Digital platemaking, commonly called Computer-to-Plate, is a method of imaging a printing plate directly from digital files. The conventional process of using film to create the negative images required for burning plates is eliminated. Information that has been stored digitally is imaged directly onto the plate with the use of laser beams. The plating process is performed off the press or it can be accomplished on presses that are specially equipped to allow direct imaging of plates on the press. CTP is often used for print processes such as offset lithography, flexography, and gravure.

Laser light is the concentrated light beam of only one wavelength, while regular light is emitted at many different wavelengths. The word "LASER" is actually an acronym for "Light Amplification by Stimulated Emission of Radiation". Laser light is coherent, monochromatic, and directional, meaning that the photons emitted by the laser are traveling in coordination, the light is of one color, and the light is concentrated and travels in a tight beam (whereas normal light sources release light that travels in many directions). Laser light is concentrated with the use of concave mirrors that bounce the light between them to create a single beam, which is focused onto an object.

The light that humans see - the visible spectrum - is only a small part of the electromagnetic spectrum. The entire spectrum ranges from gamma rays, which are the shortest wavelengths, to radio waves, which are the longest. As wavelengths get shorter, they increase in energy. Gamma rays, which are as small as a nucleus of an atom, have a tremendous quantity of energy, while radio waves, which can be hundreds of feet long, have much less energy. Ranging from the shortest wavelengths to the longest, the electromagnetic spectrum is composed of the following types of wavelengths:

• Gamma Rays
  
  
• X-rays
  
  
• Ultraviolet
  
  
• Visible Light
  
  
• Infrared
  
  
• Microwaves
  
  
• Radio Waves

All lasers have three basic components: A pumping source, a lasing medium, and a resonator.

• Pumping Source: a device that feeds the energy to the laser.
  
  
• Lasing Medium: an active medium that is able to absorb the energy from the pumping source and re-emit the energy as laser light.
  
  
• Resonator: a device, such as a set of mirrors, that amplifies the light to produce the laser beam.

A laser is usually described by the type of lasing medium that is used. Described below, are the mediums that are most often used for lasers.

Gas Lasers

Gas lasers use gases, such as helium or helium and neon, as the lasing material. Some common gas lasers include helium-neon lasers, argon-ion lasers, and carbon dioxide lasers. In another type of gas laser, the excimer laser, which is a combination of the words "excited" and "dimers", reactive gases, such as chlorine and fluorine, are combined with inert gases, such as argon, krypton, or xenon. The material is given an electrical stimulation, which produces a "dimer" (a molecule that consists of two simpler molecules that are identical) that generates ultraviolet light when the material is lased.

Liquid Lasers

Fluorescent organic dyes in a liquid suspension are used as the lasing material for liquid lasers. This type of laser is also known as a dye laser.

Solid State Lasers

Solid State lasers have lasing material distributed in a solid substance and are often pumped by diodes, which produce either flashes of light (pulsed energy) or continuous light.

Semiconductor Lasers

Also known as diode lasers, semiconductor lasers use low power and generate light from the interaction between a positive and negative junction of various semiconductor materials.