Flashcards in Exam 4 Deck (23):
How a laser works:
1. excitation - energy is added to promote electrons to higher orbitals.
2. emission - electrons returns to lower energy source.
3. stimulated emotion - causes a photon to be released.
Advantages of Lasers
- high energy
- narrow bandwidth
Types of Lasers
1. solid state
4. semiconducting diode
Advantage and Disadvantage of semiconducting diode
+ small in size, cheap
- wavelength dependent on band gap
more electrons in higher energy state, than in lower energy state; necessary for a laser.
Examples of Lasers
Order of Radiation from shortest wavlength to longest
gamma -> Xray -> UV -> infrared -> microwave -> radio
Analytical Applications of Lasers
- laser induced fluorescence
- raman scattering
- doppler effect
- CRD spectroscopy
Advantages of making instruments as small as possible
- saves lab space; makes room for more instruments
- portable; can use instruments in the field which leads to reduction of time spent in lab and cost
Disadvantages of making instruments as small as possible
short lifespan; which can impact reproducibility
reduces the amount of time needed for an analyst to go thru a number of samples
Can everything be automated?
If it is a repetitive task....
it can be automated.
What are nanoparticle properties based on?
Low angle light scattering
use laser to blast something and have light diffract off it; particle size is determined based off of light defraction
What is low angle light scattering used for?
to determine particle size
particles move around in solution; causes an issue when viewing scatter of a laser
How do you view particles when they are moving?
- CCD cameras
- Photon counters
Dynamic light scattering
"photon correlation spectroscopy"
- uses doppler broadening of raliegh scattered light as result of brownian motion
measures the rate at which particles settle throughout a liquid; larger particles settle faster than smaller particles
5 Assumption of Photosedimentation
1. particle must be smooth, spherical
2. the final velocity of the particle must be reached instantly
3. all particles have same density
4. all particles are assumed to move independently
5. the fluid behaves as a continuum with a constant viscosity