Cw Beam Research Articles

Three-dimensional, dual-color nanoscopy enabled by migrating photon avalanches with one single low-power CW beam

The development of super-resolution fluorescence microscopy is very essential for understanding the physical and biological fundamentals at nanometer scale. However, to date most super-resolution modalities require either complicated/costly purpose-built systems such as multiple-beam architectures or complex post-processing procedures with intrinsic artifacts. Achieving three-dimensional (3D) or multi-channel sub-diffraction microscopic imaging using a simple method remains a challenging and struggling task. Herein, we proposed 3D highly-nonlinear super-resolution microscopy using a single-beam excitation strategy, and the microscopy principle was modelled and studied based on the ultrahigh nonlinearity enabled by photon avalanches. According to the simulation, the point spread function of highly nonlinear microscopy is switchable among different modes and can shrink three-dimensionally to sub-diffraction scale at the photon avalanche mode. Experimentally, we demonstrated 3D optical nanoscopy assisted with huge optical nonlinearities in a simple laser scanning configuration, achieving a lateral resolution down to 58 nm (λ/14) and an axial resolution down to 185 nm (λ/5) with one single beam of low-power, continuous-wave, near-infrared laser. We further extended the photon avalanche effect to many other emitters to develop multi-color photon avalanching nanoprobes based on migrating photon avalanche mechanism, which enables us to implement single-beam dual-color sub-diffraction super-resolution microscopic imaging.

Commissioning results of single bunch selection system for the RAON heavy-ion accelerator facility

To enable neutron time-of-flight experiments at the RAON heavy-ion accelerator facility, we tested a single bunch beam selection method by combining an RF chopper and a double gap buncher in the low-energy beam transport section. The RF chopper converts a CW beam into a hundreds-nanosecond pulsed beam. Then, the double gap buncher performs bunching to shorten the pulse length to less than one radio frequency quadrupole (RFQ) cycle. Ideally, a single isolated bunch can be achieved after the RFQ. In this study, we discuss the design concept of the single bunch selection system and present initial beam commissioning results.

Thermal-stress-induced birefringence management of complex laser systems by means of polarimetry

The novel method of the thermally-induced polarization changes driven power losses (TIPCL) analysis in the complex laser systems has been developed. The measurement has been tested on the amplifier chain of the 100 J / 10 Hz laser system ‘Bivoj’ operated at HiLASE Centre. By the usage of the measured non-uniform Mueller matrix of the amplifier chain, the optimization of the ideal input and output polarization state has been calculated numerically. The results of the optimization have been applied to the laser system, thus reducing the TIPCL from originally observed more than 33% to 7.9% for CW beam and to 9% for pulsed laser beam, respectively. To the best of our knowledge, this result represents the most efficient TIPCL suppression method for complex laser systems so far. The method also allows the definition of the ideal fully polarized non-uniform pre-compensation of input beam consequently suffering from zero TIPCL.

Design study of a single bunch selection method for neutron TOF experiment at RAON heavy ion accelerator

To enable neutron time-of-flight (TOF) experiments at the RAON heavy-ion accelerator facility, we propose a single bunch beam selection method by combining a fast chopper and double gap buncher in the low-energy beam transport (LEBT) section. The fast chopper operates with switching times of tens of ns to convert a CW beam into a pulsed beam.Then, the double gap buncher performs bunching to shorten the beam pulse duration to less than one radio frequency quadrupole (RFQ) cycle.Ideally, a single isolated bunch can be achieved after the RFQ.In this study, we discuss the system design of the proposed single bunch selection scheme and present detailed beam dynamics simulations.

Reverse-Taper Mid-Infrared Quantum Cascade Lasers for Coherent Power Scaling

We present a reverse-taper quantum cascade laser (QCL) emitting at 4.6 μm, a novel-geometry device that can scale the output power while maintaining good beam quality. Buried-ridge waveguides with tapered and straight regions were formed by ICP etching and HVPE regrowth – the tapered region scales the output power, while the emitting facet is located at the narrow-end taper section, which provides mode filtering by suppressing high-order spatial modes. Beam profiles were observed under quasi-continuous-wave (QCW)/CW operation and beam quality (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) measurements along with beam-stability measurements were performed – a small degree of collimated-beam centroid movement (<0.46 mrad, peak-to-peak) was observed, along with M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> values close to 1 up to ∼1 W QCW power. Devices of shorter cavity lengths were also investigated, indicating that the output power scales with the core-region volume but results in a small increase in angular deviation.

