LASERDIS TECHNICAL INFORMATION

Technical information

The standard home video laserdisc is 30 cm (11.81 inches) in diameter and made up of two single-sided aluminum discs layered in plastic. Although appearing similar to compact discs or DVDs, Laserdiscs use analog video stored in the composite domain with analog sound and/or some form of digital audio. However, despite its analog nature, the Laserdisc at its most fundamental level is still recorded as a series of pits and lands much like DVDs and CDs are today.[10] The first Laserdiscs featured in 1978 were entirely analog but the format evolved to incorporate digital stereo sound in CD format (sometimes with a TOSlink or coax output to feed an external DAC), and later multi-channel formats such as Dolby Digital and DTS.
Since digital encoding and compression schemes were either unavailable or impractical in 1978, three encoding formats based on the rotation speed were used:
CAV (Constant Angular Velocity) or Standard Play discs supported several unique features such as freeze frame, variable slow motion and reverse. CAV discs were spun at a constant rotational speed during playback, with one video frame read per revolution and in this mode, 54,000 individual frames or 30 minutes of audio/video could be stored on a single side of a CAV disc. Another unique attribute to CAV was to reduce the visibility of crosstalk from adjacent tracks, since on CAV discs any crosstalk at a specific point in a frame is simply from the same point in the next or previous frame. CAV was used less frequently than CLV, reserved for special editions of feature films to highlight bonus material and special effects. One of the most intriguing advantages of this format was the ability to reference every frame of a film directly by number—a feature of particular interest to film buffs, students and others intrigued by the study of errors in staging, continuity, etc.
CLV (Constant Linear Velocity) or Extended Play discs do not have the "trick play" features of CAV, offering only simple playback on all but the high-end Laserdisc players incorporating a digital frame store. These high-end Laserdisc players could add features not normally available to CLV discs such as variable forward and reverse, and a VCR-like "pause". CLV encoded discs could store 60 minutes of audio/video per side, or 2 hours per disc. For films with a run–time less than 120 minutes, this meant they could fit on a single disc, lowering the cost of the title and eliminating the distracting exercise of "getting up to change the disc"—at least for those who owned a dual-sided player. The vast majority of titles were only available in CLV. (A few titles were released partly CLV, partly CAV. For example, a 140-minute movie could fit on two CLV sides, and one CAV side, thus allowing for the CAV-only features during the climax of the film.)
CAA (Constant Angular Acceleration). In the early 1980s, due to problems with crosstalk distortion on CLV extended play Laserdiscs, Pioneer Video introduced CAA formatting for extended play discs. Constant Angular Acceleration is very similar to Constant Linear Velocity save for the fact that CAA varies the angular rotation of the disc in controlled steps instead of gradually slowing down in a steady linear pace as a CLV disc is read. With the exception of 3M/Imation, all Laserdisc manufacturers adopted the CAA encoding scheme, although the term was rarely (if ever) used on any consumer packaging.
As Pioneer introduced Digital Audio to Laserdisc in 1985, they further refined the CAA format. CAA55 was introduced in 1985 with a total playback capacity of 55 minutes 5 seconds, and was necessary to resolve technical issues with the inclusion of Digital Audio. Several titles released between 1985 and 1987 were analog audio only due to the length of the title and the desire to keep the film on 1 disc (e.g., "Back to the Future"). By 1987, Pioneer had overcome the technical challenges and was able to once again encode in CAA60—allowing a total of 60 minutes, 5 seconds. Pioneer further refined CAA, offering CAA45—encoding 45 minutes of material, but filling the entire playback surface of the side. Used on only a handful of titles, CAA65 offered 65 minutes 5 seconds of playback time. The final variant of CAA is CAA70, which could accommodate 70 minutes of playback time. There are not any known uses of this format on the consumer market.

