EE5380 Principles of Photonics and Optical Engineering
Diagnostic exam questions
(all 3 problems have equal weight; solving 2 out of 3 constitutes 100%)
1. A laser beam of power P = 100 Watt is pointed vertically up to illuminate an object of
mass m (see the figure below). Assuming that the beam is 100% reflected by the object,
estimate the maximum mass of the object that the laser light pressure can keep from
falling down on Earth. Acceleration due to gravity is g = 9.8 m/s2.
m
P
2. Monochromatic light is linearly polarized, with electric field oriented at an angle  =
+30 with respect to the vertical direction (“+” sign here is just a convention for angle
measured clockwise, looking in the direction of propagation). We would like to convert it
to a linearly polarized light with horizontally (i.e., +90 or –90) oriented electric field.
We have one half-wave plate and two identical quarter-wave plates in our optical tools
inventory. Describe at least two different combinations (each consisting of one or more
waveplates) of the optical tools from our inventory that can achieve this task. For each
combination, specify the orientation of each waveplate.
3. A real object is located at position A. Its real image is constructed at position B by a thin
lens with focal distance f. The distance between A and B equals L = 100 cm. There are
two possible positions of the lens, such that when the lens is placed at either of them it
can produce image of A at B; let us call these lens positions C and D (C is closer to the
object, D is closer to the image), and the distance between C and D is d = 40 cm.
a. Find lens’ focal distance f.
b. If we place the lens at position C and add another lens, with focal distance –f, at
position D, where will the final image produced by the two-lens combination be
located?
c. Is the final image built by the two-lens combination erect or inverted (with
respect to the original object)? Drawing ray diagram is not required, but might be
helpful in solving the problem.
d. Is the final image built by the two-lens combination real or virtual? Drawing ray
diagram is not required, but might be helpful in solving the problem.
e. Is the final image built by the two-lens combination magnified or reduced
(compared to the original object)? Find the magnification (or reduction) factor.