Probe Transmission Spectrum Research Articles

On-Chip Photonic Transistor Device and Biomolecule Mass Sensor Based on a Whispering Gallery Mode Cavity Optomechanical System

Whispering gallery mode (WGM) cavities, due to their high-quality factors, small mode volumes, and simple fabrications, have potential applications in photonic devices and sensing. In this paper, we present an all-optical transistor based on a coupled realistic WGM cavity optomechanical system. In the system, the transmission of the signal field is manipulated by the optical control power, and the signal field can be efficiently attenuated or amplified depending on the power of a second gating (control) field, which indicates a promising candidate for single-photon transistors. In addition, we theoretically propose a mass sensor based on this WGM cavity optomechanical system. The mass of external biomolecules (such as smallpox virus) deposited onto WGM cavity can be measured conveniently by tracking the mechanical resonance frequency shifts due to mass changes in the probe transmission spectrum. Through detecting the mass of viruses, the kinds of different viruses can be identified. This WGM cavity optomechanical system may have potential chip scale applications in quantum information processing, quantum measurement, and on-chip sensing devices.

Phase-dependent optical response properties in an optomechanical system by coherently driving the mechanical resonator

We explore theoretically the optical response properties in an optomechanical system under electromagneti- cally induced transparency condition but with the mechanical resonator being driven by an additional coherent field. In this configuration, more complex quantum coherent and interference phenomena occur. In partic- ular, we find that the probe transmission spectra depend on the total phase of the applied fields. Our study also provides an efficient way to control propagation of amplification.

Controllable optical response in hybrid opto-electromechanical systems**Project supported by the National Natural Science Foundation of China (Grant Nos. 11304110 and 11174101), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20130413 and BK2011411), the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 13KJB140002).

We theoretically investigate the analog of electromagnetically induced absorption and parametric amplification in a hybrid opto-electromechanical system consisting of an optical cavity and a microwave cavity coupled to a common mechanical resonator. When the two cavity modes are driven by two pump fields, a weak probe beam is applied to the optical cavity to monitor the optical response of the hybrid system, which can be effectively controlled by adjusting the frequency and power of the two pump fields. We find that the analog of electromagnetically induced absorption and parametric amplification can appear in the probe transmission spectrum when one cavity is pumped on its red sideband and another is pumped on its blue sideband. These phenomena can find potential applications in optical switching and signal amplification in the quantum information process.

Electromagnetically induced transparency in a V-type multilevel system of Na vapor

We have theoretically and experimentally investigated the V-type three-level system in hot sodium atomic vapor interacting with two optical waves: probe, resonant to the D1 line, and coupling, the D2 line. Theoretically, probe transmission spectra are simulated by using a perturbative treatment including eight hyperfine levels (multilevel system) in the 3S1/2, 3P1/2, and 3P3/2 states. The spectra are composed of linear absorption, saturated absorption, and electromagnetically induced transparency (EIT) signals. By comparing this simulation with the experimental results, we concluded that we have indeed observed EIT signals when the coupling beam is resonant to the D2-line closed transition.

Ultrasensitive nanomechanical mass sensor using hybrid opto-electromechanical systems

Nanomechanical resonators provide an unparalleled mass sensitivity sufficient to detect single biomolecules, viruses and nanoparticles. In this work we propose a scheme for mass sensing based on the hybrid opto-electromechanical system, where a mechanical resonator is coupled to an optical cavity and a microwave cavity simultaneously. When the two cavities are driven by two pump fields with proper frequencies and powers, a weak probe field is used to scan across the optical cavity resonance frequency. The mass of a single baculovirus landing onto the surface of the mechanical resonator can be measured by tracking the resonance frequency shift in the probe transmission spectrum before and after the deposition. We also propose a nonlinear mass sensor based on the measurement of the four-wave mixing (FWM) spectrum, which can be used to weigh a single 20-nm-diameter gold nanoparticle with sub-femtogram resolution.

