On the non-paraxial modes of two-dimensional nearly concentric resonators

to be published in Applied OpticsA non-paraxial scalar diffraction integral is used to determine numerically the resonance modes of a two dimensional nearly concentric Fabry-Perot resonator. Numerical examples are provided and results are compared to those published by Laabs and Friberg [IEEE J. Quant. El., vol. 35, pp. 198-207, 1999]. Discrepancies are reported and further discussed on the basis of the difference between the solution space supported by the numerical method used in the present work and the one used by Laabs and Friberg

High flux polarized gamma rays production: first measurements with a four-mirror cavity at the ATF

The next generation of e+/e- colliders will require a very intense flux of gamma rays to allow high current polarized positrons to be produced. This can be achieved by converting polarized high energy photons in polarized pairs into a target. In that context, an optical system consisting of a laser and a four-mirror passive Fabry-Perot cavity has recently been installed at the Accelerator Test Facility (ATF) at KEK to produce a high flux of polarized gamma rays by inverse Compton scattering. In this contribution, we describe the experimental system and present preliminary results. An ultra-stable four-mirror non planar geometry has been implemented to ensure the polarization of the gamma rays produced. A fiber amplifier is used to inject about 10W in the high finesse cavity with a gain of 1000. A digital feedback system is used to keep the cavity at the length required for the optimal power enhancement. Preliminary measurements show that a flux of about $4\times10^6 \gamma$/s with an average energy of about 24 MeV was generated. Several upgrades currently in progress are also described

Design of a Polarised Positron Source Based on Laser Compton Scattering

We describe a scheme for producing polarised positrons at the ILC from polarised X-rays created by Compton scattering of a few-GeV electron beam off a CO2 or YAG laser. This scheme is very energy effective using high finesse laser cavities in conjunction with an electron storage ring.Comment: Proposal submitted to the ILC workshop, Snowmass 2005. v2: note number adde

Laser frequency stabilization using folded cavity and mirror reflectivity tuning

International audienceA new method of laser frequency stabilization using polarization property of an optical cavity is proposed. In a standard Fabry–Perot cavity, the coating layers thickness of cavity mirrors is calculated to obtain the same phase shift for sand p-wave but a slight detuning from the nominal thickness can produce sand p-wave phase detuning. As a result, each wave accumulates a different round-trip phase shift and resonates at a different frequency. Using this polarization property, an error signal is generated by a simple setup consisting of a quarter wave-plate rotated at 45°, a polarizing beam splitter and two photodiodes. This method exhibits similar error signal as the Pound–Drever–Hall technique but without need for any frequency modulation. Lock theory and experimental results are presented in this paper.

The distinguishing attack on Speck, Simon, Simeck, HIGHT and LEA

The purpose of the work is to estimate the resistance of lightweight block ciphers Speck, Simon, Simeck, HIGHT, LEA to a distinguishing attack. (This attack is a form of cryptanalysis on data encrypted by a cipher that allows an attacker to distinguish the encrypted data from random data.) Modern lightweight block ciphers must be designed to be immune to such an attack. It turned out that Speck, Simon, HIGHT and LEA showed a sufficient resistance to the distinguishing attack, but Simeck with 48-bit block size and 96-bit key size was not immune to this attack

CLIC Polarized Positron Source Based on Laser Compton Scattering

We describe a possible layout and parameters of a polarized positron source for CLIC, where the positrons are produced from polarized gamma rays created by Compton scattering of a 1.3-GeV electron beam off a YAG laser. This scheme is very energy effective using high finesse laser cavities in conjunction with an electron storage ring. We point out the differences with respect to a similar system proposed for the ILC

Способи обмеження перенапруг в сучасних комутаційних напівпровідникових апаратах постійного струму та їх розрахунок

