A “Green” Idea: Optical Phenomena with a Green Laser

Warning!!!! Laser Ahead!!!!

When beginning to think about what to do for my photo project, lasers immediately entered my mind. From hand held lasers that can be seen for miles and miles, to extremely high powered lasers used for science or military purposes, something about lasers peaks my interest. Interestingly, the word laser originates from the acronym LASER, or Light Amplification by Stimulated Emission of Radiation. The basic premise of lasers is that they emit "coherent" light, or light that has waves of identical phase (in-step), polarization, and frequency, rather than "incoherent" light that is totally random, in various phases, frequencies, and positions at various times. The common components of a laser are a gain medium inside of a reflective optical cavity (a mirror on each end, with one mirror having a small hole or being semi-translucent).  As light travels through the gain medium and bounces back and forth between the mirrors, it is exponentially amplified and is released as a narrow "beam" of light.  Simply, energy (typically electricity) is "pumped" into the gain medium, causing all of its atoms to be at a higher energy state. Next, "ignition" photons are tuned to a specific frequency (a similar wave function), so when they skim the atoms in the gain medium, they stimulate the release an additional photon in the same direction as the incoming photon. These two photons go on the stimulate further atoms, and they will stimulate even more atoms, etc., creating a chain reaction. Affter emmiting these photons, the atoms fall back down to a ground state to be re-energised by the energy being pumped in. Through this process, the light can be exponentially amplified, creating powerful "rays" of electromagnetic radiation (light).

Here is my photo:

A “Green” Idea: Optical Phenomena with a Green Laser

This contrived image demonstrates common optical phenomena that are not typically observed with conventional light sources (incandescent lights, fluorescent lights, or sunlight) because the rays are too spread out. The image was created using a 5mW, 532nm green laser, water tank, small mirror, and light bulb. Greater visibility of the beam was created with the dispersal of a small amount of milk throughout the water and the introduction of fog into the air above the tank. The laser demonstrates several optical concepts: reflection (Law of Reflection), refraction (Snell’s Law), and diffraction. When the ray strikes the water, two things occur. First, the majority of the ray passes through the air-water boundary, refracting (bending) and traveling through the water at an angle less than the incident angle of the aerial ray (with respect to the normal, perpendicular to the waterline). Second, a substantial amount of the ray reflects off the water’s surface, obeying the Law of Reflection (angle of incidence equals angle of reflection). Next, the ray is reflected off a mirror on the tank’s bottom where it then hits the water-air boundary again, some of the ray reflecting back into the tank (barely visible) while most passing through, refracting, and striking the light bulb. Some of the beam reflects off the bulb’s shiny surface while the rest is transmitted through the glass where it is refracted, reflected, and diffracted (due to the frosted coating), making it visibly illuminated from the inside; a “green” idea comes to “light.”


For your enjoyment, here is a fun puzzle game on laser reflections: http://games.erdener.org/laser

Attributions:
Laser Radiation Picture: http://chemistry.about.com/od/labsafety/ig/Radiation-Warning-Symbols/Laser-Radiation-Symbol.-QVX.htm
Some Laser Information: http://en.wikipedia.org/wiki/Laser