Rotation Of Polarized Light Research Articles

Precise and rapid detection of optical activity for accumulative femtosecond spectroscopy

We present polarimetry, i.e. the detection of optical rotation of light polarization, in a configuration suitable for femtosecond spectroscopy. The polarimeter is based on common-path optical heterodyne interferometry and provides fast and highly sensitive detection of rotatory power. Femtosecond pump and polarimeter probe beams are integrated into a recently developed accumulative technique that further enhances sensitivity with respect to single-pulse methods. The high speed of the polarimeter affords optical rotation detection during the pump-pulse illumination period of a few seconds. We illustrate the concept on the photodissociation of the enantiomers of methyl p-tolyl sulfoxide. The sensitivity of rotatory detection, i.e. the minimum rotation angle that can be measured, is determined experimentally including all noise sources to be 0.10 milli-degrees for a measurement time of only one second and an interaction length of 250 μm. The suitability of the presented setup for femtosecond studies is demonstrated in a non-resonant two-photon photodissociation experiment.

UV nanosecond laser-induced birefringence in LBG glasses

In this paper, we present results on UV pulsed laser-induced birefringence in La2O3–B2O3–GeO2 (LBG) glasses. Samples were irradiated at a wavelength of 355 nm delivered by an Nd–YAG laser operating in the nanosecond regime. After irradiation, glasses were analyzed by micro-Raman spectroscopy and small angle X-ray scattering (SAXS). Raman spectra show figures characteristic of a light polarization rotation effect in agreement with an anisotropic distribution of the scattering intensity observed by SAXS measurements. These results are interpreted as the interaction of the glass with the electromagnetic field of the UV beam (UV poling).

Construction and applications of an atomic magnetic gradiometer based on nonlinear magneto-optical rotation

We report on the design, characterization, and applications of a sensitive atomic magnetic gradiometer. The device is based on nonlinear magneto-optical rotation in alkali-metal (Rb87) vapor and uses frequency-modulated laser light. The magnetic field produced by a sample is detected by measuring the frequency of a resonance in optical rotation that arises when the modulation frequency equals twice the Larmor precession frequency of the Rb atoms. The gradiometer consists of two atomic magnetometers. The rotation of light polarization in each magnetometer is detected with a balanced polarimeter. The sensitivity of the gradiometer is 0.8nG∕Hz1∕2 for near-dc (0.1Hz) magnetic fields, with a base line of 2.5cm. For applications in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), a long solenoid that pierces the magnetic shields provides an ∼0.5G leading field for the nuclear spins in the sample. Our apparatus is particularly suited for remote detection of NMR and MRI. We demonstrate a point-by-point free induction decay measurement and a spin echo reconstructed with a pulse sequence similar to the Carr-Purcell-Meiboom-Gill pulse. Additional applications and future improvements are also discussed.

Shifting light with spin

NMR spectroscopy has changed enormously over the years, but signal detection has stayed the same since the technique was invented. The latest thinking literally shines a new light on things. Nuclear magnetic resonance (NMR) is used in a broad range of applications, from NMR imaging to protein structure studies. These applications usually involve the measurement of the bulk magnetic field outside the samples, so NMR signals from specific atomic nuclei acting as tiny magnets are generally not revealed. To tease out interesting information about a sample, sophisticated tricks are required. Researchers at Princeton now show that NMR signals of liquids can be detected by simply shining light through the sample and measuring the rotation of light polarization induced by the 'atomic magnets'. This new detection method will make it possible to take 'snapshots' of nuclear magnetism and study which atoms in a complex chemical are responsible for its colour and other optical properties.

Optical detection of liquid-state NMR

Nuclear magnetic resonance (NMR) in liquids and solids is primarily detected by recording the net dipolar magnetic field outside the spin-polarized sample. But the recorded bulk magnetic field itself provides only limited spatial or structural information about the sample. Most NMR applications rely therefore on more elaborate techniques such as magnetic field gradient encoding or spin correlation spectroscopy, which enable spatially resolved imaging and molecular structure analysis, respectively. Here we demonstrate a fundamentally different and intrinsically information-richer modality of detecting NMR, based on the rotation of the polarization of a laser beam by the nuclear spins in a liquid sample. Optical NMR detection has in fact a long history in atomic vapours with narrow resonance lines, but has so far only been applied to highly specialized condensed matter systems such as quantum dots. It has been predicted that laser illumination can shift NMR frequencies and thus aid detection, but the effect is very small and has never been observed. In contrast, our measurements on water and liquid 129Xe show that the complementary effect-the rotation of light polarization by nuclear spins-is readily measurable, and that it is enhanced dramatically in samples containing heavy nuclei. This approach to optical NMR detection should allow correlated optical and NMR spectroscopy on complex molecules, and continuous two-dimensional imaging of nuclear magnetization with spatial resolution limited only by light diffraction.

Experimental Observation of Optical Rotation Generated in Vacuum by a Magnetic Field

We report the experimental observation of a light polarization rotation in vacuum in the presence of a transverse magnetic field. Assuming that data distribution is Gaussian, the average measured rotation is (3.9 +/- 0.5) x 10(-12) rad/pass, at 5 T with 44 000 passes through a 1 m long magnet, with lambda = 1064 nm. The relevance of this result in terms of the existence of a light, neutral, spin-zero particle is discussed.

