, and specialized optical and electronic components. This is not to say that your dream is unrealistic or impossible - just that one must be quite determined to see such a project through to a successful conclusion and the information in this document will get you started.

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Related Information

See the chapter: Laser Information Resources for books, magazine articles, newsgroups, technical forums, and links to other laser related web sites.

There are many other documents at the Sci.Electronics.Repair FAQ Web site or one of its mirror sites which may be of use in the design and testing of laser equipment. In particular:

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What is a Laser and How Does It Work?

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A Brief Introduction to Lasers Principles and Structure

The Laser Age

Since every document on lasers must have a discussion of basic principles, this is it! If you know anything at all about lasers, you can skip to the section: Characteristics of Some Common Lasers since the summary below will probably just put you to sleep and then you might miss the rest of the excitement :-). If you want a more in-depth on-line course, see the section: On-Line Introduction to Lasers.

A laser is a source of light but unlike anything that had ever been seen or implemented before 1960 when Theodore H. Maiman of Hughes Aircraft mounted a specially prepared synthetic ruby rod inside a powerful flash lamp similar to the type used for high speed photography. When his flash lamp was activated, an intense pulse of red light burst forth from the end of the rod that was both monochromatic (a single color) and coherent (all of the waves were precisely in step). The difference between the output of a laser and that of an incandescent light bulb is like the difference between white noise and a single tone.

The laser age was born. Within a very short time, in addition to many more solid state materials, laser action was demonstrated in gasses (the ubiquitous helium-neon laser was the first gas laser though it originally only produced invisible IR wavelengths), liquids, and semiconductor crystals. Almost every conceivable material was tried in the frenzy to produce new and interesting lasers. Even some varieties of Jello(tm) brand dessert were blasted with xenon light, and according to this legend, are supposed to work fairly well. I wonder whether the flavors have to be all natural :-). (See the section: Comments on the Jello Laser Legend for a discussion on this very exciting topic.)

See Laser Stars - LASER HISTORY (1917-1996) for an interesting chronology of laser development, discovery, and applications.

In many ways, the laser was a solution looking for a problem. Well, the problems soon followed in huge numbers. It would be hard to imagine the modern world without lasers - used in everything from CD players and laser printers, fiber-optic and free-space communications, industrial cutting and welding, medical and surgical treatment, holography and light shows, basic scientific investigation in dozens of fields, industrial cutting and welding, and fusion power and Star Wars weapons research. The unique characterisics of laser light - monochromicity (the light is very nearly a single wavelength or color), coherence (all the waves are in step), and directionality (the beam is either well collimated to start or can easily be collimated or otherwise manipulated) make these and numerous other applications possible. In fact, it is safe to say that the vast majority of laser applications have not yet even been contemplated.

General Physical Characteristics of Lasers

The word 'LASER' is an acronym standing for 'Light Amplification by Stimulated Emission of Radiation'. In some ways, this is somewhat confusing since most lasers are actually oscillators (generators or sources of light) and not amplifiers (devices for increasing the strength of a signal), though such lasers are also possible and used for some applications.

The output of a laser can be pulsed or a continuous beam; visible, IR, or UV; less than a milliwatt - or millions of watts of power. However, nearly all lasers have the following in common. (One notable exception is the 'free electron laser' which operates on a totally different principle - in fact, it is probably not really accurate to call it a laser at all except for the fact that its output is intense coherent monochromatic light!):

  1. A lasing medium. This can be a solid, liquid, gas, or semiconductor material which can be pumped to a higher energy state.
  2. A means of pumping energy into the lasing medium. This can be optical, electrical, mechanical, chemical, etc.
  3. A resonator. In most cases this is some form of a Fabry-Perot cavity, a pair of mirrors, one at each end of the laser, which allow stimulated light to bounce back and forth through the lasing medium. Usually, one of the mirrors is totally reflective while the other is partially transparent to allow the laser beam to escape. The mirrors are either perfectly flat (plane) or one or both may be very slightly concave. Other configurations are possible:

Basic Laser Operation

Relax! This will be short and simple. There are numerous references with extensive information - at all levels of sophistication - on laser theory. See the chapter: Laser Information Resources for references and links to all sorts of material which will cure insomnia :-).

We present only the briefest of summaries. Some additional more specific material is presented in the chapters: Helium-Neon Lasers and Diode Lasers.

Please refer to the diagram: Basic Laser Operation whlle reading the following explanation. The numbers in () denote each step in the lasing process.

Normally, nearly all atoms, ions, or molecules (depending on the particular laser) of the lasing medium are at their lowest energy level or 'ground state' (1).

To produce laser action, the energy pumping device must achieve a population inversion in the lasing medium so that there are a majority of atoms/ions/or molecules at the upper energy level of the pair that participates in the stimulated emission. Note that those designated 'Energy Level 2' in the diagram are the ones of interest; some have been raised to 'Energy Level 1' and just sit there taking up space :-).

At random times, some of these excited atoms/ions/molecules will decay to the lower energy state on their on. In the process each one emits a single photon of light. This is called 'spontaneous emission' and by itself isn't terribly useful. It is basically the same process that accounts for the glow of a neon sign, or the phosphor coating of a fluorescent lamp or screen of a CRT (3).

However, Einstein showed that if one of these photons happens to encounter an excited atom/ion/molecule in just the right way, it will drop down to a lower energy state and emit a photon with several amazing properties compared to the original one. Among these are:

The new photon will have exactly the same polarization as well, though this is not a requirement to create a laser. However, where the resonator favors a particular polarization orientation (e.g., there is a Brewster angle window or plate in the beam path or the cavity is highly asymmetric), or in some cases, there is a particular magnetic field configuration, the output beam will also be polarized - but this is for the advanced course :-).

So, imagine the lasing medium (perhaps, it is easiest to visualize it like the glowing gas in a neon sign) spontaneously emitting these photons in all direction at random times. Most will be lost exiting the side of the discharge tube or hitting one of the mirrors at an angle and then escaping its confines.

Occasionally, however, a photon will happen to be emitted nearly parallel to the long direction of the resonator (3,4). In this case it will travel down to one of the mirrors and be able to bounce back and forth many times (with some configuration of slightly concave mirrors, if there were no losses, it could even do this indefinitely). So far, pretty boring! However, along the way, it encounters excited atoms/ions/molecules and STIMULATES them to give up their photons. As this progresses, what was once a single photon is now an avalanche of more and more photons via this stimulated emission process (5).

The resulting beam is highly monochromatic (nearly entirely one wavelength) and coherent (all the waves are in-step). It is also either well collimated (nearly parallel rays for most lasers including gas and solid state types) or appears to originate from a point source (diode lasers). In either case, the beam can easily be manipulated in ways impossible with more common light sources.

If the pumping source is adequate and enough atoms/ions/molecules are being raised to the upper energy level to maintain the population inversion while this is happening, the laser action will continue indefinitely (barring trivial problems like overheating or depletion of the power available on the National Electric Grid). This results in a continuous wave laser. If the pumping cannot be maintained or some energy levels get clogged up, the result is a pulsed laser.

There you have it! Everything else is just details :-).

For some (still easy to understand) details on the principles of operation of the ubiquitous helium-neon laser, see the section: Theory of Operation, Modes, Coherence Length, On-Line Course as well as the chapters on other specific types of lasers. Additional information on general laser characteristics may also be found in the chapter: Items of Interest.

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On-Line Introduction to Lasers

There are a number of Web sites with laser information and tutorials. One of the best so far is the Electro-Optics Technology Series: Coourse #1: Intro to Lasers. (Cord Communications, 324 Kelly Drive, P.O. Box 21206, Waco, Texas 76702-1206.

These are the subjects it covers:

This is great educational content for those who wish to gain a better understanding of the principles of laser operation. But, it is designed at a level that probably won't put you to sleep with too much heavy math :-). Also see the section: General Laser Information and Tutorial Sites for other sites that may be worth visiting.

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Characteristics of Some Common Lasers

Here is a summary of the features, power output, power supply requirements, wavelengths, beam quality, cost, and applications of diode, helium-neon, argon/krypton ion, and carbon dioxide lasers.

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Lasers for the Hobbyiest and Experimenter

Commercial Lasers Versus Amateur Laser Construction

Diode, helium-neon (HeNe), and argon/krypton (Ar/Kr) ion lasers are probably the most popular types of lasers generally available to hobbyists and experimenter (see the section: Characteristics of Some Common Lasers). This is due to the wide availability of complete lasers and laser components (new as well as surplus), and their desirable optical and physical characteristics, including the generation (in most cases) of a continuous beam, manageable power and cooling requirements, and the fact that there is no need for sophisticated laboratory facilities to keep them healthy. A major portion of this document is devoted to the practical aspects of these types of laser systems, their power sources, and related optics and electronics.

