Non-Instantaneous Polarization Dynamics in Resonant Dielectrics

摘要: Third-order optical nonlinearities are extensively utilized in both generation and characterization of ultrashort pulses. One example is the widely used method frequency-resolved gating (FROG), which can be based on a variety χ(3) effects. Any variant FROG relies instantaneity polarization response, as usually expected off-resonance. Here we demonstrate that resonant third harmonic excitation dielectric medium may exhibit surprisingly slow decay, with relaxation time constant exceeds duration shortest pulses generated to date. For this purpose, collinear (THFROG) [1] was characterize 7.5 fs Ti:sapphire laser using SiO2 or TiO2 medium. These measurements indicate decay 6.5 TiO2. Numerical solutions time-dependent Schrodinger equation (TDSE) [2] further support experimental findings.