Absorption, luminescence, lasers Flashcards
What is monochromatic light?
Light is monochromatic if its spectrum consists of a single wavelength only
What kind of special characteristics does laser light have?
- monochromatic
- coherence in time and distance - small divergence
- high light density.
What kind of special characteristics does laser light have?
- monochromatic
- coherence in time and distance - small divergence
- high light density.
List the types of interactions laser light can have with tissues.
- photothermal (laserthermy, coagulation, vaporization, carbonization)
- fluorescence, photochemical reactions
- photodissociation
- multiphoton ionization
When is electromagnetic radiation coherent?
If it consists of photons capable of forming observable interference fringes.
What basic phenomena is the generation of laser emission based on?
- population inversion is needed for light amplification to occur, and it is only possible in systems with 3 or more energy levels
- stimulated emission is needed to give rise to coherent monochromatic light.
What is the approximate coherence length of a laser and that of a classical light source?
10 ele. 10 cm and a couple of cm, respectively
Align in ascending order the following transitions according to their energy difference: vibrational, rotational and electronic!
rotational < vibrational < electronic
Write the Lambert-Beer law and interpret the variables in the formula!
lg J0/J = EcL = A
J - intensity of light after passing through a material with thickness L
Jo- incident intensity of light when it enters the sample A – absorbance (optical density or extinction)
E - molar extinction coefficient
c - concentration in mol/liter
L - optical path length.
What does the molar extinction coefficient depend on?
It depends on the type of the absorbing material, the wavelength of the light, temperature, the type of the solvent and the environment.
How many fold does the intensity of light decreases if the absorbance (optical density, extinction) of a solution is 1?
It decreases 10-fold.
What is the definition of the molar extinction coefficient?
It is the absorbance (optical density) of a solution with a concentration of 1M and an optical path length of 1 cm.
At what wavelength are the characteristic absorption maxima of proteins and nucleic acids?
proteins 280 nm, nucleic acids 260 nm
Which amino acids have reasonably high absorption?
Tyr, Trp, Phe
What is the definition of a singlet and a triplet state?
In a singlet and a triplet state the number of unpaired electrons is zero and two, respectively. In a singlet and a triplet state, the value of the resultant spin multiplicity is 1 and 3, respectively.
What are the possible ways of relaxation of an excited electron in a molecule? (List at least 5 of them!)
- vibrational relaxation
- internal conversion
- intersystem crossing
- fluorescence
- phosphorescence
- delayed fluorescence
- energy transfer to another molecule.
What are the possible ways of relaxation of an excited electron in a molecule? (List at least 5 of them!)
- vibrational relaxation
- internal conversion
- intersystem crossing
- fluorescence
- phosphorescence
- delayed fluorescence
- energy transfer to another molecule.
What is the definition of fluorescence lifetime?
The time during which the number of excited molecules decreases to 1/e-times (37 %) of its initial value.
What is a., scintillation, b., chemiluminescence, c., photoluminescence?
Processes where photon emission is elicited by
a., ionizing radiation
b., chemical reaction
c., excitation by photon
How can fluorescence quantum efficiency (yield) be defined?
(One definition is sufficient.)
The fraction of excited molecules emitting a fluorescent photon, OR the number of fluorescence photons divided by the number of absorbed photons, OR the rate constant of fluorescence divided by the rate constants of all possible de-excitation processes.
Why is the fluorescence quantum yield always smaller than one?
Because relaxation from the excited state can be accomplished not only by fluorescence emission.
What is the lifetime range of fluorescence?
t = 10 -9 – 10 -7s
What is the lifetime range of phosphorescence?
t=10 -6 –10s
Why is phosphorescence lifetime longer than fluorescence lifetime?
Because phosphorescence is the result of spin- forbidden transitions.
Why is Förster type resonance energy transfer a sensitive method for distance measurements?
Because its probability is proportional to the inverse sixth power of the separation between the donor and the acceptor.
Why is Förster type resonance energy transfer a sensitive method for distance measurements?
Because its probability is proportional to the inverse sixth power of the separation between the donor and the acceptor.
What can Förster-type resonance energy transfer be used for in biology?
For measuring inter- and intramolecular distances.
List at least five parameters which can be determined using fluorescent measurements!
- DNA, RNA, protein and lipid content of a cell, or the
quantity of any kind of material that we tagged with a
fluorescent label. - permeability of the cell membrane
- intracellular enzyme activities
- membrane potential
- intracellular calcium level
- intracellular pH
- presence and density of cell surface antigens and
receptors - mitochondrial potential and the number of
mitochondria per cell.
