Optical activity of lysozyme in solution at 532 nm via signal-reversing cavity ring-down polarimetry

Abstract

An improved optical cavity-based polarimetry method is employed to measure the optical activity of lysozyme in water solution, in the concentration range of 0-2 mg/ml. We employ a signal reversing technique, which gives the absolute optical rotation, without needing to remove the sample for a null measurement. We report an absolute sensitivity limit on the order of 0.1 mdeg, corresponding to a detection limit of <50 μg/ml for a sample volume lower than 50 μL, thus surpassing the sensitivity of existing commercial polarimeters. We discuss how these sensitivity levels can be further improved using existing methods and technologies.

Rapid parameter estimation of discrete decaying signals using autoencoder networks

“…The second type of model signals we investigate are decaying oscillations, as these become relevant in a wide range of experimental techniques, particularly within nuclear magnetic resonance (NMR) [13], optical magnetometry [15][16][17][18][19] and cavity-enhanced polarimetry [25][26][27][28][29][30][31][32] and ellipsometry [33][34][35][36]. We describe damped oscillating signals as:…”

“…A multitude of research fields rely on determination of time constants and frequencies of decaying signals, such examples include: nuclear magnetic resonance (NMR) [13] where molecular structures are analysed from precise determination of the frequency and decay constant of a damped sinusoidal signal generated by nuclear spins in magnetic fields; free-induction-decay (FID) optical magnetometry [14][15][16][17][18][19] where magnetic sensitivities depend on the precision of the measurement of the oscillating frequency; and cavity-enhanced spectroscopy and sensing methods [20][21][22][23][24] which rely on the detection of variations in the decay constant of optical cavities to identify trace gasses, measure absorption cross sections or observe chemical reactions in real time. Other cavity-enhanced methods, such as cavity ring-down polarimetry (CRDP) [25][26][27][28][29][30][31][32] and -ellipsometry (CRDE) [33][34][35][36], measure birefringence and/or dichorism of an optical medium through the precise estimation of signal-decay time and the beat frequency of polarization signals.…”

Rapid parameter determination of discrete damped sinusoidal oscillations

“…Several different research fields rely on the precise and accurate extraction of the time constants and frequencies of damped sinusoidal signals. Prominent examples include: nuclear magnetic resonance (NMR) [1], where information on the structure and the spin environment of a target molecule is extracted from precise determination of the frequency and decay constant of a damped sinusoidal signal; free-induction-decay (FID) optical magnetometry [2][3][4][5][6][7], where the magnetometric sensitivities depend on the precision of the measurement of the oscillating frequency; and pulsed/continuous-wave cavity ring-down polarimetry (CRDP) [8][9][10][11][12][13][14][15] and ellipsometry (CRDE) [16][17][18][19], where polarization-dependent absorption and refraction/reflection through/by an optical medium is extracted with high sensitivity through the precise measurement of the signal-decay time and its polarization beat frequency.…”

Continuous-Wave Cavity-Enhanced Polarimetry for Optical Rotation Measurement of Chiral Molecules

“…In this paper, we build upon the previous seminal studies on signal-reversing CRDP with pulsed lasers − and demonstrate CRDP in operation with a cw laser source. In particular, we show that electrical perturbation of the laser’s injection current provides a robust and effective way of exciting cavity modes to optimize the polarization modulation depth and to improve sensitivity.…”

“…More recently, bow-tie CRDP using pulsed lasers has been developed involving two counter-propagating linearly polarized beams, in which the effects of intracavity birefringence are cancelled by means of a signal-reversing technique and a reference Faraday rotation angle is induced by an intracavity magneto-optic crystal. − In this case, the optical rotation is then deduced from the two cavity ring-down signals without needing to remove the sample from the polarimeter. The pulsed CRDPs utilize lasers that are typically expensive and relatively bulky and have large optical linewidths (∼GHz or more).…”