Cavity linewidth narrowing by means of electromagnetically induced transparency in Rb with a longitudinal magnetic field

We demonstrate a method for further reducing the cavity linewidth by the application of a small longitudinal magnetic field on the Rb cell. Because of the magnetic field multiple electromagnetically induced transparen- cies （EITs） are observed. The center EIT linewidth is measured as a function of the magnetic field. By utilizing the center EIT we narrow the cavity linewidth to 2 MHz which is half of the cavity linewidth without magnetic field.     

实验不可分辨的Voigt线型重叠谱线的压致展宽线宽的偏差确定

通过仿真和拟合Voigt线型重叠谱线,讨论了将实验上不可分辨的两条谱线重叠后视为单条谱线时所得到的压致展宽线宽与其实际值的相对误差ε,分析了该误差与两谱线的中心位置距离δν₀和实际的压致展宽线宽δν0_Ｌ的变化规律。发现ε在谱线的压致展宽线宽远小于多普勒线宽δν_Ｄ时显得很大,与δν₀和δν0_Ｌ的变化规律较复杂;当δν0_Ｌ可与δν_Ｄ比拟时,ε随δν₀的变化趋于呈光滑的二次项函数曲线,但曲线的斜率在δν0_Ｌ小于δν_Ｄ情况下为负,而在δν0_Ｌ大于δν_Ｄ时为正。整体来说,随着δν0_Ｌ对总线宽的影响越大,ε越小。所有这些结论和相应关系数据为修正压致展宽线宽的拟合值具有积极的参考价值,并且为进一步从实验上不可分辨的重叠谱线确定精确的压致展宽系数提出了极有意义的方法和思路。     

Calculation of the cyclotron resonance linewidth in GaAsAlGaAs heterostructures

The influence of various scattering center distributions on the Landau level width and the cyclotron resonance linewidth is calculated for GaAsAlGaAs heterostructures in high magnetic fields. The filling factor dependent dielectric screening of long range potentials leads to an oscillating behavior of the linewidth. Good agreement with recent cyclotron resonance linewidth measurements is obtained.     

Linewidth and relative intensity noise measurements of longitudinal modes in ultrahigh-speed mode-locked laser diodes

The longitudinal linewidth and corresponding relative intensity noise (RIN) of 10- and 40-GHz mode-locked laser diodes are measured for the first time to our knowledge. It is shown that the cavity Q value is a dominant parameter of the linewidth. It is also shown that the linewidth of the individual modes is almost constant. This means that the phase noise of each mode is almost the same in the mode-locked condition. The RIN value is larger for modes that are distant from the center longitudinal mode. This mode dependence is a consequence of the mode partition noise.     

Coupling of nitrogen-vacancy centers to photonic crystal cavities in monocrystalline diamond

The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ～70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques. Photon correlation measurements on the spectrally filtered zero-phonon line show antibunching, a signature that the collected photoluminescence is emitted primarily by a single nitrogen-vacancy center. The linewidth of the coupled nitrogen-vacancy center and the spectral diffusion are characterized using high-resolution photoluminescence and photoluminescence excitation spectroscopy.     

线宽增强因子对外光注入半导体激光器非线性单周期振荡特性的影响

线宽增强因子是影响半导体激光器输出特性的一个重要参量,不同材料不同结构类型的半导体激光器的线宽增强因子有较大的差异.利用光注入半导体激光器的单模速率方程模型,数值研究了线宽增强因子对外光注入半导体激光器的非线性单周期振荡特性的影响.结果表明:外光注入半导体激光器的动态特性对线宽增强因子的变化极为敏感,随着线宽增强因子的增加,在负失谐注入范围内单周期振荡区域显著增大,同时注入锁定的稳态输出被大大抑制.分析了线宽增强因子对非线性单周期振荡光谱特性和振荡频率的影响,结果表明:随着半导体激光器线宽增强因子的增大,单周期振荡的频率越大|当线宽增强因子不变时,单周期振荡的频率随注入光强度和频率失谐的增加而增加.     

Sub-watt threshold, kilohertz-linewidth Raman distributed-feedback fiber laser

We report a low-threshold, narrow linewidth Raman distributed-feedback (R-DFB) fiber laser at 1109.54 nm based on a 30 cm long center π phase-shifted Bragg grating written directly in a commercially available germano-silica (Ge/Si) fiber. The R-DFB was pumped by a continuous-wave (CW) linearly polarized fiber source at 1064 nm, and the threshold power, full width at half-maximum (FWHM) linewidth and slope efficiency with respect to the incident pump power are measured to be 440 mW, <2.5 kHz (measured with a 29.75 km fiber delay line) and 13.5%, respectively. An rf spectrum analyzer confirms that the R-DFB fiber laser exhibits single-frequency performance.     

