Hyper-Rayleigh scattering with picosecond pulse trains

Area of Science:

• Nonlinear Optics
• Spectroscopy
• Laser Physics

Background:

• Hyper-Rayleigh scattering (HRS) is a nonlinear optical technique used to determine molecular hyperpolarizabilities.
• Traditional HRS measurements often require irradiance scanning, which can be time-consuming.
• Single-pulse lasers (nanosecond and femtosecond) are commonly used, but their irradiance control can be complex.

Purpose of the Study:

• To propose and verify a novel method for measuring hyper-Rayleigh scattering using laser pulse trains.
• To demonstrate the feasibility of employing a Q-switched and mode-locked Nd:YAG laser's entire pulse train for HRS.
• To compare the speed and accuracy of the pulse train method against conventional single-pulse techniques.

Main Methods:

• Utilized a Q-switched and mode-locked Nd:YAG laser to generate pulse trains for hyper-Rayleigh scattering measurements.
• Eliminated the need for irradiance scanning devices by using the complete pulse train envelope.
• Performed measurements on para-nitroaniline solutions and compared results with those obtained using nanosecond single-pulse lasers.

Main Results:

• The pulse train method achieved measurement speeds at least 20 times faster than nanosecond single-pulse methods.
• The hyperpolarizability values obtained using the pulse train method showed good agreement with literature values, similar to nanosecond pulse results.
• The technique enabled instantaneous inspection of slow luminescence contributions from multiphoton absorption.

Conclusions:

• The proposed method using laser pulse trains is a viable and significantly faster alternative for hyper-Rayleigh scattering measurements.
• This approach simplifies experimental setups by removing the need for irradiance scanning.
• The method offers additional benefits, including the simultaneous observation of multiphoton absorption-induced luminescence.