Laser Technology
Welcome to Laser Technology 101! We'll start with some basics about lasers and laser pointers, back up to cover the physics that made Laser Technology possible and finally, go thru each of the technical aspects of how lasers work and how they are used. Feel free to skip around as there is a lot of information here!
- Basic Definition of LASER
- Basics of Laser Pointers
- The Physics of Lasers
- Laser structure and how a laser works
- Laser Characteristics and Specifications
Basic Definition of A Laser
What is a Laser?
LASER is actually an acronym that stands for Light Amplification by Stimulated Emission of Radiation.
A LASER is a device that converts some form of energy (electrical, optical, chemical, etc.) into a narrow beam of a very specific kind of light defined as
- Monochromatic: Light that consists of one single color or wavelength is called monochromatic.
- Directional: Laser Light is highly directional; this means that the waves of light all travel in the same direction over very long distances, rather than scattering about
- Coherent: Coherent light means that all of the light waves are traveling along IN PHASE; that means that all of the waves are moving precisely together through time and space. When light waves are in phase, or coherent, each wave enhances (or AMPLIFIES) the strength of every other wave, so the overall impact of coherent light is much greater than if the waves were not in phase.
Physics of a Laser
Because of these properties, a laser light can be focused into a very narrow, very bright spot. While some lasers are green and others are red and some are strong enough to cut metal while others are safe to shine on your hand, all laser light is monochromatic, highly directional and coherent.
How is Laser Light different from ordinary light from a light bulb or sunlight? Light from a light bulb or from the sun does not have the specific properties of a Laser. Ordinary light a) does not have directionality… the light scatters to “light up” a room rather than a narrow spot
b) is made up of a number of different wavelengths rather than a single wavelength or color. The multiple wavelengths create which interfere with each other produce what we have come to know as "white" or "clear" light.
c) is incoherent; each wave travels OUT of synch with every other wave so there is no amplification.
What is the basic LASER structure?
One basic type of laser consists of a sealed tube, containing a pair of mirrors, and a laser medium that is excited by some form of energy to produce visible light, or invisible ultraviolet or infrared radiation.
How Lasers work
There are many different types of lasers and each uses a different type of laser medium. Common laser media include gases such as argon or a helium and neon mixture, solid crystals such as ruby, and liquid dyes or chemicals. When energy is applied to the laser medium, it becomes excited and releases energy as particles of light (photons).
A pair of mirrors at either end of the sealed tube either reflects or transmits the light (see illustration below) in the form of a concentrated stream called a laser beam. Each laser medium produces a beam of a unique wavelength and color.
What you should know about Laser Pointers
Way back when telephones had cords and were attached to the wall, you actually had to stretch, jump or sometimes climb to point at your blackboard or screen or… map. Then there were laser pointers! The first ones were clunky and heavy and some even had to be plugged in, but along with the invention of the DIODE, came the first affordable, stable and effective red laser pointers! That was back in the mid 1990’s. By the end of the millennium, we had graduated to green laser pointers and just a few years later and here we even have blue and violet laser pointers!
Here are some of the things to consider if you are buying a laser pointer:
Wavelength: is measured in nanometers and refers to the distance between the crest of one wave and the crest of the next wave. Wavelength is what gives the beam of the laser pointer its color, usually red, green or blue and sometimes violet. A green laser pointer will have a wavelength in the green range, typically 532nm and a red laser pointer will have a wavelength of between 640nm and 670nm
Output power: Power output is measured in Miliwatts or mW and is the specification that determines the safety class of the laser. Please see our SAFETY page for more information. Power Output is also partially responsible for how bright a laser pointer appears, but it is not the whole story. Visibility is a thing all its own.
Visibility: The visibility of a laser pointer is what you are concerned with and it depends on a number of factors and is not as simple as one might think. First, consider that all colors are not created equal. The human eye is actually most sensitive to light that with the wavelength 555nm. Being quite close to the typical wavelength of a green laser pointer, it begins to make sense as to why a green laser pointer at the same power output (1mW for example) will always appear brighter than a red laser pointer.
Laser Specifications
The chart below is a means by which to compare the visibility of lasers of varying wavelengths. The wavelength of 555nm (the most visible to the human eye) is set at 1.000 and is the standard against which other wavelengths are measured. The number in the relative column shows the ratio of visibility proportional to the standard of 555nm. Notice that perception of brightness is not linear. A 1 mW 532 nm green laser pointer does not actually appear 28 times brighter than a 1 mW 670 nm red laser pointer; a 1 mW green laser pointer will appear similar in brightness to a 28 mW 670 nm red one.
Distance/range: Unfortunately, while this is what most people want to know first about their laser pointer, it is essentially meaningless because light doesn't travel a specific distance and stop, or suddenly become too dim to be seen. Light travels forever, technically, so what we are really talking about here is relative brightness and visibility. See above.
APC or ACC driver: This refers to the power driver for the laser pointer. Most red pointers use Automatic Power Control (APC) to maintain the output power constant over temperature and until the batteries are nearly dead. The laser diode package itself has a built-in photodiode behind the laser diode chip for this purpose. Only the very cheap "dollar store" red laser pointers forgo this feature and simply use a current limiting resistor - as the batteries discharge, the output grows dimmer.
All OnPoint Lasers green laser pointers use an APC driver to eliminate variability and also make it harder to "boost" the output to an illegal and dangerous power level.
Battery: Most full sized laser pointers use common AAA cells which are the most economical in terms of battery replacement costs (and AAAs are certainly the most readily available). The shape and size of a pointer is determined largely by the type of battery used. The tiniest red laser pointers use button cells. Long thin laser pointers (red or green) use a pair of AAA Alkaline cells. The blue laser pointer uses a CR2 lithium cell. Whether aesthetics determines the battery design choice or vice-versa is anyone's guess.
In general, it is best to remove the batteries if the pointer won't be used for even a short time. Batteries have been known to leak and/or swell, usually once they go dead.
More information about lasers can be found here:
