Yu. Ya. Maslova

Laser-electron generator for X-ray applications in science and technology

The possibility of the creation and the application prospects of the laser-electron X-ray generator based on Thomson scattering of laser radiation on a bunch of relativistic electrons are considered. Such a generator fills the existing gap between X-ray tubes and synchrotron radiation sources, which is several orders of magnitude in terms of the brightness, average intensity, size, and also in the construction and running costs.

Proposal of a compact repetitive dichromatic x-ray generator with millisecond duty cycle for medical applications

Many practical applications of x-rays lie in the important for the society fields of medical imaging, custom, transport inspection and security. Scientific applications besides of fundamental research include material sciences, biomicroscopy, and protein crystallography. Two types of x-ray sources dominate now: conventional tubes and electron accelerators equipped with insertion devices. The first are relatively cheap, robust, and compact but have low brightness and poorly controlled photon spectrum. The second generate low divergent beams with orders of magnitude higher brightness and well-controlled and tunable spectrum, but are very expensive and large in scale. So accelerator based x-ray sources are mainly still used for scientific applications and x-ray tubes - in commercial equipment. The latter motivated by the importance for the society made an impressive progress during last decades mostly due to the fast developments of radiation detectors, computers and software used for image acquisition and processing. At the same time many important problems cannot be solved without radical improvement of the parameters of the x-ray beam that in commercial devices is still provided by conventional x-ray tubes. Therefore there is a quest now for a compact and relatively cheap source to generate x-ray beam with parameters and controllability approaching synchrotron radiation. Rapid developments of lasers and particle accelerators resulted in implementation of laser plasma x-ray sources and free electron lasers for various experiments requiring high intensity, shrt duration and monochromatic x-ray radiation. Further progress towards practical application is expected from the combination of laser and particle accelerator in a single unit for efficient x-ray generation.

Design study of compact Laser-Electron X-ray Generator for material and life sciences applications

X-ray generators utilizing Thomson scattering fill in the gap that exists between conventional and synchrotron-based X-ray sources. They are expected to be more intensive than X-ray tubes and more compact, accessible and less expensive than synchrotrons. In this work, two operation modes of Thomson X-ray source (or laser-electron X-ray generator — LEXG) are documented: quasi continuous wave (QCW) and a pulsed one. They are considered for material sciences and medical applications that are currently implemented at Synchrotron Radiation (SR) facilities. The proposed system contains a ~ 50 MeV linac and a picosecond laser with an average power ~ few hundred Watts. The Thomson X-ray source is able to deliver up to 5 × 1011 photons in a millisecond flash and an average flux of 1012–1013 phot/sec. To achieve these parameters with existing optical and accelerator technology, the system must also contain a ring for storage of e-bunches for 103–105 revolutions and an optical circulator for storage of laser pulses for 102 passes. The XAFS spectroscopy, small animal angiography and human noninvasive coronary angiography are considered as possible applications of laser-electron X-ray generator.X-Ray generations utilizing Thomson scattering fill in the gap that exists between conventional and synchrotron-based X-ray sources. They are expected to be more intense than X-ray tubes and more compact, accessible and less expensive than synchrotron. In this work, two operation modes of Thomson X-ray source are documented: quasi CW(QCW) and a pulsed one are considered for material sciences and medical applications being implemented currently at Synchrotron Radiation (SR) facilities.

Submicrosecond regular and chaotic nonlinear dynamics in a pulsed picosecond Nd:YAG laser with millisecond pumping

We propose and study both numerically and experimentally a feedback-controlled laser system capable of generating regular bursts with a submicrosecond period. Bursting is obtained in a laser that is controlled by a combination of feedbacks in which the negative feedback loop action is delayed by one cavity round trip with respect to the positive one, and the period is adjusted by relative feedback sensitivity. The proper combination of feedbacks is realized in a Nd:YAG laser with millisecond pumping by means of a single optoelectronic negative feedback unit that utilizes the signal reflected from an intracavity Pockels cell polarizer. Regular bursting (microgroups of picosecond pulses) with controlled periods from 25 to 75 cavity round trips is obtained experimentally. The development of chaotic dynamics displayed by the system at a higher pumping level differs from the Feigenbaum scenario.

Relativistic Thomson scattering in compact linacs and storage rings: a route to quasi-monochromatic tunable laboratory-scale X-ray sources

Free electron lasers are expected to become brightest hard X-ray sources in the next decade. Meanwhile a quest still exists for moderately bright but lab scale X-ray sources to fill in the gap between conventional X-ray tubes and synchrotron radiation beamlines. Thomson scattering of picosecond laser pulses on electron bunches is considered as possible solution to this problem.

Laser Physics Research Relevant to Laser-Electron X-Ray Generator

A prototype of laser unit for Laser Electron X-Ray Generator is constructed on the basis of the optoelectronic control. The laser system in which an optoelectronic negative feedback is realized by means of a signal reflected from an intracavity Pockels cell polarizer is proposed and tested. The design provides flexible control over pulse train time structure.

Laser-Electron X-Ray Generator

The possibility of developing a laser-electron x-ray generator based on the Thomson scattering of laser radiation by relativistic electrons and prospects for its application are considered. In its specifications (brightness, average intensity, and dimensions), as well as its construction and operation cost, such a generator is intermediate between x-ray tubes and synchrotron sources. The configuration of channels and experimental stations intended for applications of an x-ray laser-electron generator in studies of the elemental composition and structure of materials is discussed.

Dual Feedback Control in Solid State Lasers: Discrete Maps and Experiments

Combinations of negative and positive feedback loops were investigated on the basis of discrete map analysis, numerical simulation and experimentally with lamp and diode pumped Nd:YAG lasers. Cases with relative feedback delay in two loops equal to one laser cavity round trip time were considered. Dual feedback control allows to achieve: 1) stable operation of both continuous and pulsed lasers in a wide range of active media gain, 2) laser pulse shortening down to several tens of picoseconds and 3) regular burst mode with periods up to hundred laser cavity round trip times.

Generation of a regular sequence of short-pulse microtrains with a discretely varied repetition period

In the Nd:YAG lamp-pumped laser controlled by optoelectronic negative feedback based on an electro-optic DKDP crystal, the mode of generation of a millisecond sequence of short-pulse microtrains with a discretely varied repetition period was implemented. The microtrain repetition periods are fixed and controlled by resonances of shear acoustic oscillations of the crystal. The cavity design allowed selective excitation of the first ten acoustic modes in the period range of 8–0.5 µs.

Harmonic mode-locking and sub-round-trip time nonlinear dynamics of electro-optically controlled solid state laser

Harmonic mode-locking in a solid state laser due to optoelectronic control is studied numerically on the basis of two methods. The first one is detailed numeric simulation taking into account laser radiation fine time structure. It is shown that optimally chosen feedback delay leads to self-started mode-locking with generation of desired number of pulses in the laser cavity. The second method is based on discrete maps for short laser pulse energy. Both methods show that the application of combination of positive and negative feedback loops allows to reduce the period of regular nonlinear dynamics down to a fraction of a laser cavity round trip time.