Selective addressing of high-rank atomic polarization moments.

We describe a method of selective generation and study of polarization moments of up to the highest-rank kappa=2F possible for a quantum state with total angular momentum F. The technique is based on nonlinear magneto-optical rotation with frequency-modulated light. Various polarization moments are distinguished by the periodicity of light-polarization rotation induced by the atoms during Larmor precession and exhibit distinct light-intensity and frequency dependences. We apply the method to study polarization moments of 87Rb atoms contained in a vapor cell with antirelaxation coating. Distinct ultranarrow (1-Hz wide) resonances, corresponding to different multipoles, appear in the magnetic-field dependence of the optical rotation. The use of the highest-multipole resonances supported by a given system has important applications in quantum and nonlinear optics and in magnetometry.

Temperature characteristics of a new magneto-optical current transformer

In contrast to existing current transformers utilizing the Faraday rotation of light polarization, the principle of operation of the new sensor is based on the direct registration of the domain wall positions in an orthoferrite, a transparent ferromagnet. The results of the measurements are not affected directly by temperature changes of Faraday rotation, birefringence, fluctuations of the incident light beam, polarization distortions in fibers, etc. The amplitude of domain wall motion remains constant in a wide range of driving magnetic field frequencies from dc to hundreds kHz. With the further growth of the frequency the amplitude decreases in two times at 5 MHz. In the temperature range from 20 ◦ Ct o130 ◦ C the domain wall mobility and the bandwidth decrease in about three times.

Self-induced light polarization rotation in azobenzene-containing polymers

We report here a light-induced phenomenon—a self-induced rotation of the azimuth of elliptically polarized light passing through photobirefringent azopolymers. The experiments are carried out with films of amorphous and liquid-crystalline polymers. It has been shown that the induced rotation angle depends on the ellipticity of the input light. A theoretical analysis of the phenomenon has been done and it has been shown that light induces chiral structure in the polymer films.

Enantioselective magnetochiral photochemistry

Many chemical and physical systems can occur in two forms distinguished solely by being mirror images of each other. This phenomenon, known as chirality, is important in biochemistry, where reactions involving chiral molecules often require the participation of one specific enantiomer (mirror image) of the two possible ones. In fact, terrestrial life utilizes only the L enantiomers of amino acids, a pattern that is known as the 'homochirality of life' and which has stimulated long-standing efforts to understand its origin. Reactions can proceed enantioselectively if chiral reactants or catalysts are involved, or if some external chiral influence is present. But because chiral reactants and catalysts themselves require an enantioselective production process, efforts to understand the homochirality of life have focused on external chiral influences. One such external influence is circularly polarized light, which can influence the chirality of photochemical reaction products. Because natural optical activity, which occurs exclusively in media lacking mirror symmetry, and magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic fields, both cause polarization rotation of light, the potential for magnetically induced enantioselectivity in chemical reactions has been investigated, but no convincing demonstrations of such an effect have been found. Here we show experimentally that magnetochiral anisotropy--an effect linking chirality and magnetism--can give rise to an enantiomeric excess in a photochemical reaction driven by unpolarized light in a parallel magnetic field, which suggests that this effect may have played a role in the origin of the homochirality of life.

Surface plasmon-enhanced photoluminescence from a single quantum well

We have dramatically enhanced the photoluminescence intensity emitted from a single quantum well (typically by factors of 3–6) by covering the sample surface with a thin semitransparent metallic film. Using a photolithographically prepared gold grating, we show that this enhancement is due to the excitation of surface plasmons on the metal. By selectively turning off the surface plasmon excitation via sample or light polarization rotation, the enhancement can be suppressed.

Multispectral polarimetric glucose detection using a single Pockels cell

The preliminary design of a noninvasive glucose sensor developed in this investigation was based on the polarization rotation of light produced by optically active molecules. The polarimeter developed for this investigation was unique when compared to previous investigations in that it utilized a single Pockels cell to both modulate the signal and provide feedback within the system. The intended application of this polarimeter is to measure glucose concentrations within the aqueous humor of the eye. The purpose of this investigation was to elucidate whether the theory of superposition and multispectral analysis can be applied to the measurement of glucose in the presence of ascorbic acid and albumin, the most significant rotatory confounders found in the aqueous humor. The results of this investigation indicate that superposition of rotation at different wavelengths due to the above optically active molecules was valid for the in vitro experiments conducted. Utilizing two wavelengths of light, the concentration of hyperglycemic levels of glucose were derived in the presence of physiological concentrations of the optically active confounders ascorbic acid and albumin. It was found, except for one outlier, that the model predicted glucose concentrations to within 23%.

High contrast optical modulator based on electrically tunable polarization rotation and phase retardation in uniaxially strained (100) multiple quantum wells

We report a novel approach to the design of normal incidence multiple quantum well light modulators. The quantum confined Stark effect is utilized to tune the light polarization rotation and phase retardation created by a thermally induced in-plane anisotropic strain. An exceedingly high contrast ratio of 5000:1 is demonstrated for a normally-on device at room temperature. >