Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Experimental research on ultra-low noise fiber interferometer stabilized laser
No full text本学位论文的内容是围绕作者在攻读博士学位期间的两项主要工作。包括超低噪声光纤干涉仪稳频激光的实验研究以及利用超稳激光和光纤干涉仪对光纤本征热噪声进行测量。 光钟是目前精度最高的时间频率标准，而超稳激光作为光钟的本地振荡器，其性能水平直接影响光钟的精度水平。虽然是应光钟的诞生而诞生，但是超稳激光也是许多领域的重要工具。超稳激光可通过光学频率梳产生超低噪声的微波信号,可用来探测引力波，精密验证相对论,进行精密光谱测量。传统超稳激光技术是利用PDH(Pound-Drever-Hall)方法将激光锁定到超稳高精细度的法布里-玻罗（Fabry-Perot）腔上，该方法要求需要光路和腔的空间模式精确匹配，高真空，甚至低温恒温，光学结构复杂，系统昂贵，体积巨大,不容易对激光器的频率进行调节。为了解决这些问题，一个很有前景的方案就是将激光锁定到光纤干涉仪上，相对于高精细度稳腔超稳激光有系统简单，稳定，价格便宜，体积小，容易对频率进行调谐等诸多优势。本实验搭建了两套光纤干涉仪稳频激光系统，并且对其性能通过拍频的方法进行了评估,测量了包括拍频线宽、频率稳定度和频率噪声。测量结果是拍频线宽小于0.67Hz，短期（0.1-1s）频率稳定度小于7E-15 ，频率噪声在1Hz频偏处小于0.8 Hz2/Hz （-1 dB Hz2/Hz），从200Hz到1KHz，达到0.016 Hz2/Hz （-18 dB Hz2/Hz）。性能主要受限于光纤的本征热噪声。 目前，存在两种不同类型的理论来解释光纤本征热噪声，一个是由K.H.Wanser提出的来自于光纤内部热传导的温度弛豫而产生的噪声，在高频区域，能够与实验数据符合的非常好。另外一个Duan Lingze提出，源自于布朗运动的内部摩擦而产生的光纤长度的自发起伏，可以解释光纤本征热噪声的的低频区域特性，但是缺少实验数据的支撑。有许多基于光纤的系统，比如光纤干涉仪式传感器、光纤激光器以及光纤延迟线稳频激光器，其本征分辨率或频率稳定度受限于光纤本征热噪声，因此，对光纤本征热噪声进行理论和实验探究具有十分重要的意义。本论文开展了光纤本征热噪声的测量工作。将测量扩展至次声波段，这对于人们认识次声波段的光纤热噪声特性提供了第一个实验数据；在次声波段，发现光纤热噪声仍然符合1/f的噪声特性；验证了光纤热噪声跟光纤长度的正比光纤；确定了光纤热噪声跟载波光功率无关；发现利用聚酰亚胺涂层的光纤，可降低光纤低频区域的热噪声；实验中并没有观察到现有的热机械噪声模型所预测的共振峰，这预示着该模型可能修改或者加以完善。The content of this thesis mainly include two topics that the author gets involved in his Ph.D works. One topic is experimental research on ultra-low fiber interferometer stabilized laser, and the other is the measurement of fundamental thermal noise of the fiber, using ultra-stable laser and fiber interferometer. Currently, the most precise or accurate frequency standards are optical clocks. The precision or accuracy is directly determinated by the ultra-stable lasers, which act as local oscillators of optical clocks. They are also important tools for many other applications, such as generation of ultralow phase noise microwave signals, upgrade of fountain clock, optical communication network. Moreover, they play key roles in modern precision measurement, such as gravitational wave detection, precision testing of the theory of relativity. Currently, the lowest noise lasers are realized by stabilizing laser frequency onto an ultra-stable high-finesse Fabry–Perot cavity with the Pound–Drever–Hall (PDH) method. However, this approach requires stable and precise alignment of free-space optical elements, the system is bulky, fragile, and expensive, and they are not easy to tune the frequency. A radical alternative is to use an optical fiber delay line as a frequency reference to stabilize laser frequency. By comparing two identical laser systems, a 0.67 Hz (0.25Hz RBW, resolution bandwidth ) line-width beat note signal is achieved, and we obtain the fractional frequency instability of 7E-15 at short timescales (0.1-1 s). The frequency noise power spectral density (PSD) of two identical lasers is below -1 dB Hz2/Hz at 1 Hz and it reaches -18 dB Hz2/Hz from 200 Hz to 1 kHz. The frequency noise was limited by the fundamental thermal noise of the optical fiber. There are two type of theory models which interpreting the fundamental thermal noise , Wanser’s theory and Duan’s theory, the noise comes from spontaneous fluctuations of the local temperatures , according to Wanser’s theory, and it proved to be consistent with the measurement data at high frequencies, while Duan’s theory can explain thermal noise of the fiber at low frequencies ,but there is no experimental proof. The noise comes from the internal friction of the fiber. In many fiber-based systems, such as interferometric fiber-optic sensors, fiber lasers, and fiber-delay-line stabilized lasers, the fundamental resolution or frequency stability is limited by the intrinsic thermal noise inside optical