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Laser physics simulation program

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Laser physics simulation
program
Lionel Canioni
University Bordeaux I France
The Mode program
 Goal: visualization of laser dynamics and
operating types.
 Interacting program working on a tabletop
computer
 Useful for Graduate and undergraduate
student in lasers courses
 Illustration of the different laser operations
principle
Principle of working
 The program:
 Solve the laser master equation in an infinite time
loop
 Display continuously the physical parameters of
the laser
 Calculation at each point of the cavity and for all
time: number of photon by mode and the
population difference versus frequency
Physical model
Population evolution: D=N2-N1
d
dt
D пЂЅ пЂ­пЃ§ пЂЁD пЂ­ Deq пЂ© пЂ­ 2 пЃі J D
l2
E2
Relaxation
, pumping
пЃ§
Interaction
media EM
wave
Population equilibrium
DeqпЂЅпЂЁl2пЂ­l1пЂ©/пЃ§
l1
Intensity evolution: J
d
J пЂЅ пЂ­пЃ« J пЂ« cпЃі J D
dt
Cavity
loss, abs
Laser
Gain
E1
пЃ§
Simulations
 Master equation are solve for each cavity
mode with wave propagation equation
 All the parameters let us study a large
amount of laser type
 Cw laser , threshold, pulsed laser, CW
mode locked laser, QSwitch, mode beating
etc…
Laser Dialog Box
 Cavity parameters
 Length
 Number of resonant optical
frequency
 Optical gain media




Frequency
Emission abs cross section
Spectral width
Spectroscopic model
 Optical Pumping
 CW or Pulsed pump
 Loss
 Pump Power
 Display Control
 Continuous or step by step display
 Choose between several
representation
 Pulse propagation parameters
 Non linear coefficient and
dispersion
Cavity parameters
 Length in µm of the laser:
 The cavity length match
the gain media length
 Small cavity for visual
mode representation
 Number of resonant
optical frequency
 One can choose between
1 (single mode laser) and
41 optical frequencies
allowed in the cavity
 FP filter equivalent
Optical gain media
 Frequency
 Selection of the central
frequency by the resonant
frequency of the cavity.
Change with cavity length
change wavelength
 Spectral width
 Gain media width( arbitrary
unit)
 Emission abs cross section
 Low gain or high gain laser
 Spectroscopic model
 Homogenous or
Inhomogenous model
example gas laser or Nd Yag
laser
w
Optical Pumping
 Loss
 Accumulated during
laser propagation
 CW or Pulsed pump
 CW Pumping and
flashed pump allowed
Qswith simulation.
Flash duration and
repetition rate
available
 Pump Power
 Control the efficiency
between pump power
and optical transfer
Pulse propagation parameters
 Effective parameters
for fs propagation
 Second order
dispersion: useful for
pulse stretched
 Nonlinear coefficient:
SPM mod locking :
scattering of energy
between modes
Display Control
Choose between several representation:
 Frequency domain: mod representation, spectrum
representation
 Time domain: Difference population, output power, pulse
inside the laser rod
 Standard value: pulse width, power, intensity, wavelength
Continuous or step by step display:
 Multithread application allowed permanent tuning and
adjustment while display
Demonstration
Threshold
Threshold study:
1. Study of spontaneous emission
Starting the laser with Ds=Deq
Starting parameters: pump=0.5, Loss=0.2
Increase pump until threshold
2. Laser starting with Ds<Deq
Starting parameters: pump=3, Loss=0.2
Observation of the oscillating behavior before steady state
Power versus loss
Threshold study:
1. Study of spontaneous emission
Starting the laser with Ds=Deq
Starting parameters: pump=0.5, Loss=0.2
Increase pump until threshold
2. Laser starting with Ds<Deq
Starting parameters: pump=3, Loss=0.2
Observation of the oscillating behavior before steady state
Homogenous Inhomogenous Laser
Spectral study:
1. Study of inhomogenous laser
Starting the laser with spectra and population window
2. Homogenous Laser
Observation of the spectral narrowing
Pump pulsed: relaxation
Oscillating relaxation:
1. Study of laser relaxation
Starting the laser with inhomogenous media
Starting parameters: pump=10, Loss=0.5
Pump duration 300 fs
Pump pulsed QSwitch
1. Study of Qswitch laser
Starting the laser with homogenous media
Starting parameters: pump=2.5, Loss=0.5
Pump duration 100 fs check uncheck Qswitch button
CW Mode Locking
Pulse duration study:
1. Long Pulse
Starting parameters: pump=3.5, Loss=0.1
Increase N2 for shorter pulse, Dispersion =0
100
Pulse
duration
Intensity
50
0
0.1
0.3
N2*10-10
0.5
CW Mode Locking
Dispersion effect:
1. Short Pulse
Starting parameters: pump=3.5, Loss=0.1
N2 =0.6, Dispersion between 29 and 39
Prism tuning
Pulse Duration
100
80
60
40
20
0
29
32
35
38
Chirp
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