Exam 4 Flashcards
LASER
Light Amplification by Stimulated Emission of Radiation
How a laser works:
- excitation - energy is added to promote electrons to higher orbitals.
- emission - electrons returns to lower energy source.
- stimulated emotion - causes a photon to be released.
Advantages of Lasers
- high energy
- polarized
- coherent
- narrow bandwidth
Types of Lasers
- solid state
- gas
- dye
- semiconducting diode
Advantage and Disadvantage of semiconducting diode
+ small in size, cheap
- wavelength dependent on band gap
Population inversion
more electrons in higher energy state, than in lower energy state; necessary for a laser.
Examples of Lasers
YAG, Ruby
Order of Radiation from shortest wavlength to longest
gamma -> Xray -> UV -> infrared -> microwave -> radio
Analytical Applications of Lasers
- laser induced fluorescence
- raman scattering
- MALDI-TOF
- 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
Automation
reduces the amount of time needed for an analyst to go thru a number of samples
Can everything be automated?
NO
If it is a repetitive task….
it can be automated.
What are nanoparticle properties based on?
- composition
- size
- shape
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
Brownian motion
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
Photosedimentation
measures the rate at which particles settle throughout a liquid; larger particles settle faster than smaller particles
5 Assumption of Photosedimentation
- particle must be smooth, spherical
- the final velocity of the particle must be reached instantly
- all particles have same density
- all particles are assumed to move independently
- the fluid behaves as a continuum with a constant viscosity
Will all the stuff in water fall out of solution?
NO, not all stuff in water will fall out of solution.
