Ultraviolet Imaging

Ultraviolet (“UV”) band is one of the frequencies of band to the human eye; it is an invisible part of the “electromagnetic spectrum.” Ultraviolet band, visible light and infrared energy are all given off by the sun. UV band was discovered in 1801 by a German physicist Johann Wilhelm Ritter.

Light which is visible to the human eye covers the spectral region from about 400 to 750 nanometers. This is the radiation spectrum used in normal photography. The band of radiation that extends from about 1 nm to 400 nm is known as ultraviolet radiation. UV spectrographs divide this range into three bands. They are,

• Near UV (380–200 nm wavelength; abbrev. NUV)
• Far UV (or vacuum UV) (200–10 nm; abbrev. FUV or VUV)
• Extreme UV (1–31 nm; abbrev. EUV or XUV)

figure 1: UV band

Only near UV is of interest for UV photography, for several reasons. Ordinary air is opaque to wavelengths below about 200 nm, and lens glass is opaque below about 180 nm. UV photographers subdivide the near UV into:

• Long wave UV that extends from 320 to 400 nm, also called UV-A
• Medium wave UV that extends from 280 to 320 nm, also called UV-B
• Short wave UV that extends from 200 to 280 nm, also called UV-C

Features of UV Radiation

1. Spectrophotometry

UV radiation has been used to study the chemical structure of various substances and has been widely employed in visible spectrophotometry to determine the presence of fluorescence in a given sample.

2. Photolithography

UV is employed in fine resolution photolithography and hence is extensively used in the field of electronics.

3. Authentication of documents and collectibles

In order to prevent counterfeiting, sensitive documents like passport may include a UV watermark that can be viewed only beneath a UV light. Analyzing gems, or other valuables can also be effectively carried out under UV light.

Domains which are used ultraviolet imaging

Photography

Two ways of UV photography

1. Reflected ultraviolet

• Detection of scratches in a surface

The shorter UV wavelengths tend to scatter more strongly off surface features compared to the visible or near-IR bands. So, for example, scratches not apparent in a visible image may be visible only to a person with excellent eyesight with great difficulty when visible light strikes at a very oblique angle. In contrast, in a UV image taken at 365 nm, the scratches can be seen quite easily.

• Detection of small amounts of surface contamination

Since UV light tends to be absorbed by organic materials, traces of oil or grease are sometimes detectable on many surfaces, particularly in the deep-UV band. It is also possible to distinguish new paint from old in some situations, even when the two types of painted surfaces look identical in the visible band.

2. Ultraviolet induced

Ultraviolet photography finds practical use in medicine, dermatology, botany, criminology and theatrical applications.

figure 2: UV use in dermatology

In microscopy

A fluorescence microscope is an optical microscope which is used UV to get better resolution of the fluorescent image.

figure 3 : UV in microscope

In lithography

Extreme ultraviolet lithography is a next-generation lithography technology using an extreme ultraviolet (EUV) wavelength.

Photolithography, also termed optical lithography or UV lithography, is a process used in to pattern parts of a thin film or the micro fabrication bulk of a substrate.

figure 4: UV in lithography

In Astronomy

Using UV light, it can take images of new stars and sky objects, and can measure the chemical composition, densities, and temperature of those stars.

figure 5 : Image of sky objects

Biological Imaging

UV light allows forensics scientists to see evidence that they would otherwise be unable to see with the naked human eye. UV light illuminates substances such as,

•       blood

•       sweat/oil

•       fingerprints

•       bruises

•       bite marks

•       tattoos

•       bodily fluids

Forensic scientists use RUVIS (reflective ultraviolet imaging system) to find fingerprints. RUVIS consists of a ray of UV light that must be positioned in a proper angle onto the surface that has suspected prints. RUVIS devices use 254nm UV light.

Other Applications which used UV radiation

1. Germicidal Lamps

Germicidal lamps or low pressure mercury lamps are commonly used in laboratory. They are usually in housed fixtures such as a biological hood, but may not always limit exposure to the eyes or skin. The UV wavelength of these lamps is between 200-280 nm and work by breaking DNA which removes the capability of organisms to reproduce or kills them. Unprotected persons should not be in a room where a lamp is active. Hood lamps should be turned off after sterilization time has ended.

2. Photo-therapy Lamps

Artificial sources of UVB in phototherapy lamps are used primarily for clinical purposes. Acne, psoriasis, neonatal high levels of bilirubin, and daylight deprivation depression are some of the ailments treated with UVB. The exposures times and radiation intensities are controlled and should not cause any unusual harmful effects that one would not get in sunlight. Regardless, equipment should be monitored regularly to avoid accidental overexposure.

3. Lasers

The term "LASER" is an acronym for "Light Amplification by Stimulated Emission of Radiation.” The light from a laser has a very small divergence. The most common injury from a laser is thermal, but chronic exposure around UV lasers even outside of the beam can have the same effects as exposure to UVA or UVB. Damage to the eyes from lasers is irreversible. Face shielding when working with lasers is mandatory.

Contributed by

BayMax

H.M.N.N Herath

P.A.U Rathnasiri

D.L.S.N Liyanage

Deamons

W.A.U.C Weerasekara

F.R Arshad

R.K.A.N.G Sandunika

Radiance

U.A.A.M Adikaram

W.A.T Chathurika

L.J.M.N.A.K Balalla

Optimum
R.M.R.S Bandara
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W.A.M.T.R Herath

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M.A.M.M Mathotaarachchi
H.P.K.U Suraweera
D.M.M.N Dissanayaka