Amplification via electromagnetically induced transparency in the dressed atom basis

The probe transmission spectra of 87Rb in an operating magneto-optical trap are experimentally studied. New gain peak and new dispersion-like structure are observed.

The Inversionless Amplification in a Tripod System of 87Rb Atoms in a Magneto-optical Trap

The probe transmission spectra around the atomic transition 52S1/2, F = 2 → 52P3/2,F′ = 2 of 87Rb are measured in a magneto-optical trap by adding a coupling field around the atomic transition 52S1/2, F = 2 → 52P3/2,F′ = 2. The inversionless amplification is observed in the spectrum over the atomic transition 52S1/2, F = 2 → 52P3/2,F′ = 2. The tripod electromagnetically induced transparency is proposed to account for the amplification feature, in which population distributions among these related atomic levels play an important role.

Electromagnetically induced transparency and slow light in two-mode optomechanics

We theoretically demonstrate the mechanically mediated electromagnetically induced transparency in a two-mode cavity optomechanical system, where two cavity modes are coupled to a common mechanical resonator. When the two cavity modes are driven on their respective red sidebands by two pump beams, a transparency window appears in the probe transmission spectrum due to destructive interference. Under this situation the transmitted probe beam can be delayed as much as 4 μs, which can be easily controlled by the power of the pump beams.

Temperature and magnetic field effects on the coherent and saturating resonances in Λ- and V-type systems for the 85Rb-D2 transition

Variations of the coherent resonance, i.e. an electromagnetically induced transparency (EIT) peak with the cell temperature in Λ- and V-type systems are observed for the 85Rb-D2 transition. In a Λ-type system, the amplitude of the EIT peak gradually decreases and it is finally masked by the broadened optical pumping dips with the increase of the cell temperature. But for the V-type system, the EIT and the saturation peaks are greatly enhanced with the increase of the cell temperature. The effect of the external magnetic field on the EIT resonance is also investigated considering both types of systems. For the Λ-type system in place of a single EIT resonance, five transparency windows with broadened width and reduced contrast are obtained depending on the Zeeman levels formed by the applied magnetic field. In the V-type system, the coherent resonance peak could not be resolved in the presence of the external magnetic field, but a greater number of saturation peaks with broadened width appear in the probe transmission spectrum. A theoretical model is adopted to represent the experimental results. Good agreement is found between the experimental and numerically simulated results.

Strong magnetic coupling of an inhomogeneous nitrogen-vacancy ensemble to a cavity

We study experimentally and theoretically a dense ensemble of negatively charged nitrogen-vacancy centers in diamond coupled to a high-$Q$ superconducting coplanar waveguide cavity mode at low temperature. The nitrogen-vacancy centers are modeled as effective spin-one defects with inhomogeneous frequency distribution. For a large enough ensemble the effective magnetic coupling of the collective spin dominates the mode losses and inhomogeneous broadening of the ensemble and the system exhibits well-resolved normal-mode splitting in probe transmission spectra. We use several theoretical approaches to model the probe spectra and the number and frequency distribution of the spins. This analysis reveals an only slowly temperature-dependent $q$-Gaussian energy distribution of the defects with a yet unexplained decrease of effectively coupled spins at very low temperatures below $100\phantom{\rule{0.28em}{0ex}}\mathrm{m}\mathrm{K}$. Based on the system parameters we predict the possibility to implement an extremely stable maser by adding an external pump to the system.

Mass sensing based on a circuit cavity electromechanical system

We present a scheme for mass sensing based on a circuit cavity electromechanical system where a free-standing, flexible aluminium membrane is capacitively coupled to a superconducting microwave cavity. Integration with the microwave cavity enables capacitive readout of the mechanical resonance directly on the chip. A microwave pump field and a second probe field are simultaneously applied to the cavity. The accreted mass landing on the membrane can be measured conveniently by tracking the mechanical resonance frequency shifts due to mass changes in the probe transmission spectrum. The mass responsivity for the membrane is 0.72 Hz/ag and we demonstrate that frequency shifts induced by adsorption of one hundred 1587 bp DNA molecules can be well resolved in the probe transmission spectrum.

