Optical heterodyne

A connnon teclmique used to enliance the signal-to-noise ratio for weak modes is to inject a local oscillator field polarized parallel to the RIKE field at the detector. This local oscillator field is derived from the probe laser and will add coherently to the RIKE field [96]. The relative phase of the local oscillator and the RIKE field is an important parameter in describing the optical heterodyne detected (OHD)-RIKES spectrum. If the local oscillator at the detector is in phase with the probe wave, the heterodyne mtensity is proportional to... 

Tokmakoff A, Lang M J, Larson D S and Fleming G R 1997 Intrinsic optical heterodyne detection of a two-dimensional fifth order Raman response Chem. Phys. Lett. 272 48-54... 

Constantine S, Zhou Y, Morals J and Ziegler L D 1997 Dispersed optical heterodyne birefringence and dichroism of transparent liquids J. Phys. Chem. A 101 5456-62... 

Brown E R, McIntosh K A, Smith F W, Manfra M J and Dennis C L 1993 Measurements of optical-heterodyne conversion in low-temperature grown GaAs Appl. Rhys. Lett. 62 1206-8... 

In optical domain, preamplifier is no more an utopia and is in actual use in fiber communication. However quantum physics prohibits the noiseless cloning of photons an amplifier must have a spectral density of noise greater than 1 photon/spatial mode (a "spatial mode" corresponds to a geometrical extent of A /4). Most likely, an optical heterodyne detector will be limited by the photon noise of the local oscillator and optical preamplifier will not increase the detectivity of the system. 

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). 

Levenson, M. D., and Eesley, G. L. 1979. Polarization selective optical heterodyne detection for dramatically improved sensitivity in laser spectroscopy. Appl. Phys. 19 1-17. Librizzi, R, Viapianni, C., Abbruzzetti, S., and Cordone, L. 2002. Residual water modulates the dynamics of the protein and of the external matrix in trehalose-coated MbCO An infrared and flash-photolysis study. J. Chem. Phys. 116 1193-1200. 

Eesley, G. L., Levenson, M. D., and Tolies, W. M. 1978. Optically heterodyned coherent Raman spectroscopy. IEEE J. Quant. Electron. 14 45-49. 

Before melting and for some time after only the band at 625 cm of the AA [C4CiIm]+ cation was observed in the 600-630 cm i region. Gradually 603 cm i band due to the GA conformer became stronger. After about 10 min the AA/GA intensity ratio became constant. The interpretation [50] is that the rotational isomers do not interconvert momentarily at the molecular level. Most probably it involves a conversion of a larger local structure as a whole. The existence of such local structures of different rotamers has been found by optical heterodyne-detected Raman-induced Kerr-effect spectroscopy (OHD-RIKES) [82], Coherent anti-Stokes Raman scattering (CARS) [83],... 

Fig. 13.20. Optical heterodyne force microscopy (OHFM) and its application to a copper strip of width 500 nm, thickness 350 nm, on a silicon substrate, with subsequent chemical vapour deposition (CVD) of a silicon oxide layer followed by polishing and evaporation of a chromium layer of uniform thickness 100 nm and flatness better than 10 nm (a) amplitude (b) phase 2.5 [im x 2.5 m. Ultrasonic vibration at fi = 4.190 MHz was applied to the cantilever light of wavelength 830 nm was chopped at fo = 4.193 MHz and focused through the tip to a spot of diameter 2 im with incident mean power 0.5 mW the cantilever resonant frequency was 38 kHz. The non-linear tip-sample interaction generates vibrations of the cantilever at the difference frequency f2 — f = 3 kHz (Tomoda et al. 2003).

Kumano, N., Inagaki, K Kolosov, O. V., and Wright, O. B. (1998). Optical heterodyne force microscopy. IEEE 1998 Ultrasonics Symposium, pp. 1269-72. IEEE, New York. [319]... 

In Section II.B the fluctuations and fluctuational transitions in an OB system subject to white noise are analyzed. In Section II.C the phenomenon of stochastic resonance in the OB system is discussed in terms of linear response theory and the corresponding experimental results are presented. In Section II.D we discuss theory and experimental results for the new form of optical heterodyning noise-protected with stochastic resonance. Finally, Section II.E contains concluding remarks. 

Similar to what happens in conventional SR, the heterodyne signal and its SNR can be amplified by adding noise to the system, thus manifesting the new phenomenon of noise-enhanced optical heterodyning. 

Figure 5. Signal amplification in the optical heterodyning experiment, with co0 = 2.1 kHz and n=3.9 Hz, as a function of the internal noise intensity [29]. Inset the corresponding signal-to-noise-ratio (SNR).

In condensed-phase CARS, the effects of the nonresonant susceptibility x(3)nr are most profound when a sample with weak Raman modes is embedded in a nonlinear medium. The nonresonant background of the latter can be easily comparable to or larger than the resonant contribution from the sample of interest. This is a situation commonly encountered in biological applications of CARS microscopy. Depending on the experimental situation, the CARS detection sensitivity to weak resonances can then be restricted either by the nonresonant background or by the photon shot-noise [62]. To maximize either the relative or the absolute CARS intensity, nonresonant background suppression schemes [44, 60, 61, 63, 64] and optical heterodyne detection (OHD) techniques [65-67] have been developed during recent years. 

---