Squared Focal Intensity Distributions for Applications in Laser Material Processing

Tailored intensity profiles within the focal spot of the laser beam offer great potential for a well-defined control of the interaction process between laser radiation and material, and thus for improving the processing results. The present paper discusses a novel refractive beam-shaping element that provides different squared intensity distributions converted from the Gaussian output beam of the utilized femtosecond (fs) laser. Using the examples of surface structuring of stainless-steel on the micro- and nano-scale, the suitability of the beam-shaping element for fs-laser material processing with a conventional f-Theta lens is demonstrated. In this context, it was shown that the experimental structuring results are in good agreement with beam profile measurements and numerical simulations of the beam-shaping unit. In addition, the experimental results reveal the improvement of laser processing in terms of a significantly reduced processing time during surface nano-structuring and the possibility to control the ablation geometry during the fabrication of micro-channels.

Effect of high intensity focused ultrasound on neural compound action potential : an in vitro study

Therapeutic ultrasound is a promising field with many novel applications in medicine and biology. High intensity focused ultrasound (HIFU) provides the ability to localize the deposition of acoustic energy within the body by thermal effect. In this work a brief description of how the HIFU system works and how it can be used to produce localized thermal lesions on the pathogenic tissues in the human body will be presented. Results of acoustic characterization of a hand-held HIFU system developed in our lab will also be presented. The capabilities of creating controlled reversible and irreversible changes in the compound action potential (CAP) values of a specific neural tissue, i.e. lobster abdominal nerves by adjusting different ultrasound parameters (intensity, exposure duration, etc.) in the HIFU system will also be described. Lobster abdominal nerves were exposed to a 10s HIFU exposure. The focal intensity values for this study were chosen as 100, 175, 275, 400, 525 and 700 W .cm ⁻². It was shown that a trend of small changes in the measured CAP values (increase in the CAP amplitude) could be achieved in the five intermediate intensities, while a drastic decrease in the measured CAP values and total degeneration of the nerve could be observed with the highest focal intensity of 700 W .cm⁻².

Effect of high intensity focused ultrasound on neural compound action potential : an in vitro study

Therapeutic ultrasound is a promising field with many novel applications in medicine and biology. High intensity focused ultrasound (HIFU) provides the ability to localize the deposition of acoustic energy within the body by thermal effect. In this work a brief description of how the HIFU system works and how it can be used to produce localized thermal lesions on the pathogenic tissues in the human body will be presented. Results of acoustic characterization of a hand-held HIFU system developed in our lab will also be presented. The capabilities of creating controlled reversible and irreversible changes in the compound action potential (CAP) values of a specific neural tissue, i.e. lobster abdominal nerves by adjusting different ultrasound parameters (intensity, exposure duration, etc.) in the HIFU system will also be described. Lobster abdominal nerves were exposed to a 10s HIFU exposure. The focal intensity values for this study were chosen as 100, 175, 275, 400, 525 and 700 W .cm ⁻². It was shown that a trend of small changes in the measured CAP values (increase in the CAP amplitude) could be achieved in the five intermediate intensities, while a drastic decrease in the measured CAP values and total degeneration of the nerve could be observed with the highest focal intensity of 700 W .cm⁻².

Transient Analysis of Fresnel Zone Plates for Ultrasound Focusing Applications

Fresnel Zone Plates are planar lenses that can be used to focus ultrasound beams. This kind of acoustic lenses can play a key role in the resolution of ultrasonic NDT systems. In this type of pulse-echo applications, the pulse duration is an important parameter that specifies the axial resolution, and thus, shorter ultrasound pulses provide higher resolutions. However, acoustic lenses exhibit a transient response that should be considered when setting the pulse duration, as pulses shorter than the transient state duration result in degradation in the response of acoustic lenses in terms of focal intensity, focal displacement, and lateral and axial resolutions. In this work, a thorough analysis of the transient response of Fresnel Zone Plates is discussed, demonstrating that the transient state should be considered in order to achieve optimal focusing performance. Theoretical and numerical results are presented, showing very good agreement.

Leigh Syndrome in an Adolescent Girl: A Case Report

Leigh syndrome (LS) is a disorder of infancy and rarely late childhood. It presents with regression of mental and motor skills. Here, we present LS in an adolescent girl who presented with generalized dystonia and cognitive decline. Her infective, metabolic, endocrinal and autoimmune work up was normal. The neuroimaging showed progressive symmetric involvement of basal ganglia with focal intensity over bilateral lentiform nucleus and thalamic region. The cerebrospinal fluid (CSF) lactate level was elevated. Genetic test could not be performed; however the history of neuro-regression with extrapyramidal involvement with CSF and neuroimaging finding led to the diagnosis of Leigh’s syndrome.

Adaptive optics in laser processing

Adaptive optics are becoming a valuable tool for laser processing, providing enhanced functionality and flexibility for a range of systems. Using a single adaptive element, it is possible to correct for aberrations introduced when focusing inside the workpiece, tailor the focal intensity distribution for the particular fabrication task and/or provide parallelisation to reduce processing times. This is particularly promising for applications using ultrafast lasers for three-dimensional fabrication. We review recent developments in adaptive laser processing, including methods and applications, before discussing prospects for the future.

Sub-diffraction positioning of a two-photon excited and optically trapped quantum dot

An optically trapped, two photon excited, and sub-diffraction tracked quantum dot explores the entire focal intensity volume.