Negative dispersion mirrors in Ta2O5/: SiO2 for femtosecond Ti : Sapphire lasers by using gires-tournois interferometers

We design and experimentally demonstrate some negative dispersion mirrors with optimized Gires-Tournois interferometers. The mirror structure is composed of 38 alternating Ta2O5 and SiO2 layers and could be regarded as two sections: high-reflectivity section consisting of a series of quarter-wavelength optical thickness stacks and negative-dispersion section consisting of only 13 layers. The designed mirrors exhibit the expected performance. These mirrors were fabricated by using ion beam sputtering. By adopting such mirrors, dispersion of a mode-locked femtosecond Ti:sapphire laser has been compensated for mostly. With two series of the mirrors, 32 fs and 15 fs pulses have been obtained respectively.

飞秒脉冲激光器中色散补偿膜的设计

阐述了用光学薄膜进行色散补偿的基本原理，介绍了设计的基本过程．根据Ti：Sapphire飞秒激光器中腔内色散补偿的要求，设定了色散补偿目标，通过计算机优化，得到了一种40层的Ta2O5／SiO2介质膜系．该膜系能在720～870am范围获得大于99．5％的反射率，在510～550nm获得大于90％的透射率，在740～850nm提供较平滑的-40fs^2的群延迟色散．这样的结果经过7次反射后，可以补偿5-mm Ti：sapphire晶体产生的绝大部分群延迟色散。

钛宝石激光器中用优化Gires-Tournois镜产生15fs脉冲

根据飞秒脉冲锁模钛宝石激光器脉冲压缩的要求，介绍了负色散镜补偿色散的基本原理及其特点。详细阐述了优化Gires-Tournois(OG-T)镜的设计过程，并通过计算机优化得到理想设计膜系。采用离子束溅射的方法镀制了优化Gires—Tournois镜。测量了优化Gires-Tournois镜(编号为OGT#1)的透射率和群延迟色散，并与设计值进行了比较，分析了实测值产生偏差的原因，从而对镀膜参量进行了相应的调整，制造了第二批优化Gires—Tournois镜(编号为OGT#2)。将优化Gires—Tourn

Dispersion-compensating photonic crystal fibers with special characteristics

Based on the modified dual core structure, three kinds of special photonic crystal fibers are presented, which are extremely large negative dispersion, super-broad bond, and large area made field dispersion-compensating photonic crystal fibers (DCPCF). For extremely large negative dispersion DCPCF, the peak of negative dispersion reaches -5.9 x 10(4) ps/(mn km). Super-broad bond DCPCF has broadband large negative dispersion and the dispersion value varies linearly from -380 ps/(nm km) to -420 ps/(nm km) in the C band. The designed large area made field DCPCF has a peak dispersion of -1203 ps/(nm km) with the inner core mode area of 47 mu m(2) and outer core mode area of 835 mu m(2). Furthermore, for the large area mode field DCPCF, the experimental result is also obtained. (C) 2008 Wiley Periodicals, Inc.

Study of a four-level system in vee plus ladder configuration

We present the results of a theoretical study of a four-level atomic system in vee + ladder configuration using a density matrix analysis. The absorption and dispersion profiles are derived for a weak probe field and for varying strengths of the two strong control fields. For specificity, we choose energy levels of Rb-87, and present results for both stationary atoms and moving atoms in room temperature vapor. An electromagnetically induced absorption (EIA) peak with negative dispersion is observed at zero probe de-tuning when the control fields have equal strengths, which switches to electromagnetically induced transparency (ET) with positive dispersion (due to splitting of the EIA peak) when the control fields are unequal. There is significant linewidth narrowing in thermal vapor. (C) 2015 Elsevier B.V. All rights reserved.

