Optical mixing heterodyne

The capillary wave frequency is detected by an optical heterodyne technique. The laser beam, quasi-elastically scattered by the capillary wave at the liquid-liquid interface, is accompanied by a Doppler shift. The scattered beam is optically mixed with the diffracted beam from the diffraction grating to generate an optical beat in the mixed light. The beat frequency obtained here is the same as the Doppler shift, i.e., the capillary wave frequency. By selecting the order of the mixed diffracted beam, we can change the wavelength of the observed capillary wave according to Eq. (11). 

Dadusc, G., Ogilvie, J. R, Schulenberg, R, Marvet, U., and Miller, R. J. D. 2001. Diffractive optics-based heterodyne-detected four-wave mixing signals of protein motion From protein quakes to ligand escape for myoglobin. Proc. Nat. Acad. Sci. USA 98 6110-6115. 

Diffractive Optics-Based Four-Wave Mixing with Heterodyne Detection... 

FIG U RE 1.10 Schematic representation of the experimental setnp for diffractive optics-hased fonr-wave mixing with heterodyne detection. (From Ogilvie, J. P., Plazanet, M., Dadusc, G., and Miller, R. J. D. 2002. J. Phys. Chem. 109 10460-67. With permission)... 

V. Extension to Heterodyne-Detected Four-Wave Mixing Appendix A Time- and Frequency-Gated Autocorrelation Signals Appendix B The Signal and the Optical Polarization... 

A distinction between homodyne and heterodyne detection must be made in optical scattering and diffraction experiments. Without careful treatment of the background, there is always the risk of mixed or unknown coherence conditions, and the diffusion coefficient determined from such data may be off by a factor of two. At least for the signal and background levels present in TDFRS, heterodyne detection is always superior to homodyne, especially since the heterodyne signal, contrary to the homodyne one, turns out to be very stable against perturbations and systematic errors. Even under nearly perfect homodyne conditions the tail of the decay curve is almost unavoidably heterodyne [34]. 

The dynamical behavior of molecular liquids is directly observed via femtosecond optical Kerr effect (OKE) measurement in the time domain. The signal intensity, 5oke( ")i obtained by the measurement using an optically heterodyne-detected (OHD) technique (mixing the OKE signal with a local oscillator) can be expressed in the form ... 

The subject of phase and phase retrieval with pulsed optical signals, although it is textbook material and involves well-known signal processing concepts [64, 65], has impacted on molecular spectroscopy only recently [66] through consideration of optical control experiments. As we shall see the phase is a consideration in heterodyne laser experiments because it influences the mixing of fields incident on a square-law detector. It is well known that a quadratic phase alters the spectrum, the time envelope and the time-frequency bandwidth of a pulse. Consider a pulse ... 

The heterodyne measurement is performed as follows. The dye laser excites the trapped ion with frequency (Ol while the fluorescence is observed in a direction of about 54 to the exciting laser beam (see Fig. 2). However, both the observation direction and the laser beam are in a plane perpendicular to the symmetry axis of the trap. Before reaching the ion, a fraction of this laser radiation is removed with a beamsplitter and then frequency shifted (by 137 MHz with an acousto-optic modulator (AOM)) to serve as the local oscillator. The local oscillator and fluorescence radiations are then overlapped and simultaneously focused onto the photodiode where the initial frequency mixing occurs. The frequency difference signal is amplified by a narrow band amplifier and then frequency down-converted to 1 kHz so that it could be analyzed by means of a fast Fourier analyzer (FFT). The intermediate frequency for this mixing of the signal was derived from the same frequency-stable synthesizer which was used to drive the accousto-optic modulator producing the sideband of the laser radiation so that any synthesizer fluctuations are canceled out. 

Raj R. K., Bloch D., Snyder J. J., Camy G. and Ducloy M., High-Frequency Optically Heterodyned Saturation Spectroscopy Via Resonant Degenerate Four-Wave Mixing , Phys. Rev. Lett. Vol. 44, 1980, pp. 1251-1254. 

For CW applications of optical-heterodyne conversion, two laser fields are applied to the optoelectronic material. The non-linear nature of the electro-optic effect strongly suppresses continuous emission relative to ultrashort pulse excitation, and so most of the CW research carried out to date has used photoconductive antennae. The CW mixing process is characterized by the average drift velocity vand carrier lifetime Tq of the mixing material, typically... 

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