The first hyperpolarizability (β) spectrum of an azobenzene derivative around its two-photon resonance region is
detected carefully by hyper-Rayleigh scattering. The present work uses a fluorescence spectrometer (Edinburgh
instruments, F900) as the detector instead of interference filter and photoelectric multiplier tube (PMT). For each
wavelength, HRS emission spectrum accompanied with two-photon fluorescence (TPF) is carefully detected by changing
the detection wavelength around half of the incident wavelength. Full width to half maximum (FWHM) of the spectrum
is about 0.4nm, which is similar to that of the laser. When the incident wavelength moves into the two-photon resonance
region, TPF signal increases quickly and should be eliminated. In order to receive accurate β spectrum, the data detected
by the oscillograph should be made some emendations, such as TPF, incident energy, absorption and pulse width.
Compared with the β spectrum detected in previous works, the spectrum received in this work presents a clearer profile.
The β spectrum exhibits a similar profile as its UV-visible spectrum just with blue-shift of wavelength. It could be
explained that the electronic vibration structure in two-photon progress is different from that in one-photon progress,
while the broadening mechanism may be similar, considering the resonant two-state model (RTSM).