Background: The clinical efficiency of laser treatments is limited by the low penetration of visible light used in certain procedures like photodynamic therapy (PDT). Second Harmonic Generation (SHG) PDT is an innovative technique to overcome this limitation that enables the use of Near Infrared (NIR) light instead of visible light. NIR frequency bands present an optical window for deeper penetration into biological tissue. In this research, we compare the penetration depths of 405 and 808 nm continuous wave (CW) lasers and 808 nm pulsed wave (PW) laser in two different modes (high and low frequency). Methods: Increasing thicknesses of beef and chicken tissue samples were irradiated under CW and PW lasers to determine penetration depths. Results: The 808 nm CW laser penetrates 2.3 and 2.4 times deeper than the 405 nm CW laser in beef and chicken samples, respectively. 808 nm PW (pulse frequency—500 Hz) penetrates deeper than CW laser at the same wavelength. Further, increasing the pulse frequency achieves higher penetration depths. High frequency 808 nm PW (pulse frequency—71.4 MHz) penetrates 7.4- and 6.0-times deeper than 405 nm CW laser in chicken and beef, respectively. Conclusions: The results demonstrate the higher penetration depths of high frequency PW laser compared to low frequency PW laser, CW laser of the same wavelength and CW laser with half the wavelength. The results indicate that integrating SHG in the PDT process along with pulsed NIR light may allow the treatment of 6–7 times bigger tumours than conventional PDT using blue light.

In this work we demonstrate how to analyze the dynamics of the correlated longitudinal current noise above and below the Poissonian shot-noise level in an e-beam, by calculating the emitted transition radiation (OTR) using a complex vector field formulation which is exact in the near and far fields. We simulate a non-zero emittance electron beam, uncorrelated in the transverse cross section, but with different types of longitudinal correlations, resulting in coherent optical transition radiation. We show how this method is applied on the opposite case (suppression), by tracking simulated beam particles that correlate due to quarter-plasma oscillation during drift, and show how the OTR tracks the dynamics of the electron beam noise level.

A 6 MeV hybrid RF e-gun is currently driving a THz FEL in Ariel University. Ultra-fast electron diffraction (UED) experimental plans are currently in progress in the center, and therefore, a secondary parallel beam line is required. The addition of a secondary beamline using a single e-gun can be achieved using a dogleg section. However, the high-quality beam parameters such as emittance and electron bunch duration are significantly distorted after passing a dispersive section, such as a dogleg section, making the e-beam quality insufficient for UED experiments. In this paper, we suggest an optimization method, for the reconstruction of the beam quality after the dogleg using realistic quad-fields and sextupoles. Full 3D general particle tracer simulations of this secondary beamline were used in the optimization procedure using realistic field-maps and fringe fields of the quadrupoles, which were designed in-house, and their 3D field-maps were exported using computer simulation technology. Significantly improved beam parameters were obtained using the real quadrupoles field profile combined with an optimization procedure using a large number of electron optical optimization variables.

A 6 MeV hybrid photo-cathode gun is driving a THz-FEL in Ariel University, as well as other applications. An electron bunch with small transverse emittance is extracted from a copper photo-cathode using a 1 ps UV laser pulse, and then accelerated to a kinetic energy of 6.5 MeV. The Hybrid term is due to the unique standing wave-traveling wave sections in a single RF cavity. Since low emittance is crucial for FEL operation, the characterization of the electron beam requires measuring the transverse emittance, which will be compared with the predicted design and the 3D simulation obtained values, in order to verify their correctness. In this paper, we confirm the use of the multi-slit technique to measure emittance in the Hybrid beam in a single shot and develop a simple and convenient algorithm to be used in the experimental measurements. The experimental analysis requires image processing of the measured data, combined with a custom LabVIEW and Matlab scripts to control the hardware, and analyze the obtained data. Prior to experimentally measuring emittance, we perform a simulated experiment, using a simulated beam from the General Particle Tracer (GPT) code to test these algorithms and scripts, and compare the emittance obtained using the algorithm with GPT’s estimated emittance. Once concluded, this method will allow for a simple, fast and accurate single shot emittance measurement for the Hybrid accelerator beam.

A superradiant FEL in the THz (3 THz) region is currently operating at Ariel University. It is based on the novel ORGAD accelerator, which is a hybrid linear RF photo-cathode 6 MeV electron gun. The hybrid term stands for its unique standing wave (SW)—traveling wave (TW) structure. The undulator generates spontaneous superradiance, which corresponds to spontaneous emission when the electron bunch duration is shorter than the radiated frequency, resulting in a much higher photon yield. However, the efficiency of this scheme is still quite low. In order to achieve higher emission (by improved efficiency), we intend to implement a new and promising radiative interaction scheme: tapering-enhanced superradiance (TES). This particular undulator design employs a tapered (amplitude) undulator in the zero-slippage condition to obtain a significantly more powerful and efficient THz radiation source. At the current stage, the scheme is designed for emission at approximately $0.5$ THz. The design and start-to-end simulations demonstrate significant enhancement of superradiant energy and extraction efficiency using this method compared to a reference uniform case.