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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
п‚§ Goal: visualization of laser dynamics and
operating types.
п‚§ Interacting program working on a tabletop
computer
student in lasers courses
п‚§ Illustration of the different laser operations
principle
Principle of working
п‚§ The program:
п‚§ Solve the laser master equation in an infinite time
loop
п‚§ Display continuously the physical parameters of
the laser
п‚§ 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
l1
Intensity evolution: J
d
J пЂЅ пЂ­пЃ« J пЂ« cпЃі J D
dt
Cavity
loss, abs
Laser
Gain
E1
пЃ§
Simulations
п‚§ Master equation are solve for each cavity
mode with wave propagation equation
п‚§ All the parameters let us study a large
amount of laser type
п‚§ Cw laser , threshold, pulsed laser, CW
mode locked laser, QSwitch, mode beating
etcвЂ¦
Laser Dialog Box
п‚§ Cavity parameters
п‚§ Length
п‚§ Number of resonant optical
frequency
п‚§ Optical gain media
п‚§
п‚§
п‚§
п‚§
Frequency
Emission abs cross section
Spectral width
Spectroscopic model
п‚§ Optical Pumping
п‚§ CW or Pulsed pump
п‚§ Loss
п‚§ Pump Power
п‚§ Display Control
п‚§ Continuous or step by step display
п‚§ Choose between several
representation
п‚§ Pulse propagation parameters
п‚§ Non linear coefficient and
dispersion
Cavity parameters
п‚§ Length in Вµm of the laser:
п‚§ The cavity length match
the gain media length
п‚§ Small cavity for visual
mode representation
п‚§ Number of resonant
optical frequency
п‚§ One can choose between
1 (single mode laser) and
41 optical frequencies
allowed in the cavity
п‚§ FP filter equivalent
Optical gain media
п‚§ Frequency
п‚§ Selection of the central
frequency by the resonant
frequency of the cavity.
Change with cavity length
change wavelength
п‚§ Spectral width
п‚§ Gain media width( arbitrary
unit)
п‚§ Emission abs cross section
п‚§ Low gain or high gain laser
п‚§ Spectroscopic model
п‚§ Homogenous or
Inhomogenous model
example gas laser or Nd Yag
laser
w
Optical Pumping
п‚§ Loss
п‚§ Accumulated during
laser propagation
п‚§ CW or Pulsed pump
п‚§ CW Pumping and
flashed pump allowed
Qswith simulation.
Flash duration and
repetition rate
available
п‚§ Pump Power
п‚§ Control the efficiency
between pump power
and optical transfer
Pulse propagation parameters
п‚§ Effective parameters
for fs propagation
п‚§ Second order
dispersion: useful for
pulse stretched
п‚§ Nonlinear coefficient:
SPM mod locking :
scattering of energy
between modes
Display Control
Choose between several representation:
п‚§ Frequency domain: mod representation, spectrum
representation
п‚§ Time domain: Difference population, output power, pulse
inside the laser rod
п‚§ Standard value: pulse width, power, intensity, wavelength
Continuous or step by step display:
п‚§ Multithread application allowed permanent tuning and
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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