Electro-optic Detection Research Articles

Calibration error analysis of electro-optical detection systems

We present detailed analysis of calibration process error for electro-optical detection systems, which can be simplified as the plane rotation around a non-orthogonal axis. By means of octonions it firstly proves that the plane rotation around a non-orthogonal axis can be decomposed into rotations around two perpendicular axes. The rotation is further divided into three steps, and the calibration error is hence discussed and obtained. The simulation and test results indicate that there are large calibration errors in calibration process. The pointing error can be effectively improved after separating error components, which provides a more accurate set data for further compensation.

Terahertz electro-optical detection: optical phase or energy measurements

Models of different available single-photodetector electro-optic sampling schemes are considered from the unified theoretical position. It is taken into account that under electro-optic terahertz wave detection, not only do the polarization states of the femtosecond optical pulse components change but the modules of their amplitudes are also varied. As a result, information concerning the terahertz wave can be obtained not only using the conventional ellipsometry readout scheme (probe-phase sampling) but also by simple measuring of the induced power of the optical pulses (probe-energy sampling). Spectral sensitivities of both of these electro-optic sampling methods are calculated for the cases of nonlinear-optical crystals with zinc-blende symmetry (like ZnTe) and the crystals with one active component of the second-order optical susceptibility tensor (like PPLN). It is found that the ratio between spectral sensitivities of the pure probe-phase and pure probe-energy schemes is proportional to the ratio between the optical and terahertz wave frequencies in all types of the crystals. It is shown that the signal in the near-zero optical transmission point scheme, which is the best for terahertz imaging, has a mixed character. While the contribution of the probe-phase sensitivity appears to be due to spatially nonuniform residual birefringence of the nonlinear zinc-blende crystal, the probe-energy part of the sensitivity has a uniform distribution and can be increased by the angle misalignment of the optical polarization element.

Tandem Electrooptic Modulation and Interferometric Detection: Theory and Application

This paper expands upon the RF photonic theory of electrooptic phase and intensity modulation detection as seen when coupled in tandem with an asymmetric Mach-Zehnder interferometer through the derivation of power transfer functions for such optical-microwave configurations. An inspection of the theory is presented and validated through experimental results. Several applications of a modulation/interferometric architecture are also reviewed, delineating the importance of a valid model for predicting the behavior of similar analog optical systems.

Electro-optical detection of ZnO-Based unbalanced fabry-perot resonators

Zinc oxide films prepared by magnetron sputtering are introduced to the electro-optical detection to improve the voltage sensitivity. With the help of large piezoelectric effect, ZnO films make up for the deficiency of the low electro-optical coefficient. In this paper, we illustrated the mechanism of piezo-induced enhancements, and measured the electric signals on the line of coplanar waveguides. This method breaks through the limit of material species for optoelectronically responsive sensing, and shows promising applications in optical detection.

Continuous-wave terahertz field imaging based on photonics-based self-heterodyne electro-optic detection

We demonstrate a photonics-based self-heterodyne electro-optic field imaging technique at terahertz (THz) frequency. An optical intensity beat generated by mixing two frequency-detuned free-running lasers is used for both the generation and the detection. The frequency of the beat for detection is shifted by an optical frequency shifter to realize coherent heterodyne measurement with free-running lasers. Neither mechanical delay lines nor phase-locked synthesizers are required for the amplitude and the phase imaging of the THz field, and the system simplicity is thus improved. The amplitude and phase of the THz field (125GHz) radiated from a horn antenna are simultaneously imaged, and the standard deviation of the phase measurement is found to be 0.18rad.

Spectral Properties of THz Quantum-Cascade Lasers: Frequency Noise, Phase-Locking and Absolute Frequency Measurement

Quantum cascade lasers combine desirable features, namely high optical power and compactness, as no other coherent source in the field of THz generation. While their maximum operating temperature is progressively increasing, getting close to the range accessible by Peltier cooling, their range of application is expanding into new fields, such us molecular spectroscopy and their use as local oscillators. These applications would benefit from the investigation and improvement of the laser coherence properties. In this contribution we report the exploitation of electro-optic coherent detection based on a near-IR frequency comb to measure the frequency noise of a free running 2.5 THz quantum cascade laser. An intrinsic linewidth quantum limit of ~230 Hz has been measured, in good agreement with the Schawlow-Townes theoretical prediction. The same detection scheme is then exploited to phase-lock the quantum cascade laser line to a multiple of the comb tooth spacing, while a second comb allows to precisely measure the THz frequency. Such a dual frequency comb experimental setup thus yields a narrow line THz emission traceable to a microwave frequency standard.

Feasibility study of a single-shot 3D electron bunch shape monitor with an electro-optic sampling technique

We developed a three-dimensional electron bunch charge distribution (3D-BCD) monitor with single-shot detection, and a spectral decoding based electro-optic (EO) sampling technique for a nondestructive monitor enables real-time reconstruction of the three-dimensional distribution of a bunch charge. We realized three goals by simultaneously probing a number of Pockels EO crystals that surround the electron beam axis with hollow and radial polarized laser pulses. First, we performed a feasibility test as a simple case of a 3D-BCD monitor probing two ZnTe crystals as EO detectors installed on the opposite angle to the electron beam axis and confirmed that we simultaneously obtained both EO signals. Since the adopted hollow probe laser pulse is not only radially polarized but also temporally shifted azimuthally, some disorders in the radial polarization distribution of such a laser pulse were numerically analyzed with a plane-wave expansion method. Based on the above investigations, the 3D-BCD monitor is feasible both in experimental and numerical estimations. Furthermore, we previously developed a femtosecond response organic crystal as a Pockels EO detector and a broadband probe laser ($\ensuremath{\ge}350\text{ }\text{ }\mathrm{nm}$ in FWHM); the 3D-BCD monitor realizes 30- to 40-fs (FWHM) temporal resolution. Eventually, the monitor is expected to be equipped in such advanced accelerators as XFEL to measure and adjust the electron bunch charge distribution in real time. The 3D-BCD measurement works as a critical tool to provide feedback to seeded FELs.

Stabilization and mode locking of terahertz quantum cascade lasers

We present the stabilization of terahertz (THz) quantum cascade lasers (QCLs) to a harmonic of the repetition rate of femtosecond fiber lasers. The technique that we have developed is 1) inherently broadband, i.e., it allows the stabilization of virtually any THz QCL regardless its emission frequency, and 2) can be implemented using different detection techniques such as electrooptic or photoconductive detection. Using electrooptic detection, we demonstrate phase locking of a 2.5-THz QCL, producing an RF beatnote with 70 dB of dynamic range in a bandwidth of 100 Hz. In addition, we show how the broadband character of the phase-locking technique can be used to coherently sample the emission of a multimode THz QCL that is actively mode-locked by current modulation at the roundtrip frequency.

Magnetic particles–based biosensor for biogenic amines using an optical oxygen sensor as a transducer

We have developed a fibre optic biosensor with incorporated magnetic microparticles for the determination of biogenic amines. The enzyme diamine oxidase from Pisum sativum was immobilized either on chitosan-coated magnetic microparticles or on commercial microbeads modified with a ferrofluid. Both the immobilized enzyme and the ruthenium complex were incorporated into a UV-cured inorganic–organic polymer composite and deposited on a lens that was connected, by optical fibres, to an electro-optical detector. The enzyme catalyzes the oxidation of amines under consumption of oxygen. The latter was determined by measuring the quenched fluorescence lifetime of the ruthenium complex. The limits of detection for the biogenic amines putrescine and cadaverine are 25–30 μmol L−1, and responses are linear up to a concentration of 1 mmol L−1.

Electro-optical detection of THz radiation in Fe implanted LiNbO3

In this letter, the authors present first observation of terahertz generation from Fe implantation of LiNbO3 crystal substrate. LiNbO3 single crystal is grown by Czochralski method. Metal nanoparticles synthesized by Fe ion implantation were implanted into LiNbO3 single crystal using metal vapor vacuum arc (MEVVA) ion source. 1kHz, 35fs laser pulsed centered at 800nm were focused onto the samples. Terahertz was generated via optical rectification. The findings suggest that under the investigated implantation parameter, a spectral component in excess of 0.44THz emission were found from Fe ion implantation of LiNbO3.

Inverse Attitude Solution Model and Numerical Simulation of a 2-DOF Stabilized Platform

Considering the attitude stabilization requirements for an unmanned marine platform equipped with electro-optic detection equipment, a stabilized platform based on a 2-DOF parallel mechanism has been designed. The stabilized platform, especially for the requirements of small space and high load inertia, has such transmission branch chain with fixed ball-screw. The structure, DOF and kinematics of the platform has been analyzed, besides, the mathematical model of the platform's attitude inverse solution has been established. Numerical simulation for the derivate mathematical model and ADAMS simulation analysis has been done. In order to verify the correctness of the mathematical model, the motion process of the load-platform is described by a time function. The time function of the drive components calculated from the above two ways is used for the comparison of numerical simulation and ADAMS simulation. The results prove that the mathematical model established in this paper and ADAMS simulation results coincide.

Measurement of quasi-isentropic compressibility of helium and deuterium at pressures of 1500–2000 GPa

The quasi-isentropic compressibility of helium and deuterium plasmas at pressures of up to 1500–2000 GPa has been measured using devices with spherical geometry and an X-ray diagnostic complex comprising three betatrons and a multichannel imaging system with electro-optic gamma detectors. A deuterium density of 4.5 g/cm3 and a helium density of 3.8 g/cm3 have been obtained at pressures of 2210 and 1580 GPa, respectively. The internal energy of a deuterium plasma at the indicated pressure is about 1 MJ/cm3, which is about 100 times greater than the specific energy of condensed chemical explosives. Analysis of the obtained data shows that the degree of helium ionization under the achieved plasma compression parameters is about 0.9.

Universal phase relation between longitudinal and transverse fields observed in focused terahertz beams

We directly observe longitudinal electromagnetic fields in focused freely propagating terahertz (THz) beams of radial and linear polarization. Employing electro-optic detection, which is phase sensitive, allows one to selectively detect longitudinal and transverse field components. A phase shift of π/2 between the transverse and longitudinal field components is revealed. This phase shift is of universal nature, as it does not depend on the mode, frequency and focusing conditions. We show that the universal phase relation is a direct consequence of the divergence-free nature of electromagnetic waves in vacuum. In the experiments, we observe the phase shift of π/2 for all frequency components of single-cycle THz radiation pulses of both radial and linear polarization. Additionally, we show that the longitudinal field of a radially polarized THz beam has a smaller spot size as compared with the transverse field of a linearly polarized beam that is focused under the same conditions. For field-sensitive measurements this property can be exploited even for moderate focusing conditions. Furthermore, the phase-sensitive detection of longitudinal electromagnetic fields opens up new possibilities to study their interaction with electronic excitations in semiconductor nanostructures.

Electrically Induced Conformational Change of Peptides on Metallic Nanosurfaces

Surface immobilized biomolecular probes are used in many areas of biomedical research, such as genomics, proteomics, immunology, and pathology. Although the structural conformations of small DNA and peptide molecules in free solution are well studied both theoretically and experimentally, the conformation of small biomolecules bound on surfaces, especially under the influence of external electric fields, is poorly understood. Using a combination of molecular dynamics simulation and surface-enhanced Raman spectroscopy, we study the external electric field-induced conformational change of dodecapeptide probes tethered to a nanostructured metallic surface. Surface-tethered peptides with and without phosphorylated tyrosine residues are compared to show that peptide conformational change under electric field is sensitive to biochemical modification. Our study proposes a highly sensitive in vitro nanoscale electro-optical detection and manipulation method for biomolecule conformation and charge at bio-nano interfaces.

Low-temperature THz time domain waveguide spectrometer with butt-coupled emitter and detector crystal

A compact high-resolution THz time-domain waveguide spectrometer that is operated inside a cryostat is demonstrated. A THz photo-Dember emitter and a ZnTe electro-optic detection crystal are directly attached to a parallel copper-plate waveguide. This allows the THz beam to be excited and detected entirely inside the cryostat, obviating the need for THz-transparent windows or external THz mirrors. Since no external bias for the emitter is required, no electric feed-through into the cryostat is necessary. Using asynchronous optical sampling, high resolution THz spectra are obtained in the frequency range from 0.2 to 2.0 THz. The THz emission from the photo-Dember emitter and the absorption spectrum of 1,2-dicyanobenzene film are measured as a function of temperature. An absorption peak around 750 GHz of 1,2-dicyanobenzene displays a blue shift with increasing temperature.

