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221.
Summary The results of an investigation are presented in which it is shown how the spatial inhomogeneity of a laser field modifies
the multiphoton free-free transition cross-sections compared to the case of a homogeneous field. This kind of investigation
is required to make more close contact with experiments in intense fields, as in these cases the inhomogeneity is produced
by the focusing of the laser beam. Furthermore, taking into account the intensity spatial distribution allows us to achieve
in an effective way the asymptotic decoupling of the scattered particles from the field, which is very important for theoretical
models using asymptotic initial and final states embedded in the field. Differential and total cross-sections are calculated
over a wide range of parameters as functions of the scattering angle, of the incoming-particle energy and of the laser intensity
and frequency. The laser spatial inhomogeneity is found to wash out most of the oscillating behaviour of multiphoton differential
cross-sections, derived within the model of a homogeneous laser. Little modifications are, instead, found in the total cross-sections
which are simply scaled to slightly lower values. Crosssections with zero photon exchange are increased, while those with
photon exchanges are lowered. This yields the result that the sum of all the ≪inhomogeneous≫ cross-sections is equal to the
sum of all the ≪homogeneous≫ ones (sum rule). The multiphoton free-free transition differential cross-sections are found to
be very sensitive quantities which may be used to get information on the laser properties and on their nonlinear behaviour,
when these are not precisely known.
To speed up publication, the authors of this paper have agreed to not receive the proofs for correction. 相似文献
222.
S V Deshmukh 《Pramana》1978,11(6):755-760
The effect of Gaunt factor correction on temperature estimation over a range 100 to 1500 eV had been studied. Greene’s analytical
expression for the quantum mechanical Gaunt factor averaged over Maxwellian distribution is used. Transmission ratios are
calculated with and without Gaunt factor for various combinations of beryllium foils, taking into account x-ray emission due
to free-free transitions. A significant difference (≳ 15%) is observed between the temperatures estimated from classical and
quantum mechanical curves, above 600 eV. Selection of foil combinations useful for estimating higher temperatures is also
discussed. 相似文献
223.
M. W. Evans 《Foundations of Physics Letters》1996,9(2):191-204
The B cyclics of electrodynamics, which relate transverse and longitudinal fields in vacuo, are one photon relations which are also valid on a macroscopic scale. In the same way, the Maxwell equations in the received view were originally phenomenological relations between electric and magnetic fields, but, in the received view are also written down for one photon. Point by point replies to van Enk are given. 相似文献
224.
225.
Sunil Kumar 《Pramana》1985,25(3):291-309
The theory of the coherent, two-photon resonant interaction of a monochromatic field with N atoms is given. It is seen that
the dynamics of the atom-field system can be completely determined when the field is “strong”. Two specific examples are given:
(i) two-photon absorption by atoms in ground state, and (ii) stimulated two-photon emission by fully excited atoms, assuming
a coherent field in both cases. In case (ii), the field shows photon-antibunching after the decay of half of the atoms. The
merits of our approach are shown by comparing with other treatments. Our results can also be applied to certain degenerate
four-wave mixing processes which are described by a similar Hamiltonian. 相似文献
226.
Summary The relaxation of quadrupole orientation induced by means of optical pumping in a cesium vapour is experimentally studied,
and the results are compared to the theoretical predictions. The optical detection process of this type of orientation is
also discussed as a function of the polarization and spectral profile of the detection light.
Riassunto Si studia sperimentalmente il rilassamento dell'orientamento quadrupolare indotto mediante pompaggio ottico in un vapore di cesio e i risultati sono confrontati con le previsioni teoriche. Si discute anche il processo ottico di determinazione di questo tipo di orientamento in funzione della polarizzazione e del profilo spettrale della luce di rilevamento.
Резюме Экспериментально исследуется релаксация квадрупольной ориентации, индуцированной с помощью оптической накачки в парах цезия. Полученные результаты сравниваются с теоретическими предсказаниями. Также обсуждается процесс оптического детектирования этого типа ориентации в зависимости от поляризации и спектрального профиля детектируемого света.相似文献
227.
针孔单光子发射计算机断层(SPECT)成像的空间分辨率通常是根据Anger经验公式来进行估算,与实际测量存在较大偏差.本文通过对针孔成像的物理过程进行分析,提出了一个近似度更高的计算公式.利用精确的蒙特卡罗方法模拟针孔SPECT成像,采用OSEM(ordered subsets expectation maximization)算法对投影数据进行图像重建,并与模具实验进行比较,验证了理论公式的适用性.同时还讨论了体素尺寸、几何映射获取投影矩阵以及探测器尺寸与成像物体尺寸比值对断层图像空间分辨率的影响.实验结果显示,该理论公式所估算的空间分辨率比实验值平均偏小约10%,而Anger经验公式所估算的空间分辨率比实验值平均偏大约60%.因此,该理论公式能更好地估算针孔SPECT成像的空间分辨率,可为针孔SPECT系统的设计和使用提供有价值的参考. 相似文献
228.
229.
采用时域法中的时间相关单光子计数方法记录荧光寿命,时间相关单光子计数采用多波长通道同时记录荧光光子数,可以提高计数效率和信息量,还可以在稳态图像中分离不同荧光团,形成4维图像。并采用多光子激发技术,利用长波长光源发出的两个或多个光子可以激发出一个短波长的光子。多个光子必须几乎同时到达激发点,才能提供被激发分子足够的能量以产生荧光。多光子激发波长较长,生物组织对其散射减小,因而可以穿透到更深层的组织,从而提高荧光成像深度和空间分辨力,并减少对活体样品的损伤。 相似文献
230.
Energy average formula of photon gas rederived by using the generalised Hermann-Feynman theorem 下载免费PDF全文
By virtue of the generalised Hermann-Feynmam theorem we re-derive the energy average formula of photon gas. This is another useful application of the theorem. 相似文献