Atom detection and photon production in a scalable, open, optical microcavity

A microfabricated Fabry-Perot optical resonator has been used for atom detection and photon production with less than 1 atom on average in the cavity mode. Our cavity design combines the intrinsic scalability of microfabrication processes with direct coupling of the cavity field to single-mode optical waveguides or fibers. The presence of the atom is seen through changes in both the intensity and the noise characteristics of probe light reflected from the cavity input mirror. An excitation laser passing transversely through the cavity triggers photon emission into the cavity mode and hence into the single-mode fiber. These are first steps toward building an optical microcavity network on an atom chip for applications in quantum information processing.     

具有脉冲增益调制自由电子激光器的光场混沌

用唯象理论模型讨论了储存环型自由电子激光振荡器的光场混沌问题.通过理论分析和数值模拟发现:当激光共振腔内的增益调制由周期振荡型变为周期脉冲型时,随着调制参数的改变,光场强度随时间的变化仍然要经过一个由倍周期分叉进入混沌状态的过程。相应的最大Lyapunov特征指数证明了光场混沌的存在。进一步研究表明:周期脉冲型增益调制比周期振荡型增益调制更接近于实际情况,因为它给出的光场时间结构与实验测得的结果更接近.     

Efficient noise suppression of an amplified diode-laser by optical filtering and resonant optical feedback

We present the noise suppression of an amplified diode laser by using an optical filter and resonant optical feedback. The intensity noise of the amplified diode laser has been significantly decreased by using the optical filter cavity. It was further suppressed and reached the shot noise limit at 15 MHz by introducing resonant optical feedback from the transmission of the filter cavity. The filter cavity transmits 53% of injection power, and the output power of the filter cavity is more than 200 mW. The observed frequency fluctuations were less than 100 kHz in one minute. This level of noise suppression and output power may allow diode lasers to be utilized in many quantum-optics experiments. PACS 42.55-f; 42.55-Px; 42.50.-p     

Asymmetric Fabry-Pérot interferometric cavity for fiber optical sensors

Good linearity and wide dynamic range are the advantages of asymmetric Fabry-Pérot (F-P) interferometric cavity, whose realization has been long for. Based on optical thin film characteristic matrix theory, an asymmetric F-P interferometric cavity with good linearity and wide dynamic range is designed. And by choosing the material of two different thin metallic layers, the asymmetric F-P interferometric cavity is successfully fabricated. The design theory and method of this asymmetric F-P interferometric cavity have been described in detailed. In this paper an asymmetric F-P interferometric cavity used in fiber optical sensor is reported.     

Optical gain by simultaneous photon and phonon confinement in indirect bandgap semiconductor acousto-optical cavities

Optical gain that could ultimately lead to light emission from silicon is a goal that has been pursued for a long time by the scientific community. The reason is that a silicon laser would allow for the development of low-cost, high-volume monolithic photonic integrated circuits created using conventional CMOS technologies. However, the silicon indirect bandgap—requiring the participation of a proper phonon in the process of light emission—is a roadblock that has not been overcome so far. A high-Q optical cavity allowing a very high density of states at the desired frequencies has been proposed as a possible way to get optical gain. However, recent theoretical studies have shown that the free-carrier absorption is much higher than the optical gain at ambient temperature in an indirect bandgap semiconductor, even if a high-Q optical cavity is formed. In this work, we consider a particular case in which the semiconductor material is engineered to form an acousto-optical cavity where the photon and phonon modes involved in the emission process are simultaneously confined. The acousto-optical cavity confinement effect on the light emission properties is characterized by a compound Purcell factor which includes both the optical as well as the acoustic Purcell factor (APF). A theoretical expression for the APF is also introduced. Our theoretical results suggest that creating an acousto-optical cavity the optical gain can overcome the photon loss due to free carriers as a consequence of the localization of phonons even at room temperature, paving the way towards the pursued silicon laser.     

Laser beam patterns of an optical cavity formed by two twisted cylindrical mirrors

Propagation of an elliptical Gaussian beam in a multiple-pass optical cell formed by two twisted cylindrical mirrors has been described by means of complex curvature tensors. Using the ABCD tensor approach various light patterns were computed for the use in tunable laser absorption spectroscopy with a multiple-pass optical cell. Light patterns with high beam-spot density can be also defined for a cavity formed by two twisted cylindrical high-reflectivity mirrors. In order to achieve higher cavity output intensity, a high-reflectivity cylindrical mirror cavity with at least one mirror that has a central transparent spot for laser beam injection has been described for applications in non-resonant cavity enhanced absorption spectroscopy. The author was with TDL Sensors Ltd., when the experimental part of this work was performed.     

