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Description
In the past few decades ultrafast laser physics has blossomed into a mature field, as seen by the Nobel Prizes awarded for chirped pulse amplification (2018) and high-harmonic generation (2023). With the realization of light pulses on the order of a few optical cycles comes an increasing demand for suitable pulse measurement techniques. Since the 1990s, Frequency-Resolved Optical Gating (FROG) has gone through numerous iterations and has become the standard method for ultrashort pulse reconstruction.
To reconstruct pulses with femtojoule-level energies and/or bandwidths approaching or exceeding an octave, cross-correlation FROG (XFROG) variations are particularly useful. A common approach to XFROG, OPA-XFROG (Optical Parametric Amplifier XFROG) records the spectrally resolved output of an optical parametric amplifier versus gate delay and uses the XFROG algorithm to retrieve the intensity and phase of the unknown pulse.
We introduce KICKING FROG (Kerr-Instability amplification Cross-correlation Induced Nonlinear Generation FROG), which replaces OPA with Kerr-instability amplification to extend XFROG characterization to pulses with broader bandwidths. Compared to OPA-XFROG, KICKING FROG offers greater bandwidth, tunability, and reduced cost, making it well-suited for broadband visible-pulse characterization.
Kerr-instability amplification (KIA) is a nonlinear optical process extending four-wave mixing to extreme intensities, where two pump photons are destroyed to amplify a seed and create an idler (2ω_p=ω_s+ω_i). Conservation of energy and momentum dictate non-collinear intensity-dependent phase matching. KIA can exceed the bandwidth and tunability of OPA and NOPA systems while enabling the use of any χ^3 (Kerr) medium rather than the rarer χ^2 materials required for OPA. In addition, Kerr polarization rotation enables background-free signal generation, further improving sensitivity for weak-pulse reconstruction down to the femtojoule regime. We will discuss applications of broadband background-free amplification for spectroscopy.
Fig. 1: Spectrogram generated from KICKING FROG. The seed is generated by supercontinuum generation in sapphire. We scan the pump-seed delay and record the spectrogram of the amplified pulse. We reconstruct the seed and pump pulses using our XFROG algorithm.
| Keyword-1 | Ultrashort pulses |
|---|---|
| Keyword-2 | Four-wave mixing |
| Keyword-3 | Background-free spectroscopy |