fibers. Thus, it is important to have both an experimental and theoretical understanding of the thermal noise in optical fibers. We expanded the measurement to the range of infrasonic frequencies, and found the 1/f noise spectrum characteristic in the infrasonic frequencies, we provided the evidence that the fundamental thermal noise was proportional to the fiber length, and there has no relations between the thermal noise and the power of light source. When measuring the thermal noise of the polyimide (PI) coating fiber , we found that the thermal noise is lower than the SMF-28 of the same length in the low frequencies, which indicate a possible way reduce the thermal noise in optical fiber at low Fourier frequencies. The resonance peaks of the thermomechanical noise predicted by Duan have not been observed in the experiment, this inconsistence between the experimental and the model proposed by Duan indicates, perhaps, a new physical mechanism need to be further investigated
Controllable Collisions and Dynamics in Ultracold Alkali-Alkaline-Earth(-like) Mixtures
No full text利用外场调节超冷原子气体中的相互作用是目前被广泛采用的制备超冷分子的方法。以此为出发点，本论文重点研究碱金属-（类）碱土金属体系中可操控的冷碰撞散射问题，分两方面展开：一是双原子分子能级结构的理论分析工作，这是研究碰撞问题及分子态间转移动力学的基础；另一个是对碱金属-（类）碱土金属体系中的Feshbach 共振机制进行分析，进而探索制备冷分子的可能性。 首先，以RbSr 分子为例，我们详细讨论了碱金属-（类）碱土金属分子中的相互作用势能形式及振动态、转动态能级结构。通过相对论框架下的从头计算方法得到的势能曲线，我们计算了一系列振动态跃迁的Franck-Condon 系数，并据此选取合适的中间态来证明实现将分子转移到绝对基态的受激拉曼绝热转移通道的可行性，模拟的由弱束缚态分子到绝对基态的单边转移效率可达77%。 在计算相互作用势能的基础上，我们对碱金属原子与（类）碱土金属原子在外磁场下碰撞过程中的Feshbach 共振机制进行了探索。通过对基态碱金属-亚稳态（类）碱土金属体系的理论分析，我们发现确实存在由各向异性的相互作用势能诱发的宽的Feshbach共振。各向异性耦合主要来源于不同分波通道间的耦合以及不同精细结构能级通道的耦合，且这两者均与亚稳态（类）碱土金属原子的轨道角动量自由度相关。然而，这些较宽的共振也伴随着很大的非弹性碰撞损失率（在10?10 cm3s?1 量级），即磁场下亚稳态原子会弛豫到能级较低的精细结构能级或塞曼子能级上，这将极大地限制利用Feshbach共振在该体系中实现分子的制备，特别是将分子转移到基态将是一个特别复杂且难以精确操控的过程。 最后简要介绍了RbYb 光缔合实验中的两个设计工作，即能同时减速两种原子的塞曼减速器和磁光阱磁场线圈的制作与测量。 总之，本文围绕利用外场下的原子碰撞实现分子制备这一主题，系统地对碱金属-（类）碱土金属这一实验上极具挑战的分子体系进行了分析，包括计算相互作用势能形式的从头计算方法，到对分子振动态转移过程的模拟，以及对利用Feshbach 共振来制备该体系分子的可能性探索，这些结论对未来该体系的理论及实验研究均具有重要的启发和指导意义。Tuning the interatomic interactions with external fields is currently the most widely used method to create ultracold molecule. For this point, the dissertation focuses investigations on cold collisions in alkali-alkaline-earth(-like) system, mainly in two aspects: one is theoretical analyses of the diatomic molecular structures, which is required in research on collision problem and transferring dynamics between molecular states; another is analysis on the Feshbach mechanism in alkali-alkaline-earth(-like) system, and further exploring the possibility of forming ultracold molecule. First, we present the calculation details on the interatomic potentials and rovibational level structures of RbSr molecule. Accroding to the Franck-Condon factors for series of vibrational transitions based on the potential energy curves yielded with relativistic ab initio quantum chemistry methods, a proper intermediate state is chosen to demonstrate the feasibility of transferring molecule into the absolute ground state, and the simulated one-way transfer efficiency from weakly-bound state to absolute ground state can reach 77%. With detailed knowledge of the atomic interaction potentials, we make an exploration of the magnetic Feshbach resonance in alkali-alkaline-earth(-like) system. Theoretical scattering calculations on collisions between ground-state alkali-metal atom and metastable-state alkaline-earth(-like) atom lead to a conclusion that, unlike the role of the electronic spin degree of freedom in collisions of two alkali-metal atoms, the orbital degrees of freedom from p electron of the metastable atoms, which induce not only mixings between different partial waves but also couplings between channels in