Generation of stable and tunable optical frequency linked to a radio frequency by use of a high finesse cavity and its application in absorption spectroscopy

The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques. A stable and tunable optical frequency at wavelength of 1.5 μm obtained by a cavity with high finesse of 96000 and a fiber laser has been demonstrated, calibrated by a commercial optical frequency comb. The locking performances have been analyzed by in-loop and out-loop noises, indicating that the absolute frequency instability could be down to 50 kHz over 1 s and keep to less than 110 kHz over 2.5 h. Then, the application of this stabilized laser to the direct absorption spectroscopy has been performed. With the help of balanced detection, the detection sensitivity, in terms of optical density, can reach to 9.4×10^-6.     

CONCEPTUAL DESIGN OF BESSEL BEAM CAVITY FOR FREE-ELECTRON LASER

The conventional cavity for a free-electron laser (FEL) oscillator usually forms an optical beam of Gaussian mode, which undergoes transverse spread along the interaction region. The transverse divergence of an optical beam will induce reduction of the FEL gain from three aspects: degenerating filling factor, causing diffraction loss and limiting the effective interaction distance. Bessel optical beam has been experimentally demonstrated diffraction-free characteristics in its propagation, which provides a possibility of improvement of FEL gain. In this paper, we present a conceptual design of a Bessel beam cavity for the free-electron laser oscillator. This cavity generates nondiffracting optical beam in the wiggler, resulting in improving the filling factor, decreasing the diffraction loss and elongating the effective interaction distance.     

Study of dispersion and absorption of an ensemble of spherical particles inside an optical cavity and new possibilities of predicting the optical characteristics of biological media by intracavity laser spectroscopy

Optical characteristics, namely, dispersion and absorption spectra of an ensemble of spherical particles randomly oriented inside an optical cavity are investigated. The study is based on the self-consistent matching of new data from the inhomogeneous optical cavity with data from the scattering of an ensemble of spherical particles of different size, randomly oriented in free space. As a result, a new model, which self-consistently accounts for multiple scattering in the optical cavity, has been developed to predict absorption and dispersion of ensembles of spherical particles. This model is supposed to enhance potentiality of the intracavity method for plotting wavelength dependences of optical characteristics of media. A specific calculation of dispersion and absorption dependences on the wavelength shows that this method can be used for investigation of biological media consisting of spherical particles, in particular, erythrocyte suspension.     

Measurement of the comb dynamics for feedback control of an etalon-based coupled optoelectronic oscillator

The response of an optical frequency comb from an etalon-based coupled optoelectronic oscillator to changes in drive current, optoelectronic loop phase, modulator bias, and laser cavity length has been measured. It is found that controlling the phase of the optoelectronic loop is best suited for control of the pulse repetition rate, whereas controlling the laser cavity length is best for stabilization of the optical carrier frequency. Moreover, by measuring the instabilities of the carrier frequency at the fixed-point frequency of the optoelectronic phase, changes to the optoelectronic phase can be decoupled from changes to the laser cavity.     

Spectrum control and shaping of optical pulses in optical fibre interferometers

This paper discusses the use of single-mode fibre ring interferometers for injection laser line narrowing and for enhancement of optical emission power. The efficient launching into fibre ring interferometers of multi-frequency external cavity injection laser emission, in both the c.w. and mode-locking regime, has been achieved. Matching the optical lengths of the external cavity and fibre interferometer allowed the measurement of mode width of such a laser. A method is proposed for shaping optical pulses in fibre ring interferometers from constant intensity frequency modulated emission. The mode-locking regime of all-fibre external cavity injection lasers has been achieved.     

Sustained saturation in a free-electron laser oscillator at perfect synchronism of an optical cavity.

The first observation of sustained saturation in a free-electron laser (FEL) oscillator at perfect synchronism of an optical cavity is presented. A simultaneous measurement of FEL power and absolute detuning length of the optical cavity ( deltaL) has clearly shown that the FEL efficiency becomes maximum at deltaL = 0.0+/-1 microm, although it has been considered that only a transient state exists at deltaL = 0 due to the well-known laser lethargy effect. The observed efficiency detuning curve is well reproduced by our numerical simulation including a small shot-noise effect.     

