532 nm法拉第光学滤波器传输特性

本文对工作在波长为532.33nm的激发态钾(K)原子法拉第光学滤波器进行了分析与讨论。结果表明这种工作在钾4P1／2←8S1／2跃迁谱线的滤波器的峰值透过率为50%,等效带宽为4GHz。同时滤波器的传输特性跟激光泵浦功率以及外加磁场强度并不是线性相关;所需激光泵浦功率的范围为0.8～6mW*cm－2。     

Narrowband switchable dual-passband atomic filter with four-wave mixing optical amplification

By using Faraday optical filter combined with four-wave mixing (FWM) amplifier, a narrow bandwidth optical amplifying atomic filter with switchable dual-passband is demonstrated experimentally. The two transmission peaks of the filter correspond to the Stokes and anti-Stokes frequencies, exhibiting a Raman gain in 13- and 17-fold, respectively, with bandwidth of ～120 MHz. By properly setting pump laser detuning, switching between filter passbands is realized. We also investigate the dependence of peak transmission on both pump laser intensity and Rb cell temperature. This atomic filter can find practical applications in long-distance laser communications and laser remote-sensing systems.     

Faraday laser at Rb 1529 nm transition for optical communication systems

We experimentally demonstrate a Faraday laser at Rb 1529 nm transition by using a performance-improved Rb electrodeless-discharge-lamp-based excited-state Faraday anomalous dispersion optical filter as the frequencyselective element. Neither the electrical locking scheme nor the additional frequency-stabilized pump laser are used. The frequency of the external-cavity diode laser is stabilized to the Rb 1529 nm transition, and the Allan deviation of the Faraday laser is measured by converting the optical intensity into frequency. The Faraday laser can be used as a frequency standard in the telecom C band for further research on metrology, microwave photonics, and optical communication systems.     

Transmission characteristics of an excited-state induced dispersion optical filter of rubidium at 775.9 nm

The operation of an ultra-narrow bandwidth optical filter based on the 5P3/2 → 5D3/2 excited-state transition in rubidium vapor is reported. The 5D3/2 state is excited by a circularly polarized pump beam at 780 nm from a diode laser. The filter displays a single 398-MHz bandwidth at a peak transmission of 9.0%, which is narrower than the Doppler bandwidth. The dependence of peak transmission on the pump intensity and cell temperature is also given.     

Theory and experiment for atomic optical filter based on optical anisotropy in rubidium

An atomic optical filter based on optical anisotropy induced by another left-circularly polarized pump field is theoretically and experimentally investigated in the 5S_1/2–5P_3/2–5D_3/2 ladder-type system of rubidium vapor. The filter displays a single peak transmission of 14.4% with 396 MHz bandwidth narrower than Doppler width. Furthermore, the variation of peak transmission versus pump intensity, pump detuning and cell temperature are also given. The theoretical and experimental results are in good agreement, which can enhance understanding of operation mechanism for this category of filter. The narrow-bandwidth filter is useful for free-space optical systems and laser spectroscopy.     

Analyses of transmission characteristics of Rb, Rb and Rb Faraday optical filters at 532 nm

In this paper, the transmission characteristics for Rb, ⁸⁵Rb and ⁸⁷Rb Faraday optical filters at 532 nm that can be used to detect the practical and important frequency-doubled Nd:YAG laser are analyzed and discussed. The theoretical model of an excited-state Faraday optical filter based on the hyperfine structures of atomic system in the intermediate field, what is to our knowledge, is firstly reported. This model predicts that the peak transmission is approximately 50% with an equivalent bandwidth of less than 3 GHz for filters operating on the 5P_1/2 → 10S_1/2 transition in Rb, ⁸⁵Rb and ⁸⁷Rb vapors, respectively. Moreover, the transmission property of ⁸⁷Rb atomic vapor is superior to that of Rb, ⁸⁵Rb atomic vapors, which makes it more suitable for the operation material of Faraday optical filters by comparison with natural Rb vapor.     