The study considers switching surges at semiconductor switches of semiconductor devices of the direct current at the time of switching electric circuits; such surges occur due to the energy accumulated in the inductive elements of the mains at the load disconnection.As the cost of power semiconductor devices is determined not only by the voltage that they are able to handle but also by the class of the device that determines the amount of the blocked voltage, an important task is to use special measures to reduce these surges down to levels that are close to the network parameters.The aim of this study was to develop a methodology for calculating the parameters of a regulator of switching surges on the basis of a series of parallel-connected energy-intensive varistors used in semiconductor devices of the direct current.On the basis of studying the transient processes that occur in such surge restrictors of voltage in semiconductor devices of the direct current at load switching, analytical expressions have been developed for calculating the basic parameters of the voltage regulator.As a result, an engineering method has been devised for calculating the parameters of varistor surge regulators in hybrid and contactless semiconductor devices of the direct current at a given level of surge admissible for this class of devices. The research findings facilitate high accuracy at a small amount of time in choosing fully controlled semiconductor devices with regard to the current and voltage when designing modern switching semiconductor apparatus that work with the direct current; this helps solve the basic tasks of planning.The suggested voltage regulator for semiconductor switching apparatus of the direct current effectively limits switching surges in the circuits of power semiconductor devices to below 2.5 Unom. It significantly surpasses such parameters as the dimensions, weight and cost of resistive-capacitive surge limiters previously used in semiconductor contactors. Moreover, it can reduce the class level of fully controlled power semiconductor devices that are used in semiconductor switches of such apparatus.Показано, что в современных полупроводниковых аппаратах постоянного тока для ограничения коммутационных перенапряжений до установленного уровня целесообразно запасённую в индуктивности сети энергию рассеивать с помощью ограничителя перенапряжений, выполненного на последовательно-параллельно включенных энергоёмких варисторах. Разработана методика расчёта его параметров, приведены примеры расчёта.Показано, що в сучасних напівпровідникових апаратах постійного струму для обмеження комутаційних перенапруг до встановленого рівня доцільно запасену в індуктивності мережі енергію розсіювати за допомогою обмежувача перенапруг, виконаного на послідовно-паралельно увімкнених енергоємних варисторах. Розроблена методика розрахунку його параметрів та наведені приклади розрахунку.

Розробка удосконалених методик розрахунку комутаційних перенапруг в напівпровідникових апаратах змінного струму

The study focuses on switching overvoltage applied to semiconductor switches of semiconductor AC devices at the moment of switching electric circuits owing to the energy that has accumulated in the inductive elements of the mains and a disconnectable load.Since the cost of power semiconductor devices is determined both by the current with which they are compatible and the class of the device that determines the amount of blocked voltage, it is important to use special measures that would reduce the voltage and make it closer to that of the network. Usually, the voltage is reduced with the help of protective RC-circuits and nonlinear surge suppressors (varistors).The aim of the research was to refine the methods of calculating the switching overvoltage and parameters of protection circuits in semiconductor devices with account for the diversity of semiconductor switches and their dynamic characteristics since the current methods of calculation do not fully account for them and, therefore, are not fully precise.The newly developed methods of calculating the switching surge consider dependence of the reverse recovery of power semiconductor devices on the rate of current decline in their circuit as well as high resistance of modern semiconductor devices to the effect of ultra-high voltage slew rates. The methodology also takes into account the conditions of the load switching with the help of these devices.The developed methodology of selecting parameters for the RC-protective circuit accounts for the nature of any switching transients and significantly extends the range of protective circuit parameters.The proposed surge suppressor for semiconductor AC switching devices is additionally supplied with a varistor that is connected in parallel to the RC-circuit, which allows a significant reduction in the capacitance of the circuit condenser and the leakage current and approximately 30% reduction in the rate of switching surges. This would greatly reduce the class of power semiconductor devices.Выполнены исследования коммутационных перенапряжений, прикладываемых к полупроводниковым ключам полупроводниковых аппаратов переменного тока при коммутации электрических цепей. Предложена уточнённая методика расчёта величины этих перенапряжений для полупроводниковых ключей, зашунтированных защитными RC-цепями с варисторами, учитывающая как динамические характеристики силовых приборов полупроводниковых ключей, так и разных вариантов исполнения последних. Методика позволяет значительно повысить точность расчёта параметров защитных цепей. Приведены примеры расчёта коммутационных перенапряжений для наиболее распространённых условий работы полупроводниковых аппаратов.Виконані дослідження комутаційних перенапруг, прикладених до напівпровідникових ключів напівпровідникових апаратів змінного струму при комутації електричних кіл. Запропонована уточнена методика розрахунку величини цих перенапруг для напівпровідникових ключів, зашунтованих захисними RC-колами разом з варисторами, яка враховує як динамічні характеристики силових приладів напівпровідникових ключів, так і різних варіантів виконання останніх. Методика дозволяє значно підвищити точність розрахунку параметрів захисних кіл. Наведені приклади розрахунку комутаційних перенапруг для найбільш розповсюджених умов роботи напівпровідникових апаратів