Efficiency of frequency-pulsed excitation of a micron-sized spherical microcavity by chirped ultrashort laser radiation

Peculiarities of internal optical field resonant excitation inside micron-sized spherical transparent dielectric cavity illuminated by a train of ultrashort laser pulses are investigated. On an example of water microdroplet is shown that optimal tuning of incident radiation to a selected high-Q resonance electromagnetic cavity mode can be realized by varying temporal interpulse interval in a laser train together with linear frequency modulation of every pulse (chirp). Efficiency of resonant particle excitation by a chirped picosecond pulses train can be considerably increased as compared to unchirped pulse train and CW excitation also.     

The efficiency of parallel quantum memory for light in a cavity configuration

We present a new scheme of quantum memory for optical images (spatially multimode light fields) that allows mapping the quantum state of the signal onto the long-lived coherence of the ground state of an ensemble of stationary atoms or impurity centers. The memory medium is embedded in an optical cavity with degenerate transverse modes, which increases the effective optical thickness of the medium and allows one, in principle, to store information in optically thin atomic layers. Since, in reality, storage and retrieval of limited-duration signals, including signals shorter than the lifetime of the field in the cavity, is of interest, we do not use the low-Q cavity approximation. The influence of losses due to partial reflection of the nonstationary signal field incident on a coupling mirror on the storage efficiency is considered. We used the method of approximate impedance matching, wherein losses due to reflection can be minimized by controlling the coupling parameter of the light field with memory medium in time, thus creating conditions for destructive interference of the signal and local fields on the coupling mirror. The influence of diffraction on the transverse resolution of memory at the writing and readout stages is investigated, and the number of effectively stored transverse spatial modes of the signal is estimated.     

Quantum dynamics of a mechanical resonator driven by a cavity

We explore the quantum dynamics of a mechanical resonator whose position is coupled to the frequency of an optical (or microwave) cavity mode. When the cavity is driven at a frequency above resonance the mechanical resonator can gain energy and for sufficiently strong coupling this results in limit-cycle oscillations. Using a truncated Wigner function approach, which captures the zero-point fluctuations in the system, we develop an approximate analytic treatment of the resonator dynamics in the limit-cycle regime. We find that the limit-cycle oscillations produced by the cavity are associated with rather low levels of energy fluctuations in the resonator. Compared to a resonator at the same temperature which is driven by a pure harmonic drive to a given average energy, the cavity-driven oscillations can have much lower energy fluctuations. Furthermore, at sufficiently low temperatures, the cavity can drive the resonator into a non-classical state which is number-squeezed.     

强耦合腔-QED系统中原子的纳秒脉冲激发光谱研究

本文在多原子强耦合腔-QED系统中,利用脉冲宽度为5 ns的强脉冲光在垂直于腔轴方向直接激发原子,脉冲的峰值功率为40 mW,通过光学腔观测激发原子辐射到腔中的光子获得相应的激发光谱。我们发现当光场频率和原子跃迁失谐±80 MHz时原子激发率达到最大,而在共振时原子激发被抑制。我们建立了脉冲光与三能级原子相互作用的模型,通过缀饰态能够解释此现象。     

Pigtailing the high-Q microsphere cavity: a simple fiber coupler for optical whispering-gallery modes

We demonstrate a simple method for efficient coupling of standard single-mode optical fibers to a high- Q optical microsphere cavity. Phase-matched excitation of whispering-gallery modes is provided by an angle-polished fiber tip in which the core-guided wave undergoes total internal reflection. In the experimental setup, which included a microsphere with both an input and an output coupler, the total fiber-to-fiber transmission at resonance reached 23% (total insertion loss, 6.3 dB), with loaded quality factor Q>/=3x10(7) and unloaded Q approximately 1.2x10(8) at 1550 nm. A simple pigtailing method for microspheres permits their wider use in fiber optics and photonics devices.     

Spin coherence during optical excitation of a single nitrogen-vacancy center in diamond

We examine the quantum spin state of a single nitrogen-vacancy (NV) center in diamond at room temperature as it makes a transition from the orbital ground state (GS) to the orbital excited state (ES) during nonresonant optical excitation. While the fluorescence readout of NV-center spins relies on conservation of the longitudinal spin projection during optical excitation, the question of quantum phase preservation has not been examined. Using Ramsey measurements and quantum process tomography of the optical excitation process, we measure a trace fidelity of F=0.87±0.03, which includes ES spin dephasing during measurement. Extrapolation to the moment of optical excitation yields F≈0.95. This result provides insight into the interaction between spin coherence and nonresonant optical absorption through a vibronic sideband.     

