The technique of obtaining an image of a 3D body on a 2D photographic plate is termed as holography. The stored image is called a hologram. The whole process is based on the interference produced by the interaction of two-beam monochromatic light waves under certain conditions.
The hologram is recorded when a part of the emitted laser beam or reference beam goes directly to the photographic plate and the other part being object beam is reflected from the object and made to fall on the photographic plate, hence interfering with the reference beam to produce an interference pattern, which is called a hologram. Even if the hologram is broken into pieces, single pieces produce the whole image of the body with reduced intensity.
Holography is used for diagnosis in various fields of medicine, non-destructive testing, holographic information storage, display devices and pattern-matching procedures in credit cards and identity card verification. It is also used for establishing a secret communication system by storing secret documents, maps and objects as holograms and reconstructing the image only at the receivers’ end. It is expected that in the near future, holography may even be used for target recognition from air to ground, and we may have holographic movies and TVs.
Properties of a laser like wide bandwidth and narrow beam width over long distances enable its utility in this field. The semiconductor laser is generally used for optical-fibre communication, which is excited directly by electric current to yield a laser beam in the infrared region. Capacity of the communication channel is directly proportional to the bandwidth of frequency. So at optical frequencies, the information-carrying capacity is higher than at lower frequencies.
Communication of signals where light is used as a signal carrier and optical fibres as transmission medium is called optical-fibre communication. The first ever optical-fibre communication system was established in 1977. Since then, millions of dollars have been spent on long-distance communication where data or signals are converted into light pulses or codes using a suitable light source.
Light signals are transmitted through the core of optical fibres, amplified at the receiving end and converted into readable electrical signals by decoding light signals and, hence, getting the required original information. As light has high information-carrying capacity, optical-fibre communication is most probable these days. Moreover, light can easily be transmitted through extremely-thin hair-like fibres to large distances without reducing the intensity.
Advantages of optical-fibre communication are:
1. High information-carrying capacity
2. Free from electromagnetic interference
4. Minimum signal leakage
Due to these advantages this system finds many applications in the field of telecommunications. The telecommunication market for optical fibres has exploded in several developed countries like the USA, the UK, France, Denmark, Germany and Japan.
No talk on laser in medicine can be done without mentioning Leon Goldman, the father of laser medicine. He was the first to use laser to treat a skin disease, which developed as dermatology.
Photo-rejuvenation is a process in which lasers are used to evaporate moisture from tissues responsible for wrinkles, dark spots and the like, from the face and create a layer of self-healing wounds.
Lasers have been extensively used in surgery, the very first being eye surgery where a laser was used to weld detached retinas and photocoagulate the vessels that grow in retinas, thereby blocking vision. Laser beams easily pass through transparent portions of the eye, including the cornea and lenses, to reach the region where energy of the laser is absorbed and used for treatment.
Traditionally, the use of xenon arc lamps and sunlight to focus over the choroid coat was really painful and required high-level anesthesia. Introduction of high-pulsed lasers like Nd:YAG was a major breakthrough when dealing with eyes. When focused on a tiny spot at the detached retina in order to weld it to the choroid coat, it leads to painless surgery.
Lasers are also used to burn small tumors on the surface of the eye or its vessels. These are being used to treat coma, cataract, sealing of retina and viral diseases of the eye.
As lasers are less damaging than x-rays, these are extensively and effectively used to treat different types of cancers by removing those enlarged tissues that are responsible for the cancer.
Lasers are also effective in curing diseases of gynecology, ear, nose, throat, tongue, palate and cheeks. These are effective in reducing tumors, too.
Photodynamic therapy (PDT) is the new form of cancer treatment, which combines laser with light-sensitive dye, hemato-porphyrin derivative (HPD), which is derived from cow’s blood, and travels through the body of a patient and settles in malignant tissues. An argon red light is used to activate the HPD, which energises to release a highly-reactive chemical that destroys cancer cells. Reports say that PDT is 80 to 90 per cent successful in causing total regression of tumors.
Lasers are also used to treat colonic and gastro-intestinal cancers. Tools like endoscopes use laser energy to destroy neuro-plastic tissue while preserving the bowel wall integrity. Lasers also find a role in clearing kidney stones.
Lasers are used for dental treatment, too. Using a process called laser glazing to perform tooth decay clearance, a high-intensity laser is focused on the decayed tissues of the tooth. This destroys the infections in the affected areas in a fraction of a second.
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