Coherent pump-probe spectroscopy in sodium vapor: From electromagnetically induced transparency to parametric amplification

We have theoretically and experimentally investigated coherent pump-probe spectra for the $3{S}_{1/2}$-$3{P}_{1/2}$ $D1$ transition of sodium atomic vapor. Probe transmission spectra in the presence of a coupling beam exhibit dramatic changes depending on experimental conditions. In the weak-excitation, low-atomic-density limit, the spectra are mainly characterized by electromagnetically induced transparency (EIT) and saturated absorption, but for the strong-excitation, high-density case, parametric amplification (PA) is dominant, featuring high probe gain and Stokes-wave generation. We have developed a theory that can explain these two seemingly totally different phenomena (EIT and PA) within the same theoretical framework by manipulating a few experimentally controllable parameters, and have successfully reproduced the observed spectra. Other than the main spectral features, many other interesting physical processes have been predicted and observed.

Dark Raman resonances due to Ramsey interference in vacuum vapor cells

We investigate the evolution of the atomic coherence between Zeeman sublevels with $\ensuremath{\Delta}{m}_{F}=2$ in the region between pump and probe laser beams, in a Rb vapor cell using the Hanle configuration. The transmission of the probe beam, placed inside the hollow pump beam, shows the narrowing of the Hanle resonance (at external magnetic field $B=0$) by Ramsey fringes whose separation from the central peak depends on the distance between the beams. The temporal evolution of the pump induced alignment is evident from the changes of the probe transmission spectra with increasing the angle between linear polarizations of each beam. Experimental results are in agreement with the results of the model which calculates probe fluorescence by solving time-dependent optical Bloch equations, from the time when atom enters the pump beam to the time when it leaves the probe beam. The results for total excited state populations were averaged over atomic velocities distribution.

Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling

The nonstationary pump-probe interaction between short laser pulses propagating in a resonant optically dense coherent medium is considered. Special attention is paid to the case where the density of two-level particles is high enough that a considerable part of the energy of relatively weak external laser fields can be coherently absorbed and reemitted by the medium. Thus, the field of the medium reaction plays a key role in the interaction processes, which leads to collective behavior of an atomic ensemble in the strongly coupled light-matter system. Such behavior results in fast excitation interchanges between the field and a medium in the form of optical ringing, which is analogous to polariton beating in solid-state optics. This collective oscillating response, which can be treated as successive beats between light wave packets of different group velocities, is shown to significantly affect the propagation and amplification of the probe field under its nonlinear interaction with a nearly copropagating pump pulse. Depending on the probe-pump time delay, the probe transmission spectra show the appearance of either a specific doublet or coherent dip. The widths of these features are determined by the density-dependent field-matter coupling coefficient and increase during the propagation. Besides that, the widths of the coherent features, which appear close to resonance in the broadband probe spectrum, exceed the absorption-line width, since under the strong-coupling regime, the frequency of optical ringing exceeds the rate of incoherent relaxation. Contrary to stationary strong-field effects, the density- and coordinate-dependent transmission spectra of the probe manifest the importance of collective oscillations and cannot be obtained in the framework of a single-atom model.

Effects of finite beam size and crossing angle on space–time–frequency-resolved pump–probe spectroscopy of optically transparent materials

A theoretical formulation that treats the correlated space–time–frequency characteristics of pump–probe transmission spectra in optically transparent media is presented. The influence of a spatial aperture on time–frequency-resolved pump–probe signals with a finite beam size and crossing angle is demonstrated for some typical optical crystals. The breakdown of the conventional plane-wave and collinear configuration approximations that neglect spatial dispersion of laser fields is highlighted via both theory and experiment. It is shown that the spatial correlation in the time–frequency-resolved pump–probe polarization is a basic feature of nonlinear optical spectroscopy of optically thick materials, as the light pulses are practically of finite spatial overlap with a crossing geometry. The possibility of utilizing appropriately arranged spatial apertures to measure the properties of nonlinear materials such as the nonlinear refractive index and the two-photon absorption cross section are addressed.