History OF LASERDISC

Laserdisc technology, using a transparent disc,[1] was invented by David Paul Gregg in 1958 (and patented in 1961 and 1990).[2][3] By 1969 Philips had developed a videodisc in reflective mode, which has great advantages over the transparent mode. MCA and Philips decided to join their efforts. They first publicly demonstrated the videodisc in 1972. Laserdisc was first available on the market, in Atlanta, on December 15, 1978, two years after the VHS VCR and four years before the CD, which is based on Laserdisc technology. Philips produced the players and MCA the discs. The Philips/MCA cooperation was not successful, and discontinued after a few years. Several of the scientists responsible for the early research (Richard Wilkinson, Ray Dakin and John Winslow) founded Optical Disc Corporation (now ODC Nimbus).
In 1979, the Museum of Science and Industry in Chicago opened their "Newspaper" exhibit which used interactive Laserdiscs to allow visitors to search for the front page of any Chicago Tribune newspaper. This was a very early use of digitally interactive technology in museums and could even be among the first.[citation needed]
The first Laserdisc title marketed in North America was the MCA DiscoVision release of Jaws in 1978. The last two titles released in North America were Paramount's Sleepy Hollow and Bringing Out the Dead in 2000. The last Hong Kong-released Laserdisc format-movie was Tokyo Raiders. A dozen or so more titles continued to be released in Japan, until the end of 2001. Production of Laserdisc players continued until January 14, 2009 when Pioneer stopped making them.[4][5][6]
It was estimated that in 1998, Laserdisc players were in approximately 2% of US households (roughly two million).[7] By comparison, in 1999, players were in 10% of Japanese households.[8] Laserdisc was released on June 10, 1981 and a total of 3.6 million Laserdisc players were sold in Japan.[9] A total of 16.8 million Laserdisc players were sold worldwide of which 9.5 million of them were sold by Pioneer.[4][5][6]
Laserdisc has been completely replaced by DVD in the North American retail marketplace, as neither players nor software are now produced there. Laserdisc has retained some popularity among American collectors and, to a greater degree, in Japan, where the format was better supported and more prevalent during its life. In Europe, the Laserdisc has always remained an obscure format. The format was, however, chosen by the British Broadcasting Corporation (BBC) for the BBC Domesday Project in the mid-1980s, a school-based project to commemorate 900 years since the original Domesday Book in England.

Laserdisc

The Laserdisc (LD) is an obsolete home video disc format, and was the first commercial optical disc storage medium. Initially marketed as Discovision in 1978, the technology was licensed and sold as Reflective Optical Videodisc, Laser Videodisc, Laservision, Disco-Vision, DiscoVision, and MCA DiscoVision until Pioneer Electronics purchased the majority stake in the format and marketed LaserDisc in the mid to late 1980s.
While LaserDisc produced a consistently higher quality image than its rivals, the VHS and Betamax systems, the laserdisc never obtained more than a niche market with videophiles in America. In Europe, it remained largely an obscure format. It was, however, much more popular in Japan and in the more affluent regions of South East Asia, such as Hong Kong and Singapore. Laserdisc was the prevalent rental video medium in Hong Kong during the 1990s.
The technology and concepts provided with the Laserdisc would become the forerunner to Compact Discs and DVDs.

X-ray

When X-rays of sufficient frequency (energy) interact with a substance, inner shell electrons in the atom are excited to outer empty orbitals, or they may be removed completely, ionizing the atom. The inner shell "hole" will then be filled by electrons from outer orbitals. The energy available in this de-excitation process is emitted as radiation (fluorescence) or will remove other less-bound electrons from the atom (Auger effect). The absorption or emission frequencies (energies) are characteristic of the specific atom. In addition, for a specific atom small frequency (energy) variations occur which are characteristic of the chemical bonding. With a suitable apparatus, these characteristic X-ray frequencies or Auger electron energies can be measured. X-ray absorption and emission spectroscopy is used in chemistry and material sciences to determine elemental composition and chemical bonding.
X-ray crystallography is a scattering process; crystalline materials scatter X-rays at well-defined angles. If the wavelength of the incident X-rays is known, this allows calculation of the distances between planes of atoms within the crystal. The intensities of the scattered X-rays give information about the atomic positions and allow the arrangement of the atoms within the crystal structure to be calculated.

Spectroscopy

Spectroscopy was originally the study of the interaction between radiation and matter as a function of wavelength (λ). In fact, historically, spectroscopy referred to the use of visible light dispersed according to its wavelength, e.g. by a prism. Later the concept was expanded greatly to comprise any measurement of a quantity as function of either wavelength or frequency. Thus it also can refer to a response to an alternating field or varying frequency (ν). A further extension of the scope of the definition added energy (E) as a variable, once the very close relationship E = hν for photons was realized (h is the Planck constant). A plot of the response as a function of wavelength—or more commonly frequency—is referred to as a spectrum; see also spectral linewidth.
Spectrometry is the spectroscopic technique used to assess the concentration or amount of a given species. In this case, the instrument that performs such measurements is a spectrometer or spectrograph.
Spectroscopy/spectrometry is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them.
Spectroscopy/spectrometry is also heavily used in astronomy and remote sensing. Most large telescopes have spectrometers, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the Doppler shift of their spectral lines.