While many other types of lasers may be constructed including mercury vapor ion, nitrogen, excimer, dye, ruby, Nd/YAG, chemical, free electron, and X-ray, most of these are less commonly available as surplus. There could also be problems obtaining the 100 million volt particle accelerator required for the free electron laser and the small thermonuclear device needed to pump the X-ray laser :-).

Now, back down to earth....

Where you are really interested in actually constructing any of these types of lasers from basic materials (e.g., not by simply hooking together commercial laser tubes and power supplies), check out the chapters beginning with: Amateur Laser Construction which include general information on the types and requirements for home-built lasers, setting up a laser lab, introduction to vacuum systems and glass working, and other really exciting topics.

General Comments on Lasers as a Hobby:

(From: Richard Alexander (RAlexan290@gnn.com)).

How much do you like to build things? Would you prefer to assemble a bunch of parts, or do you want to blow your own glass tubes, too? Do you have any mechanical experience? Do you build electronic kits? Keep in mind that you will often be working with intense light (enough to instantly damage your unprotected eyes, and maybe your unprotected skin) and high voltages.

All laser experimenters (and optics types, too) should have a copy of "Scientific American"'s "Light and Its Uses." [5] It gives construction plans for a Helium-Neon (you blow the glass tube yourself), an argon ion (even more complicated), a CO2 (designed and built by a high school student, and able to cut through metal), a dye, a nitrogen (a great first laser, but watch out for UV light) and a diode laser (obviously, you buy the diode laser and assemble the driver circuit from the plans they supply). They also explain how to make holograms using visible and infrared light, microwaves and sound. There are other projects, too. The book is getting fairly old (the HeNe dates to the '60s), but it's still a great reference.

A nitrogen laser may be built for under $200 (maybe less than half that amount if you are lucky). It requires no mirror alignment (since it has no mirrors). The technology for building this laser was available to Ben Franklin, so there is nothing too critical in it. The hazards it presents are lots of ultraviolet light (spark discharges and laser beam), high voltage (necessary to arc across a 1/4 inch spark gap in a nitrogen environment) and circuit etcher (the main capacitor is made from an etch circuit board).

Once built, the nitrogen laser can drive many other projects. It can be used as a pump for the dye laser, for example. It will light up anything fluorescent. It is a pulse laser (10 ns) that can be repetitively pulsed (120 Hz is a likely frequency). Megawatt power is possible, but the total energy is low (due to the short pulses).

"Electronics Now" (formerly, Radio Electronics) has a laser projects column that started several months ago. I'm trying to think up a project I can submit to them. They said they would welcome projects for the laser column.

Helium-Neon laser tubes may be bought from many mail-order companies. I bought one from Meredith Instruments in Arizona. They cost about $15, and the power supply can be built or bought for about another $20. You have the option of buying tubes with mirrors attached or not. You might want to buy the mirrors attached, because aligning those mirrors is extremely tedious. I was given an "A" for constructing a working Helium-Neon laser from the parts in the Laser Lab in less than an hour. The class was given two semesters to gain the experience they needed to do that.

If you want more than one color from lasers, there are various ways to do it, but none of them are as nice as one might like. For $3000 or so, you can buy a Helium-Neon laser that will produce laser light ranging from infrared to blue. All you have to do is turn a dial on the back.

Laser light shows usually use argon ion or krypton lasers. These are able to produce most of the colors of visible light, and they can also be dialed to the desired color. However, they usually cost several thousand dollars ($40,000 is not too unusual) and require either forced air or water cooling or a combination.

A dye laser is the usual solution to the multi-color problem. They are inexpensive and simple. They aren't especially tunable, unless you change the dye, although a diffraction grating can be used to tune a particular dye to various colors. One common dye that can be used in a dye laser is the green dye found in radiator antifreeze.

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Laser Safety

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Introduction to Laser Safety

You Only Received One Set of Eyeballs?

Lasers have tended to be high glamor devices popular with with hobbyists, experimenters, entertainers, and serious researchers alike. However, except for very low power lasers - those with less than a fraction of a mW of beam power - they do pose some unique hazards particularly with respect to instant and permanent damage to vision.

There are several reasons for this even for lasers which do not represent any sort of burning or fire risk:

See the section: Laser Safety Sites for links to much more information on general laser safety, laser safety organizations, and regulatory agencies.

A popular graveyard joke in the laser industry is: "Do not stare into the beam with your remaining good eye". Nonetheless, laser safety is no laughing matter.

Why a 1 mW Helium-Neon Laser Still Appears Bright a Mile Away

At a distance of 1 mile (1,609 m), the beam from a typical helium-neon laser (which is a quite well collimated source) will have spread to a diameter of roughly 4 feet (48 inches, 1.3 m). However, it will still appear quite bright. Why is this so?

(Portions of the following from: Don Klipstein (don@Misty.com)).

The fraction of light entering the eye for a large diameter beam is pupil area divided by beam area.

Assuming a pupil diameter of 1/4 inch (6.3 mm, rather dilated but not fully dark adapted which may approach 1 cm). The portion of the beam entering the eye would then be the square of (1/4)/(48), which is about 27 millionths of the total. Since the 4 foot diameter beam is not uniform but dimmer towards the edges, I would say the eye could get about 35 millionths of the beam near the center or 35 nanowatts (35 nW).

Note that close to the laser, the pupil size is going to be larger than the beam diameter (which is typically less than 1 mm) and pupil size larger than this will not affect the maximum possible power entering the eye (though it will affect the probability of this occurring. (One suggested laser safety practice is to brightly illuminate the laser lab to make your pupils smaller. Even though there are times this will not reduce the severity of the worst case, a smaller target reduces likelihood of this happening.)

However, where the beam diameter is equal to or larger than the pupil diameter, the difference in pupil diameter between bright and dark adapted eyes will be very significant - more than a 30-fold difference in power entering the eye for this analysis.

I calculate that a 4 foot diameter 1 mW 632.8 nM beam appears about as bright as a 100 W bulb does 88 feet away.

Although 35 nW is definitely eye-safe, it may look quite bright against pitch black surroundings especially when the eye is fully dark adapted (the pupil is wide open and the combined retinal/neural sensitivity is maximum as it is after awhile when out at night) and may quickly result in a noticeable afterimage. The effect is probably enhanced by the knowledge that the light source is a laser and thus potentially damaging to your eyesight.

As a side note, the 1,710 lumen output of a typical 100 watt incandescent bulb is about the same lumens as *10 Watts* of 632.8 nm light!

Also see the section: How much light does a 5 W laser really produce?.

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Safety Issues With Respect to Small Lasers

The most common types of lasers generally available to hobbyists - CD laser diodes, visible laser diodes, laser pointers, and small HeNe lasers, are all rated Class II or IIIa. See the section: Laser safety classification.

Class II lasers should be relatively low risk if even minimal precautions are taken. However, Class IIIa lasers must be taken much more seriously if the beam is well collimated - as it would be from a laser pointer or HeNe laser tube.

In addition, with helium-neon lasers, high voltage power supplies are involved so there is the added shock hazard resulting from touching or accidentally coming in contact with uninsulated connections. See the document: Safety Guidelines for High Voltage and/or Line Powered Equipment before working on any type of equipment which uses line voltage or produces high voltage. Most of these are quite low power so the actual risk of electrocution from the high voltage side is relatively small but there may be AC line voltage involved and there can be collateral damage from a reflex response to the shock. In addition, a homemade power supply, in particular, may use components which are grossly oversized for the application (due to low cost availability) like a 15,000 V, 400 W neon sign transformer even though only under 10 W of power is actually needed (we definitely do NOT recommend this approach).

Furthermore, you may come across a truly high power CO2 or argon ion laser, or even a 50 mW helium-neon tube. These, rated Class IIIb or Class IV, represent much more significant risks of both instant permanent eye damage even from momentary reflections from shiny (specular) surfaces as well a very real fire hazard. In addition there is a very real danger of electrocution from the high voltage high current power supplies used to power these beasts. Since this document does not deal in detail with these types of lasers, the essential additional precautions that must be taken are not covered. However, you must handle them properly for your own safety and the safety of others around you and your surroundings. Note that other people in the area may actually be more likely to get caught by the beam. The reason? You will be aware of what NOT to look at while they will be looking in the direction of the action not having a clue of what to expect! Don't take chances.

The following very large number is designed to impress: The power density of a 1 mW laser beam when focused to a spot of around 2 um (which isn't difficult with a simple convex lens) is around 250,000,000 W per square meter!

Be Extremely Careful When Working with any laser!

(From: Tjpoulton (tjpoulton@aol.com)).

A 1 mW diode will probably not cause damage if you briefly look into it, but I wouldn't encourage you to try it. While it probably won't do anything bad, it is not good to become comfortable with the idea of checking the operation of lasers by looking into them. If you are a hobbyist who uses lasers quite a bit, there is a good chance you will, at some point, end up with an unmarked diode. It could emit any wavelength at any power level, and how bright the beam appears when you shine it on something has no bearing on the power level. Looking into an unmarked diode just because the beam is dim could (and probably will) have disastrous results. I have a 1 W 808 nm laser diode, and it appears much dimmer than a .5 mW 670nm beam when focused into a .2 mm spot. When focused in that way, it will easily engrave plastic and burn paper and wood (and skin). Just because it looks dim doesn't mean it won't instantly blind you.

(From: Daniel P. B. Smith (dpbsmith@world.std.com)).

Be aware that eye damage that is localized to a small area of the eye is not very noticeable. For example, few people ever notice the existence of the large blind spot where the optic nerve enters the eye even though it is rather huge (10 degrees or so) and not all that far from central vision. A laser wouldn't necessarily have to make you totally blind; it could just wipe out a teeny patch here and a teeny patch there. This kind of damage would be very insidious; each time you'd say "Wow! That was bright! lucky I didn't get blinded" - while slowly and cumulatively losing your sight...

Laser Pointer Safety

There have apparently been some recent (UK) articles about eye injuries from careless or malicious use of common laser pointers. At the very least, this industry is probably inadequately regulated with all sorts of claims about laser power levels and deliberate or unintended (due to poor quality control) sale of devices with power even beyond the approved safety limits. However, actual cases of permanent eye damage from momentary or unintentional exposure to the beam are hard to confirm.

While I absolutely agree that intentionally aiming a laser into the anyone's eye is basically stupid (unless you are having eye surgery), one must be careful in interpreting the meaning of 'momentary'. I can see kids playing a game of chicken with a laser pointer and that 'momentary' actually being more like a minute or two!

For that matter, how come no one has banned butane lighters or matches? :-). They are cheaper, more readily available, and certainly result in more injury, death, and destruction in the hands of kids than laser pointers! Or, cigarettes.... Sorry, I will get off my soap box now....... No, I don't expect an answer.

However, I think 1 mW would probably a good upper limit especially with the newer 635 nm pointers since they appear so much brighter it is therefore adequate - and certainly when green laser pointers become readily available and inexpensive.

(From: Gregory Makhov (lsdi@gate.net)).

As chair of the ILDA (International Laser Display Association) laser safety committee, I have been carefully following the thread on laser pointer safety (in the sci.optics newsgroup - search at DejaNews for the complete saga). I have seen most of the articles in the press on laser incidents/accidents in the UK. If you have a source of factual evidence concerning these 'injuries', I would greatly appreciate the information. My own experience with laser pointers would indicate that a level of 5 milliwatts and below is unlikely to cause injury unless self-inflicted and for a substantial duration (several seconds). I say self-inflicted, as it is unlikely that another person could direct the laser accurately into someone's eye at any significant range. Almost immediately after the initial exposure to the beam, the pupil shrinks to a very small size (a few millimeters) which is an awfully small target to illuminate from a distance of even a few meters.

However, if there is any medical evidence of these injuries, and some documentation of how they occurred (laser power, range, duration, etc.) I am most interested.

Caution About Depending on Neutral Density Filters for Protection

(From: Don Klipstein (don@Misty.com)).

While thumbing through some gel filter sample packs, it has occurred to me that there are neutral density gel filters - and that they are not truly neutral. Both Gam and Rosco ones are somewhat neutral through to about 700 nM - and become more transparent as wavelength increases through the low and mid 700's. They are nearly transparant above about 750 nM.

They also have a slight peak at 380 nM, where they are a bit more transparent than they are to visible light. Transmission at 380 can exceed the average visible transmission for darker grays.

This is because these filters are made gray with some kludge of dyes rather than something truly neutral-density. They also do not equally attenuate all visible wavelengths; they have transmission peaks around 480 (greenish blue) and 600 (orange), and absorption peaks around 450 (mid-blue) and the mid 500's (yellowish green). Different brands may have some differences, as well as having some similarities. They probably have some but not all dyes in common.

I do not know whether the infrared transparency is an unavoidable consequence of dying plastics/gels, or something intentional to reduce filter heating. I do know that the colored filter gels are also nearly transparent to most wavelengths from the upper 700's (sometimes low 700's) through probably at least around 1500 nM.

