Lets explore some of the fundamentals of lasers – how they work, the various types and some of their applications. The word 'LASER' is an acronym standing for 'Light Amplification by Stimulated Emission of Radiation'. 

A laser is a source of light but unlike anything that had ever been seen or implemented before 1960. This was 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 laser age was born. Within a very short time, in addition to many more solid state materials, laser action was demonstrated in gasses 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 legend, are supposed to work fairly well.  

Put very simply, the basis for all lasers consists of three parts. The first is the lasing medium. This can be a solid, liquid, gas, or semiconductor material which can be pumped to a higher energy state. The second is a means of pumping energy into the lasing medium. This can be optical, electrical, mechanical or chemical. The third is a resonator. The laser works by pumping energy into the lasing medium, which then becomes excited, and causes energy to be given of in the form of photons (light), which then is bounced inside the resonator to produce a coherent beam of light. 

The most important aspect of a laser beam from an alignment tool point of view is that it provides a perfectly straight reference line with no mechanical parts. 
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 characteristics 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. 

Characteristics of some common lasers 

Diode lasers consist of a semiconductor laser diode 'chip' driven by low voltage power supply. They are available in various colours from Red (635 nm, actually may appear slightly orange-red) through deep Red (670 nm) and beyond. Green and blue laser diodes have been produced in various research labs but until recently, only operated at liquid nitrogen temperatures, had very limited life spans (~100 hours or worse), or both. Recent developments suggest that long lived room temperature blue and green diode lasers will be commercially available very soon. Violet (around 400 nm) laser diodes are just going into production.
Power: 0.1 mW to 5 mW (most common), up to 100 W or more available. The highest power units are composed of arrays of laser diodes, not a single device.  

Some applications: CD players and CDROM drives, LaserDisc, MiniDisc, other optical storage drives; laser printers and laser fax machines; laser pointers; sighting and alignment scopes; measurement equipment; high speed fibre optic and free space communication systems; pump source for other lasers; bar code and UPC scanners; high performance imagers and typesetters, small (mostly) light shows.  

Cost: $15 to $10,000 or more.  

Helium-Neon (HeNe) lasers. Most common are sealed HeNe plasma tube with internal mirrors, high voltage power supply. External mirror HeNe lab lasers also available and expensive. Red (632.8 nm, actual appearance is actually orange-red) is most common by far. Orange (611.9), yellow (594.1 nm), green (543.5 nm), and IR (1,523.1 nm) HeNe lasers are also readily available. 

Power: 0.5 to 10 mW (most common), up to 250 mW or more available.
Some applications: Industrial alignment and measurement; blood cell counting and analysis, medical positioning and surgical sighting (for higher power lasers); high resolution printing, scanning, and digitization; bar code and UPC scanners, non-contact measuring and monitoring; general optics and holography; small to medium size light shows, laser pointers, LaserDisc and optical data storage.
Cost: $25 to $5,000 or more depending on size, quality, new or surplus.

Carbon dioxide (CO2) lasers. Sealed (small) or flowing gas design. High voltage DC, RF, electron beam or other power supply. These lasers generally produce invisible infrared light.  

Power: A few watts to 100 kW or more.  

Some applications: Industrial metal cutting, welding, heat treatment and annealing; marking of plastics, wood, and composites, and other materials processing, and medicine including surgery.  

Cost: New systems go for several $K to 100s of $K depending on specific type and output power. Used/surplus low to moderate power (up to 100 W) flowing gas systems may be available for under $500.  

The Largest and Smallest Lasers 

By far the largest pulsed solid state laser on the face of the earth (at least for awhile) will be at the National Ignition Facility being constructed at Lawrence Livermore National Laboratory. It will produce about 1.8 MJ per pulse with a peak output power of over 500 Terawatts. The NIF laser will be about the size of a football STADIUM with 192 beam lines and over 7,300 major optical components including some 3,000 glass slab amplifiers nearly a meter across! Its estimated construction cost is more than $1,200,000,000 with an annual operating budget of about $60,000,000. 

The smallest lasers in common use are diode lasers like those found in CD players, barcode scanners, and telecommunications equipment. The active region is a fraction of a millimeter long and as little as 1 x 3 micrometer in width and height. The entire semiconductor chip is about the size of a grain of sand. Even smaller 'microlasers' have been developed and some are in commercial production. In principle, a single atom can be the active medium in a laser.

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