Semiconductor lasers

Semiconductor lasers are also solid-state lasers but have a different mode of laser operation.
Commercial laser diodes emit at wavelengths from 375 nm to 1800 nm, and wavelengths of over 3 µm have been demonstrated. Low power laser diodes are used in laser printers and CD/DVD players. More powerful laser diodes are frequently used to optically pump other lasers with high efficiency. The highest power industrial laser diodes, with power up to 10 kW (70dBm), are used in industry for cutting and welding. External-cavity semiconductor lasers have a semiconductor active medium in a larger cavity. These devices can generate high power outputs with good beam quality, wavelength-tunable narrow-linewidth radiation, or ultrashort laser pulses.


A 5.6 mm 'closed can' commercial laser diode, probably from a CD or DVD player.
Vertical cavity surface-emitting lasers (VCSELs) are semiconductor lasers whose emission direction is perpendicular to the surface of the wafer. VCSEL devices typically have a more circular output beam than conventional laser diodes, and potentially could be much cheaper to manufacture. As of 2005, only 850 nm VCSELs are widely available, with 1300 nm VCSELs beginning to be commercialized,[19] and 1550 nm devices an area of research. VECSELs are external-cavity VCSELs. Quantum cascade lasers are semiconductor lasers that have an active transition between energy sub-bands of an electron in a structure containing several quantum wells.
The development of a silicon laser is important in the field of optical computing. Silicon is the material of choice for integrated circuits, and so electronic and silicon photonic components (such as optical interconnects) could be fabricated on the same chip. Unfortunately, silicon is a difficult lasing material to deal with, since it has certain properties which block lasing. However, recently teams have produced silicon lasers through methods such as fabricating the lasing material from silicon and other semiconductor materials, such as indium(III) phosphide or gallium(III) arsenide, materials which allow coherent light to be produced from silicon. These are called hybrid silicon laser. Another type is a Raman laser, which takes advantage of Raman scattering to produce a laser from materials such as silicon.

Fiber-hosted lasers

Solid-state lasers where the light is guided due to the total internal reflection in an optical fiber are called fiber lasers. Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have high surface area to volume ratio which allows efficient cooling. In addition, the fiber's waveguiding properties tend to reduce thermal distortion of the beam. Erbium and ytterbium ions are common active species in such lasers.
Quite often, the fiber laser is designed as a double-clad fiber. This type of fiber consists of a fiber core, an inner cladding and an outer cladding. The index of the three concentric layers is chosen so that the fiber core acts as a single-mode fiber for the laser emission while the outer cladding acts as a highly multimode core for the pump laser. This lets the pump propagate a large amount of power into and through the active inner core region, while still having a high numerical aperture (NA) to have easy launching conditions.
Pump light can be used more efficiently by creating a fiber disk laser, or a stack of such lasers.
Fiber lasers have a fundamental limit in that the intensity of the light in the fiber cannot be so high that optical nonlinearities induced by the local electric field strength can become dominant and prevent laser operation and/or lead to the material destruction of the fiber. This effect is called photodarkening. In bulk laser materials, the cooling is not so efficient, and it is difficult to separate the effects of photodarkening from the thermal effects, but the experiments in fibers show that the photodarkening can be attributed to the formation of long-living color centers

LASER MODE OF OPERATIONS

Modes of operation
The output of a laser may be a continuous constant-amplitude output (known as CW or continuous wave); or pulsed, by using the techniques of Q-switching, modelocking, or gain-switching. In pulsed operation, much higher peak powers can be achieved.
Some types of lasers, such as dye lasers and vibronic solid-state lasers can produce light over a broad range of wavelengths; this property makes them suitable for generating extremely short pulses of light, on the order of a few femtoseconds (10-15 s).
Continuous wave operation
In the continuous wave (CW) mode of operation, the output of a laser is relatively constant with respect to time. The population inversion required for lasing is continually maintained by a steady pump source.
Pulsed operation
In the pulsed mode of operation, the output of a laser varies with respect to time, typically taking the form of alternating 'on' and 'off' periods. In many applications one aims to deposit as much energy as possible at a given place in as short time as possible. In laser ablation for example, a small volume of material at the surface of a work piece might evaporate if it gets the energy required to heat it up far enough in very short time. If, however, the same energy is spread over a longer time, the heat may have time to disperse into the bulk of the piece, and less material evaporates. There are a number of methods to achieve this.
Q-switching
Main article: Q-switching
In a Q-switched laser, the population inversion (usually produced in the same way as CW operation) is allowed to build up by making the cavity conditions (the 'Q') unfavorable for lasing. Then, when the pump energy stored in the laser medium is at the desired level, the 'Q' is adjusted (electro- or acousto-optically) to favourable conditions, releasing the pulse. This results in high peak powers as the average power of the laser (were it running in CW mode) is packed into a shorter time frame.