High brilliance beam investigations at the universal linear accelerator

The more than 45-year-old GSI-UNILAC (universal linear accelerator) as well as the heavy ion synchrotron SIS18 will serve as a high-current heavy ion injector for the new Facility for Antiproton and Ion Research (FAIR) synchrotron SIS100. UNILAC will serve together with the SIS18 as FAIR injector for short intense pulse operation; the newly developed heavy ion linac Helmholtz linear accelerator shall deliver cw beams, still required for the comprehensive research program at GSI. In the context of an advanced machine investigation program in combination with the ongoing UNILAC upgrade program, a dedicated beam investigation campaign has been carried out in order to characterize front-to-end high-current medium and heavy ion beam behavior at GSI-UNILAC. A very high beam brilliance at the end of transfer line from UNILAC to SIS18 was achieved recently for medium heavy ion beams in a machine experiment campaign. This is an important step paving the way to fulfill the FAIR heavy ion high-intensity beam requirements. Results of high-current uranium beam measurements applying the novel technique of pulsed hydrogen gas stripping (at $1.4\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$) will be presented as well.

High-current H2 + beams from a filament-driven multicusp ion source.

We report the results from a new multicusp ion source (MIST-1) that produces record steady-state currents of H2 + (1 mA) from this type of ion source with high purity (80% H2 +). We built MIST-1 to fulfill the stringent beam purity and beam quality requirements for IsoDAR, a proposed discovery-level neutrino experiment, requiring a 10 mA, 60 MeV/amu continuous wave (cw) proton beam on the target. IsoDAR will use a cyclotron accelerating H2 + ions and using a novel radio frequency quadrupole (RFQ) direct injection method. Systematic measurements, varying discharge voltage, discharge current, and gas pressure, indicate that the ideal operating regime is at low pressure, high discharge current, and high discharge voltage. We have measured the combined species emittance after the source extraction to be <0.05 π-mm-mrad (rms, normalized) for a 0.95 mA beam. Beyond showing high currents and high H2 + fraction, our measurements agree well with high fidelity simulations. These results show the feasibility of using a multicusp ion source for IsoDAR and the RFQ direct injection prototype and paves the way to record breaking cw beam currents of 5 mA H2 + (equivalent to 10 mA protons) from compact cyclotrons, ideal for underground installation.

Angular momentum of the vortex ultrashort pulsed beam with a smaller beam waist.

The angular momentum (AM) of light has important implications for many fields of optics research, such as optics communication, quantum information and laser-scan microscopy. Thus, in this paper, we intend to investigate the average AM of the vortex ultrashort pulsed beam (VUPB), which is generated and widely applied in the field of high-intensity and ultrafast regimes. According to the vector potential, we firstly derive the electromagnetic field of the VUPB, then analyze the spatial intensity, the phase profile and the polarization state of the beam. We explore that the total AM per photon of VUPB is not n ℏ value when the beam waist w0 is of wavelength or sub-wavelength order, since the polarization of VUPB is changed from linear to circular polarization with the decrease of beam waist, which introduces the conversion of the orbital AM to the spin AM. Moreover, based on the conservation of the total AM, the minimum waist of VUPB can be obtained, which is dependent on the pulse duration time α and topological charge n. Finally, the average AM of the fractional VUPB expressed by the superposition of the integer VUPB with different weights, is analyzed, which is not equal to the AM of fractional CW beam μ - sin (2μπ)/2π (μ is the fractional topological charge), but is associated with the beam waist w0 and α. Therefore, we think that the AM of VUPB can be controlled by adjusting the α and w0.

Photo-acoustic response and optical features of 2D-TlGaSe2 and GaAs semiconductors

The paper focuses on investigation of the acoustic-optical properties of 2D-TlGaSe2 and GaAs semiconductors using laser pulses. We present the photo-darkening experiments performed by using CW light in spectral ranges below the band gap of TlGaSe2. The data provides evidence that photo-acoustic signals (PAS) for the above band gap are significantly stronger and linear in 2D-TlGaSe2 while they are distorted by nonlinear processes in isotropic GaAs. The comparison discloses characteristic parameters of TlGaSe2, namely a high factor and a negative sign in the refraction coefficient with pressure, a low absorption coefficient and absence of band filling; all guarantee stabile energy conversion by thermoelastic deformation mechanism. Below the band gap range, we found a new kind of PAS in TlGaSe2 on near surfaces. Likewise, we demonstrate that in such spectral range the giant Stark effect in TlGaSe2 is created by focused CW beams. The Stark effect produces local optical darkening which can provide explosion at extreme light power. Likely, both effects could be related to the planar stacking faults in 2D-TlGaSe2, which produce a spontaneous charge separation on layers.

Single Molecule Flourescence Methods to Monitor Site-Specific Fluctuations of Cy3 Monomer and Dimer Labeled DNA Constructs within Macromolecular Machines

Local fluctuations of the sugar-phosphate backbones of DNA (a form of DNA ‘breathing’) play key roles in protein-DNA assembly and enzymatic function. By monitoring spectroscopic signals from single-molecules of DNA constructs labeled with optical probes that are either rigidly inserted into the sugar-phosphate backbones or attached using flexible linkers, it is possible to study local conformational fluctuations within DNA at specific sites, and the dependence of these fluctuations on base sequence and secondary structure. Here we present two experimental single molecule spectroscopic methods, recently developed in our laboratory, to monitor the local fluctuations of Cy3-labeled DNA constructs. Both methods combine single-molecule total internal reflection fluorescence (TIRF) microscopy with polarized, phase-modulated optical excitation to detect, alternatively, linear and nonlinear optical signals. In Method 1 we use a linearly polarized continuous wave (cw) beam to excite the sample, so that the emitted fluorescence contains information about the rotational motion of a Cy3 monomer labeled DNA construct, or alternatively, the relative conformational changes of a Cy3 dimer inserted into the DNA sugar-phosphate backbones. In Method 2, we use sequences of broadband optical pulses to excite the sample, so that the ensuing fluorescence contains information about the linear absorbance spectrum, and alternatively, the two-dimensional fluorescence spectrum (2DFS). The latter experiments can be used to monitor the details of local conformational changes of a Cy3 dimer labeled DNA construct. Together, the two methods can be used to study biomolecular dynamics with varying levels of time resolution and structural information. For example, Method 1 can be applied to study sub-millisecond equilibrium fluctuations of Cy3 labeled DNA constructs, while Method 2 is well suited to monitor conformational transitions of a Cy3 labeled DNA construct during a biochemical reaction.

Comparative analysis of the potential of state-of-the-art lasers and new prototypic high-power beam sources for cutting nonmetals

At Fraunhofer IWS Dresden, different, partially prototypic high-power continuous wave (cw) beam sources for the remote laser processing of nonmetals with galvanometric-driven scanner systems are available. The emitted wavelengths of the lasers cover the range from visible light to mid-infrared. A spectroscopic analysis was performed to gain insight into the processability of typical nonmetal materials with single wavelengths. The wavelength-depending absorption was calculated based on the measured reflectivity and transmissivity of the selected materials. Relating to these results, the theoretic potential of the beam sources was verified in a comparable cutting research. The investigated work pieces are representatives of the groups of thermoplastics and thermosets, fiber-reinforced polymers, glasses, natural fiber textiles, and cellulosic based materials. The laser systems were divided in two groups for the investigation. To get a reference of the processability with state-of-the-art cw systems, a CO2 laser with a wavelength of 10.6 μm and a solid-state Yb:YAG fiber laser with 1.07 μm were used. The new prototypic beam sources were a green laser with a wavelength of 0.515 μm, a CO laser with a range of 5.3–5.8 μm, and a CO2 laser with 9.3 μm in a power range from 1 to 1.5 kW. Differences in the possible focusability are caused by the wavelengths and given beam qualities. For a direct comparison, these differences needed to be compensated. To get comparable intensities, the spot diameter in the working distance for each laser was set to 250 μm. This allows to process the materials with almost the same intensities. Since the laser sources with the short wavelengths offer a better focusability, experiments with the smallest possible focus diameters for the used optics were performed to get an optimized ablation result. Finally, the aim of the research was to evaluate the suitability of the available beam sources for new fields of application. The latest results of experimental and theoretical investigations on the remote laser processing of nonmetals with a wide range of laser wavelength will be presented and discussed.