different fine structure manifolds, introduce the anisotropic interactions for producing broad enough Feshbach resonances. However, the resonances also suffer from large inelastic rate at the magnitude of 10?10 cm3s?1 to lower-lying fine structure states or Zeeman sublevels, which will be an obstacle for associating ultracold polar molecules with both electron spin and electric dipole momentum, especially the process of transferring the molecule to ground state will be complex and indisciplinable. Finally we make a brief introduction of the design, construction and test of the dual-species Zeeman slower and the water-cooled magnetic coils for the magneto optical trap in our RbYb photoassociation experiments. In conclusion, the dissertation intends to explore some new points on molecular formation via cold collisions controlled by external field. The results and conclusions on the specially challenging alkali-alkaline-earth(-like) system, including the ab initio methods for calculating interaction potentials, the simulations of the vibrational state transferring procedure, and the exploration on the possibility of producing ultracold molecule via magnetic Feshbach resonance, provide promising inspirations and directions for future theoretical and experimental studies on such systems
Investigations on Characteristics and Applications of Spatiotemporally Focused Femtosecond Laser Pulses
No full text近年来，飞秒激光微加工技术以其对透明材料的三维加工能力被广泛地应用于微光学、微流体、微电子学等领域。同时人们发现飞秒激光与透明材料相互作用过程中会产生许多有趣的现象， 包括折射率的修饰、纳米孔洞、纳米光栅结构的形成以及非互逆直写效应等。 为了从时间域和空间域精确地操控飞秒激光与透明材料的相互作用，人们发明了多种飞秒脉冲整形技术，包括空间整形技术、时域整形技术、偏振整形技术以及时空聚焦技术等。 其中飞秒激光时空聚焦技术在微纳加工中的应用引起了广泛的关注， 利用该技术可以获得各向同性的直写加工分辨率，抑制焦点以外的非线性效应。 最近的研究发现时空聚焦的飞秒脉冲具有独特的光场特征，包括脉冲前沿倾斜和光强平面倾斜。 与此同时，人们发现时空聚焦脉冲与介质相互作用时会产生许多新奇的现象， 例如在透明材料中的非互逆直写效应， 以及在中心对称的气体介质中产生二次谐波等。 虽然最近的研究已经证明这些现象与焦点处的脉冲前沿倾斜有关，但时空聚焦飞秒脉冲与材料相互作用的完整物理图像目前尚不清晰，其独特的光场特性尚未得到有效的利用。 基于上述研究背景，本论文对飞秒激光时空聚焦的光场特征进行深入研究，在此基础上对时空聚焦的飞秒激光与透明材料相互作用进行实验探索。主要工作和创新性成果如下： 1. 提出了一种飞秒激光时空聚焦脉冲焦点处脉冲前沿倾斜的干涉测量技术。该技术引入传统聚焦的参考脉冲与时空聚焦脉冲在焦点处发生干涉。通过测量焦平面干涉条纹的空间位移与两个脉冲的相对延时之间的关系，实现对时空聚焦脉冲的脉冲前沿倾斜的精确测量。实验证明该技术对于焦点位于空气中或透明材料内部的情况均适用，因此该技术可以对脉冲与透明材料相互作用的区域直接进行测量，对进一步研究时空聚焦脉冲与透明材料的相互作用有重要意义。 2. 利用飞秒激光泵浦-探测阴影成像技术，对时空聚焦飞秒脉冲在熔融石英内部诱导等离子体的产生与演化过程进行时间分辨成像。发现等离子体轨迹相对于脉冲传播的方向有一定角度的偏折，引起这种现象的原因是焦点处脉冲前沿倾斜造成的等离子体不对称分布。 由于电离是时空聚焦飞秒脉冲诱导透明材料改性的最基础过程，该研究有助于从本质上揭示非互逆直写等现象的物理图像，并对时空聚焦技术在微纳加工中的应用有指导意义。 3. 分别利用时空聚焦和传统聚焦的飞秒激光在多孔玻璃内部诱导纳米光栅，发现时空聚焦的情况下纳米光栅具有不对称的空间分布。通过对纳米光栅的演化过程进行系统研究，发现其独特的不对称空间分布源自于时空聚焦光场固有的强度平面倾斜。该研究对进一步理解纳米光栅形成的物理机制有重要意义，并为纳米光栅形态的操控提供了有效手段Recently, femtosecond laser micromachining has been widely applied in many research fields such as microoptics, microfluidics and microelectronics for its unique capability of three-mensional microfabrication inside transparent materials. In the meanwhile, it was discovered that interaction of femtosecond laser pulses with transparent materials can lead to many interesting phenomena, such as refractive index modification, formation of nanovoids and nanogratings, and nonreciprocal writing. For precisely manipulating the interaction of femtosecond laser with transparent materials in both spatial and temporal domains, several femtosecond pulse shaping techniques have been developed, including spatial pulse shaping, temporal pulse shaping, pulse polarization control, and spatiotemporal focusing. In particular, applications of spatiotemporal focusing technique in femtosecond laser micromachining has attracted much attention, for such technique allows three dimensional isotropic fabrication resolution, eliminates nonlinear effect out of focus. It has been discovered by several recent investigations that the spatiotemporally focused pulse has some intriguing characteristics, including