MgF2 Window Research Articles

Developments of a large area VUV sensitive gas PMT with GEM/μPIC

A new large area UV photon detector with micro pattern gaseous detectors isdeveloped and evaluated.A semitransparent CsI photocathode deposited on a MgF2 window wascombined with 10cm × 10cm GEM and μPIC.Using Ar+C2H6 (10%) gas, we achieved the gas gain of more than 105 which is enough to detect single photoelectron.We, then, irradiated vacuum UV photons (VUV, around 172nm) from the newly developed LaF3(Nd)scintillator to the detector and the single photoelectrons were successfully detected. We also demonstrated the imaging capability of the detector with μPIC readout systems.

Separation of high order harmonics with fluoride windows

The ensemble of lower orders produced in high order harmonic generation can be efficiently temporally separated by propagation in a fluoride window while still preserving their femtosecond pulse duration. We present calculations for MgF2, CaF2, and LiF windows for the third, fifth, and seventh harmonics of 800 nm. We use this simple and inexpensive technique in a pump/probe experiment to resolve femtosecond dynamics in the ethylene molecule.

Cell Design for Picosecond Time-Resolved Infrared Spectroscopy in High-Pressure Liquids and Supercritical Fluids

The design of a new high-pressure infrared (IR) cell for carrying out picosecond time-resolved infrared (ps-TRIR) spectroscopy in supercritical fluids is described. We have employed thin (2 mm) MgF(2) windows in order to overcome possible undesirable nonlinear optical effects caused by the extremely high peak powers of ultrashort ultraviolet (UV)/visible pulses. The design of our cell allows for the study of systems at pressures of up to 5500 psi at temperatures of up to approximately 50 degrees C. The MgF(2) windows enable the excitation of samples with both UV and visible light pulses and these windows are transparent across much of the mid-infrared region. We have demonstrated the use of this cell by examining the photochemistry of Fe(CO)(5) in supercritical Kr (sc Kr).

The development of gaseous detectors with solid photocathodes for low-temperature applications

There are several applications and studies in fundamental research, which require the detection of VUV light at cryogenic temperatures. For these applications, we have developed and successfully tested special designs of gaseous detectors with solid photocathodes able to operate at low temperatures: sealed gaseous detectors with MgF2 windows and windowless detectors. We have experimentally demonstrated that both primary and secondary (due to the avalanche multiplication inside liquids) scintillation light can be recorded by photosensitive gaseous detectors. The results of this work may allow one to significantly improve the operation of some noble liquid TPCs.

Photoemission Experiments for Charge Characteristics of Individual Dust Grains

Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 2–10 µm diameter are levitated in a vacuum chamber at pressures ∼10-5 torr and exposed to a collimated beam of UV radiation in the 120–200 nm spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV wavelength with a spectral resolution of 8 nm. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on test particles of silica and polystyrene to determine the photoelectric yields and surface equilibrium potentials when exposed to UV radiation. A brief description of an experimental procedure for photoemission studies is given and some preliminary laboratory measurements of the photoelectric yields of individual dust particles are presented.

Laboratory tests of the space patrol EUV radiometer

In the spectral range from 113–300 nm laboratory tests and calibration of the EUV radiometer were made by means of a deuterium lamp with a MgF2 window. An open secondary electron multiplier was used as a detector in combination with filters of LiF, CaF2, and SiO2. The results of the measurements with inclusion of the quantum yields of the secondary electron multiplier are presented.

Ｘｅ２エキシマーランプを用いた有機シリコン原料の気相における光分解

Photochemical dissociation of Tetraethoxysilane (TEOS) used as an organic silicon source in the gas phase was investigated by in-situ mass spectrometry. The vacuum uliraviolet (VUV) sources for inducing photochemical reaction were Xe2 excimer lamp (172 nm : 7.2 eV) and Hg lamp (185 nm : 6.5 eV). TEOS was dissociated by irradiation of VUV in the gas phase, while releasing alkyl groups such as CxHy (x= 1-2, y=2-5). Moreover, almost all Si-O bonds of TEOS were not broken at the energy of Xe2 excimer light. It has been found that the species produced by photochemical reaction in the gas phase have long lifetime of at least more than 2 minutes. Finally, the film deposited on the MgF2 window has strong light absorption from visible to ultraviolet region, because the film contains organic compounds.

