Entangled-Photon Fluorescence Microscopy

9800300 Teich拟议的研究涉及一种新形式的显微镜的发展：纠缠光子荧光显微镜。最近基于经典(或激光)光的双光子激发的荧光显微镜的发展是由于这种技术相对于单光子激发的主要优势：一对低能量的光子可以沉积与单个紫外光光子一样多的能量，从而以更大的穿透深度、更高的分辨率和更小的沿光路吸收的损坏风险来激发样品中的荧光分子。然而，为了用激光等经典光源获得双光子吸收，需要一个非常大的光子通量密度来将两个光子放置在足够小的体积和足够小的时间窗口内以实现吸收。在这种情况下，飞秒脉冲的高功率激光被直接用于光源，这可能会产生不希望看到的光毒性和光漂白。另一方面，由非线性晶体中的自发参数下转换过程产生的纠缠光在很短的时间窗口和很小的体积内包含本征成对的光子。可以使用小得多的光子通量密度，纠缠光子对的吸收与光子通量密度成正比，而对于普通的双光子吸收，光子通量密度是二次的。每对光子的能量之和是一个常数，等于下转换的泵浦光子的能量，而飞秒激光产生的光子的能量之和要宽得多。与激光等经典光源相比，这些特性导致了使用非经典纠缠光的独特优势。简单地说，在低光子通量密度下，纠缠光是一种比传统经典激光更有效的双光子激发源。因此，在提供相同数量的用于检测的荧光的同时，避免使用弱纠缠光源来造成比直接激光光源更小的损害。对纠缠光子荧光显微镜的可行性进行了实验研究。利用非线性参数下转换产生用于荧光团激发的纠缠光。将通过测量诱导荧光来对双光子吸收率进行基础研究。

9800300 Teich The proposed research pertains to the development of a new form of microscopy: entangled-photon fluorescence microscopy. The recent surge in the development of fluorescence microscopy based on two-photon excitation using classical (or laser) light has been driven by the principal advantages of this technique over single-photon excitation: a pair of low-energy photons can deposit as much energy as a single ultraviolet photon thereby exciting a fluorescent molecule within a sample with greater penetration depth, better resolution, and less risk of damage upon absorption along the optical path. However, in order to obtain two-photon absorption with a classical light source such as a laser, a very large photon-flux density is necessary to place two photons within a small enough volume and within a small enough time window to effect the absorption. In this case, a femtosecond-pulsed high-power laser is used directly &- the source of light, which can produce undesired phototoxicity and photobleaching. On the other hand, entangled light generated by the process of spontaneous parametric downconversion in a nonlinear crystal comprises intrinsically paired photons within a very short time window and small volume. Far smaller photon-flux densities can be used and the absorption of entangled-photon pairs is directly proportional to the photon-flux density, whereas for ordinary two-photon absorption it is quadratic in the photon-flux density. The sum of the photon energies in each pair is a constant and equal to the energy of the downconverted pump photon, whereas the sum energy is far broader for photons from a femtosecond laser. These features lead to unique advantages with the use of nonclassical entangled light when compared to classical light sources like a laser. Simply put, at low photon-flux densities entangled light is a more efficient source of two-photon excitation than a conventional classical laser source. The use of a weak entangled-light source is therefore expec ted to cause less damage than that caused by a direct laser source while providing the same amount of fluorescent light for detection. An experimental investigation of the feasibility of entangled-photon fluorescence microscopy is proposed. Entangled light for fluorophore excitation will be generated using nonlinear parametric downconversion. A basic study of the two-photon absorption rate will be carried out using measurements of the induced fluorescence.