How to Obtain Coherent Light

Coherent light is composed of photons (or waves) that all have the same wavelength and phase. Common light sources, such as light bulbs and the sun, do not produce coherent light. You can produce coherent light, however, using certain devices such as lasers. The following procedure describes how you can obtain coherent light by constructing a basic laser.

Instructions

1. Obtain a material to serve as a gain medium. Different gain media produce different wavelengths (colors) of laser light. You can use, for example, a mixture of helium and neon gases to serve as a gain medium.

2. Make an optical resonator using two mirrors. The mirrors must have appropriate shapes and placements relative to each other to form an optical resonator. One mirror should be highly reflective, but the other should be only partially reflective. The partially reflective mirror allows a portion of the laser light to escape.

3. Place the gain medium between the two mirrors. If you're using a gas, the gas must, of course, be isolated in a transparent container of some sort (the container may also encase the mirrors).

4. Use a "pump" to create population inversion in the gain medium. Depending on the type of gain medium you chose in Step 1, the type of pump you need may vary; some gain media require optical pumps (light sources).

5. Activate the pump to obtain coherent light. If properly constructed, the laser should produce coherent light of a single color.

Tips & Warnings

• Population inversion is a situation where more electrons reside at a higher (excited) energy level than at a given lower level. This condition is typically required for most lasers to produce coherent, monochromatic light (that is, to "lase").

• Laser light can be dangerous if you don't treat it with respect. Most lasers cannot do any harm to skin, but they can do significant damage to eyes. Protect your vision by carefully aiming lasers to avoid looking directly at the beam and to avoid shining the beam in another person's eyes.