Selective nonlinear optical excitation with pulses shaped by pseudorandom Galois fields

Abstract

We demonstrate high-resolution high-contrast nonlinear optical spectroscopy based on phase-modulated ultrashort pulses. The problem of causing selective nonlinear optical excitation at one frequency while minimizing background is framed in terms of low autocorrelation binary sequences. We investigate phase functions with up to 608-bit resolution for their ability to induce two-photon excitation or stimulated Raman scattering, and find the highest theoretical and experimental signal-to-noise ratios yet reported. We confirm our findings by measuring experimental two-photon excitation spectra.

Nonlinear imaging of nanostructures using beams with binary phase modulation

“…A simple way to reduce this complexity is to utilize binary shaping of the local phase of the beams, e.g., 0 and π. Previously, binary phase shapes have been utilized to increase the excitation selectivity in a variety of spectroscopy techniques [28][29][30][31] and to decrease the spot size of high-order optical beams [32,33]. To the best of our knowledge, binary phase shaping has not yet been applied to control the focal field distributions and resulting effects in driving the nonlinear emission from nanostructures.…”

Binary phase shaping for selective single‐beam CARS spectroscopy and imaging of gas‐phase molecules

“…The use of a minimal autocorrelation sequence to modulate the phase, however, ensures that the excitation at nearby frequencies is suppressed. [15] Following the considerations above, the phase mask across the pump-Stokes part of the spectrum is built as follows (see the diagrams in Fig. 1).…”

“…Using pseudorandom binary phase shaping (BPS), we have demonstrated previously high-contrast excitation selectivity for second-harmonic generation, two-photon excited fluorescence, and stimulated Raman scattering. [15] We have also applied BPS for mode-selective CARS in liquid samples. [9] Here we extend it to selective excitation of gas-phase molecules.…”

Remote Chemical Detection Using SUPER-CARS

“…Previously developed technology from our group has been shown to compensate phase distortions for over 30 meters and could be used for distances up to a kilometer, ensuring accurate phase delivery to the remote target [4]. In addition, the single-beam CARS signal can be improved, as the selective nonlinear excitation of the Raman transition has been shown to be optimized with the use of Galois field theory, in which pseudorandom binary phase sequences are used to optimize the signal to noise ratio (S/N) and contrast ratio (CR) of nonlinear optical processes [5]. …”