半导体泵浦铷蒸气激光器出光实验

针对中心波长780 nm的商用连续波半导体激光器,使用斩波器将连续激光变为脉冲输出形式,用2400 line/mm的平面全息光栅搭建Littrow外腔将线宽压窄至0.2 nm以下。采用透镜组对线宽压窄后的半导体激光进行光束整形,半导体激光经线宽压窄和光束整形后,经透镜聚焦进长约8 mm的铷蒸气泡进行半导体泵浦碱金属激光实验。首次出光得到17.5 mW的基模线偏振铷激光;在最新的改进实验中,半导体泵浦铷激光输出功率已达到2.8 W。     

考虑光镊效应的飞秒激光双光子加工线宽

采用自由基浓度起伏理论结合光镊集聚效应,理论研究了飞秒激光双光子加工的线宽问题。根据双光子光聚合过程中自由基浓度随时间变化的关系,考虑光镊效应对自由基分布范围的影响,得到了飞秒激光双光子加工线宽的表达式。研究了线宽随扫描速度与激光功率的变化关系,并讨论了不同光引发剂对线宽的影响。得到了以自由基浓度起伏为基础,并考虑光镊效应的双光子加工线宽表达式,该结果与实验结果相符。研究结果为飞秒激光双光子加工的研究提供了新的思路,为光镊集聚效应对线宽影响的实验研究提供了理论依据。     

High resolution emission spectra of laser-excited molecular iodine as the excitation frequency is tuned through and away from resonance

We have studied the ΔJ = 2 rotationally shifted emission lines in the region of the strong absorption of molecular iodine which occurs within the 5145 Å argon ion laser line. We used an etalon tuned, single frequency argon ion laser with a linewidth of 20 MHz to excite the iodine emission and recorded the spectra of the rotational lines with Fabry-Perot spectrometers having resolutions up to 70 MHz (0.0023 cm^-1). To overcome Doppler linewidth limitations we took spectra of the emission at small angles to the exciting beam and found the lines to have widths less than our instrumental resolution and frequencies which accurately tuned with the incident laser frequency. We recorded the emission lines for laser frequencies in the absorption line center and out into the absorption wing. Our spectra show that the intensity of the emission lines follows the absorption line profile while the frequency of the emission lines is determined by the laser frequency; the intensity is maximum at the absorption line center, falling by 10⁴ as the laser frequency is moved off the line center, while the line position maintains a constant frequency shift from the laser frequency.     

To narrow laser linewidth by utilizing dispersion characteristics of Gires-Tournois etalon

A longer laser resonator length is benefit for laser linewidth, but harmful for single-frequency operation. A novel way is suggested to narrow the bandwidth of a Fabry-Perot （FP） cavity through increasing the derivative of one round-trip phase shift with respect to the frequency. It can be implemented by replacing one of two FP mirrors with a Gires-Tournois etalon （GTE）, called FPCT, as a dispersion element. FPGT resonator has additional axial modes due to the GTE reflection phase shift. Theoretical analyses show that the bandwidth of additional axial modes can be 1% of that of a conventional FP cavity. A distributed feedback （DFB） laser diode can employ FPGT resonator to achieve ultra-narrow linewidth laser. It is shown that the effect of refractivity fluctuation in the gain medium on the linewidth is little, and kilohertz linewidth is achievable for such a device.     

Noise-induced linewidth in frequency combs

Frequency combs generated by trains of pulses emitted from mode-locked lasers are analyzed when the center time and phase of the pulses undergo noise-induced random walk, which broadens the comb lines. Asymptotic analysis and computation reveal that, when the standard deviation of the center-time jitter of the nth pulse scales as n(p/2) where p is a jitter exponent, the linewidth of the kth comb line scales as k(2/p). The linear-dispersionless (p=1) and pure-soliton (p=3) dynamics in lasers are derived as special cases of this time-frequency duality relation. In addition, the linewidth induced by phase jitter decreases with power P(out), as (P(out))(-1/p).     

29.2 W, 20 kHz linewidth all fiber single-frequency MOPA laser

We demonstrate a high power all fiber single-frequency MOPA laser. The center wavelength of the single-frequency fiber laser seed is 1064 nm with a linewidth narrower than 20 kHz. A two-stage power amplification configuration is employed. A single-frequency fiber laser with an output power of 29.2 W is obtained, and the optical to optical efficiency is 78%.     

