1. Pump and probe techniquel
t = 2Dl/c t BS To
Sample
Probe
Pump
Femtosecond
Laser pulse
Mirror

2. Time-resolved optical measurements
In reflection direction:
Linear reflectivity
EO & MO sampling
Second-harmonic generation
Nonlinear optical signal
Probe
Pump t
Sample
In transmission direction:
Linear transmission
EO & MO sampling
Second-harmonic generation
Nonlinear optical signal

3. Coherent phonon spectroscopy: GaAs as example
Bulk LO phonon
8.8 THz
Fourier Power Spectrum
Time-Resolved Second-Harmonic Generation (TRSHG) measurement

4. Two-pump and probe technique
1st Pump
2nd Pump
Dl2 Dl BS
t =2Dl/c BS M
t2=2Dl2/c
Probe
Probe
Femtosecond
laser pulse M BS
2nd Pump
1st Pump M

5. 2nd pump induced carrier-phonon interaction: GaAs as example
Initial 0 fs
2nd 330 fs
LO phonon-hole
coupling mode
Bulk LO phonon
8.8 THz
LO phonon-electron
coupling mode
Fourier Power Spectrum