Variation in the magnetic structure of a single-domain particle ensemble and its response to an rf pulse

A set of equations in the Gilbert form that describes the motion of the magnetization vector in an ensemble of interacting magnetic nanoparticles is numerically solved for the case of high-amplitude rf pulses. Based on the numerical solution, the magnetic structure of spherical particle ensembles showing cubic anisotropy at certain parameters of the variable field is studied. This phenomenon is shown to have a threshold. The dependence of the field threshold amplitude on the acting pulse repetition rate and amount of magnetic interaction is determined. It is demonstrated that a change in the magnetic structure of the interacting particle ensembles causes a change in the spectrum of the response. This fact can be used for pulsed rf writing and readout of information based on ferromagnetic resonance.     

Time response of a coupled atoms-cavity system

We study the time response of a quantum optical system to a step excitation. The system is composed of a collection of N two-level atoms coupled to a single mode of the electromagnetic field of an optical cavity. The size of the step excitation is not limited to the low-intensity regime. Before the system reaches steady state there is an oscillatory exchange of energy between the atoms and the cavity. We compare the experimental results quantitatively with theoretical calculations and with previous transmission spectroscopy measurements.     

Hologram recording and reading in discrete resonance ring cavity

Holograms are recorded and restored in a resonant ring cavity. The experimental data shows enhanced diffraction efficiencies off the holograms. To maintain the optical resonance of the cavity during writing or reading the hologram we propose discrete resonance ring cavity system. The experimental data is compared with those of the conventional system with no cavity resonance.     

Nuclear spins of ionized phosphorus donors in silicon

We demonstrate the coherent control and electrical readout of ionized phosphorus donor nuclear spins in (nat)Si. By combining time-programed optical excitation with coherent electron spin manipulation, we selectively ionize the donors depending on their nuclear spin state, exploiting a spin-dependent recombination process at the Si/SiO(2) interface, and find a nuclear spin coherence time of 18 ms for the ionized donors. The presented technique allows for spectroscopy of ionized-donor nuclear spins and enhances the sensitivity of electron nuclear double resonance to a level of 3000 nuclear spins.     

LiF∶F2晶体中实现三维光数据存储的实验研究

基于LiF∶F2晶体在近红外飞秒脉冲激光作用下产生F2色心向F+3色心的转变,以及两种色心荧光光谱的不同,实现了荧光反射共焦读出和多光子写入的三维光数据存储的原理性实验.钛宝石再生放大器输出的脉冲宽度100 fs、中心波长800 nm、重复频率1 kHz的超短脉冲激光束,用数值孔径0.68的显微物镜聚焦到LiF：F2晶体内部,通过移动晶体实现了三维逐位式数据写入；用405 nm的连续蓝光激发存储位,通过探测F+3色心产生的540 nm荧光,实现了对信息位进行快速非破坏性的反射共焦读出.与多光子三维存储的透射共焦散射读出和相衬读出相比,格式与现存光盘技术兼容,结构简单；更重要的是,存储信息位是依靠荧光光谱的变化,折射率变化很小,可以有效增加读出层数.     

Optomechanical entanglement between a movable mirror and a cavity field

We show how stationary entanglement between an optical cavity field mode and a macroscopic vibrating mirror can be generated by means of radiation pressure. We also show how the generated optomechanical entanglement can be quantified, and we suggest an experimental readout scheme to fully characterize the entangled state. Surprisingly, such optomechanical entanglement is shown to persist for environment temperatures above 20 K using state-of-the-art experimental parameters.     

Generation of a self-chirped few-cycle optical pulse in a FEL oscillator

We study the generation of a self-chirped optical pulse in a free-electron laser (FEL) oscillator. In a high-gain FEL oscillator, the frequency chirp is induced in the slippage region as a result of superradiant FEL resonance, and this time-frequency correlation evolves continuously into a few-cycle regime, if the optical cavity length is perfectly synchronized to the electron bunch interval. Numerical simulations based on the slowly evolving wave approximation and experimental results are presented.     

Incoherent and coherent writing and erasure of cavity solitons in an optically pumped semiconductor amplifier

Cavity solitons in semiconductor amplifiers were, from the beginning of their study and observation, obtained either spontaneously or in a controlled manner by local coherent excitation. We describe two experiments that demonstrate coherent and, we believe for the first time, incoherent writing and erasure of cavity solitons in an optically pumped vertical-cavity semiconductor amplifier by short optical pulses.     

