Laser

A laser is a device that emits light through a specific mechanism for which the expression laser is an acronym: Light Amplification by Stimulated release of Radiation. This is a combined quantum-mechanical and thermodynamical procedure discussed in more detail below. As a light source, a laser can have various properties, depending on the reason for which it is designed and calibrated. A typical laser emits light in a contracted, low-divergence beam and with a well-defined wavelength. This is in contrast to a light source such as the incandescent light bulb, which emits into a large solid angle and over a wide spectrum of wavelength. These properties can be summarized in the term coherence.
Light of a specific wavelength that passes through the increase medium is amplified; the neighboring mirrors ensure that the majority of the light makes many passes through the gain medium. Part of the light that is between the mirrors passes through the partially apparent mirror and appears as a beam of light. The process of supplying the power required for the amplification is called pumping and the energy is typically supplied as an electrical current or as light at a diverse wavelength. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the form of the beam.

Chair

A chair is a piece of furniture for sitting, consisting of a seat, a back, and sometimes arm rests, generally for use by one person. Chairs also often have four legs to support the sit raised above the floor. Without back and limb rests it is called a stool. A chair for more than one human being is a couch, sofa, settee, loveseat, recliner or bench. A split footrest for a chair is known as an ottoman, hassock or poof. A chair mounted in a vehicle or in the stage is simply called a seat. The back often does not expand all the way to the seat to allow for ventilation. Likewise, the back and sometimes the seat are made of permeable materials or have holes drilled in them for decoration and ventilation.
The back may extend above the stature of the head. Headrests for seats in vehicles are important for prevent whiplash injuries to the neck when the vehicle is occupied in a rear-end collision.
Chair design considers planned usage, ergonomics, as well as non-ergonomic functional requirements such as size, stack ability, fold ability, weight, durability, stain confrontation and artistic design.