耦合场线宽：抑制电磁诱导吸收

原子相干对吸收的相长干涉导致电磁诱导吸收，这是一类新的相干效应. 以三个电偶极跃迁构成N型链，中间跃迁作为探测跃迁的四能级系统为例，揭示耦合场线宽抑制电磁诱导吸收的强度. 这并非与电磁诱导透明系统中耦合场线宽产生或者增强吸收的情形相矛盾，线宽仍然是抑制系统的相干性. 关键词： 电磁诱导吸收 耦合场线宽 原子相干 退相干     

Temperature dependence of the broad A1 (TO) phonon Raman linewidth in BaTiO3

The temperature dependence of the A₁ (TO) broad phonon linewidth is discussed. It is shown that it can adequately be accounted for by assuming a simple model where the Ti ions are sitting off the center of the unit cell and tunneling through a double well in the direction of the ferroelectric axis.     

Narrow linewidth CW amplification of a Tm-doped double-clad fiber MOPA system

A Tm-doped double-clad fiber MOPA system is built. Amplification characteristics of a Tm-doped double-clad narrow linewidth fiber master oscillator (MO) are investigated both experimentally and numerically. Linewidth of the fiber MO is only 112 pm at 3 W output. The output and efficiency of the MOPA system increase with the injected seed power. When the seed power is increased to 2 W, a maximum output of 10.5 W is obtained with a slope efficiency of 41.5%. Spectral center of the output lies at 1996.7 nm with the linewidth no bigger than 120 pm throughout the experiment.     

Delay self-heterodyne measurement of narrow linewidth laser frequency drift characteristic

Resonator integrated optic gyro (RIOG), which employs narrow linewidth laser, is a high-accuracy inertial rotation sensor based on the Sagnac effect. The performance of RIOG is greatly affected by the frequency drift of narrow linewidth laser. A simple, effective method to measure the relative frequency drift of narrow linewidth laser based on delayed self-heterodyne technique is proposed in this paper. The measurement range and sensitivity can easily be satisfied by setting the length difference of the fiber segments between two interferometer arms. The relationship between the length difference and the frequency drift is derived based on the given principle of measuring the relative frequency drift. Then the laser frequency drift measuring setup is established and the experiment results demonstrate that a center frequency drift rate is less than 2 MHz/6.7 s under the room-temperature. Moreover, the measuring setup is applied to test the modulation coefficient of piezoelectric-transducer (PZT), and the modulation coefficient of 9.62 MHz/V is obtained, which satisfies the requirements of RIOG closed-loop operation.     

Combined effect of light intensity and temperature on the magnetic resonance linewidth in alkali vapor cell with buffer gas

One of the peculiar phenomenons in non-zero magnetic resonance magnetometer is that, with the increase of the temperature, the magnetic resonance linewidth is narrowed at first instead of broadened due to the increasing collision rate. The magnetometer usually operates at the narrowest linewidth temperature to obtain the best sensitivity. Here, we explain this phenomenon quantitatively considering the nonlinear of the optical pumping in the cell and did experiments to verify this explanation. The magnetic resonance linewidth is measured using one amplitude-modulated pump laser and one continuous probe laser. The field is along the direction orthogonal to the plane of pump and probe beams. We change the temperature from 53℃ to 93℃ and the pumping light from 0.1 mW to 2 mW. The experimental results agree well with the theoretical calculations.     

Color center laser and electron impact excitation: Doppler-free spectroscopy in excited helium states

A cw single mode color center laser was used to study infrared transitions between n = 4 and n = 6 states in helium by Doppler-free intermodulated fluorescence spectroscopy. Excited helium atoms are produced by bombarding ground-state helium atoms with low energy electrons. With pulsed excitation and gated detection, the resolution approaches the natural linewidth.     

Control and active stabilization of the linewidth of an ECDL

The linewidth of a polarization-locked external cavity diode laser (ECDL) is explored employing heterodyne as well as self-heterodyne measurements. We use a model capable of providing the individual contributions of white, pink and red noise to the overall linewidth to analyze the measured beat spectra. These spectra are obtained while tuning the external cavity as well as a function of pump current and feedback level. By virtue of our locking technique, we find that the linewidth can be adjusted and minimized by simply altering the setpoint of the closed-loop control. This control of the linewidth is applicable for any ECDL using polarization locking. For our particular ECDL, we are able to tune the overall linewidth from ??8?kHz to 20?kHz. Moreover, we achieve a lower white noise level of the ECDL compared to a free running one.