An imaging proton spectrometer for short-pulse laser plasma experiments

The ultraintense short pulse laser pulses incident on solid targets can generate energetic protons. In addition to their potentially important applications such as in cancer treatments and proton fast ignition, these protons are essential to understand the complex physics of intense laser plasma interaction. To better characterize these laser-produced protons, we designed and constructed a novel spectrometer that will not only measure proton energy distribution with high resolution but also provide its angular characteristics. The information obtained from this spectrometer compliments those from commonly used diagnostics including radiochromic film packs, CR39 nuclear track detectors, and nonimaging magnetic spectrometers. The basic characterizations and sample data from this instrument are presented.     

Two-screen single-shot electron spectrometer for laser wakefield accelerated electron beams

The laser wakefield acceleration electron beams can essentially deviate from the axis of the system, which distinguishes them greatly from beams of conventional accelerators. In case of energy measurements by means of a permanent-magnet electron spectrometer, the deviation angle can affect accuracy, especially for high energies. A two-screen single-shot electron spectrometer that correctly allows for variations of the angle of entry is considered. The spectrometer design enables enhancing accuracy of measuring narrow electron beams significantly as compared to a one-screen spectrometer with analogous magnetic field, size, and angular acceptance.     

A magnetic transport electron spectrometer for in-beam measurements

A compact magnetic transport electron spectrometer has been built having an overall efficiency of 0.92%, a resolution Δp/p of 18% and a maximum transmitted energy of 3 MeV. Limitations to accuracy in intensity measurements due to non-isotropic electron angular distributions have been discussed.     

Development of a time-resolved soft x-ray spectrometer for laser produced plasma experiments

A 2400 lines/mm variable-spaced grating spectrometer has been used to measure soft x-ray emission (8-22 A?) from laser-produced plasma experiments at Lawrence Livermore National Laboratory's Compact Multipulse Terrawatt (COMET) Laser Facility. The spectrometer was coupled to a Kentech x-ray streak camera to study the temporal evolution of soft x rays emitted from the back of the Mylar and the copper foils irradiated at 10(15)?W/cm(2). The instrument demonstrated a resolving power of ～120 at 19 A? with a time resolution of 31 ps. The time-resolved copper emission spectrum was consistent with a photodiode monitoring the laser temporal pulse shape and indicated that the soft x-ray emission follows the laser heating of the target. The time and spectral resolutions of this diagnostic make it useful for studies of high temperature plasmas.     

An electron transmission spectrometer with a trochoidal electron monochromator

The design of an electron transmission spectrometer is described and test measurement results for naphthalene, 1,3-dichlorobenzene, and phenylacetylene molecules are given. The trochoidal electron monochromator allows one to reach a 30-meV resolution at a half-height volt-ampere characteristic.     

New magnetic electron spectrometer with directional sensitivity for a satellite application

Design and test of a new magnetic electron spectrometer with excellent angular and rather small energy resolution is described. The system is specifically designed for a space flight application to analyze the angular distribution of energetic electrons. Incident electrons with energies between 15 and 270 keV are focused with respect to the direction of incidence. Reasonable directional focusing is obtained over an angular range of 60 degrees with a resolution of 5 degrees. This magnetic electron spectrometer is part of the energetic particle instrument (EPI) developed for the European Space Agency (ESA) GEOS program. GEOS-1 was launched on April 20, 1977, and injected into a 12-h orbit. The instrument has worked successfully since the switch-on-phase in the beginning of May 1977.     

Small-size terahertz spectrometer using the second harmonic of a femtosecond fiber laser

Possible implementations of a small-size terahertz spectrometer with a subpicosecond resolution on the basis of a femtosecond fiber laser are considered. An experimental sample of a spectrometer is fabricated. This spectrometer employs the method of optical rectification in a ZnTe nonlinear crystal and the Dember (photodiffusion) effect on the InAs semiconductor surface to generate terahertz radiation and the polarization-optical method to detect radiation. System operation is demonstrated by an example of measuring the terahertz absorption spectrum of water and determining the refractive index of the β-BBO crystal. The basic spectrometer parameters are found: spectral range, spectral resolution, and dynamic range of the terahertz spectrum amplitude.     

