Dimitri Geskus
Questions
About slides 4, 6, and 7:
Q1: Answer with Yes or No and explain in your own words what happens. Support you answer by
drawing a simple energy level diagram having 4 ions that have absorbed one or an infinite amount of
pump photons (yes, that will be 6 drawings for the following 6 questions).
For example a 4-level energy diagram with 4 ions drawn into it, before any absorption looks like:
When absorbing one pump photon, can one create overall optical gain in a:
a. 4-energy level material
b. 3-energy level material
c. 2-energy level material
When absorbing infinite pump photons, can one create overall optical gain in a:
d. 4-energy level material
e. 3-energy level material
f. 2-energy level material
About Slide 8:
Q2: The ytterbium ion seems to have only two energy levels, how is it possible that this ion can be
used as optical amplifier?
About slide 9:
Q3: When using an Yb doped material, why do you need a larger population inversion to achieve net
gain at 980 nm compared to achieving net gain at 1025 nm?
Q4: At which wavelength can one achieve the highest gain, at 980 nm or 1025 nm?
Fredrik Laurell
a) Where are the difficulties and advantages in building laser in the solid-state relative to gas and
liquid lasers?
b) Originally flash lamps where used to pump solid-state lasers, but diodes are more common now.
Why? Are there situations when flash lamps are preferred?
Valdas Pasiskevicius
1. Any method used in analytical microscopy needs a calibration, which includes answering following
question: what is the functional relation between the concentration of the species being measured
and the signal that the microscope measures at a given excitation intensity? For usual confocal laser
scanning microscope the dependence is linear. Nonlinear microscopy methods might have linear or
quadratic dependence. Which dependence on concentration you would expect in following nonlinear
methods: (a) SHG, (b) SFM, (c) TPFE, (d) CARS, (e) heterodyne CARS, (f) SRS.
2. In all microscopy methods which aim to be sensitive to specific molecular species or specific
chromophores there are parasitic signals appearing on the detector due to different linear and
nonlinear processes. That limits contrast in microscopy. Which parasitic processes specifically we
need to be aware of in: (a) standard linear confocal laser microscopy, (b) TPFE microscopy, (c) CARS
microscopy, (d) SRS microscopy?
Johan Nilsson
1. Name two laser dopants commonly used for high-power fiber lasers.
2. List three advantages of the fiber geometry for lasers and amplifiers.
3. What are the advantages of cladding-pumping?
Gunnar Björk
In a separate PDF-file.
Stefan Kröll
Suggested discussion questions:
c ‒ is the speed of light in vacuum
n ‒ is the index of refraction
vp = c/n is the phase velocity
f ‒ is the light frequency
𝑐
𝑣𝑔 =
𝑑𝑛 is the group velocity
𝑛+𝑓
𝑑𝑓
1. Give explicit physical examples (at least one per case and not just an equation) where a) vp <
c
b) vp > c
c) vg < c
d) vg > c
2. What is the difference between material slow light and structural slow light and when could
it matter which of these slow light effects that we have? A useful reference here may be R.
W. Boyd, J. Opt. Soc. Am. B 28, A38 (2011).
Anders Larsson
In a separate PDF-file.
Stefan Maier
Question: Concentrating electromagnetic radiation from the far to the near field.
1. Explain the concepts of quality factor and effective mode volume in order to characterize an
optical cavity. For conventional dielectric cavities, what is the lower limit of the mode volume?
2. Describe how nanoscale light localization can be achieved using a plasmonic system, specifically
metallic nanoparticles. What is the physical nature of a localized surface plasmon. Give a couple of
application examples.
Markus Pollnau
1. Linewidth of a passive resonator
a) How does the linewidth of a passive resonator depend on
your reasoning, assume that the intrinsic round-trip losses are discrete losses (opposed to continuous
propagation losses), as defined by LRT in one of the lecture slides!
b) Calculate the linewidth of a passive resonator with a resonator length of 1 mm, filled by a medium
of refractive index 1.5, with intrinsic round-trip losses of 1% and a mirror transmission of 5%!
2. Linewidth of an active resonator
For the same resonator as in question 1, assuming that the medium is an active medium, calculate
the linewidth for a gain that equals
a) 1% of the losses,
b) 99.9% of the losses,
c) the losses!
d) Why will the situation described in c) never happen?
Walter Margulis
Consider the expression below, derived to calculate the evolution of the amplitude of the envelope
of the electric field of a pulse propagating along an optical fiber. Here, we considered amongst other
simplifications that the transverse and longitudinal components of the electric field can be
separated, the slowly-varying approximation is valid and that the electric dipole approximation
describes well the polarization of the glass fiber.
i∂A/∂z = -iαA/2 + 1/2 β2 ∂ 2A/∂T 2 - γ |A| 2 A
a) What do the four terms represent physically?
Consider now the attenuation negligible. Four regimes can be studied:
1)
2)
3)
4)
When the pulse is very long and the power low
When the pulse is short and the power low
When the pulse is long and the power high
When the pulse is short and the power high
b)
c)
d)
e)
f)
What happens to the pulse envelope width and the spectral content in case 1)
What happens to the pulse width and spectrum in case 2)
What happens to the pulse width and spectrum in case 3)
What happens to the pulse width and spectrum in case 4) when β2 is positive
What happens to the pulse width and spectrum in case 4) when β2 is negative