Acceleration of sub-relativistic electrons with an evanescent optical wave at a planar interface.

We report on a theoretical and experimental study of the energy transfer between an optical evanescent wave, propagating in vacuum along the planar boundary of a dielectric material, and a beam of sub-relativistic electrons. The evanescent wave is excited via total internal reflection in the dielectric by an infrared (λ = 2 µm) femtosecond laser pulse. By matching the electron propagation velocity to the phase velocity of the evanescent wave, energy modulation of the electron beam is achieved. A maximum energy gain of 800 eV is observed, corresponding to the absorption of more than 1000 photons by one electron. The maximum observed acceleration gradient is 19 ± 2 MeV/m. The striking advantage of this scheme is that a structuring of the acceleration element's surface is not required, enabling the use of materials with high laser damage thresholds that are difficult to nano-structure, such as SiC, Al2O3 or CaF2.

Optical gating and streaking of free electrons with sub-optical cycle precision.

The temporal resolution of ultrafast electron diffraction and microscopy experiments is currently limited by the available experimental techniques for the generation and characterization of electron bunches with single femtosecond or attosecond durations. Here, we present proof of principle experiments of an optical gating concept for free electrons via direct time-domain visualization of the sub-optical cycle energy and transverse momentum structure imprinted on the electron beam. We demonstrate a temporal resolution of 1.2±0.3 fs. The scheme is based on the synchronous interaction between electrons and the near-field mode of a dielectric nano-grating excited by a femtosecond laser pulse with an optical period duration of 6.5 fs. The sub-optical cycle resolution demonstrated here is promising for use in laser-driven streak cameras for attosecond temporal characterization of bunched particle beams as well as time-resolved experiments with free-electron beams.

Demonstration of electron acceleration in a laser-driven dielectric microstructure.

The enormous size and cost of current state-of-the-art accelerators based on conventional radio-frequency technology has spawned great interest in the development of new acceleration concepts that are more compact and economical. Micro-fabricated dielectric laser accelerators (DLAs) are an attractive approach, because such dielectric microstructures can support accelerating fields one to two orders of magnitude higher than can radio-frequency cavity-based accelerators. DLAs use commercial lasers as a power source, which are smaller and less expensive than the radio-frequency klystrons that power today's accelerators. In addition, DLAs are fabricated via low-cost, lithographic techniques that can be used for mass production. However, despite several DLA structures having been proposed recently, no successful demonstration of acceleration in these structures has so far been shown. Here we report high-gradient (beyond 250 MeV m(-1)) acceleration of electrons in a DLA. Relativistic (60-MeV) electrons are energy-modulated over 563 ± 104 optical periods of a fused silica grating structure, powered by a 800-nm-wavelength mode-locked Ti:sapphire laser. The observed results are in agreement with analytical models and electrodynamic simulations. By comparison, conventional modern linear accelerators operate at gradients of 10-30 MeV m(-1), and the first linear radio-frequency cavity accelerator was ten radio-frequency periods (one metre) long with a gradient of approximately 1.6 MeV m(-1) (ref. 5). Our results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems. This would enable compact table-top accelerators on the MeV-GeV (10(6)-10(9) eV) scale for security scanners and medical therapy, university-scale X-ray light sources for biological and materials research, and portable medical imaging devices, and would substantially reduce the size and cost of a future collider on the multi-TeV (10(12) eV) scale.

Fracture of the femoral prosthesis after total hip replacement.

Although fracture of the femoral component is a well-known complication of total hip replacement, especially with the earlier types of prosthesis, it is seldom recognized in its initial stages. A series of 22 fractures of the femoral component of the prosthesis in 19 patients is presented for the benefit of the general practitioner and the radiologist, who, it is stressed, should both be aware of this complication and able to recognize the signs of a possible fracture, so that early treatment may be given to avoid excessive bone loss in the upper femur. The clinical features are described and discussed.

Results of geometric arthroplasty for rheumatoid and osteoarthritis of the knee.

The Geometric Total Knee Arthroplasty was one of the earliest unconstrained knee arthroplasties available for the replacement of knees severely affected by destructive arthritis. This paper presents the results of Geometric knee arthroplasty performed by surgeons of the Alfred Hospital, Melbourne, during the years 1973 to 1977, this being the initial five years experience with this procedure. One hundred and fifty arthroplasty operations were performed in 106 patients, 78 for osteoarthritis and 72 for rheumatoid arthritis, with the average time from operation to review being four years. The Geometric arthroplasty was used in 147 of these operations. Assessment was based on a modification of the British Orthopaedic Association Knee Function Assessment Chart (1978) and 137 knees were available for review. Eighty nine percent of patients suffering osteoarthritis, and 79% of patients with rheumatoid arthritis were satisfied or enthusiastic with their prosthesis. Nineteen percent of rheumatoid patients and 4% of osteoarthritic patients considered the result of their operation disappointing. In both groups, the operated knee constituted minimal persisting disability to the patient when reviewed. Seventeen knees (11.3%) were assessed as unsatisfactory, of which 7 (4.6%) were due to infection, and 5 (3.3%) were due to loosening. Revision procedures were performed in 7 knees (5%), for instability or loosening. Improvements in arthroplasty design have resulted in alternative prostheses now being chosen by most surgeons for knee replacement, and the long term results of these newer prostheses must be evaluated with those results obtained using the original geometric prosthesis.

The Assessment of Acute Injuries of the Knee, with the Results of Early Ligament Repair.

Accurate assessment of the degree of damage sustained in an acute injury to the knee joint is of importance in determining treatment, and therefore to the future function of that joint. Adequate investigation, including examination of the joint under a general anesthetic with "strain" radiographs, is necessary. The results of surgical repair of ruptured ligaments in 22 knees arc reported, these results confirming the value of early ligament repair.