1. Really Basic Optics Instrument Sample Sample Prep Instrument Out put
Signal (Data)
Polychromatic light
Selected
light
Turn off/diminish intensity
Sample
interaction
Select
light
Turn on different wavelength
select
source
detect

2. Really Basic Optics Key definitions Phase angle
Atomic lines vs molecular bands
Atomic Line widths (effective; natural)
Doppler broadening
Molecular bands
Continuum sources Blackbody radiators
Coherent vs incoherent radiation

3. Really Basic Optics A Sin=opp/hyp  y  /2 3/2  2 90o phase angle
/2 radian phase angle

4. Emission of Photons
Electromagnetic radiation is emitted when electrons relax from excited states.
A photon of the energy equivalent to the difference in electronic states
Is emitted
Ehi e
Elo
Frequency 1/s

5. Really Basic Optics Key definitions Phase angle
Atomic lines vs molecular bands
Atomic Line widths (effective; natural)
Doppler broadening
Molecular bands
Continuum sources Blackbody radiators
Coherent vs incoherent radiation

7. Theoretical width of an atomic spectral line

8. Natural Line Widths frequency Line broadens due Uncertainty
Doppler effect
Pressure
Electric and magnetic fields
frequency
Lifetime of an excited state is typically 1x10-8 s

9. Typical natural line widths are 10-5 nm
Example: nm
Typical natural line widths are 10-5 nm

10. Line broadens due
Uncertainty
Doppler effect
Pressure
Electric and magnetic fields

11. Line broadens due
Uncertainty
Doppler effect
Pressure
Electric and magnetic fields
The lifetime of a spectral event is 1x10-8 s
When an excited state atom is hit with another high energy atom
energy is transferred which changes the energy of the
excited state and, hence, the energy of the photon emitted.
This results in linewidth broadening.
The broadening is Lorentzian in shape.
We use pressure broadening
On purpose to get a large
Line width in AA for some
Forms of background
correction
FWHM = full width half maximum
o is the peak “center” in frequency units

12. Line spectra – occur when radiating species are atomic particles which
Experience no near neighbor interactions
Line broadens due
Uncertainty
Doppler effect
Pressure
Electric and magnetic fields
Line events
Can lie on top
Of band events
Overlapping line spectra lead to band emission

13. Continuum emission – an extreme example of electric and magnetic
effects on broadening of multiple wavelengths
High temperature solids emit Black Body Radiation
many over lapping line and band emissions influenced by
near neighbors

14. Stefan-Boltzmann Law
Planck’s Blackbody Law
= Energy density of radiation
h= Planck’s constant
C= speed of light
k= Boltzmann constant
T=Temperature in Kelvin
= frequency
Wien’s Law
As  ↓(until effect of exp takes over)
As T,exp↓, 

15. Really Basic Optics Key definitions Phase angle
Atomic lines vs molecular bands
Atomic Line widths (effective; natural)
Doppler broadening
Molecular bands
Continuum sources Blackbody radiators
Coherent vs incoherent radiation

16. Incoherent radiation
The Multitude of emitters, even if they emit
The same frequency, do not emit at the
Same time A B
Frequency,, is the
Same but wave from particle
B lags behind A by the
Phase angle 

17. Begin END: Key Definitions Using Constructive and Destructive
Interference patterns based on phase lag
By manipulating the path length can cause an originally coherent beam
(all in phase, same frequency) to come out of phase can accomplish
Many of the tasks we need to control light for our instruments
Constructive/Destructive interference
Laser
FT instrument
Can be used to obtain information about distances
Interference filter.
Can be used to select wavelengths

18. More Intense Radiation can be obtained by Coherent Radiation
Lasers
Beam exiting the cavity is in phase (Coherent) and therefore enhanced
In amplitude

19. Argument on the size of signals that follows is from Atkins, Phys. Chem. p. 459, 6th Ed
Stimulated Emission
Light Amplification by Stimulated Emission of Radiation
Photons can stimulate
Emission just as much
As they can stimulate
Absorption
(idea behind LASERs
Stimulated Emission) * o
The rate of stimulated event is described by :
Where w =rate of stimulated emission or absorption
Is the energy density of radiation already present at the frequency of the transition
The more perturbing photons the greater the
Stimulated emission
B= empirical constant known as the Einstein coefficient for stimulated absorption or emission
N* and No
are the populations of upper state and lower states

20. can be described by the Planck equation for black body radiation at some T
frequency
In order to measure absorption it is required that the
Rate of stimulated absorption is greater than the
Rate of stimulated emission
If the populations of * and o are the same the net absorption is zero as a photon is
Absorbed and one is emitted

21. Need to get a larger population in the excited state
Compared to the ground state (population inversion)
Degeneracies of the different energy levels
Special types of materials have larger excited state degeneracies
Which allow for the formation of the excited state population inversion
Serves to “trap” electrons in the excited
State, which allows for a population
inversion E
pump

22. Constructive/Destructive interference
Laser
FT instrument
Can be used to select wavelengths
Can be used to obtain information about distances
Holographic Interference filter.
Radiation not along the
Path is lost
mirror
mirror
Stimulated emission
Single phase
Along same path
=Constructive Interference
Coherent radiation
Multiple directions,
Multiple phase lags
Incoherent radiation

23. FTIR Instrument Constructive/Destructive interference Laser
FT instrument
Can be used to select wavelengths
Can be used to obtain information about distances
Holographic Interference filter.

24. Time Domain: 2 frequencies
1 “beat” cycle

25. B
Fixed mirror A C
Moving mirror
Beam
splitter
IR source
detector
Constructive interference occurs when

26. -2
-1
+1

27. INTERFEROGRAMS
Remember that:
Frequency of light

28. An interferometer detects a periodic wave with a frequency of 1000 Hz when moving at a velocity of 1 mm/s. What is the frequency of light impinging on the detector?

29. No need to SELECT
Wavelength by using
Mirror, fiber optics,
Gratings, etc.