Validation of the Linear IFMIF Prototype Accelerator (LIPAc) in Rokkasho

For the development of the International Fusion Materials Irradiation Facility (IFMIF) aiming at material tests for fusion power plants, the construction of the Linear IFMIF Prototype Accelerator (LIPAc) has been conducted at Rokkasho, Japan under the Broader Approach Agreement. The commissioning of LIPAc has been progressing significantly. The world most powerful RFQ successfully accelerated proton beam of 58 mA, and an important project milestone of the acceleration of deuteron beam to 5 MeV with the beam current of 125 mA in pulse mode was successfully achieved. The result proves the validity of the present RFQ design. The adjustment and tuning of the RF power system and the injector for enabling an operation at maximum performances played an important role in achieving this result. For the next step, the preparation of the high duty cycle operation of RFQ is underway. The installation of the HEBT (High Energy Beam Transport line) and the beam dump accepting 1 MW, CW beam, has been completed and a new beam transport line is under manufacturing. Also the assembly of the Superconducting RF (SRF) linac to accelerate the beam up to 9 MeV started in a clean room in Rokkasho.

Parity-violating electron scattering

Parity violating electron scattering has been a very useful tool for probing the structure of neutral currents and providing detailed information on electroweak form factors. A pioneering SLAC measurement in the mid-70’s provided an important early test of the Standard Model. Modern electron accelerators provide high intensity (&gt;100 μA), CW beams with polarizations as high as 85%. Experiments such as SAMPLE, A4, HAPPEX and G0 have exploited these capabilities and obtained new information on electroweak strange form factors in the Q2 range of 0.1-1.0 GeV2. That activity continues. Other experiments are designed to provide stringent tests of the Standard Model. E-158 at SLAC recently measured the weak charge of the electron. Qweak is a challenging new experiment at JLAB which is designed to measure the weak charge of the proton. This will probe for physics beyond the Standard Model corresponding to energy scales of more than 5TeV.

Design of an optically-locked interferometer for attosecond pump-probe setups.

We present the design and performance of an active stabilization system for attosecond pump-probe setups based on a Mach-Zehnder interferometer configuration. The system employs a CW laser propagating coaxially with the pump and probe beams in the interferometer. The stabilization is achieved with a standalone feedback controller that adjusts the length of one of its arms to maintain a constant relative phase between the CW beams. With this system, the time delay between the pump and probe beams is stabilized within 10 as rms over several hours. The system is easy to operate and only requires a few minutes to set up before any pump/probe measurements.

Isotope production by the high current proton beam of CYCIAE-100

CYCIAE-100, a 100 MeV high current compact cyclotron has been constructed and first beams were extracted in 2014. The machine has 5 beam lines for multi-application purposes. N1, one of the beam lines, is designed for high current beam transportation, for beam dump tests and isotope production. In 2016, a mA proton beam was tested on the internal target. In 2017 and 2018, 200 μA and 520 μA proton beams were extracted and transported to the beam dump respectively. In addition to increasing the cw beam power of 52 kW extracted from the machine and transported to the beam dump, this paper will also present the simultaneous dual-beam extraction from CYCIAE-100 and the improvement of the uniformity of the beam spot on the target, which will benefit isotope production.

Space charge and microbunching studies for the injection arc of MESA

For intense electron bunches traversing through bends, as for example the recirculation arcs of an energy recovery linac (ERL), space charge (SC) may result in beam phase-space degradation. SC modifies the electron transverse dynamics in dispersive regions along the beam line and causes emittance growth for mismatched beams or for specific phase advances. On the other hand, longitudinal space charge together with dispersion can lead to the microbunching instability (MBI). The present study focuses on the 180° low energy (5 MeV) injection arc lattice for the multi-turn Mainz Energy-recovering Superconducting Accelerator (MESA), which should deliver a CW beam at 105 MeV for physics experiments with an internal target. We will discuss matching conditions with space charge together with the estimated microbunching gain for the arc. The implication for the ERL operation is outlined, using 3D envelope and tracking simulations.

