Short-wavelength Light Sources Research Articles

Sensitivity of nonlinear photoionization to resonance substructure in collective excitation.

Collective behaviour is a characteristic feature in many-body systems, important for developments in fields such as magnetism, superconductivity, photonics and electronics. Recently, there has been increasing interest in the optically nonlinear response of collective excitations. Here we demonstrate how the nonlinear interaction of a many-body system with intense XUV radiation can be used as an effective probe for characterizing otherwise unresolved features of its collective response. Resonant photoionization of atomic xenon was chosen as a case study. The excellent agreement between experiment and theory strongly supports the prediction that two distinct poles underlie the giant dipole resonance. Our results pave the way towards a deeper understanding of collective behaviour in atoms, molecules and solid-state systems using nonlinear spectroscopic techniques enabled by modern short-wavelength light sources.

Electrochromic properties of bipolar pulsed magnetron sputter deposited tungsten–molybdenum oxide films

There are great interests in electrochromic technology for smart windows and displays over past decades. In this study, the WMoOx thin films were deposited onto indium tin oxide glass and silicon substrates by pulsed magnetron sputter system with W and Mo targets. The films were deposited with fixed W target power while the variant parameter of Mo target power in the range 50, 100, 150 and 200W was investigated. The working pressure was fixed at 1.33Pa with a gas mixture of Ar (30sccm) and O2 (15sccm). The film thickness increased with the Mo target power. Higher plasma power resulted in a crystalline structure which would reduce the electrochromic property of the film. The influence of plasma powers applied to Mo target on the structural, optical and electrochromic properties of the WMoOx thin films has been investigated. WMoOx films grown at Mo target powers less than 100W were found to be amorphous. The films deposited at 150W, which is the optimal fabrication condition, exhibit better electrochromic properties with high optical modulation, high coloration efficiency and less color memory effect at wavelength 400, 550 and 800nm. The improvement resulted from the effect of doping Mo has been tested. The maximum ΔT (%) values are 36.6% at 400nm, 65.6% at 550nm, and 66.6% at 800nm for pure WO3 film. The addition of Mo content in the WMoOx films provides better resistance to the short wavelength light source and can be used in the concerned application.

Crystalline undulator radiation and motion behavior in the vicinity of the resonance line

Searching for new light source, especially short wave-length coherence light source has attracted extensive attention. The using of the crystalline undulator radiation as a short wave-length coherence light source is most likely to be one of the options. From the viewpoints of potential and field, the centrifugal force generated by periodic bent crystal is regarded as centrifugal potential, the particle motion equation is reduced to Mathieu equation with Duffing-type, and from the energy viewpoint the stability of the system is discussed. The behaviors of particles in the vicinity of the resonance are analyzed by perturbation method; the jump phenomena and instable behavior are revealed. The results show that the stability of the system is related to its parameters, and only properly adjusting these parameters, the bifurcation and instability for the system can be avoided in principle.

Noninvasive monitoring with strongly absorbed light

The transmission of light through tissue is used in noninvasive monitoring, in particular photoplethysmography. Investigations involving the transmission of wavelengths absorbed by bilirubin (short wavelength visible light) have been limited, due to strong absorption by haemoglobin. Achieving transmission of these wavelengths through tissue may advance noninvasive monitoring of substances like bilirubin. This work investigates the use of high power light sources together with improvements in signal-to-noise ratio as a means of enabling the transmission of strongly absorbed light through tissue. A custom device using multiple high-power short-wavelength visible light sources together with low power red and infrared sources, and background light cancellation to improve signal-to-noise ratio, was constructed. Transmission of 454-1200 nm light through tissue was achieved, with pulsations present in measured signals. The transmission through tissue of multiple wavelengths of strongly absorbed light can be achieved by using high power light sources in conjunction with cancelling the effect of background light. Use of these techniques may allow investigations into the noninvasive monitoring of substances such as bilirubin using photoplethysmography.

Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

Parametric excitation and stability of crystalline undulator radiation

Looking for a new light source, especially short-wavelength coherent light source has attracted much attention. A possibility and basic conditions are discussed by using crystalline undulator field radiation as a short-wavelength laser; it is pointed out that the short-wavelength laser has not yet been available so far which is due to not only technical reasons, but also physical reasons. In this paper, the physical problem is analyzed by using parametric excitation method. Introducing the sine-squared potential, the particle motion equation is reduced to a pendulum equation with a damping term and parameter excitation term in the framework of classical mechanics and the dipole approximation. A stability of the system is discussed using Melnikov method, and the critical condition of the system is also analyzed. The results show that the stability of the system relates to its parameters. By adjusting these parameters appropriately, the stability of the system can be ensured in principle.

Organic Thin-Film Transistors with Tailored Liquid Sources of High-κ HfO2 Using Excimer Laser Irradiation

The characteristics of organic thin-film transistors (OTFTs) with tailored liquid sources of HfO2 as a high-κ insulator were investigated using excimer laser irradiation. We have demonstrated that the OTFT characteristics were improved more by short wavelength light source irradiation than UV irradiation to cleave chemical bonds of organic residues in the alkoxy-derived HfO2 films. The field-effect mobilities and on–off ratios obtained for one shot of excimer laser irradiation were 0.18 cm2 V-1 s-1 and 750, respectively.

Laser-driven amplification of soft X-rays by parametric stimulated emission in neutral gases

The high-order harmonics of short laser pulses created in a nonlinear medium are a useful source of extreme-ultraviolet and soft-X-ray radiation. A newly discovered phenomenon that amplifies this emission even further could improve the efficiency of short-wavelength light sources.

A high-speed laser for future data-communication links

Optimized designs significantly improve the transmission rate of standard short-wavelength light sources.

Synchrotron Radiation From Laser-Accelerated Monoenergetic Electrons

In this paper, we report on the generation of incoherent synchrotron radiation in the visible spectral range which is produced by laser-accelerated electrons with 55-75-MeV energy as they propagate through an undulator. Simultaneous detection of electron and photon spectra allows for precise comparison between experimental results and undulator theory. First- and second-order undulator radiation was detected. The agreement between experiment and theory and the exclusion of other effects proves that the observed radiation is generated in the undulator. Beyond that, this experiment introduces laser-accelerated electrons into the radio-frequency accelerator domain of synchrotron light sources. This marks a noticeable step toward a new, compact, and brilliant short-wavelength light source.

Application of inclined-exposure and thick film process for high aspect-ratio micro-structures on polymer optic devices

In this paper we apply an inclined-exposure technology, while also using a polymeric material to make 3D optical micro-structure like dove prism and hardened reflecting mirrors in blue-DVD pickup head module. In contrast to the more common type of inclined mirrors, single-lensed reflecting mirrors, the micro-reflecting mirror being developed within the scope of this paper possesses the qualities that it requires no metal for its reflecting surface, and it is structurally stable. When used in micro-optical systems, it is less prone to experiencing structural changes and impact to the system’s optical paths as a result of heat generated from the light source. The fabrication technology for dove prism being developed can be used to easily fabricate highly integrated micro-optical systems. The structure being fabricated can reach a height of 1.8 mm, while the degree of surface roughness meets the necessary Marechal optic quality criterion. In this paper we will also issue of the structure of the SU-8 material being wider at the top and narrower at the bottom due to short-wavelength light source having shallower penetration. The polymeric material used has a high penetration rate of 95% (red light), and is low in cost. As such, we may apply and consolidate micro-structures in TIR, CD/DVD, SPR, and micro-PIV systems, or optical systems in general. These novel methods can be employed for the fabrication of nontraditional 3D structures on photo polymer for Optical MEMES applications.

Behaviour of scintillators under XUV free electron laser radiation

Free electron lasers (FEL) are new generation accelerator-based short wavelength light sources providing high pulse intensity and femtosecond pulse duration, which enable investigation of interaction of elementary excitations in solids under extreme conditions. Using the FLASH facility of HASYLAB at DESY (Hamburg, Germany), we investigated the response of different materials with scintillating properties based on intrinsic emissions to the 25.6 and 13.8 nm FEL radiation by means of time-resolved luminescence spectroscopy. FLASH delivered single pulses of 25 fs duration having energy per pulse up to 30 μJ resulting in power densities of ∼10 12 W/cm 2 on crystals. As a function of excitation density we observed the shortening of lifetime and non-exponential behaviour of emission decays in CaWO 4, while the emission spectra recorded are comparable to those obtained at conventional excitation sources.