Resonant nonstationary amplification of polychromatic laser pulses and conical emission in an optically dense ensemble of neon metastable atoms

Experimental and numerical investigation of single-beam and pump-probe interaction with a resonantly absorbing dense extended medium under strong and weak field-matter coupling is presented. Significant probe beam amplification and conical emission were observed. Under relatively weak pumping and high medium density, when the condition of strong coupling between field and resonant matter is fulfilled, the probe amplification spectrum has a form of spectral doublet. Stronger pumping leads to the appearance of a single peak of the probe beam amplification at the transition frequency. The greater probe intensity results in an asymmetrical transmission spectrum with amplification at the blue wing of the absorption line and attenuation at the red one. Under high medium density, a broadband of amplification appears. The theoretical model is based on the solution of the Maxwell-Bloch equations for a two-level system. Different types of probe transmission spectra obtained are attributed to complex dynamics of a coherent medium response to broadband polychromatic radiation of a multimode dye laser.

Pump-probe spectroscopy of atoms cooled in a 3D lin lin optical lattice

We describe the pump-probe spectroscopy of atoms cooled in a 3D lin⊥lin optical lattice. Our pump-probe configuration consists of two laser fields detuned with respect to the lattice fields. This scheme allows to clearly identify in the probe transmission spectrum the Brillouin and Raman resonances, by studying their positions as functions of the angle between the pump and probe beams. We describe these resonances in detail, and compare the experimental results to the theoretical predictions. Our conclusions are supported by transport-spectroscopy measurements, which allow to distinguish between contributions to the light scattering from propagating and non-propagating atoms.

Dark propagation modes in optical lattices

We examine the stimulated light scattering onto the propagation modes of a dissipative optical lattice. We show that two different pump-probe configurations may lead to the excitation, via different mechanisms, of the same mode. We found that in one configuration the scattering on the propagation mode results in a resonance in the probe transmission spectrum while in the other configuration no modification of the scattering spectrum occurs, i.e. the mode is dark. A theoretical explanation of this behaviour is provided.

PUMP-PROBE SPECTROSCOPIC ANALYSIS OF FREE INDUCTION DECAY IN GaAs/AlxGa1-xAs QUANTUM WELL STRUCTURES

The theoretical formulation for pump-probe spectroscopic analysis of free induction decay has been made using semiclassical time dependent perturbation technique in GaAs/AlxGa1-xAs quantum well structure. The pump pulse is considered to be tuned below the band edge and the excitation intensity is assumed to be in the moderate power regime so that the only many-body effect that dominates is the excitonic effect. The probe transmission spectrum features the characteristic resonance frequencies of the system concerned. The temporal nature of the transmitted probe signal is also found to characterize the ultrafast free induction decay of the pump induced polarization, which is recorded by the low intensity probe transmission in the system.

Nonlinear spectroscopy in the strong-coupling regime of cavity QED

A nonlinear spectroscopic investigation of a strongly coupled atom-cavity system is presented. A two-field pump-probe experiment is employed to study nonlinear structure as the average number of intracavity atoms is varied from N≈4.2 to N≈0.8. Nonlinear effects are observed for as few as 0.1 intracavity pump photons. A detailed semiclassical simulation of the atomic beam experiment gives reasonable agreement with the data for N≳2 atoms. The simulation procedure accounts for fluctuations in atom-field coupling which have important effects on both the linear and nonlinear probe transmission spectra. A discrepancy between the simulations and the experiments is observed for small numbers of atoms (N≲1). Unfortunately, it is difficult to determine if this discrepancy is a definitive consequence of the quantum nature of the atom-cavity coupling or a result of the severe technical complications of the experiment.