A comparison of two high performance inverse photoemission bandpass detectors

By performing inverse photoemission experiments on the same sample at the same time with two different detectors, their performance has been directly compared. The first detector is based on one of the most promising solid-state detector designs. It is comprised of a focused mesh electron multiplier and a CaF2 window. The second detector is a Geiger–Müller tube which uses dimethyl ether and a MgF2 window. Although it has already been demonstrated that detectors based on this design work, the dimethyl ether Geiger–Müller tubes are not widely used, and we show that it is essential to compensate for detector dead time effects for the detector to be practicably useful. Once this is done, the dimethyl ether Geiger–Müller tube has a sensitivity that is approximately 20 times greater than that of the solid-state detector. Furthermore, it is easy to operate and it does not appear to suffer from the problems that are normally associated with iodine Geiger–Müller detectors.

Experimental Evidence for the Dominance of vuv Photons in Remote Hydrogen Plasma Treatments

AbstractThe flux of vacuum ultraviolet (VUV) and ultraviolet (UV) photons from a hydrogen plasma was detected by fluorescence measurements of sodium salicylate sheets with and without a MgF2 window. In order to expose the samples to the same photon flux in all experiments, the power input to the microwave plasma source was adjusted. Polyethylene (PE), polypropylene (PP), and polystyrene (PS) were treated with VUV radiation or with a remote hydrogen plasma. The mass loss and the CH-absorption loss were recorded by in situ quartz crystal micro balance and by in situ IR reflection absorption spectroscopy, respectively. The VUV irradiation and plasma treatment caused similar effects in the case of PE, PP showed an increased polymer ablation in plasma treatments, and for PS a negligible loss in mass and CH absorption was detected in plasma and VUV treatments.

Bolometric diagnostics in Tokamak de Varennes

Radiative power from the main and divertor plasmas of Tokamak de Varennes (TdeV) is measured using a compact bolometric diagnostic. The diagnostic is comprised of a multichannel pin-hole camera and several collimated bolometers. The electronic circuit of the bolometers permits remotely controlled in situ calibration of the detectors. The pin-hole camera, with its 17 channels of thermistor bolometers, monitors the plasma poloidal cross section horizontally. In the same camera housing reside a pair of wide angle metal film bolometers that measure the total radiative losses from the main plasma, and a 16 channel x-ray-ultraviolet photodiode array. Five collimated thermistor bolometers project the vertical view of the plasma poloidal cross section. The divertor plasma losses are monitored by six pairs of collimated thermistor bolometers installed at different toroidal locations. One pair in the lower and three pairs in the upper divertor chamber measure the global power loss from the plasma in front of the outboard divertor plates. Two other pairs of bolometers located just behind the inclined divertor plate, measure the poloidal distribution of the plasma losses from the divertor plate to the X point with an improved spatial resolution. Three divertor bolometers and one of the wide angle bolometers in the main plasma are covered with MgF2 windows, for rough spectral analysis of the radiative power loss. Examples of bolometric measurements of the radiative loss and its distribution in the TdeV during plasma detachment, plasma biasing and lower hybrid current drive and heating experiments are given.

Multiple hollow-cathode vacuum-ultraviolet plasma source excited by pulsed glow discharge

A multiple hollow-cathode vacuum-ultraviolet source excited by a pulsed glow discharge in a mixture of Xe and He has been developed. A MgF2 window with a diameter of 55 mm was used, and the repetition frequency was varied between 3 and 9 kHz. Stable output was maintained for about 3 h. Measurements of 147 nm radiant illumination were made at various distances from the window at various repetition frequencies. The peak radiant illumination decreased while the average radiant illumination increased with increasing repetition frequency. The output power density near the center of the window could be estimated from the relationship between measured radiant illumination and distance from the window. The peak and average output power densities at 6 kHz were 30 and 1.5 W/m2, respectively.