基于多台阶反射光栅的飞秒脉冲压缩装置

反射式光栅对是一种具有负色散性质的器件,可用于飞秒激光脉冲的压缩和展宽,具有无材料色散的优点。给出了一种基于多台阶反射光栅的脉冲压缩装置。该装置为倍密度光栅结构,由两个周期分别为40μm和20μm的四台阶反射式光栅组成。实验得到的衍射效率可以达到70%以上,输入脉冲经过两个光栅的衍射后会按原路返回,从而达到色散补偿的效果。利用此压缩装置,脉冲宽度为66.8 fs的输入脉冲压缩至接近傅里叶变换极限脉冲,即46.6 fs,由此证明只要多台阶光栅效率足够高,此装置就有可能成为不同于棱镜对进行飞秒脉冲腔内和腔外压缩的另一种途径。

负色散镜的设计、制备及在掺钛蓝宝石激光谐振腔内的使用

根据钛宝石激光器的要求设计了性能优良的两种负色散镜（NDM1和NDM2）。NDM1同时引入啁啾效应和GT效应产生大的群延迟色散量以减少光在负色散镜上的反射次数。NDM2仅引入GT效应产生较小的群延迟色散以补偿腔内自相位调制带来的部分啁啾。选用离子束溅射法制备了这两种负色散镜。用分光光度计测试了它们的透射率。结果表明，所制备的负色散镜的性能与设计性能非常接近。使用这两种负色散镜进行掺钛蓝宝石激光谐振腔内色散补偿实现了飞秒脉冲锁模，获得了15fs的超短脉冲。

Experimental study of mode field evolution of dual-core photonic crystal fiber

The accurate mode field profile of high negative dispersion dual-core photonic crystal fiber (DCPCF) is measured. The mode field evolution of DCPCF with wavelength is studied experimentally for the first time. The measurement result shows that no individual inner core mode or outer core mode exists, but two modes coexist simultaneously, and either one of them is dominant. The mode field evolution versus wavelength indicates that the wavelength range where the modes coupling takes place between inner core and outer core is broader than that of theoretical design.

地磁场的长期变化

In this paper, we studied the secular variations of the main geomagnetic field during 1900-2000 in details. Emphasis is put on three aspects of the secular variations, i.e. westward drifts and intensity variations of non-dipole part, the decay of the dipole field. Firstly, we introduced the method of correlation analysis of moving random pattern into Geomagnetism in order to overcome the weakness of available methods on westward drift studies. We had committed testing and modifying the method, and analyzed the westward drifts and intensity variations of the non-dipole parts of geomagnetic field and 6 planetary-scale geomagnetic anomalies by this way. The globe and area characters of the westward drifts and intensity variations were discussed in detail. Second, the lat-dependence and dispersion of drift velocities were examined carefully. The results showed the velocities of the different wavelengths (from m = 1 to m = 10) geomagnetic potential were changing with the latitude. The lat-dependence of drift velocities is related to the latitude distributing of the geomagnetic potential. There was a negative dispersion in the westward drift, namely, the components of long wavelength drift faster than that of short wavelengths. Finally, we calculated the moments of the geomagnetic dipole, and found that the intensity of the dipole fields has been decreasing. Linking to the results in paleomagnetism, we draw a conclusion that the geomagnetic polarities may be reversed in 700 years.

Solitons and their resonances on two-dimensional superfluid films

The dynamics of saturated two-dimensional superfluid4He films is shown to be governed by the Kadomtsev-Petviashvili equation with negative dispersion. It is established that the phenomena of soliton resonance could be observed in such films. Under the lowest order nonlinearity, such resonance would happen only if two dimensional effects are taken into account. The amplitude and velocity of the resonant soliton are obtained.

Environmentally stable high-power soliton fiber lasers that use chirped fiber Bragg gratings

Environmentally stable high-power erbium fiber soliton lasers are constructed by Kerr or carrier-type mode locking. We obtain high-energy pulses by using relatively short fiber lengths and providing large amounts of negative dispersion with chirped fiber Bragg gratings. The pulse energies and widths generated with both types of soliton laser are found to scale with the square root of the cavity dispersion. Kerr mode locking requires pulses with an approximately three times higher nonlinear phase shift in the cavity than carrier mode locking, which leads to the generation of slightly shorter pulses with as much as seven times higher pulse energies at the mode-locking threshold.