Normal mode splitting and ground state cooling in a Fabry-Perot optical cavity and transmission line resonator

Optomechanical dynamics in two systems which are a transmission line resonator and Fabrya-Perot optical cavity via radiation-pressure are investigated by linearized quantum Langevin equation. We work in the resolved sideband regime where the oscillator resonance frequency exceeds the cavity linewidth. Normal mode splittings of the mechanical resonator as a pure result of the coupling interaction in the two optomechanical systems is studied, and we make a comparison of normal mode splitting of mechanical resonator between the two systems. In the optical cavity, the normal mode splitting of the movable mirror approaches the latest experiment very well. In addition, an approximation scheme is introduced to demonstrate the ground state cooling, and we make a comparison of cooling between the two systems dominated by two key factors, which are the initial bath temperature and the mechanical quality factor. Since both the normal mode splitting and cooling require working in the resolved sideband regime, whether the normal mode splitting influences the cooling of the mirror is considered. Considering the size of the mechanical resonator and precooling the system, the mechanical resonator in the transmission line resonator system is easier to achieve the ground state cooling than in optical cavity.     

Sub-wavelength probing and modification of photonic crystal nano-cavities

In this work we present a sizeable and reversible spectral tuning of the resonances of a two-dimensional photonic crystal nano-cavity by exploiting the introduction of a sub-wavelength size glass tip. The comparison between experimental near-field data and results of numerical calculations shows that the spectral shift induced by the tip is proportional to the local electric field intensity of the cavity mode. This observation proves that the electromagnetic local density of states in a microcavity can be directly measured by mapping the tip-induced spectral shift with a scanning near-field optical microscope. Moreover, a non-linear control on the cavity resonance is obtained by exploiting the local heating induced by near-field laser excitation at different excitation powers. The temperature gradient due to the optical absorption results in an index of refraction gradient which modifies the dielectric surroundings of the cavity and shifts the optical modes.     

Effect of the optical excitation signal intensity on the impulse response of a metal-semiconductor-metal photodiode

The effect of the optical excitation signal intensity on the impulse response of a photodetector based on a set of metal-semiconductor-metal (MSM) rectifier contacts is studied. The response of the detector is better at a low optical excitation signal. When the energy of an optical excitation pulse is high, the response can be improved by increasing the bias voltage. The advantages of a GaN-based MSM diode in detecting high- energy radiation pulses are established. It is shown that the speed of the GaN-based MSM detector may reach 25 ps for a 60-pJ optical excitation pulse at a wavelength of 290 nm.     

High-resolution cavity-tuned ringdown spectrometer using a narrow-bandwidth pulsed laser source

A novel method of cavity ringdown spectroscopy is proposed to achieve high spectral resolution with tunable narrow bandwidth pulsed lasers. We demonstrate a cavity-tuned ringdown configuration in which only a single cavity mode is kept excited near the carrier frequency of a narrow bandwidth pulse laser. This is done simply by making a cavity resonance actively track the frequency reference served by the cw injection seed of the pulsed laser source. We present the servo mechanism used in the cavity resonance tracking, reliable procedures for transverse mode matching, and the evidence of single longitudinal mode excitation. The spectrometer performance is tested to record weak molecular overtone features of acetylene around the wavelength of 570 nm, showing cavity tracking stability within 5-MHz uncertainty which overcomes the bandwidth limit of pulsed laser sources itself. PACS 42.62.Fi; 42.60.Da; 33.20.Kf     

Diffractive responses to optical wave-train excitations in nanotube-doped nematics

Diffractive properties of temporary holographic gratings were studied in cells of the homogeneously aligned nematic E7 doped with a trace of carbon nanotubes. These phase gratings were induced by interference modulation of the pulsed wave-train excitation of two coherent writing beams, in conjunction with an externally applied dc voltage. The effects of the optical excitation on the diffraction efficiencies and the decay time constants were observed to be strongly dependent on the pulse width of the writing beams. PACS 42.40.Lx; 42.70.Df; 42.70.Ln; 81.05.Tp     

Manipulating atomic coherence and interference in a coupled atom-cavity system

Collective coupling of multiple atoms with a cavity mode produces two normal modes that are separated in energy by Vacuum Rabi splitting. We show that quantum coherence and interference can be produced by a control laser that couples the atoms confined in the cavity mode from free space, which leads to suppression of the normal mode excitation, or polariton excitation of the cavity-atom system. The control laser splits the normal mode of the cavity-atoms system and opens two excitation channels. The destructive quantum interference between the two channels renders the cavity-atoms system opaque to the light coupled into the cavity mode. We demonstrate suppression of the normal mode (polariton) excitation by the destructive quantum interference in an experiment with cold Rb atoms confined in an optical cavity.