Optics Flashcards
How does RI vary in a uniaxial crystal?
In x and y directions -> n_0^2
In z direction -> n_e^2
What is the difference between negative and positive uniaxial crystal?
negative - n_e
positvity - n_e>n_0 - extraordinary axis is the slow axis
Sketch the propagation of light in a uniaxial crystal
What is n_e as a function of angle?
Differnce between types 1 and 2 phase matching
1 - driving waves have same polarisation and opposite to output
o + o = e, e + e = o
2 - driving waves have opposite polarisations
e + o = e, e+o = o
What is the relationship between k and n?
k = w/nc
How does dispersion effect phase matching?
Since most materials have positive dispersion we expect the refractive index to be greater for higher frequencies
When is second harmonic generation intensity maximised?
At the phase matching angle
When phi is pi/4 since this maximises the product of E_x and E_y
Angular tolerance =
1/sin(2* matching angle)
Why is it desirable to have a matching angle of pi/2?
Increased angular tollerance. Achieved by heating crystal to alter value of refractive index.
How is beam walk off caused?
An e wave has a direction of energy transfer not parallel to the wave vector. This means e and o don’t propagate parallel to each other, limiting the useful length of a crystal.
What si the beam walk off angle?
tan (p + o) = (n_0/n_e)^2 tan(o)
where o is angle of propagation and p is walk off
What is parametric down conversion?
Where a pump beam is converted into a low frequency idler and a high frequecny signal.
w_p = w_s - w_i
Why is parametric down conversion useful?
Can generate wavelengths at which there are no useful lasers.
What is degenerate down conversion and why is it usful?
Parametric down conversion where the idler and signal have the same frequency and are thus indistinguishable. Useful in QIP.
