摘要:

On étudie théoriquement le rendement de conversion photonique dans les amplificateurs à colorants, en tenant compte des pertes par émission spontanée amplifiée (superfluorescence). On résoud analytiquement le système d'équations cinétiques dans le cas du régime stationnaire. On obtient deux relations, l'une donnant la répartition spectrale de la superfluorescence, l'autre reliant l'énergie de sortie de l'amplificateur à l'énergie à l'entrée et à l'énergie d'excitation. A l'aide des relations obtenues on étudie un amplificateur à rhodamine 6G excité par un laser à néodyme doublé en fréquence. On montre que le rendement de conversion photonique varie peu avec l'excitation quand l'amplification en simple passage varie de plusieurs ordres de grandeur. De plus, on montre qu'il existe une énergie d'entrée minimale au delà de laquelle le rendement de conversion est bon (> 90 pour cent) quelle que soit l'énergie d'excitation et que les excitations transversale et longitudinale conduisent à des rendements de conversion à peu près identiques.

ISSN:0030-3909    

DOI:10.1080/713819782

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The formation of a holographic lattice recorded by a light wavelength not coinciding with the colour-centre absorption bands has been verified in NaCl crystals, which were coloured up to very high colour-centre concentrations by using an electron beam. Properties of the lattice were studied both experimentally and by using theories presented by Kogelnik [6] and Ninomiya [5].

ISSN:0030-3909    

DOI:10.1080/713819780

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The theory of multilayer dielectric mirrors with residual absorptance is re-examined to determine whether lower absorptances and therefore higher reflectances can be achieved than with the usual type of alternating quarter-wave system. It is shown that considerable improvements are indeed possible if the layers of the material with high refractive index and residual absorption are made with optical thickness less than a quarter-wave, and the other layers with correspondingly greater optical thickness. Simple formulae are derived for the factor of improvement and the required optical thickness of the films of low refractive index. Moreover, by applications of the concept of potential transmittance and the principle of equivalent layers, a relationship is established between the desired limiting reflectance of the system and the necessary number of layers.

ISSN:0030-3909    

DOI:10.1080/713819785

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

We investigate the three-dimensional distributions of loci and visibility of the fringes observed in the image region of a diffuse object in double-exposure holographic interferometry. The loci are shown to represent the contour lines of surface displacement in a certain direction and have the local spatial frequency proportional to the amounts of rotation and strain of the object, while the visibility is a function of the ratio of the amount of the speckle movement caused by the object deformation to the mean speckle size, depending on aperture size. The results of the computer calculation based on the analytical relations are graphically exhibited for typical cases.

ISSN:0030-3909    

DOI:10.1080/713819786

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The effect of partial coherence of both the source and the detector in a scanning microscope is investigated. The transfer function for the system is derived and various special cases discussed. If the effective source and effective detector are coherent and incoherent, respectively, the microscope (Type 1) is of the form of the scanning transmission electron microscope (STEM). If the effective source and the effective detector are both coherent, the microscope (Type 2) is of the form of the scanning acoustic microscope. Scanning optical microscopes of both these types may be constructed. The effect of using a Type 2 scanning microscope in dark-field is discussed. This arrangement has the advantage over the Type 1 dark-field microscope that imaging for weak contrast specimens may be made linear.

ISSN:0030-3909    

DOI:10.1080/713819784

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A hybrid image processing system with active feedback is capable of producing patterns that oscillate in space and time. The term ‘hybrid’ implies a combination of optical and TV-electronic components in our feedback system, where the TV camera looks at its own monitor. Some of the observed oscillating patterns are without precedence, especially if the imaging process from monitor to camera target is ‘non-congruent’. The term ‘non-congruent’ implies that the signal from a given point on the monitor will not return to its former place after passing through the loop. Image rotation and magnification mismatch are prominent examples of ‘non-congruent’ processes in that context. One goal is to study the generation of these fascinating picture oscillations. Another goal is to learn how to prevent these oscillations in situations where they are undesirable, as, for example, in transfer-function synthesis by active feedback.

ISSN:0030-3909    

DOI:10.1080/713819792

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The optical parametric oscillator and amplifier involving the analogue of the inverse Cerenkov effect is considered, the effect being due to the non-linear interaction between the plane wave of pumping (with a frequency yp) incident at an angle onto an optical waveguide and the waves (with frequencies ys, yvsatisfying the relation ys+ yv= yp) generated in the waveguide. For the oscillator an appreciable non-linear reflection from (transmission through) the waveguide layer of the pumping wave is discovered and shown to appear in new directions compared to those known in optics. Also, the transformation by the reflection (transmission) of the pumping wave into the waves with new frequencies 2 ys, 2yvis predicted. The possible effect of additional (higher-order) non-linear processes on the oscillator dynamics is discussed. A travelling-wave parametric amplifier involving the analogue of the inverse Cerenkov effect is also considered. Here, differing from the usual optical parametric amplifiers the intensities of generated waves (limited by the non-linear Cerenkov losses) are shown to exceed appreciably the intensity of the incident pumping wave. Possible difference and sum-frequency generation involving the analogue of the inverse Cerenkov effect in a waveguide is noted as well.

ISSN:0030-3909    

DOI:10.1080/713819787

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0030-3909    

DOI:10.1080/713819793

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0030-3909    

DOI:10.1080/713819789

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0030-3909    

DOI:10.1080/713819790

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor