Module 19 - ALS/FSIS

Emission Wavelength

Wavelength of light emitted when it changes from excited state to ground state; viewed as fluorescence

Excitation wavelength

Wavelength of light that causes it to go to a higher energy or excited state

Fluorescence

Phenomenon where light is emitted due to excitation; the item must be excited first by one wavelength resulting in emission of other wavelength

Chemiluminescence

Chemical reaction that produces light (luminol/bluestar)

Barrier filters

Enable visualization for fluorescence by preventing transmission of light at the same wavelength as the excitation light to the eye

Electromagnetic spectrum

UV - Visible light - Infrared

(420nm - 450nm blue - 520nm green - 760nm)

420nm wavelength is good for ….

UV LIGHT - purple in color good wavelength for searching un-enhanced blood, GSR, bone, teeth, good excitation wavelength for basic yellow 40 dye stain

450nm can be used for

Blue in color, excites multiple bodily fluids, excites DFO

490nm - 500nm

Aqua to cyan in color, useful for fiber searches, excited DFO

Full Spectrum Imaging System (FSIS) has the following

3 positions filters: 254nm (UV), 550nm (orange), 830nm (IR)

Dual 254nm UV light

LED Lamps: 365nm (UV), 455nm (blue), 525nm (green), 625nm (red), 850nm (IR)

850nm best used for

GSR or Blood Spatter

w/ 830nm IR filter

FSIS exposure control

Controls exposure time in seconds

FSIS Gain

Controls camera gain (the higher camera gain, the brighter the image)

FSIS Gamma

Adjusts the image contrast

FSIS integration

Integration helps capture prints on a curved or shiny surface.

Dual 77 Laser wavelengths

445nm - blue light / yellow filter used

520nm - green light / orange filter used