Sub-Doppler bandwidth atomic optical filter

We demonstrate what is to our knowledge the first atomic optical filter that uses velocity selection to achieve a passband width that is less than the Doppler width of the filtering transition. A narrow-linewidth pump laser is used to induce circular birefringence in a narrow velocity class of atoms in a dense potassium vapor for 694-nm light resonant with the 4P(3/2)-6S(1/2) transition. The filter displays a single 170-MHz passband at a peak transmittance of 9.5%. The bandwidth is an order of magnitude lower than that of previously demonstrated atomic optical filters.     

Temporal characteristics of narrow-band optical filters and their application in lidar systems

The temporal characteristics of two different narrow-band optical filters at 532 nm are reported. Both filters operate on the 4P(1/2) - 8S(1/2) atomic transition of potassium vapor, where the 4P(1/2) state is excited by a 770-nm, 10-ns laser pulse. The filters operate on the principle of circular birefringence induced by either the Faraday effect or two-photon transition, which is confirmed by experiments. The characteristic decay times of the filters are 5 and 0.015 mus, which is significant for the design of optical gating and signal processing with matched filters for ocean lidar.     

Frequency-locking of a CW dye laser to some absorption lines of a neon discharge by a Faraday filter

Single-mode oscillations of a CW dye laser at the center of five absorption lines from the 1s states to the 2p states of neon were obtained by means of a neon discharge Faraday filter, without any other frequency-selective elements. The most striking thing observed is that saturated absorption takes place at the center of several absorption lines in a Faraday filter, in addition to optical rotation.     

On an excited state Faraday anomalous dispersion optical filter at moderate pump powers for a Brillouin-lidar receiver system

We present our recent progress towards a practical implementation of a remote sensing measurement technique of oceanic temperature profiles. Our approach combines the advantages of fiber amplifiers with the high spectral resolution of Faraday anomalous dispersion optical filters. In this paper, we focus on the edge filter characteristics of an excited state Faraday anomalous dispersion optical filter at moderate pump powers as the receiver unit for the Brillouin-lidar.     

Self-rotation of optical polarization in rubidium vapor

We present an experimental and theoretical study of self-rotation of optical polarization in a rubidium vapor.The atomic vapor is placed in a magnetic shielding cavity to suppress the Faraday rotation effect.In our experiment,Doppler-free spectroscopy configuration is used,and F = 2 → F ’ = 3 transition of 87Rb D2 line is chosen.We observe self-rotation of optical polarization effect at different pump light ellipticities.A theoretical analysis is then provided based on the experimental conditions.Theoretical simulation and experimental results are in good agreement.     

Peculiarities of the inverse Faraday effect induced in iron garnet films by femtosecond laser pulses

The inverse Faraday effect in iron garnet films subjected to femtosecond laser pulses is experimentally investigated. It is found that the magnitude of the observed effect depends nonlinearly on the energy of the optical pump pulses, which is in contradiction with the notion that the inverse Faraday effect is linear with respect to the pump energy. Thus, for pump pulses with a central wavelength of 650 nm and an energy density of 1 mJ/cm², the deviation from a linear dependence is as large as 50%. Analysis of the experimental data demonstrates that the observed behavior is explained by the fact that the optically induced normal component of the magnetization is determined, apart from the field resulting from the inverse Faraday effect, by a decrease in the magnitude of the precessing magnetization under the influence of the femtosecond electromagnetic field.     

Demonstration of Faraday anomalous dispersion optical filter with reflection configuration

A narrow linewidth Faraday anomalous dispersion optical filter(FADOF)with reflection configuration is achieved for the first time based on the cesium(Cs)ground state 6S_1/2 to the excited state 6P_3/2 transition at 852 nm.Compared with the conventional FADOF with transmission configuration,reflection-type FADOF can greatly improve the transmittance of optical filter under the same experimental parameters,because it allows signal light to go and return through the atomic vapor cell.In our experiment,peak transmittance at Cs 6S_1/2 F=4-6P_3/2 transition is 81%for the reflection-type FADOF,and while 54%for the transmission-type FADOF when the temperature of Cs vapor cell and the axial magnetic field are 60℃and 19 G.The idea of this reflection-type FADOF design has the potential to be applied to the FADOF operating between two excited states to obtain higher transmittance.     

