23-02-2013, 09:10 AM
Basic principles of ultrafast lasers
Basic principles.ppt (Size: 1.99 MB / Downloads: 80)
Mode-locking Mechanisms
Active mode-locking
Acousto-optic modulator
Synchronous pump mode-locking
Passive mode-locking
Saturable absorber (dye, solid state)
Optical Kerr effect
Optical Kerr Effect
Intensity dependent refractive index: n = n0 + n2I(x,t)
Spatial (self-focusing)
provides loss modulation with suitable placement of gain medium (and a hard aperture)
Temporal (self-phase modulation)
provides pulse shortening mechanism with group velocity dispersion
Group Velocity Dispersion (GVD)
High-intensity modes have smaller cross-section and are less lossy. Thus, Kerr-lens is
similar to saturating absorber!
Some lasing materials (e.g. Ti:Sapphire) can act as Kerr-media
Kerr’s effect is much faster than saturating absorber allowing one generatevery
short pulses (~5 fs).
Components of an Ultrafast Laser
Pulse shortening mechanism
Self phase modulation and group velocity dispersion
Dispersion Compensation
Starting Mechanism
Regenerative initiation
Cavity perturbation
Saturable Absorber (SESAM)