Extended Data Fig. 1: Direct up-conversion of BSV.

(a) When the BSV pulse energy is 30 nJ, the 3^rd and 5^th harmonics of the BSV frequency are measurable. Note that the spectral width is much narrower than the sidebands because the BSV bandwidth is limited to 50 nm, corresponding to a coherence time of 75 fs. (b) Without the bandpass filter on the BSV beam, up to the 7^th harmonic is measured with a BSV energy of 37 nJ (the 3^rd harmonic is not measured in this case as it is outside the detected range of the spectrometer). Single-shot measurements of this spectrum allow to retrieve the g⁽²⁾(0) = 7.9 and 4.9 for the 5^th and 7^th harmonics of the BSV beam, respectively.