Because of this, dark filter gel combinations are probably unsafe for directly viewing the sun, and are probably unsafe for attempting to protect eyes from infrared lasers.

Accidents Can Happen

(From: Brian Sutin (sutin@sol.ucolick.org)).

Several years ago there was a long thread in rec.guns, where people posted their stories about all the accidents or near accidents they had experienced with firearms. These were all seemingly intelligent people like computer programmers and scientists and engineers. Still, while dealing with a simple device with only a few knobs, they managed somehow, sooner or later, and while trying to obey all the safety rules, to blast a hole in something or someone. Educational reading.

There was a really good story recently posted right here (sci.optics). Some guy was working with a laser and then took off his goggles, and blew out some of his eye. Dumb. Then, rather than realizing that the goggles don't work if they are not worn, he decided that he just wouldn't wear them at all, and he would Be Real Careful. This is called People Who Don't Learn From Their Mistakes. Let's hope he doesn't take up firearms.

When you have goggles on (assuming that they are the right kind, and you should make damn sure they are), you have very good protection against loss of vision. When you take them off, you don't. A movement of a mirror, lens, or baffle can cause a specular reflection, total internal reflection, or refraction right into your eye. This isn't something to anticipate -- that's why it is called an accident. Even with all the appropriate precautions, accidents can still happen.

Imagine that you are working with the laser off, aligning some mirror, no goggles, and you spill your coffee over the on-off switch to the laser power. Oops. Collect insurance.

Back to Laser Safety Sub-TOC.

Laser Safety Classifications

A Smorgasbord of Acronyms

There are ANSI standards, OSHA, FDA (CDRH) standards, and military standards. The best discussion of these, plus general treatment of the topic, is a book by Sliney and Wolbarsht, "Safety with Lasers and Other Optical Sources," Plenum Press, New York.

The following is based on material from the University of Waterloo - Laser Safety Manual.

All lasers are classified by the manufacturer and labelled with the appropriate warning labels. Any modification of an existing laser or an unclassified laser must be classified by the Laser Safety Officer prior to use. The following criteria are used to classify lasers:

  1. Wavelength. If the laser is designed to emit multiple wavelengths the classification is based on the most hazardous wavelength.
  2. For continuous wave (CW) or repetitively pulsed lasers the average power output (Watts) and limiting exposure time inherent in the design are considered.
  3. For pulsed lasers the total energy per pulse (Joule), pulse duration, pulse repetition frequency and emergent beam radiant exposure are considered.

Lasers are generally classified and controlled according to the following criteria:

The following relates the laser classifications to common laser types and power levels:

(From: Richard Trotman (trotman@udel.edu)).

I'm paraphrasing from "Introduction to Lasers", C.O.R.D., 1990:

The classifications depend on the wavelength of the light as well.

Hobbyist Projects and Laser Safety Classifications

While many of the partial circuits and complete schematics in this document can and have been used in commercial laser products, important safety equipment has generally been omitted to simplify their presentation. These range from simple warning labels for low power lasers (Class I, II, IIIa) to keyswitch and case interlocks, beam-on indicators, and other electrical and mechanical safety devices for higher power lasers. Laser safety is taken very seriously by the regulatory agencies. Each classification has its own set of requirements.

The following brief summary is just meant to be a guide for personal projects and experimentation (non-commercial use) - the specifics for each laser class may be even more stringent:

Where you plan to offer a product commercially, there are very specific requirements - and equally severe penalties for non-compliance!

(From: Steve Roberts (osteven@akrobiz.com)).

"CDRH has fangs and will use them. I have a friend who sold helium-neon laser power supply kits without stickers, certification, and registering. His legal bills alone were $8,000, not to mention the hefty fine his company paid."

For more information, spend an afternoon (more or less) starting at the CDRH Device Advice Web site which includes major portions of the relevant laser regulations and registration procedures on-line. "Device Advice is set up with pages that describe these procedures and link you to the appropriate documents on the CDRH Homepage such as guidance documents, databases, and manuals that will both assist in meeting marketing requirements and answer many questions you may have."

Also, see the chapters on 'Control Measures' in the laser safety manuals at the Laser Safety Links web site and the other laser safety links in the chapter: Laser Information Resources of this document.

Back to Sam's Laser FAQ Table of Contents. Back to Laser Safety Sub-TOC. Forward to Items of Interest.