Fall 2007
Optical Sciences 421/521 Homework 1
OPTI 421/521 – Introductory Opto-Mechanical Engineering
Homework 4: Tolerancing for alignment
Undergraduate OPTI421 students can work in pairs for this assignment, jointly submitting
one report per team.
The following optical system is used to focus a collimated HeNe laser beam onto a Position
Sensing Detector (PSD).
The system requirements are:
20 mm entrance pupil diameter
Nominal EFL = 140 mm
Wavelength = 632.8 nm (HeNe)
Diffraction limited operation, SR > 80%
(A fine focus adjustment can be made by moving the PSD.)
The resolution for this adjustment is 5 um
A nominal optical design has been supplied, see the following page. The design residual of this
system is <0.001 λ rms.
A top level system budget has been performed in terms of rms wavefront error:.
Optical alignment 0.04 λ rms
Lenses 0.04 λ rms
Operational changes 0.04 λ rms
RSS 0.07 λ rms
Your job is to perform an initial strawman budget for the alignment errors, adding up to 0.04 λ
rms. You should include all degrees of freedom for mounting the lenses including tilt, decenter,
and axial position. Assume focus compensation.
You should use a ray trace program such as Zemax, CodeV, Oslo, to determine the sensitivities.
Then create a spreadsheet to help set the tolerances to sensible values. (The sensitivities can be
provided to you if you do not have access to such a program.)
You should write a report called “Mounting requirements for focusing doublet.” Next week you
will tolerance the lens elements themselves. Later in the term, you will design the support cells,
including tolerances for thermal effects.