用阈值表达式研究长外腔半导体激光器的双稳特征

利用外腔半导体激光器（ＥＣＬＤ）在不同频率振荡所需的阈值载流子密度的表达式及相关的折射率表达式他它的双稳特性,由此导出了在外腔半导体激光器的ｐ－ｖ（功率－频率）曲线上出现双稳的条件以及双稳环宽度的解析表达式。     

Phase-sensitive reflection of squeezed vacuum field in optical cavity

We experimentally investigate the optical cavity for various coupled regimes with an injected squeezed vacuum state. We measure the quantum fluctuation spectra of the reflected field of an optical cavity using the homodyne detection and present the spectral dependence on the absorption and dispersion properties of the cavity in the under-coupled, critically-coupled, and over-coupled regimes. The spectra lineshape is phase sensitive with the phase shift induced by the cavity. Moreover, we find that the over-coupled optical cavity has obvious advantage in the manipulation of quantum fluctuation.     

CO2的腔增强吸收与高灵敏吸收光谱研究

腔增强吸收光谱(CEAS)是在衰荡吸收光谱的基础上发展起来的一种新型的直接吸收光谱技术.文章报道了用中心输出波长为1.573μm的窄线宽连续可调谐半导体激光器(DFB封装)作光源,用两块高反射率平凹透镜(在1.573μm附近,凹面反射率R～99.4%,曲率半径r～1 m)组成对称共焦腔作吸收池的腔增强吸收光谱系统.采用扫描腔长的方法改变谐振腔的模式,当激光器的输出频率与谐振腔的某一腔模之间满足共振匹配关系时,激光被耦合到谐振腔内,用探测器接收透过谐振腔的光信号,同时用波长计精确测量激光器的输出波长.在33.5 cm长的吸收池内测量了吸收强度为1.816×10-23cm-1·(molecule·cm-2)-1的二氧化碳分子的弱吸收谱线,探测灵敏度达到了6.78×10-7 cm-1.实验结果表明,腔增强吸收光谱具有灵敏度高,装置简单,易于操作等优点.     

Stimulated Raman Scattering at Induced Acoustic Vibrations of Elastic Particles in Suspensions Placed in an Optical Cavity

The stimulated low-frequency Raman scattering at acoustic vibrations of elastic inclusions in a liquid heterogeneous medium placed in an external open optical cavity has been investigated. The amplitudes of stationary field oscillations in the cavity at the frequencies of the excitation and the first Stokes component are found within a two-dimensional model. The specific features of the oscillation in dependence of the parameters of the cavity and Raman-active medium have been studied based on the simulation results.     

Dynamical properties of DIT based all-optical switch

In this work, we investigate dynamical properties of a DIT based all-optical switch for different cases of multilevel quantum dot added into photonic crystal optical cavity. Dynamic operation of optical switch is calculated and investigated by solving the Heisenberg motion equation for atom-like transition operators of inserted quantum dot into the cavity. As an example a dynemic equation has been calculated for 3, 4 and 5-levels nanocrystals are studied numerically. Transmitted optical field is studied for a train of step pulses as the control field to obtain switching behavior. Finally optical transient behavior of the proposed optical switch is evaluated and optimized to operate fast.     

Observation of absorptive optical bistability in a fabry-perot cavity containing multiple atomic beams

Using an arrangement of highly collimated sodium atomic beams in a Fabry-Perot cavity absorptive optical bistability has been observed. The response of the optically bistable system was investigated on a time scale of the order of 100 times the characteristic time of the cavity. Even so a non steady state behaviour of the system was observed. Good qualitative agreement with the two-level atom mean field radiation theory has been obtained.     

Cavity waveguide-output laser

We propose for the first time a laser configuration which couples the cavity standing wave field directly with an optical fibre or optical fibre taper using its polished face as an output coupling mirror. A method for direct, active and paraxial launching of laser emission into an optical fibre, adaptable for various laser active media, has been achieved on this basis. Some of the important parameters of this laser are expressed in analytical form. Experimental verification of the proposed idea has been conducted on the basis of a dye laser. Excellent intensity distribution has been obtained beyond the optical fibre output. Launching efficiency exceeding 80% has been predicted and measured experimentally.     

A laser cavity used as an etalon for interferometric control of its own field

A quantitative relationship between the cavity parameters and the angular structure of the emission scattered in a parallel-plane active cavity filled with an arbitrary set of optical elements has been determined. The multipath interference into the active cavity is demonstrated to have properties which differ radically from similar processes in the etalon—among other things the relatively low finesse of the cavity interference rings is independent of the mirror quality and is a function of the Fresnel number only. The use of the operating laser cavity as an etalon for precise control of its own mode wave parameters is discussed.