Second Harmonic Generation
Second Harmonic Generation:
SHG is a second-order nonlinear optical process,
which requires an environment without a centre of
symmetry to produce signals. Two photons (ω
p) are
mixed in the sample to generate a third photon (2ω
p)
Several indigenous tissue components are known to
exhibit SHG which can be used to generate label free
images. Collagen fibres are a well-known source of
SHG; the picture below shows an SHG image of
collagen fibres within a rat tail tendon.
SHG deposits no energy into the sample due to the
emitted SHG photon energy being equal to the total
absorbed excitation photon energy.
Example
Collagen in a rat tail tendon viewed with SHG