An optical spectrometer for a confocal scanning laser microscope

An optical spectrometer for the visible range has been developed for the confocal scanning laser microscope (CSLM) Phoibos 1000. The spectrometer records information from a single point or a user-defined region within the microscope specimen. A prism disperses the spectral components of the recorded light over a linear CCD photodiode array with 256 elements. A regulated cooling unit cools the diode array, thereby reducing the detector dark current to a level, which allows integration times of up to 60 s. The spectral resolving power, λ/Δλ, ranges from 400 at λ = 375 nm to 100 at λ = 700 nm. Since the entrance aperture of the spectrometer has the same diameter as the detector aperture of the CSLM, the three-dimensional spatial resolution for spectrometer readings is equivalent to that of conventional confocal scanning, that is, down to 0.2 μm lateral and 0.8 μm axial resolution with an N.A.=1.3 objective.     

A compact, multiangle electron spectrometer for ultraintense laser-plasma interaction experiments

Experiments on the multiterawatt (MTW) laser at the Laboratory for Laser Energetics will study the effect of the focal-spot shape on the forward acceleration and collimation of electrons. A compact electron spectrometer has been developed to record the energy spectra of electrons ejected in the interaction of the laser at multiple angular locations simultaneously. The modular system with replaceable magnets provides an adjustable energy band, currently 0.2-6 MeV. The detector is an array of imaging plates. The device is designed to operate in the high-noise environment (bremsstrahlung and Compton x rays, gamma rays, and scattered electrons), while being compact enough to fit in the 30 cm radius MTW target chamber. The detector geometry and shielding were optimized with the particle/radiation transport code GEANT4. Calibration was performed with beta sources. The required dynamic range, sensitivity, and resolution were confirmed with initial MTW experimental data.     

Performance of a short "magnetic bottle" electron spectrometer

In this article, a newly constructed electron spectrometer of the magnetic bottle type is described. The instrument is part of an apparatus for measuring the electron spectra of free clusters using synchrotron radiation. Argon and helium outer valence photoelectron spectra have been recorded in order to investigate the characteristic features of the spectrometer. The energy resolution (E/ΔE) has been found to be ～30. Using electrostatic retardation of the electrons, it can be increased to at least 110. The transmission as a function of kinetic energy is flat, and is not impaired much by retardation with up to 80% of the initial kinetic energy. We have measured a detection efficiency of most probably 0.6(-0.1) (+0.05), but at least of 0.4. Results from testing the alignment of the magnet, and from trajectory simulations, are also discussed.     

Apparatus for laser-assisted electron scattering in femtosecond intense laser fields

An apparatus for observation of laser-assisted electron scattering (LAES) in femtosecond intense laser fields was developed. The unique apparatus has three essential components, i.e., a photocathode-type ultrashort pulsed-electron gun, a toroidal-type electron energy analyzer enabling simultaneous detection of energy and angular distributions of scattered electrons with high efficiency, and a high repetition-rate data acquisition system combined with a high power 5 kHz Ti:sapphire laser system. These advantages make extremely weak femtosecond-LAES signals distinguishable from the huge elastic scattering signals. A precise method for securing a spatial overlap between three beams, that is, an atomic beam, an electron beam, and a laser beam, and synchronization between the electron and laser pulses is described. As a demonstration of this apparatus, an electron energy spectrum of the LAES signals with 1.4 × 10(12) W/cm(2), 795 nm, 50 fs laser pulses was observed, and the detection limit and further improvements of the apparatus are examined.     

改进的飞秒激光加工微型光波导方法

分析了垂直式加工中加工区域光强分布不对称的原因,从理论上总结出改进这种不对称的方法。在分析了仅引入单个透镜就能实现这一改进的可行性后,实验验证了这种改进方法。未改进之前加工出的光波导其端口两个方向直径之比为10:1,甚至更高;而改进后的比例则非常接近1:1。通过对光强不对称的改进,该方法有光路简单,无能量损失的优势。     

A photoelectron velocity map imaging spectrometer for experiments combining synchrotron and laser radiations

A velocity map imaging/ion time-of-flight spectrometer designed specifically for pump-probe experiments combining synchrotron and laser radiations is described. The in-house built delay line detector can be used in two modes: the high spatial resolution mode and the coincidence mode. In the high spatial resolution mode a kinetic energy resolution of 6% has been achieved. The coincidence mode can be used to improve signal-to-noise ratio for the pump-probe experiments either by using a gate to count electrons only when the laser is present or by recording coincidences with the ion formed in the ionization process.     