a tilted pulse front and a tilted peak intensity plane. In the meanwhile, it was found that the interaction of spatiotemporally focused pulse with solid or gaseous media can lead to several interesting phenomena, such as the nonreciprocal writing in transparent materials and second harmonic generation in centrosymmetric gas media. Although it has been confirmed by several recent researches that these phenomena have direct connection with pulse front tilt of spatiotemporally focused spot, the complete physical picture behind them is still lacking, and the unique characteristics of spatiotemporally focused pulse has not been completely utilized. Based on these considerations, in this thesis we make an intensive study on the characteristics of spatiotemporally focused pulses, and on this basis we make experimental exploration on the interaction of spatiotemporally focused femtosecond pulse with transparent materials. The main results and innovations of this thesis are listed as follows: 1. An interferometric measurement technique of pulse front tilt of spatiotemporally focused femtosecond laser pulses is developed. A conventional focused pulse is introduced as a reference pulse, and interference occurs in the focal plane between the reference pulse and spatiotemporally focused pulse. Accurate measurement of pulse front tilt is achieved by examination of the spatial displacement of the interferometric fringe as a function of time delay between the two pulses. It is confirmed by the experiment that such technique is applicable when the pulse is focused in air or transparent materials. Thus the measurement can be directly made in the interaction site of the pulse with transparent materials, which has important significance to make further investigations on the interaction of spatiotemporally focused pulses with transparent materials. 2. Time-resolved shadowgraphs of the generation and evolution of plasma induced by spatiotemporally focused femtosecond laser pulse in fused silica glass are made using a pump- probe shadow imaging technique. The observation shows that the track of the plasma is curved with respect to the direction of the pulse propagation, which is attributed to an asymmetric density distribution of the transient plasma produced in the focal volume caused by the pulse front tilt. As the photoionization is the most fundamental process in the modifications in transparent materials with spatiotemporally focused pulses, such investigation is beneficial to reveal the substantial physical picture of the nonreciprocal writing, and instructive to the applications of spatiotemporal focusing technique in femtosecond laser micromachining. 3. In-volume nanogratings are formed in porous with both conventionally and spatiotemporally focused femtosecond laser pulses, and it is discovered that in the case of using the spatiotemporally focused laser, the nanoplanes in the nanogratings are asymmetrically distributed. Based on the systematic investigations on the formation of the nanogratings, it is revealed that the asymmetrical distribution originates from the intensity plane tilt in the spatiotemporally focused spot. Such investigations have important significance to further understanding of the physical mechanism behind the nanograting formation, and provide an effective approach on the controlling of geometries of nanogratings
相干衍射成像的新进展及其在波前测量领域的应用
No full text传统的相干衍射成像(CDI)是专门为X-射线或者电子束等短波长光源而发展起来的相位成像技术,相比于干涉仪或者数字全息等传统相位测量方法,CDI的优点主要表现在光路简单和对光学元件质量要求低两个方面,但由于收敛速度慢和对复杂样品的测量可靠性较低,长期以来在光学频段使用很少。2004年PIE(Ptychographic Iterativ
Narrow-linewidth hybrid integrated external cavity diode laser for precision applications
