Studies of Optical Spectral Holeburning using Raman Coherent Population Trapping

9421304金在这个方案中，考虑了折叠三能级波长系统中拉曼相干布居俘获的光谱烧孔问题。这是一种允许存储(和检索)光学数据的新技术，与传统方案相比具有潜在的显著优势。每个数据脉冲由对应于波长转换的两个支路的两个光学频率组成。有关脉冲幅度和间隔的信息是以自旋相干而不是光学相干编码的。这种相干是由双光子过程产生的，因此它的幅度与两个频率的电场幅度(即几何平均强度)的乘积成正比，并与拍频同相振荡。因此，可以存储分别以拍频的几何平均强度和相位编码的幅度和相敏光学数据。这种数据存储和检索方案可能比现有技术具有显著优势。例如，写入窗口由两个时间尺度决定：自旋相干的均匀衰减时间和双光子关联时间。这放宽了光学数据存储的两个限制。首先，只有基态相干性，而不是光学相干性，必须长久存在。注意到在室温下某些固体中存在寿命长达约1秒的自旋相干，这项技术为找到高于液氮温度的高密度光学数据存储材料打开了可能性。其次，激光频率不必高度稳定，因为如果例如通过声光调制从另一个激光频率产生一个激光频率，则可以使双光子关联时间独立于单频线宽。最后，该系统可以用来提高存储密度，因为除了自旋相干性，拉曼激发还可以产生光学相干性。因此，光学数据可以存储在二维频率空间中烧制的孔中，从而导致五维数据存储。在时间域图像中，这种组合方案对应于写入窗口的扩展，使得存储器容量(在单个位置)超过由光学非均匀线宽与均匀线宽的比率施加的电流基本限制。将研究利用拉曼相干布居俘获的光学光谱烧孔的基本物理，以确定其在光学数据存储和图像处理方面的潜在应用。这将通过在稀土掺杂晶体中进行光谱烧孔的实验和理论研究来实现。具体的实验包括：掺杂晶体中拉曼布居陷阱的基本特征，使用适度稳定的激光在固体中存储和检索具有拉曼激发的自旋回波的光学数据，以及在二维频率空间中通过光谱空穴燃烧来增强存储密度的基本演示。理论计算将包括两个以上的基态，以便更接近于实际系统的特征。最后，根据实验和理论结果，对拉曼布居俘获实用化光存储的可行性进行了预测。***

9421304 Kim In this proposal, optical spectral holeburning is considered with Raman coherent population trapping in a folded three level lambda system. This is a novel technique which allows storage (and retrieval) of optical data with potentially significant advantages over conventional schemes. Each data pulse is composed of the two optical frequencies corresponding to the two legs of the lambda transition. The information about the pulse amplitudes and separations are encoded in the spin-rather than optical-coherence. This coherence is created by a two-photon process, so that its amplitude is proportional to the product of the amplitudes of electric fields (i.e., geometric mean intensity) of the two frequencies, and oscillates in phase with the beat frequency. Thus, both amplitude and phase sensitive optical data, encoded in the geometric mean intensity and the phase of the beat frequency, respectively, can be stored. This scheme of data storage and retrieval may have significant advantages over existing techniques. For example, the write window is determined by two time scales: the homogeneous decay time of the spin coherence, and the two-photon correlation time. This relaxes two constraints of optical data storage. First, only the ground-state coherences, and not the optical coherences, have to be long lived. Noting that spin coherences with lifetimes up to approx.1 second are known to exist in certain solids at room temperature, this technique opens up the possibility of finding high density optical data storage materials above liquid nitrogen temperature. Second, the laser frequency does not have to be highly stabilized, since the two photon correlation time can be made independent of single frequency linewidth if one laser frequency is generated from the other via acousto-optic modulation, for example. Finally, this system may be used to enhance the storage density since, in addition to the spin coherence, the Raman excitation can create optical coherence. Therefore, optical data can be stored in holes burnt in a two-dimensional frequency space, leading to a five-dimensional data storage. In the time domain picture, such a combined scheme corresponds to extension of the write window, enabling the memory capacity (at a single position) to exceed the current fundamental limit imposed by the ratio of the optical inhomogeneous to homogeneous linewidths. The basic physics of optical spectral holeburning using Raman coherent population trapping will be studied to determine suitability for potential applications to optical data storage and image processing. This will be accomplished by performing experimental and theoretical studies of spectral holeburning in rare-earth doped crystals. Specific experiments include basic characterization of Raman population trapping in a doped crystal, storage and retrieval of optical data with Raman-excited spin echoes in solids using modestly stabilized lasers, and basic demonstration of enhanced storage density via spectral hole burning in a two dimensional frequency space. Theoretical calculations will include more than two ground-states in order to more closely match the characteristics of the actual systems. Finally, projections will be made, based on the experimental and theoretical results, as to the feasibility of practical optical memories with Raman population trapping. ***