Electro-optical measurement of sub-ps structures in low charge electron bunches

Electro-optical detection of THz coherent synchrotron radiation is a nondestructive method for measuring subpicosecond electron bunches or subpicosecond substructures on otherwise longer electron bunches. With a new diagnostic setup at the Swiss Light Source, which combines an amplified Yb fiber laser and a suitable GaP crystal, we demonstrate sampling as well as spectrally resolved single-shot measurements of sliced electron bunches containing as little as a few pC of charge. The single-shot measurements not only allow for a precise electric field characterization but also for a detailed analysis of the timing jitter between the electron bunch and the synchronized Yb fiber laser. The measurements of subsequent turns in the storage ring show distinct deviations from the simulations and we find strong indications that this discrepancy is caused by radiation loss through coherent synchrotron radiation itself, which is not included in many of today's simulation codes.

Extending electro-optic detection to ultrashort electron beams

We propose a technique to extend noninvasive electro-optic detection of relativistic electron beams to bunch lengths of $\ensuremath{\simeq}10\text{ }\text{ }\mathrm{fs}$. This is made possible by detecting the frequency mixing that occurs between the optical probe and the space charge fields of the beam, while simultaneously time resolving the resulting mixed frequency signal. The necessary formalism to describe this technique is developed and numerical solutions for various possible experimental conditions are made. These solutions are then compared to simulation results for consistency. Finally, the method to reconstruct the original bunch profile from the proposed diagnostic is discussed and an example showing a 15 fs test beam reconstructed to within an accuracy of 15% is given.

Nuclear reactor pulse tracing using a CdZnTe electro-optic radiation detector

CdZnTe has previously been shown to operate as an electro-optic radiation detector by utilizing the Pockels effect to measure steady-state nuclear reactor power levels. In the present work, the detector response to reactor power excursion experiments was investigated. Peak power levels during an excursion were predicted to be between 965MW and 1009MW using the Fuchs–Nordheim and Fuchs–Hansen models and confirmed with experimental data from the Kansas State University TRIGA Mark II nuclear reactor. The experimental arrangement of the Pockels cell detector includes collimated laser light passing through a transparent birefringent crystal, located between crossed polarizers, and focused upon a photodiode. The birefringent crystal, CdZnTe in this case, is placed in a neutron beam emanating from a nuclear reactor beam port. After obtaining the voltage-dependent Pockels characteristic response curve with a photodiode, neutron measurements were conducted from reactor pulses with the Pockels cell set at the 1/4 and 3/4 wave bias voltages. The detector responses to nuclear reactor pulses were recorded in real-time using data logging electronics, each showing a sharp increase in photodiode current for the 1/4 wave bias, and a sharp decrease in photodiode current for the 3/4 wave bias. The polarizers were readjusted to equal angles in which the maximum light transmission occurred at 0V bias, thereby, inverting the detector response to reactor pulses. A high sample rate oscilloscope was also used to more accurately measure the FWHM of the pulse from the electro-optic detector, 64ms, and is compared to the experimentally obtained FWHM of 16.0ms obtained with the 10B-lined counter.

Electro-optical detection based on large Kerr effect in polymer-stabilized liquid crystals

In this Letter, polymer-stabilized liquid crystals with experimentally observed large electro-optic effect are introduced to the electro-optical detection to improve the voltage sensitivity. The Kerr constant of materials prepared in this study reached as high as 7.2×10(-9) m/V(2), increasing by 1000 times the sensitivity of the conventional electro-optical materials. The noncontact detection configuration, using a laser beam as a probe, enables quick two-dimensional scanning measurements.

Study of broadband THz time-domain spectroscopy at different relative humidity levels

Two detection techniques of broadband terahertz (THz) time-domain spectroscopy-THz air-biased coherent detection (THz-ABCD; from 0.3 to 14 THz) and electro-optical (EO) detection (from 0.3 to 7 THz) - are both performed at several different relative humidity levels. The THz power exponentially decays with the increase in relative humidity. The dynamic range of the main pulse in the time domain linearly decreases as the relative humidity increases from 0% to 40%, and linear fittings show that the slopes are -0.017 and -0.019 for THz-ABCD and EO detection, respectively. Because of the multiple reflections caused by the crystal in the common EO detection, THz-ABCD has better spectral resolution (17 GHz) than that of EO detection (170 GHz). The spectrum of water vapor absorption measured by THz-ABCD is also compared with that measured by the Fourier transform infrared spectroscopy (FTIR).