fluorescence imaging of fingerprints-Katherine

Question 1

oblique illumination

Answer 1

good for fingerprints in dust

Question 2

specular (oblique top) illumination

Answer 2

specular illumination to detect marks on smooth surfaces

only some diffuse reflections reach imager and therefore pale

used for fingerprints on reflective surfaces

Question 3

dark field illumination

Answer 3

used when fingerprints in grease, oil or sweat are on transparent surface

shows light fingerprint ridges against dark background

Question 4

co-axial illumination

Answer 4

used for marks on patterned, reflective background

fingerprint appears as dark ridges against a light background

Question 5

polarised light

Answer 5

detect marks in contaminant on a reflective background

component of depolarised light through depolariser

images of light ridges against a dark background

Question 6

mechanism of fluorescent chemicals

Answer 6

fluorescence occurs in less than 10-8 sec

if longer time then delay called phosphorescence

colour given out is of less energy than colour used to excite the electron into higher lying states.

light in UV, blue, green or yellow are used to excite fluorescence

results in light in the yellow, orange, red or infrared region of the spectrum

reflected and scattered incident light are filtered out

Question 7

ALS

Answer 7

lamp ALS emits light over a range of wavelengths in visible

laser emits light of just one colour

Question 8

what 3 things is the emission of light due to?

Answer 8

heat
chemical reaction
prior excitation with light

Question 9

what is luminescence lifetime?

Answer 9

the decay time for the luminescence intensity once the excitation is cut off

Question 10

what are the two types of photoluminescence?

Answer 10

fluorescence (short lifetime)

phosphorescence (long lifetime)