5. lasers. introduction to lasers laser acupuncture, laser scalpel and laser w/r head
TRANSCRIPT
Gaussian Beam
(m)
)(W/m
0
20
20
20
2
edgebeamce at thetandis:r
beamofthe centeratirradience:E
eEE
the centerce r from tanthe disatIrradiancer/r
r
Laser Longitudinal Mode
m
LmmL
2integer):(
2
hs wavelengt75010800
10300229
6
L
m
Optical resonance:
where λ: wavelength of the resonating frequency, L: length of the cavity, m : an integral
Eg. laser diode : cavity length = 300 m; AlGaAs : gap wavelength 800nm How many wavelength will fit into the cavity ?
m
LmmL
2integer):(
2
Multi-(Longitudinal) Mode Laser
Cavity resonance frequency
Spacing between the adjacent frequency ( frequency spacing )
Wavelength spacing
0 : free space value of the wavelength
nL
mcf
2
nL
cf
2
)nL
(c
f
2
20
20
n
cv v: velocity of the wave in cavity
c : speed of light
n : refractive index of cavity material
Eg. Laser diode : cavity length = 300 m
refractive index = 3.6 ; line width of the cavity = 2 nm
peak radiating wavelength 0 = 800 nm
Find output spectrum from the laser
frequency spacing:
wavelength spacing:
mode number:
Hz.nL
cf 9
6
8
1013910300632
103
2
nm.)(
c
f2750
103
10139108008
92920
modes) 6most (at 51.5275.0
2m