Modelocked Thermal Frequency Combs for Ultrashort Chaotic Quantum Optics

Modelocked thermal frequency combs (MTCs) are generated by employing spectrally narrowed amplified spontaneous emission (ASE) seeded into an electro‐optic frequency comb generator. The MTC emits 2‐ps duration ultrashort pulses at a repetition rate of 10 GHz. Autocorrelation of the MTC pulses confirms a reduced coherence time,  ps, aligning with the narrowed bandwidth of the ASE seed. Intensity correlations of optically gated MTC pulses at a repetition rate of 250 MHz reveal nearly ideal thermal photon statistics with an experimental , yielding an intrinsic after background noise removal. As a practical application, second harmonic generation (SHG) is performed utilizing the optically gated MTC pulses as a pump and experimental intensity correlations, , are examined for the SH photons. An entire transition in , continuously changing from six to two by increasing the pump strength, agrees with the single‐mode analytical model. Furthermore, time‐resolved pulse height correlations allow to simultaneously acquire power variations in SHG and third harmonic generation against the pump. With the maximum peak intensity, , realized in a periodically poled waveguide for SHG, the demonstration highlights the potential for various applications in chaotic quantum optics experiments that necessitate ultrashort, high‐intensity, single‐spatiotemporal‐mode thermal pulses.