Download a) Given the transfer function of a detector (below), label and

1. a) Given the transfer function of a detector (below), label and describe these terms:
i. dynamic range
ii. linear dynamic range
iii. sensitivity
iv. responsivity
b) Imagine you are using an optical detector to characterize the output power of a light source with increasing
voltage. If you assumes that your detector response is linear in the range at which you are taking
measurements, but in fact your output changes non-linearly with your incident radiant power how will this
affect the interpretation of your measured data?
c) In the above experiment, you are taking the measurement in the lab with all the lights on. Even worse, the
AC just broke down and the room temperature reaches about 80 F. Please list all possible sources that can
induce inaccuracy in your measurements. Compare their differences and how you can eliminate or reduce them.
2.
Please use your drawing to illustrate how PMT and APD work and compare the mechanisms which enable
them to achieve signal amplification. Also, explain why is it hard to make a detector that has high
detectivity while also preserves a high detection speed?
3. You are assigned a project to measure water concentration in a rat burn wound model using an optical
technique. In this technique, you project light onto the sample and capture the reflected light from the
wound using a photodetector.
You purchase a 25mW short wave infrared LED with FWHM of 27nm centered at 1450 nm. This peak
wavelength is close to a peak in water absorption spectra. Your next step is to choose a photodetector with
a sensitive material. Which semiconductor material do you choose among Si (1.12 eV), GaP (2.26 eV), GaN
(3.44eV), and InAs (0.36eV)? Please provide quantitative proof for your decision.
4. Say that we take an optical fiber with indices of refraction of 1.450 and 1.436, with a core
radius of a=50µm.
(a) Which index is the core and which is the cladding?
(b) If this were a step index fiber (in air), calculate the numerical aperture and maximum
acceptance angle.
(c) What is the effective f/# of the step index fiber?
(d) Say that we want to couple light from the step index fiber into a detector. Take a lens with a
focal length of +25 mm and diameter 5 mm. What is the f/# of this lens?
(e) Place the fiber at the focal point of this lens and align the center of the fiber with the center of
the lens. Will all of the light from the fiber couple into this lens?
5. a) Please label the type of the fibers and explain how you identify them.
b) Plot how the output pulse would look like for each fiber. Explain how the structures of the fiber affect
the pulses coming out of the fiber.
6. Compare the optical sectioning effect of two photon excited fluorescence microscopy to confocal
fluorescence microscopy. List the pros and cons of each imaging technology.
7. Please explain how the magnification and NA of the objective affect the resolution of the system.
8. You have laser scanning microscope equipped with a 20x dry objective (NA=0.55), a 40x dry objective (NA =
0.8), a 60x dry objective (NA = 0.95) and a 60x water immersion objective (f# = 0.74). The system has a 380
nm continuous laser source with 400mW power, a 490 nm continuous laser source with 100mW power, 780
nm continuous laser source with 800mW power, a 770nm 150 fs pulsed laser and 200mW power.
Which laser source and objective would you chose for the following situations and why.
a) Study the metabolic activities in breast cancer cells especially the activities in mitochondria. The
mitochondria are stained with Rhodamine.
b) Image a non-stained skin biopsy from a melanoma patient.
c) A time elapse study of embryo development (last for 48 hours). The cells are stained with DAPI.
Rhodamine spectrum
Rhodamine spectrum
DAPI spectrum