Off-resonance laser frequency stabilization using the Faraday effect

We present a simple technique for stabilization of a laser frequency off resonance using the Faraday effect in a heated vapor cell with an applied magnetic field. In particular, we demonstrate stabilization of a 780 nm laser detuned up to 14 GHz from the (85)Rb D(2) 5(2)S(1/2) F = 2 to 5(2)P(3/2) F' = 3 transition. Control of the temperature of the vapor cell and the magnitude of the applied magnetic field allows locking ~6-14 GHz red and blue detuned from the atomic line. We obtain an rms fluctuation of 7 MHz over 1 h without stabilization of the cell temperature or magnetic field.     

基于光偏振旋转效应的碱金属气室原子极化率测量方法及影响因素分析

利用原子自旋效应能够实现超高灵敏度的惯性和磁场测量。一类操控原子自旋处于无自旋交换弛豫态的器件可以进行物理参数测量。碱金属气室为该类器件的敏感表头。碱金属原子密度与原子极化率是碱金属气室的重要参数,对研究原子自旋处于无自旋交换弛豫态有着重要的作用。光的偏振效应在量子计算和原子物理研究中发挥了重要作用。利用光的偏振效应能够实现对碱金属原子密度与原子极化率的检测。提出一种基于光偏振旋转效应的碱金属原子极化率测量方法。首先对碱金属气室加恒定磁场,利用激光作为检测光,根据光偏振旋转原理,检测通过气室的偏振光的法拉第旋转角,得到碱金属气室原子密度。然后将碱金属原子抽运,利用激光作为检测光,检测通过气室的偏振光的偏转角,得到碱金属原子极化率。该方法在测量原子极化率的过程中也测量了碱金属原子密度,实现利用一套系统测量两个重要参数,具有快速测量和高灵敏度等特点,简化了实验设备及过程。对两种偏转角进行仿真分析,得到该方法实验时检测激光波长变化对偏转角的影响,根据仿真图得到检测激光波长的可取范围,验证了该方法的可行性。最后分析激光器波长波动与磁场波动对其测量精度的影响,提出实验对激光器与磁场的要求。     

Cs Faraday anomalous dispersion optical filter for blue pulsed laser

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On an ESFADOF edge-filter for a range resolved Brillouin-lidar: The high vapor density and high pump intensity regime

The temperature profile in the upper ocean mixed layer is of great interest for oceanography, weather forecast and climate studies—especially regarding the strong coupling between the atmosphere and the ocean. A lidar system based on Brillouin-scattering can provide such data over an extended region of the ocean. In this paper we report on studies of an excited-state Faraday anomalous dispersion optical (ESFADOF) edge-filter that, when employed as a receiver in a Brillouin-lidar, will enable range-resolved remote measurements from mobile platforms. We focus on the transmission of such a filter operating on the 5P _3/2→8D _5/2 Rb transition (543.30 nm), and its dependence on the vapor density in the high pump intensity regime. Due to quenching processes such as energy-pooling enhanced by nonlinear radiation trapping, as well as plasma formation, a limit on the lower ESFADOF level number density exists. Beyond this threshold the achievable ESFADOF transmission is limited to a few percent. However, our studies show for the first time measured ESFADOF spectra with steep transmission edges with a transmission change of 15% within a few gigahertz.     

Theoretical Investigation of Potassium Faraday Dispersion Optical Filter at 766 nm

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Optical limitation in resonant Faraday media

Optical limitation in resonant Faraday media sandwiched between crossed polarizers is analyzed both theoretically and experimentally. In this technique resonant Faraday rotation permits a net transmission at low intensity levels, whereas the setup transmission is quenched at higher intensities when the active transition is completely saturated. This technique offers many advantages, such as a very low fluence threshold (~12 nJ/cm(2) in cesium vapor), a high intensity range (more than 4 orders of magnitude for polarizer losses of 10(-5)), and quasi invulnerability to optical damage, which make this technique attractive for the protection of fixed-wavelength operated detectors.     

Theoretical Investigation of Potassium Faraday Dispersion Optical Filter at 766 nm

A potassium Faraday dispersion optical filter (FDOF) is theoretically studied for the 4P3/2←4S1/2 transition including hyperfine effects. The optimum filter operating condition is also obtained. The single peak bandwidth of the optical filter is about 0.86 GHz and equivalent noise band width is 2.4 GHz. The transmission is approximately 94.1% percent under the optimum condition.