STATUS AND PERSPECTIVES OF PHOTOINJECTOR DEVELOPMENTS FOR HIGH BRIGHTNESS BEAMS

The development and reliable operation of high brightness electron sources are key issues for next generation short wavelength light sources and a future linear collider. This paper will concentrate on photo emission based injector developments for various projects which require individual solutions and face specific problems and challenges. A selective overview of developments and experimental results will be presented demonstrating that for a large parameter range dedicated photo injectors are able to fulfill the specific stringent requirements on beam quality and other beam parameters, e.g. the time structure of the beam.

UV-SLPT for Gas Sensor Research on MISiC Devices

A modified Scanning Light Pulse Technique (SLPT) setup that can be used to evaluate SiC-based gas-sensitive field-effect devices is introduced. This is exemplified with measurements on a Pt-MISiC capacitor that has a metal thickness gradient. The device shows large responses to hydrogen and ammonia in air. The H2 and NH3 responses show a complementary dependence on the Pt film thickness at 140degC. The temperature dependence differs however for the two gases. The measurement setup uses UV transparent optics together with mechanical chopping of light from a short wavelength light source. The spatial resolution of the system is found to be approximately 50 mum

Measurement of Vacuum Ultraviolet Radiation with Diamond Photo Sensors

A thin-film diamond UV sensor is a solar-blind photo detector sensitive to only vacuum ultraviolet regions. We have used this sensor to measure the intensity of vacuum ultraviolet light emitted from a xenon excimer lamp, a short-wavelength light source, and the sensor has shown stable sensitivity over 98-hour radiation with an irradiance of 10mW/cm2 of xenon excimer lamp. Therefore, the diamond UV sensor is promising as a photo detector able to measure vacuum ultraviolet radiation, the use of which is increasing.

Novel Photon Processes with Efficient Short-Wavelength Light Sources

Novel Photon Processes with Efficient Short-Wavelength Light Sources

Leaky-waveguide configuration for quasi-phase-matched second-harmonic generation

We consider quasi-phase-matched (QPM) second-harmonic generation in a leaky-waveguide structure in which the fundamental is a guided mode and the second harmonic is radiated into the substrate. Under a no-pump-depletion approximation and using the coupled-mode theory, we show through numerical calculations that by an appropriate choice of the thickness of the index depression region of the leaky waveguide one can achieve conversion efficiencies and tolerance values that are intermediate between QPM and QPM Čerenkov configurations. The proposed configuration thus possesses the advantages of both QPM guided-to-guided and Čerenkov configurations and hence should be of interest in the realization of short-wavelength light sources.

Inverse Compton γ-ray source for nuclear physics and related applications

Abstract The development of intense, short-wavelength FEL light sources has opened opportunities for new applications of high-energy Compton-backscattered photons. These applications range from medical imaging with X-rays to high energy physics with photon colliders. In this paper we discuss the practical aspects applications using polarized Compton backscattered γ-rays in the 5–150 MeV range from the Duke storage-ring-driven FEL. Such applications include: nuclear physics, cancer therapy, radiographic imaging, radiation effects testing, and positron production for material science studies.

Development and applications of a plasma waveguide for intense laser pulses

The demonstration of optical guiding of high-intensity laser pulses in a plasma fiber waveguide [C. G. Durfee III and H. M. Milchberg, Phys. Rev. Lett. 71, 2409 (1993)] has opened the way to new advances in the development of nonlinear optics-based short-wavelength light sources, soft x-ray lasers, and compact laser-driven charged particle accelerators, and offers a new practical realm in which to study, control, and apply nonperturbative laser–matter interactions at ultrahigh intensity. An overview of selected experimental and theoretical results and their applications is presented.

Development of short-wavelength coherent XUV light sources at SIOFM

Recent progress on the development of short-wavelength coherent XUV light sources at SIOFM is presented, including the space- and time-resolved observation of short-wavelength lasing by lithium-like Si11+, Ca17+, and Ti19+ ions and H-like F8+ ion, and the theoretical design for new approaches, such as controlled expansion cooling, x-ray pumping and strongly radiative cooling.