Compact disc players

C07-0007. A compact disc player uses light of frequency 3.85 X lO s to read the information on the disc, (a) What is this light s wavelength (b) In what portion of the electromagnetic spectrum (visible, ultraviolet, and so on) does this wavelength fall (c) What is the energy of one mole of photons at this frequency ... 

Pick-up lenses for digital versatile disc (DVD) players, recorder and super audio compact disc players,... 

The laser hght used in compact disc players has A = 780 nm. In what region of the electromagnetic spectrum does this hght appear What is the energy of this hght in kilojoules per mole ... 

The laser in an audio compact disc player uses light with a wavelength of 7.80 X lO2 nm. What is the frequency of this light What is the energy of a single photon of this light ... 

Nicad batteries are used in a large variety of appliances, including compact disc players, cell phones, pocket recorders, handheld power tools, cordless telephones, laptop computers, camcorders, and scanner radios. A few automobile manufacturers have explored the possibility of using nicad batteries in electric cars. For example, the Mitsubishi Corporation of Japan built and marketed an experimental car called the Libro EV that operated on either traditional lead batteries or on nicad batteries. 

Infrared diode lasers are used in compact disc players and laser printers, and in bar code readers (see Chapter 11). They are solid-state devices, typically constructed of gallium arsenide, and energy is pumped into them at a low potential... 

New challenges should open in the future for colloidal silicas and silicates. Opportunities exist, for example, in microelectronics, a 500 billion industry worldwide, spanning from consumer products such as compact disc players to supercomputers (94). As Tummala said (94) ... 

Such a light-emitting diode is not yet a laser. However, it is easy to use the radiative electron-hole recombination in a p-n junction as the basis of a laser. Population inversion can be realized by rapidly taking away the electrons which have fallen into the holes of the valence band. These lasers are nowadays widely used (optical communication, compact disc player). An additional large advantage is their small dimension (< I mm). 

The potential application of this glass is in high-density optical recording (used, for example, in compact disc players). In such devices the information density increases with dccrca.sing sire of the focus spot of the laser. This sire varies inversely quadratically with the wavelength. Since the available diode lasers emit in the near infrared, there is a considerable amount of research going on to obtain a blue-emitting diode laser. There are three possibilities, viz. 

The disadvantage of all dye lasers is their complexity, their physical size, and their costs, which preclude the adoption of these systems for routine analysis. Semiconductor DLs, however, meet the requirements of practical spectrochemical analysis. They are small, reliable devices, which do not need to be aligned and have very stable power output. Produced on a large scale (as the scanning device in compact disc players), the costs of semiconductor DLs have been greatly reduced. 

The lasers used in supermarket scanners emit red light at a wavelength of 633 nm. Compact disc players use lasers that emit light (that is not visible) at 840 nm. Which photons— those emitted by supermarket scanners or compact disc (CD) players-contain more energy per photon ... 

Gallium arsenide is used to make semiconductor diode lasers for use in fiber optic communications, compact disc players,and laser printers. Also, computer chips are being developed using gallium arsenide, because it conducts an electrical signal five times faster than presently used silicon. 

See the essay Lasers and Compact Disc Players at the end of Section 7.3.) The basic component of most of these electronic devices is silicon, which is a semiconductor. A semiconductor is a material that has low electrical conductivity at room temperature, but increases in conductivity as the temperature increases. This contrasts with the behavior of metals, which are generally good electrical conductors, although their conductivity decreases with increasing temperature. 

Lasers and Compact Disc Players 276 Superconductivity 537 Buckminsterfullerene—A Third Form of Carbon 11 Silica Aerogels, the Lightest"Solids" 550 Materials jh g Dlscovery of NyIoo 1040... 

The batteries found in a portable compact disc player or other small electronic device are frequently alkaline dry cells. These cells do not have a carbon rod cathode, as in the zinc-carbon cell. The absence of the carbon rod allows them to be smaller. Figure 2.3b shows a model of an alkaline battery. This cell uses a paste of Zn metal and potassium hydroxide instead of a solid metal anode. The half-reaction at the anode is as follows. 

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