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Register a new userEvanescent-wave and open-air chiral sensing via signal-reversing cavity-enhanced polarimetry
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Sensing chirality is of fundamental importance to many fields, including analytical and biological chemistry, pharmacology, and fundamental physics. Recent developments have extended optical chiral sensing using microwaves, fs pulses, superchiral light, and photoionization. The most widely used methods are the traditional methods of circular dichroism and optical rotation (OR). However, chiral signals are typically very weak, and their measurement is limited by larger time-dependent backgrounds and by imperfect and slow subtraction procedures. Here, we demonstrate a pulsed-laser bowtie-cavity-enhanced polarimeter with counter-propagating beams, which solves these background problems: the chiral signals are enhanced by the number of cavity passes; the effects of linear birefringence are suppressed by a large induced intracavity Faraday rotation; and rapid signal reversals are effected by reversing the Faraday rotation and subtracting signals from the counter-propagating beams. These advantages allow measurements of absolute chiral signals in environments where background subtractions are not feasible: we measure optical rotation from chiral vapour in open air, and from chiral liquids in the evanescent wave (EW) produced by total internal reflection at a prism surface. EW-OR of (+)-maltodextrin and (-)-fructose solutions confirm the Drude-Condon model for Maxwells equations in isotropic optically active media. In particular, the effective optical rotation path length, near index matching, is equal to the Goos-Hanchen shift of the EW. The limits of this polarimeter, when using a continuous-wave laser locked to a stable high-finesse cavity, should match sensitivity measurements for linear birefringence ($3times 10^{-13}$ rad), which is several orders of magnitude more sensitive than current chiral detection limits, transforming the power of chiral sensing in many fields.
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We present a new cavity-based polarimetric scheme for highly sensitive and time-resolved measurements of birefringence and dichroism, linear and circular, that employs rapidly-pulsed single-frequency CW laser sources and extends current cavity-based spectropolarimetric techniques. We demonstrate how the use of a CW laser source allows for gains in spectral resolution, signal intensity and data acquisition rate compared to traditional pulsed-based cavity ring-down polarimetry (CRDP). We discuss a particular CW-CRDP modality that is different from intensity-based cavity-enhanced polarimetric schemes as it relies on the determination of the polarization-rotation frequency during a ring-down event generated by large intracavity polarization anisotropies. We present the principles of CW-CRDP and validate the applicability of this technique for measurement of the non-resonant Faraday effect in solid SiO$_2$ and CeF$_3$ and gaseous butane. We give a general analysis of the fundamental sensitivity limits for CRDP techniques and show how the presented frequency-based methodology alleviates the requirement for high finesse cavities to achieve high polarimetric sensitivities, and, thus, allows for the extension of cavity-based polarimetric schemes into different spectral regimes but most importantly renders the CW-CRDP methodology particularly suitable for robust portable polarimetric instrumentations.
Quantum communication is a holy grail to achieve secure communication among a set of partners, since it is provably unbreakable by physical laws. Quantum sensing employs quantum entanglement as an extra resource to determine parameters by either using less resources or attaining a precision unachievable in classical protocols. A paradigmatic example is the quantum radar, which allows one to detect an object without being detected oneself, by making use of the additional asset provided by quantum entanglement to reduce the intensity of the signal. In the optical regime, impressive technological advances have been reached in the last years, such as the first quantum communication between ground and satellites, as well as the first proof-of-principle experiments in quantum sensing. The development of microwave quantum technologies turned out, nonetheless, to be more challenging. Here, we will discuss the challenges regarding the use of microwaves for quantum communication and sensing. Based on this analysis, we propose a roadmap to achieve real-life applications in these fields.
Researchers routinely sense molecules by their infrared vibrational fingerprint absorption resonances. In addition, the dominant handedness of chiral molecules can be detected by circular dichroism (CD), the normalized difference between their optical response to incident left- and right- handed circularly polarized light. Here, we introduce a cavity composed of two parallel arrays of helicity-preserving silicon disks that allows to enhance the CD signal by more than two orders of magnitude for a given molecule concentration and given thickness of the cell containing the molecules. The underlying principle is first-order diffraction into helicity-preserving modes with large transverse momentum and long lifetimes. In sharp contrast, in a conventional Fabry-Perot cavity, each reflection flips the handedness of light, leading to large intensity enhancements inside the cavity, yet to smaller CD signals than without the cavity.
Quantum resources can enhance the sensitivity of a device beyond the classical shot noise limit and, as a result, revolutionize the field of metrology through the development of quantum-enhanced sensors. In particular, plasmonic sensors, which are widely used in biological and chemical sensing applications, offer a unique opportunity to bring such an enhancement to real-life devices. Here, we use bright entangled twin beams to enhance the sensitivity of a plasmonic sensor used to measure local changes in refractive index. We demonstrate a 56% quantum enhancement in the sensitivity of state-of-the-art plasmonic sensor with measured sensitivities on the order of $10^{-10}$RIU$/sqrt{textrm{Hz}}$, nearly 5 orders of magnitude better than previous proof-of-principle implementations of quantum-enhanced plasmonic sensors. These results promise significant enhancements in ultratrace label free plasmonic sensing and will find their way into areas ranging from biomedical applications to chemical detection.
We demonstrate the generation of coherent phonons in a quartz Bulk Acoustic Wave (BAW) resonator through the photoelastic properties of the crystal, via the coupling to a microwave cavity enhanced by a photonic lambda scheme. This is achieved by imbedding a single crystal BAW resonator between the post and the adjacent wall of a microwave reentrant cavity resonator. This 3D photonic lumped LC resonator at the same time acts as the electrodes of a BAW phonon resonator, and allows the direct readout of coherent phonons via the linear piezoelectric response of the quartz. A microwave pump, $omega_p$ is tuned to the cavity resonance $omega_0$, while a probe frequency, $omega_{probe}$, is detuned and varied around the red and blue detuned values with respect to the BAW phonon frequency, $Omega_m$. The pump and probe power dependence of the generated phonons unequivocally determines the process to be electrostrictive, with the phonons produced at the difference frequency between pump and probe, with no back action effects involved. Thus, the phonons are created without threshold and can be considered analogous to a Coherent Population Trapped (CPT) maser scheme.
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