1. Laser oscillation Laser is oscillator
Ruby laser example
Laser is oscillator
Like servo with positive feedback
Greater than unity gain
Laser gain and losses
Laser turn-on and gain saturation
Gain decreases as output power increases
Saturation

2. Fabry-Perot cavity for feedback
High reflectivity mirrors
Low loss per round trip
Must remember resonance conditions
round trip path is multiple of l

3. Laser longitudinal modes
Classical mechanics analog
High reflectivity Fabry-Perot cavity
Boundary conditions
field is zero on mirrors
Multiple wavelengths possible
agrees with resonance conditions
Fabry-Perot boundary conditions
Multi-mode laser
Multiple resonant frequencies

4. Single longitudinal mode lasers
Insert etalon into cavity
Use low reflectivity etalon
low loss

5. Laser transverse modes
Wave equation looks like harmonic oscillator
Ex: E = E e -iwt
Separate out z dependence
Solutions for x and y are Hermite polynomials
Transverse laser modes
Frequencies of transverse modes

6. Single transverse mode lasers
Put aperture in laser
Create loss for higher order modes
Multi-longitudinal Multi-transverse&long Single mode

7. Gaussian beams Zero order mode is Gaussian Intensity profile:
beam waist: w0
confocal parameter: z
far from waist
divergence angle
Gaussian propagation

8. Power distribution in Gaussian
Intensity distribution:
Experimentally to measure full width at half maximum (FWHM) diameter
Relation is dFWHM = w 2 ln2 ~ 1.4 w
Define average intensity
Iavg = 4 P / (p d2FWHM)
Overestimates peak: I0 = Iavg/1.4

9. Resonator options Best known -- planar, concentric, confocal
Confocal unique
mirror alignment not critical
position is critical
transverse mode frequencies identical
Special cases
Types of resonators