Circular polarization

About: Circular polarization is a research topic. Over the lifetime, 15201 publications have been published within this topic receiving 234418 citations.

Rotational Doppler effect in nonlinear optics

Abstract: The change in pitch of a passing car engine is a classic example of the translational Doppler effect, but rotational Doppler shifts can also arise, as shown for circularly polarized light passing through a spinning nonlinear optical crystal. The translational Doppler effect of electromagnetic and sound waves has been successfully applied in measurements of the speed and direction of vehicles, astronomical objects and blood flow in human bodies1,2,3,4,5,6,7,8, and for the Global Positioning System. The Doppler effect plays a key role for some important quantum phenomena such as the broadened emission spectra of atoms9 and has benefited cooling and trapping of atoms with laser light10,11,12. Despite numerous successful applications of the translational Doppler effect, it fails to measure the rotation frequency of a spinning object when the probing wave propagates along its rotation axis. This constraint was circumvented by deploying the angular momentum of electromagnetic waves13—the so-called rotational Doppler effect. Here, we report on the demonstration of rotational Doppler shift in nonlinear optics. The Doppler frequency shift is determined for the second harmonic generation of a circularly polarized beam passing through a spinning nonlinear optical crystal with three-fold rotational symmetry. We find that the second harmonic generation signal with circular polarization opposite to that of the fundamental beam experiences a Doppler shift of three times the rotation frequency of the optical crystal. This demonstration is of fundamental significance in nonlinear optics, as it provides us with insight into the interaction of light with moving media in the nonlinear optical regime.

Production and measurement of circular polarization in the VUV.

Abstract: A comprehensive analysis of the production and detection of circularly polarized VUV light using reflection optics is presented. Experimental results using gold reflectors are given. The necessary measurements to determine all Stokes parameters of an arbitrary VUV light beam are discussed.

Electrically Small, Low-Profile, Huygens Circularly Polarized Antenna

Abstract: The design, simulation studies, and experimental verification of an electrically small, low-profile, broadside-radiating Huygens circularly polarized (HCP) antenna are reported. To realize its unique circular polarization cardioid-shaped radiation characteristics in a compact structure, two pairs of the metamaterial-inspired near-field resonant parasitic elements, the Egyptian axe dipole (EAD) and the capacitively loaded loop (CLL), are integrated into a crossed-dipole configuration. The EAD (CLL) elements act as the orthogonal electric dipole (magnetic dipole) radiators. Balanced broadside-radiated electric and magnetic field amplitudes with the requisite 90° phase difference between them are realized by exciting these two pairs of electric and magnetic dipoles with a specially designed, unbalanced crossed-dipole structure. The electrically small (ka = 0.73) design operates at 1575 MHz. It is low profile $0.04\lambda _{\mathbf {0}}$ , and its entire volume is only $0.0018\lambda _{\mathbf {0}}^{\mathbf {3}}$ . A prototype of this optimized HCP antenna system was fabricated, assembled, and tested. The measured results are in good agreement with their simulated values. They demonstrate that the prototype HCP antenna resonates at 1584 MHz with a 0.6 dB axial ratio, and produces the predicted Huygens cardioid-shaped radiation patterns. The measured peak realized LHCP gain was 2.7 dBic, and the associated front-to-back ratio was 17.7 dB.

Sensitive Instrument for the Study of Circular Polarization of Luminescence

Abstract: A sensitive instrument is described for the measurement of the extent of circular polarization of light emitted by chiral molecules. In this instrument the intensity of the circularly polarized component of the luminescence light is selectively modulated by an electro‐optic or photoelastic light modulator, while the unpolarized component of the luminescence is unaffected. The modulated light beam is detected by a photomultiplier and the ac component of the electric signal produced is amplified by a phase‐sensitive amplifier tuned to the modulation frequency. The light used for the excitation of the sample and the luminescence light are monochromated. An accessory is described which produces controlled mixtures of unpolarized and circularly polarized light and thus permits calibration of the output of the instrument in terms of the degree of circular polarization of the light under examination. Signal to noise ratios of 20 have been readily obtained with luminescence which is circularly polarized to an extent of 10−3 to 10−4.

Photoelectron circular dichroism in core level ionization of randomly oriented pure enantiomers of the chiral molecule camphor.

Abstract: The inner-shell photoionization of unoriented camphor molecules by circularly polarized light has been investigated from threshold to a photoelectron kinetic energy of ∼65 eV. Photoelectron spectra of the carbonyl C 1s orbital, recorded at the magic angle of 54.7° with respect to the light propagation direction, show an asymmetry of up to 6% on change of either the photon helicity or molecular enantiomer. These observations reveal a circular dichroism in the angle resolved emission with an asymmetry between forward and backward scattering (i.e., 0° and 180° to the light beam) which can exceed 12%. Since the initial state is an atomiclike spherically symmetric orbital, this strongly suggests that the asymmetry is caused by final-state effects dependent on the chiral geometry of the molecule. These findings are confirmed by electron multiple scattering calculations of the photoionization dynamics in the electric-dipole approximation.