Design and measurement of a Cu L-edge x-ray filter for free electron laser pumped x-ray laser experiments

An inner-shell photoionized x-ray laser pumped by the Linac Coherent Light Source (LCLS) free electron laser has been proposed recently. The measurement of the on-axis 849 eV Ne?Kα laser and protection of the x-ray spectrometer from damage require attenuation of the 1 keV LCLS beam. An Al/Cu foil combination is well suited, serving as a low energy bandpass filter below the Cu L-edge at 933 eV. A high resolution grating spectrometer is used to measure the transmission of a candidate filter with an intense laser-produced x-ray backlighter developed at the Lawrence Livermore National Laboratory Jupiter Laser Facility Janus. The methodology and discussion of the observed fine structure above the Cu L-edge will be presented.     

Microwave spectrometer for saturated absorption experiments

A spectrometer has been built to perform Doppler-free saturated absorption experiments in the millimeter range (30-300 GHz); a plane-cylindrical resonator between Stark plates has been used. With that device, inverted Lamb-dips have been observed at 115 GHz with a width 25 times below the Doppler width. However, the essential feature of this apparatus is to allow the application of Stark field typically of 2500 V/cm, leading to such specific uses as the Stark tuned Lamb-dip, level-crossing, and mode-crossing experiments. Typical examples are given and other applications are proposed.     

Versatile electron spectrometer for surface studies

An electron spectrometer is described which is designed to measure a variety of electron spectra of solid surfaces in ultrahigh vacuum. The instrument is capable of the high-energy resolution (10-15 meV) required for vibrational inelastic electron scattering from atoms and molecules on surfaces. It has also been designed to carry out angle-resolved photoemission measurements, Auger electron spectroscopy, and energy-loss measurements of electronic excitations. The performance of the instrument in these modes of operation is discussed.     

用于双聚焦磁质谱仪的电子轰击离子源的设计与研究

本文设计了一种用于双聚焦磁质谱仪的电子轰击离子源,运用静电透镜软件simion的仿真模拟研究了它的离子光学系统,研究了离子光学系统电压参数和离子束的初始半散角对拉出离子效率和离子束宽度的影响.     

Initial experimental results on a magnetic beam separator spectrometer for the SEM

This article describes preliminary experiments to test the concept of scanning electron microscope (SEM) using a round magnetic beam separator to perform energy spectroscopy. Two experiments with an add-on attachment inside a conventional SEM were performed, one to estimate the sector image aberrations and the other to capture an energy spectrum of scattered electrons. The experiments show that the sector image aberrations lie well below 2 nm and that it is possible to capture the energy spectrum of secondary electrons.     

A practical electron spectrometer for chemical analysis

This paper describes the basic parameters which have been considered in the design of a practical electron spectrometer optimized for micro-chemical analysis in a 100 kV transmission electron microscope fitted with a scanning unit. Constructional factors and the operation of this spectrometer are discussed, as well as data acquisition. Typical results are presented to illustrate the operative modes. Both the prototype spectrometer and subsequent copies of it now are being utilized sucessfully in studies related to materials and biological sciences.     

Acousto-optic modulator system for femtosecond laser pulses

Femtosecond laser pulses have made a revolution in multiphoton excitation microscopy, micromachining, and optical storage for their unprecedented high peak power. However, modulation of their intensity with acousto-optic modulator (AOM) is frustrated by dispersion which results in a significant stretch in pulse width. Here we report a scheme composed of two acousto-optic deflectors (AODs) to modulate the intensity of the femtosecond laser pulses with simultaneous compensation for the temporal dispersion. With commercial AODs, we demonstrated such an AOM system for the femtosecond laser pulses with overall transmission efficiency of around 80%. The pulse width of the exit beam is 115-177 fs for an input pulse of 110 fs, across the wavelength range of 720-920 nm when the temporal dispersion compensation is optimally tuned at 800 nm. The fluorescence intensity in a two-photon microscopy experiment performed using this system increased 5.5-fold over that of the uncompensated AOM.