Low-temperature poly Si TFTs via BLDA for a Ne-sputtered Si film using sputtered gate SiO2

ABSTRACTAmorphous SiO2 and amorphous Si films were deposited on glass using radio frequency (RF) sputtering, and were subsequently poly-crystallized using blue-laser diode annealing (BLDA) scanned by a CW beam. Ne, which has a smaller atomic radius than Ar, was used for the sputtering of the Si film. For the gate insulator, a small amount of O2 gas diluted with Ar was flown during the sputtering to optimize the SiO2 film with a low leakage current. A simple TFT structure with a metal source and drain (S/D) was adopted to realize a low-temperature process with a low fabrication cost. Furthermore, to confirm the effectiveness of the sputtered gate oxide, a poly-Si TFT adopting a Si film deposited using plasma-enhanced chemical vapor deposition (PE CVD) for the channel was fabricated and was compared with the TFT with a sputtered Si film for the channel. Reasonable Vg-Id characteristics were obtained for both poly-Si TFTs. The TFT structure with a metal S/D formed through a low-temperature sputtering-based process is expected to be applied to Si TFTs on an arbitrary flexible panel.

Generation of quasi continuous-wave electron beams in an L-band normal conducting pulsed RF injector for laboratory astrophysics experiments

We report on an approach to produce quasi continuous-wave (cw) electron beams with an average beam current of milliamperes and a mean beam energy of a few MeV in a pulsed RF injector. Potential applications are in the planned laboratory astrophysics programs at DESY. The beam generation is based on field emission from a specially designed metallic field emitter. A quasi cw beam profile is formed over subsequent RF cycles at the resonance frequency of the gun cavity. This is realized by debunching in a cut disk structure accelerating cavity (booster) downstream of the gun. The peak and average beam currents can be tuned in beam dynamics simulations by adjusting operation conditions of the booster cavity. Optimization of the transverse beam size at specific positions (e.g., entrance of the plasma experiment) is performed by applying magnetic focusing fields provided by solenoids along the beam line. In this paper, the design of a microtip field emitter is introduced and characterized in electromagnetic field simulations in the gun cavity. A series of particle tracking simulations are conducted for multi-parametric optimization of the parameters of the produced quasi cw electron beams. The obtained results will be presented and discussed. In addition, measurements of the parasitic field emission (PFE) current (dark current) in the PITZ gun will be exemplarily shown to distinguish its order of magnitude from the produced beam current by the designed field emitter.

Automatic detection of recoil-proton tracks and background rejection criteria in liquid scintillator-micro-capillary-array fast neutron spectrometer

We describe an analysis procedure for automatic unambiguous detection of fast-neutron-induced recoil proton tracks in a micro-capillary array filled with organic liquid scintillator. The detector is viewed by an intensified CCD camera. This imaging neutron detector possesses the capability to perform high position-resolution (few tens of μm), energy-dispersive transmission-imaging using ns-pulsed beams. However, when operated with CW or DC beams, it also features medium-quality spectroscopic capabilities for incident neutrons in the energy range 2–20 MeV.In addition to the recoil proton events which display a continuous extended track structure, the raw images exhibit complex ion-tracks from nuclear interactions of fast-neutrons in the scintillator, capillaries quartz-matrix and CCD. Moreover, as expected, one also observes a multitude of isolated scintillation spots of varying intensity (henceforth denoted ”blobs”) that originate from several different sources, such as: fragmented proton tracks, gamma-rays, heavy-ion reactions as well as events and noise that occur in the image-intensifier and CCD. In order to identify the continuous-track recoil proton events and distinguish them from all these background events, a rapid, computerized and automatic track-recognition-procedure was developed.Based on an appropriately weighted analysis of track parameters such as: length, width, area and overall light intensity, the method is capable of distinguishing a single continuous-track recoil proton from typically surrounding several thousands of background events that are found in each CCD frame.

Wavelength diversification of high-power external cavity diamond Raman lasers using intracavity harmonic generation.

We report a high power quasi-continuous-wave (QCW) 620 nm laser from an external cavity diamond Raman laser utilizing intracavity frequency doubling in lithium triborate. Output power of 30 W for durations of 0.25 ms at 15% conversion efficiency was achieved with a beam quality factor M2 = 1.1 from a free-running Nd:YAG pump laser of M2 = 1.5. The critical design parameters that affect conversion efficiency and power were analysed with the aid of an analytical model. By adaptation to other pump technologies, the diamond approach provides a novel pathway towards high brightness CW beam generation in the visible and ultraviolet regions.