摘要:

Temporally and spatially resolved measurements of the spectral output of a commercially available 25 W quasi-c.w. diode-laser array have been made. The 5 nm temperature-induced wavelength sweep during the 200 μs pulse reduces the effectiveness of the array as a pump for solid-state lasers. By using a reflector behind a side-pumped Nd : YAG rod to minimize the effects of the wavelength sweep, the 1·06 μm laser produced 6·5 W, 180 μs pulses, and 6·1 kW, 44 ns pulses whenQ-switched.

ISSN:0950-0340    

DOI:10.1080/09500348914550011

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

It has long been believed that no Hermitian optical phase operator exists. However, such an operator can be constructed from the phase states. We demonstrate that its properties are precisely in accord with the results of semiclassical and phenomenological approaches when such approximate methods are valid. We find that the number-phase commutator differs from that originally postulated by Dirac. This difference allows the consistent use of the commutator for inherently quantum states. It also leads to the correct periodic phase behaviour of the Poisson bracket in the classical regime.

ISSN:0950-0340    

DOI:10.1080/09500348914550021

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Up to now, the non-symmetric Fourier transform (NFT) of an object has been made using conventional refractive optics such as cylindrical and/or spherical lenses. In this paper, we propose the use of a holographic optical element in conjunction with refractive lenses to improve the design flexibility of NFT systems working with parallel beam illumination. Experimental results are presented.

ISSN:0950-0340    

DOI:10.1080/09500348914550031

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Reflection of travelling and evanescent plane waves by a four-wave mixing phase-conjugator is studied in detail. No restrictions are imposed on the nonlinear interaction strength, the angle of incidence or the frequency mismatch between the pump-beams and the incoming waves. We only assume that the incident field is weak compared to the pump fields, which justifies a classical field description of the pumps. The wave-vectors, amplitudes and phases for the various waves are evaluated, without the slowly-varying amplitude approximation. Familiar phase-matching resonances for certain values of the interaction length are recovered, and in addition strong resonances are found if the angle of incidence is finite and the incident light is not in perfect resonance with the pumps. The latter resonances appear at the transitions from a travelling to an evanescent wave. The significance of finite angles of incidence and evanescent waves for spectroscopic applications is pointed out.

ISSN:0950-0340    

DOI:10.1080/09500348914550041

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The temporal behaviour of the V configuration of a three-level two-mode system is investigated with the two modes initially in a coherent state. The photon number, atomic inversion, reduced atomic fluctuations, squeezing in the field quadratures, cross-correlation between the photon numbers in the two modes, and finally bunching and antibunching effects are investigated. A relation between squeezing and cross-correlation is established.

ISSN:0950-0340    

DOI:10.1080/09500348914550051

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The diffraction-based and geometrical optics-based optical transfer functions (DOTF and GOTF) are calculated for three types of variable-spacing diffraction gratings. The three types are: (a) a conventional grating, (b) a holographically produced grating and (c) a mechanically ruled variable-spacing grating. They are mounted on a Seya-Namioka monochromator.

ISSN:0950-0340    

DOI:10.1080/09500348914550061

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The interferometric properties of two types of images are investigated. One image is formed by conventional holographic interferometry, the other using a speckle carrier technique. The second process employs a diffuse reference beam, with the spherical carrier being replaced by a speckle carrier in the register state.

ISSN:0950-0340    

DOI:10.1080/09500348914550071

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Transmission holograms in dichromated gelatin are studied under conditions when a number of spurious gratings (both transmission and reflection types) are also present due to boundary reflections at recording. It is shown that the experimental results, in the form of transmitted power against incident angle measured on the developed hologram, agree well with the predictions of a simple, linear theoretical model based on coupled wave theory.

ISSN:0950-0340    

DOI:10.1080/09500348914550081

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The extrapolation in the space domain of a partially observed low space-bandwidth product (SBP) sequence or, equivalently, the resolution of the Fourier spectra in the frequency domain, in the presence of appreciable noise, is considered. The unknown sequence estimate is based on a number of acquired samples on a given measurement interval and the prior knowledge of the signal frequency bandlimit. Using an approach similar to a Monte-Carlo method, the extrapolated sequence samples are constructed from variably sized elementary grains. The new iterative algorithm, at each iteration step, based on a random-number generator, decides both the sample position to be considered and the sign of a grain that might be added to the current sample value. A sample update in each iteration step is either accepted or rejected in accordance with an appropriate decision rule. While exploiting the extrapolated sequence frequency bandlimit as a constraint, this decision rule is based on a non-increasing l1-norm of a cumulative error vector. As the extrapolated sequence approaches its final form, the elementary grain size is decreased to allow for subtle sample updates. A heuristic schedule for gradual change of the elementary grain size, similar to the temperature schedule of the simulated annealing method, is used. A pre-processing, which compensates for the model inconsistency that is due to either the presence of noise and/or the lack of precision of the linear degradation operator, is also introduced. Furthermore, it is shown that an additional constraint, such as a given signal upper bound, greatly improves the quality of reconstruction. Several simulation examples, for the extrapolation of low-SBP sinusoidal and other arbitrary sequences and in the presence of a high level of noise, are presented.

ISSN:0950-0340    

DOI:10.1080/09500348914550091

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The flip-flop synthesis method was suggested by Southwell for synthesis of two-component multilayer coatings. The introduction of a third refractive index is proposed in order to simplify the resulting systems and make them technologically feasible. The thickness optimization procedure, which avoids very thin layers, is recommended. Two examples of synthesis of broad-band anti-reflection coatings are presented.

ISSN:0950-0340    

DOI:10.1080/09500348914550101

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor