Ocean Optics Collimation tester - Manual (Page 4)

Collimation Tester Instructions
4 CT-10000-000-05-201401
The wavefront radius, at the observation screen, is given by the following equation, with the
wavelength, 'λ, in the same units as S and d:
R = sd/λ sin A
►
Procedure
To find the wavefront radius at the lens plane,
1. Add the distance of the lens from the screen for a converging wavefront, or subtract the
distance for a diverging wavefront.
2. Measure the values of shear, fringe spacing and angle.
3. Divide the distance between several fringes by the number of fringes to get the average
spacing.
Where the shear is appreciable, it can be measured by placing a thin wire in the beam and measuring
the separation of the two images. Shear can be calculated by the following relation,
Where:
I = Angle of incidence
N = Index of refraction
T = Plate thickness
S = T sin 2I
(N
2
- sin
2
I)
½
The index of the glass used is:
• 1.530 at 405 nm,
• 1.522 at 489 nm,
• 1.515 at 633 nm, and
• 1.507 at 1060 nm.
To find the divergence of the laser beam, divide the width of the lens or beam by the radius of the
curvature.