Repetition Rate Of Several Tens Research Articles

Synthesis of magnesium oxide and zinc oxide powders in a glow discharge plasma at atmospheric pressure

Investigation of the processes involved in the synthesis of magnesium oxide and zinc oxide powders using the thermal effects of an atmospheric-pressure glow discharge plasma in an inert gas flow are described. The discharge operates in a repetitively pulsed mode with pulse repetition rate of several tens of kilohertz and pulse duration up to 12 μs, discharge current of 600 mA and voltage up to 300 V. These parameters lead to thermal erosion of magnesium or zinc inserts in a molybdenum crucible. The chemical and phase composition of the erosion products were determined using TEM/EDS and X-ray diffraction analysis, and the composition of the plasma was assessed by optical emission spectrometry. This experimental approach allows fabrication of powders of these metal oxides with characteristic particle size 10–50 nm, and the formation of coatings of these materials in a one-step process.

Pulses on Demand in Fibre and Hybrid Lasers

This paper presents an investigation of pulse-on-demand operation in fibre and hybrid lasers. Two methods for efficient gain control that enable the generation of laser pulses at arbitrary times with controlled pulse parameters are presented. The method of direct modulation of the pump power in the high-power laser oscillator is shown to generate pulses with a duration in the nanosecond range, with repetition rates varying during operation from a single shot to over 1 MHz. An advanced method using a combination of marker and idler seeding a fibre amplifier chain is investigated. Such a system can easily achieve repetition rates of several tens of MHz. The lasers’ performances were successfully tested in a real environment on an industrial platform for laser transfer printing. Similar concepts were used for a laser source with ultrashort laser pulses (femtosecond range) on demand by using a mode-locked seed as a source and a solid-state amplifier to achieve high pulse energy and peak power.

Conceptual Design of a Laser Driver for a Plasma Accelerator User Facility

The purpose of the European project EuPRAXIA is to realize a novel plasma accelerator user facility. The laser driven approach sets requirements for a very high performance level for the laser system: pulse peak power in the petawatt range, pulse repetition rate of several tens of Hz, very high beam quality and overall stability of the system parameters, along with 24/7 operation availability for experiments. Only a few years ago these performances were considered unrealistic, but recent advances in laser technologies, in particular in the chirped pulse amplification (CPA) of ultrashort pulses and in high energy, high repetition rate pump lasers have changed this scenario. This paper discusses the conceptual design and the overall architecture of a laser system operating as the driver of a plasma acceleration facility for different applications. The laser consists of a multi-stage amplification chain based CPA Ti:Sapphire, using frequency doubled, diode laser pumped Nd or Yb solid state lasers as pump sources. Specific aspects related to the cooling strategy of the main amplifiers, the operation of pulse compressors at high average power, and the beam pointing diagnostics are addressed in detail.

Efficiency of cavity-enhanced high harmonic generation with geometric output coupling

Cavity-enhanced high-order harmonic generation (HHG) affords broadband, coherent extreme-ultraviolet (XUV) pulse trains with repetition rates of several tens of MHz. Geometrically coupling out the intracavity generated XUV beam through a small on-axis hole in the cavity mirror following the HHG focus has enabled scaling the photon energies attainable with this technology to 100 eV and more, promising new applications of XUV frequency-comb spectroscopy and attosecond-temporal-resolution, multidimensional photoelectron spectroscopy and nanoscopy. So far, in this approach the features of the macroscopic response of the gas target are neither accessible directly nor indirectly via the out-coupled XUV beam due to the loss of spatial information caused by the truncation at the hole. Here, we derive a simple analytical model for the divergence of the intracavity harmonic beam as a function of experimental design parameters such as gas target position, cavity geometry and driving pulse intensity, thereby establishing a connection between the measured XUV spectra and the macroscopic response of the intracavity nonlinear medium. We verify this model by comparison to numerical simulations as well as to systematic measurements, and apply it to elucidate a trade-off between the efficiency of geometric output coupling and that of the HHG process, and the underlying physical mechanisms. These findings illuminate the share of the output coupling efficiency to the overall HHG conversion efficiency and provide—together with previously studied plasma-related enhancement limitations—a holistic means of optimizing the overall efficiency with this architecture that uniquely combines high repetition rates with high photon energies. Furthermore, quantitatively connecting the output coupled, observable XUV radiation to the nonlinear conversion at the cavity focus allows for a better insight into the dynamics of intracavity HHG and might benefit other applications of femtosecond enhancement cavities, such as high-repetition-rate HHG spectroscopy.

Reactive oxygen species-related plasma effects on the apoptosis of human bladder cancer cells in atmospheric pressure pulsed plasma jets

Helium/oxygen atmospheric pressure plasma jets driven by pulsed dc voltage with repetition rate of several tens of kilohertz are utilized for plasma-cell interactions. The effect of operating parameters on the apoptosis of cultured human bladder (EJ) cancer cells is investigated. The parameters such as applied voltage, pulse repetition frequency, and duty ratio determine the plasma dose. The apoptotic changes in cells with plasma treatment are detected by staining assay and flow cytometry. Apoptosis rates are observed to correlate well with both the plasma dose and the levels of intracellular and extracellular reactive oxygen species.

Induction of apoptosis in human breast cancer cells by a pulsed atmospheric pressure plasma jet

By using an atmospheric pressure plasma jet driven by pulsed dc voltage with repetition rate of several tens of kilohertz, we were able to induce apoptosis in cultured human breast cancer cells (MCF-7). The apoptotic changes in cells with plasma treatment were detected by flow cytometry and fluorescence staining assay. A significant portion of these cells was observed to exhibit the apoptotic fragmentation. Helium plasma with additive O2 gas was found to be effective in the induction of apoptosis. This plasma jet provides an effective mode of human breast cancer cell therapy.

Construction of super-resolution microscope based on cw laser light source

We constructed a super-resolution microscope system based on a cw laser light source. Electro-optical modulators convert the cw laser light into a light pulse with a width of 15ns and provide a repetition rate of 100kHz. The performance of the microscope was evaluated using 100nmϕ fluorescence microbeads. The fluorescence signal from the beads can be detected with very low statistical fluctuation. The super-resolution image was obtained with better signal to noise ratio compared with that given by a pulse laser light source with a repetition rate of several tens of hertz. The fluorescent size of the beads was 150nm, which is 2.3 times smaller than the diffraction limit. Experimental results confirmed that the two-point resolution also overcomes the diffraction limit. The constructed system is expected to become a commercial microscope.

Sub-Picosecond Optical Pulse Generation with Repetition Rate of Several Tens of Gigahertz Using Electrooptic Standing-Wave Phase Grating with Periodic Domain Inversion

We propose and demonstrate a novel electrooptic spatiotemporal modulator for sub-picosecond optical pulse generation with a repetition rate of several tens of gigahertz. The pulse generation is directly accomplished with an electrooptic standing-wave phase grating with periodic domain inversion that operates over 10 GHz. This device produces a phase distribution that is like a sinusoidal standing wave in the beam cross section. The output optical beam undergoes Raman–Nath diffraction with diffracted beams whose intensities vary temporally. When we extract a certain diffracted beam, we can obtain a pulse train. A near-Fourier-transform-limit pulse train with a repetition rate of twice the modulation frequency can be obtained using the zero-order undiffracted beam. In the experiment, we found that our new device operates as theoretically predicted and that we can obtain a pulse train with a pulsewidth of about 1 ps from the fabricated device at the maximum modulation power. By improving the modulation efficiency of the device or by further increasing of the modulation frequency, a sub-picosecond optical pulse train with a repetition rate of several tens of gigahertz can be generated by the new device.

High-frequency repetitively pulsed operating regime in high-power wide-aperture lasers

A technique for obtaining a repetitively pulsed operating regime in high-power wide-aperture lasers is proposed and experimentally realised. In this regime, the laser emits a train of pulses with a duration of 0.1 — 1 μs and a pulse repetition rate of several tens of kilohertz. The main properties of the pulsed regime are theoretically analysed and the proposed technique is tested in detail employing a test-bench gas-dynamic laser. The results of the test confirmed the conclusions of the theoretical analysis. The possibility of realising a repetitively pulsed regime in high-power wide-aperture lasers without a reduction in the average output power is experimentally demonstrated.

Plasma supported processing with high-average-power infrared-lasers

Pulsed CO 2-lasers with their high intensities allow rather narrow heat affected zones to be obtained, such as required in many laser manufacturing processes. Plasma sustained laser target interaction phenomena were investigated which are observed above critical threshold power densities, with specific values for each type of material. These surface induced, highly ionized absorption waves are largely influencing the energy transfer from the coherent laser radiation field towards the targets. Experiments carried out at ISL were aimed at investigating plasma parameters by the use of high resolution, fast optical, electrical and optronical techniques including laser diagnostics. The results reveal improved absorption conditions by the use of high average power pulsed lasers which are operated even at rather low repetition rates of several tens to hundred pps.