Studies of Optical Spectral Holeburning using Raman Coherent Population Trapping

在这个提议中，考虑了折叠三能级λ系统中的光谱烧孔和拉曼相干布居俘获。这是一种新的技术，它允许存储（和检索）的光学数据具有潜在的显着优势，超过传统的计划。每个数据脉冲由对应于λ跃迁的两个分支的两个光频率组成。关于脉冲幅度和间隔的信息被编码在自旋相干性而不是光学相干性中。这种相干性是由双光子过程产生的，使得其振幅与电场振幅的乘积成比例（即， 几何平均强度），并且与拍频同相振荡。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位敏感光学数据。 这种数据存储和检索方案可能比现有技术具有显著的优点。例如，写入窗口由两个时间尺度确定：自旋相干的均匀衰减时间和双光子相关时间。这放松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，必须是长寿命的。注意到自旋相干性与寿命高达约。1秒是已知存在于某些固体在室温下，这种技术开辟了寻找高密度的光学数据存储材料的可能性高于液氮温度。 第二，激光频率不必高度稳定，因为如果一个激光频率通过例如声光调制从另一个激光频率产生，则可以使双光子相关时间与单频线宽无关。最后，该系统可用于增强存储密度，因为除了自旋相干性之外，拉曼激发可产生光学相干性。 因此，光学数据可以存储在二维频率空间中烧成的孔中，导致五维数据存储。在时域图中，这样的组合方案对应于写入窗口的扩展，使得存储器容量（在单个位置处）能够超过由光学不均匀线宽与均匀线宽的比率所施加的当前基本限制。 将研究利用拉曼相干布居捕获的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的适用性。这将通过对稀土掺杂晶体中的光谱烧孔进行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俘获的基本表征，使用适度稳定的激光器在固体中用拉曼激发的自旋回波存储和检索光学数据，以及通过二维频率空间中的光谱烧孔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，以便更接近地匹配实际系统的特性。最后，根据实验和理论结果，对利用拉曼布居俘获实现实际光存储器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. ***