No full textA butterfly-packaged narrow-linewidth hybrid integrated external cavity diode laser module based on the polarization maintaining fiber Bragg grating is reported. The module emits at the wavelength of 1550 nm and provides 21 GHz of continuous tunability. It produces >= 20 mW of polarization maintaining fiber-coupled output power with intrinsic Lorentz linewidth <= 3 kHz and RIN <= 140 dB root vHz@100 kHz. To qualify the reliability of the laser module under harsh environmental conditions, random vibration test and high-low temperature cycling test are carried out, and no degradation of the power current characteristic is observed
Laser conditioning mechanism revealed by defect and absorption variation in the bulk and at the surface of KDP/DKDP crystals
No full textPrevious works proved that laser conditioning process was able to improve laser induced damage thresholds (LIDTs) in the bulk of KDP/DKDP crystals. In this paper, it's also demonstrated that laser conditioning process was an effective method to improve LIDTs at their surface. The variation of scattering defects and absorption in the bulk of DKDP crystals during laser pre-exposure was investigated by combining light scattering technique and on-line transmittance measurement technique. Laser-induced disappearance of scattering defects and decrease of absorption revealed the mitigation process of laser damage initiators in the bulk of KDP/DKDP crystals. At the surface of KDP/DKDP crystals, most of damage initiators were the invisible defects. Laser conditioning process could mitigate the invisible defects, but it's hard to mitigate the indentation with fractures. Therefore, it's admitted that laser conditioning process could help to improve the optical properties of crystal material, but it's hard to improve the properties of optical finishing
基于改进的全内反射显微技术检测玻璃亚表面缺陷
No full text光学元件亚表面缺陷是限制其激光损伤阈值的主要因素之一。因此,对亚表面缺陷进行准确检测和去除是提升光学元件损伤特性的重要手段。全内反射显微技术是一种无损的,易于实现的亚表面缺陷检测技术。但是,现有的全内反射显微检测技术只能定性或半定量地表征亚表面缺陷。本文利用一种改进的全内反射显微技术检测玻璃元件亚表面缺陷。在传统的全
大口径数字波面干涉仪量值传递及测量不确定度的研究
No full text高功率激光系统中使用了大量的大口径平面光学元件,为了满足大口径、高精度光学元件制造能力,提高光学元件的加工精度,在各个关键生产工序环节以及光学元件终检环节均配备了大口径干涉仪,这些干涉仪基本上可以分为进口和国产自研两种型号。为了保证各个环节中干涉仪测量数据的一致性,如何实现各个工序环节间的干涉仪量值传递的准确性是目前工程加工检测中急需解决的问题。本文对大口径数字
Review of ultra-high density optical storage technologies for big data center
No full textIn big data center, optical storage technologies have many advantages, such as energy saving and long lifetime. However, how to improve the storage density of optical storage is still a huge challenge. Maybe the multilayer optical storage technology is the good candidate for big data center in the years to come. Due to the number of layers is primarily limited by transmission of each layer, the largest capacities of the multilayer disc are around 1 TB/disc and 10 TB/cartridge. Holographic data storage (HDS) is a volumetric approach, but its storage capacity is also strictly limited by the diffractive nature of light. For a holographic disc with total thickness of 1.5mm, its potential capacities are not more than 4TB/disc and 40TB/cartridge. In recent years, the development of super resolution optical storage technology has attracted more attentions. Super-resolution photoinduction-inhibition nanolithography (SPIN) technology with 9 nm feature size and 52nm two-line resolution was reported 3 years ago. However, turning this exciting principle into a real storage system is a huge challenge. It can be expected that in the future, the capacities of 10TB/disc and 100TB/cartridge can be achieved. More importantly, due to breaking the diffraction limit of light, SPIN technology will open the door to improve the optical storage capacity steadily to meet the need of the developing big data center