• Probably the most common application of lasers is their use in CD and DVD players.  A tiny spot of laser light from a diode laser is focused onto the spinning plastic disk which has a metalized coating.  The coating has a series of "lands" and "pits" in it which represents the digital data stored on the disk.  The strength of the reflections of the laser by the disk surface, is read by a photo detector and conversed into a stream of "1" and "0" signals, fed to the computer or decoder chip, which then converts it back into the original data.
• Construction applications where pipes or rails must be laid on a very straight line use the beam of a low power laser as a guide. In digging underground, the centre of a tunnel can be kept accurately aligned with a laser beam (see photo - left).  Home construction also uses a laser device with a spinning mirror that can project a line around a room allowing for accurate placement of windows, doors or even electrical outlets.
• Lasers are used to align drills and rivet machines, a laser dot shows the operator where the hole or rivet will be placed. Similarly, a line of laser light projected onto the material can show a saw operator where the cut will occur in the material.
• Holography is the production of a 3D photograph using a laser as the source of illumination. Holographic images can be artistic as well as practical allowing the study of fragile objects which can not withstand repeated handling. Holograms can also be used for vibration and stress analysis allowing the detection of hidden defects in materials such as aircraft parts long before they become a problem. Commercial aircraft tires and high performance automotive tires are tested this way.  Beacuse holograms are difficult and expensive to reproduce, they are used on credit cards and certain product pckages as a verification that the item is an original.
• You are probably familiar with the bar code scanner in your local supermarket or store. These units scan a pattern of red light from a low power HeNe or diode onto a window or out of a small hand held unit. The reflections from the UPC (Universal Product Code) on the products placed or dragged across the window are detected. The reflections are converted into computer code and fed to the cash register. This looks up the product, charges you the correct price, prints the sales slip and also keeps track of the inventory so that the store will know when to re-order popular items.
• In manufacturing, scanned laser beams can be used for non-contact defect detection where more or less light is reflected from moving material if a defect is present.  Lasers can also be used to rapidly check the size or parts in automated manufacturing to insure they are within tolerances.

    In most laser based communications systems, the laser beam is conducted by a glass fiber optic usually no thicker than a human hair (see photo - right). As light operates at much higher frequencies and speeds than the voice and data information it carries, many conversations or data transmissions can be multiplexed (encoded) onto one fiber optic.  By using different laser lines (colours) and encoding many transmissions onto each line, thousands of transmissions can be carried on a single hair thin glass fiber as in modern telephone and data backbone systems.
    Much of the information you access through the Internet is transmitted by fiber optic cables from major node to major node and even to your ISP.  At the ISP or major nodes, the data can be recovered form the fiber optic and then sent along DSL or Cable lines to your home or school.  These transmitters use high speed modulation of laser diodes to send the data thought the fibers.  The data is converted from light to electronics at the receiving end; the server is queried, the page you requested is converted from electronic impulses to light impulses; sent to your ISP, which then converts it back to electronic signals that are forwarded to your computer (this is a simplified explanation that omits routing issues).