Laser physics simulation program

Lionel Canioni University Bordeaux I France

The Mode program

 Goal: visualization of laser dynamics and operating types.   Useful for Graduate and undergraduate student in lasers courses  Interacting program working on a tabletop computer 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

   

D



D eq

  2 

J D

Relaxation , pumping Interaction media EM wave Population equilibrium

D eq

l2l1/ l2 E2 l1 Intensity evolution: J

d dt

J

  

J



c



J D

Cavity loss, abs Laser Gain E1  

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

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

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 50 0 0.1

0.3

N2*10 -10

0.5

Pulse duration Intensity

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 100 80 60 40 20 0 29 32 35 38 Chirp