Optical/UV Flashcards
Order of UV/IR
UV C, B, A
Visible
IR A, B, C
UV wavelengths
UV A 315 - 380/400nm
UV B 280 - 315nm
UV C 100 - 280nm
IR wavelengths
IR A 760/780 - 1400nm
IR B 1.4 - 3 μm
IR C 3μm - 1mm
Light delivery
Deliver light away from where it is generated - optical fires use total internal reflection. Low loss and high bandwidth.
How does a photodiode work
Converts incident light into electrical current. Creates electron hole pair that produces current. Si/Ge used to create photodiodes that detect in visible range.
PMTs
Good for low light levels but fragile and need stable power supply.
Thermopile
Converts thermal to electrical energy - output in response to temp.
Light interaction with tissues
Reflection
Absorption
Scattering
Fluorescence
Laser doppler flowmetry
Measure blood flow in tissue. Skin illuminated by coherent collimated laser beam. Reflected light collected, moving particles (RBCs) doppler shift light and can calculate speed and concentration of RBCs from this.
Laser Doppler Imaging
Use same principle as LDF but build up image. Used in assessment of burn depth.
Pulse oximetry
Wavelength of light affects how it is absorbed. Shine IR and visible through finger and see what is absorbed, difference based on amount of haemoglobin and oxygen. (Not necessarily suggesting not enough oxygen - miss CO poisoning as Hb still bounded to CO)
Tissue Oxygen Saturation
Use reflected or scattered light instead of absorbed. Uses visible light spectroscopy to quantify HbO2 in different depths of skin as white light reflected is split into components and converted to signal
Near IR Imaging
Light near IR on skin - IR camera can image this and display in visible spectrum. Can see deeper veins. Needs to be aligned perfectly and not real time image
Microscopy
Imaging on small scale using lenses and bright visible light Enhances characteristics such as staining. Look at capillaries in nail folds.
Optical Coherence tomography
Two beams of light have travelled same optical distance. Areas of sample reflecting a lot of light create greater interference - tells us about spatial dimensions and locations of structures.
