Lasers how Light and Matter Interact

Lasers are a big part of our every day life from the laser pointers used by your professor in class, to the device used to scan the bar code on your groceries, to the many medical applications used to interact human tissues. Light comes in many colors, and lasers can be selected with a variety of colors as well.

The essential components of a laser consist of a light source and a media that selects the wavelength of interest. For example, a light source such as a flashlamp would create white light that would excite a media such as a crystal embedded with a transition metal complex such as neodymium. The white light hits the atoms and causes electrons in the crystal to become excited. Electrons are very mobile and can occupy different energy levels. You might think of this as getting on an elevator and going to different energy level floors. Before light hits the media of the laser, the electrons in the crystal are on the ground level. When light hits the crystal the electrons are provided with energy to get on the elevator’ and head on up to the top floor. Electrons in the higher levels are in an excited’ state. They have lots of extra energy but cannot remain on the top floor. When energy in the electron is dissipated or given off bright colored light is emitted. This is how the laser uses the crystal to tune the wavelength. The wavelengths emitted show up at certain frequencies. For a neodymium YAG laser these fundamental wavelengths are 1064, 532 and 266 nanometers. A nanometer is a very small unit, 1/1000,000,000 of a meter.

Lasers can be continuous beam or pulsed. Continuous lasers are lower energy. This is why you can point certain laser beams at your eye and not get blinded by them. Pulsed lasers are very high energy because they have very short flashes of light on the order of nanoseconds, picoseconds and femptoseconds. All the energy gets packed into this short energetic beam, whereas continuous lasers have the energy spread out.

Lasers have been used in some scientific research to measure how photosynthesis occurs, the speed at which chemical reactions occur and for looking a fluid dynamics in jet and automobile engines. In the checkout line at grocery store, helium neon lasers are used. If you have every looked down when your groceries are being scanned you will see a grid of low energy red light. The red light comes from the red wavelengths produced by helium and neon gas in a that laser. Carbon dioxide, He Ne and Nd:YAG lasers are one of the many lasers being used for medical purposes(1).

The next time you see a laser in the grocery store remember that light is interacting with matter (a neodymium crystal, carbon dioxide or helium neon gas) to create laser light of various colors. The cycle continues when we use laser light to interact with the bar code on our favorite ice cream or when we go to the dermatologist to get our pimples cleared up. Light energy and matter are constantly in flux with one another and lasers are a vital part of everyday life and technology. We would be lost without that bright laser pointer as our guide.