Determination of absolute hydrogen atom densities by Lyman- alpha absorption

We developed a method for the determination of absolute hydrogen atom densities based on the absorption of the hydrogen Lyman- alpha line. The underlying simplified mathematical model describes the source as well as the absorber as Doppler-broadened line profiles with characteristic temperatures. The experimental apparatus consists of a Lyman- alpha source (a DC glow discharge of hydrogen diluted in helium), the system under investigation (absorber) and a simple VUV spectrometer, which is not able to resolve the line profile. The three parts are separated by MgF2 windows or lenses, which are fairly transparent to Lyman- alpha radiation. By knowing the gas kinetic temperature of the lamp as well as that of the absorber, atomic hydrogen densities can be determined from the absorption measurements. In order to check the reliability of the method, a special furnace was used to ensure a well-defined absorber. Investigations clearly demonstrated that absolute hydrogen atom densities can be determined with an accuracy better than +or-50%, which is sufficiently accurate for model calculations of the gas phase chemistry in our plasma-based diamond deposition process. However, at present such high accuracies can be obtained only within a restricted parameter range.

Photon-induced impurity production in TEXTOR

Analysis of the residual neutral gas during plasma discharges in the tokamak TEXTOR shows considerable amounts of neutral CO and CO 2. Details of these observations have suggested that the CO 2 and part of the CO neutral gas is released from the surfaces by photon-stimulated desorption processes. To prove this suggestion additional mass-spectroscopic measurements have been performed in a chamber vacuum-sealed from the TEXTOR vacuum by a MgF 2-window which is transparent for wavelengths above about 110 nm. It has been confirmed that CO 2 and CO molecules together with H 2 are released from the walls of the chamber by the photons penetrating from the TEXTOR plasma through the window. The overall desorption rate has been estimated to be between 10 −4 and 10 −5 molecules/photon and a linear relation between the amount of desorbed molecules and the total radiation from the plasma has been found. The results are discussed in view of the overall impurity release from the walls and limiters of TEXTOR.

A wide wavelength range spectrometer (1150–8000 Å) for the RFX reversed field pinch experiment

This paper describes the vacuum Czerny–Turner spectrometer with a 1.33 m focal length installed on the RFX fusion experiment. The optics are coated with MgF2 and the image intensifier, protected by a vacuum sealed MgF2 window, features a dual photocathode system, CsTe on one half and S20 on the other; thus the instrument covers efficiently the wide spectral range from the MgF2 limit to the near infrared. Sensitivity at short wavelengths is limited by the reflectance of mirrors and the transmittance of the MgF2 window. The detector is completed by a fast optical multichannel analyzer whose 1024 photodiodes can be read out in a time of 250 μs. The instrument can also be operated in a duochromator mode by deflecting the diffracted beam onto a second detector system, where two photomultipliers are applied to two exit slits, one fixed and the other remotely movable in such a way that the intensity ratios of two lines can be monitored for diagnostic purposes. Some examples of obtained spectra illustrating the instrument performance and comprising first results from the RFX plasma are presented.

A Particular Photo-CVD Apparatus for Hydrogenated Amorphous Silicon Deposition

ABSTRACTA new PHOTO-CVD apparatus has been built in order to deposit a – Si : H films and other kinds of amorphous thin films by a technique which is both simple and versatile. This apparatus is composed of three chambers connected together: a load-lock chamber, a process chamber and a third chamber for in-situ analysis of deposited films. A peculiarity of the lamp, a dielectric discharge lamp which can work with noble gases like Xe or Kr, is that it can be completely dismounted without breaking the vacuum in order to clean the optical MgF2 window. By this method, the deposition chamber can be kept in very clean conditions. In this apparatus, we started to deposit a – SixC1−x: H of very good quality, taking their thickness into account. These films have been completely characterized by chemical (RBS, ERDA) and optical (PDS) methods. Their quality can be compared with quality of a – Si : H samples of the same thickness obtained by PECVD.

Static Charge Elimination of Charged Matter by Vacuum UV Irradiation

Air is photoionized by the irradiation of vacuum UV light emitted from a deuterium lamp with a MgF2 window. The short wavelength transmission limit of this lamp is 112 nm, which corresponds to the photon energy of 11 eV, and nitric oxide is firstly produced by photochemical reaction and photoionized by those photons having an energy of 11 eV. The lamp behaves like a radio isotope, and its irradiation accelerates the charge elimination of charged matter in air.

High-temperature window seals for VUV experiments

A simple and reliable technique for sealing laser quality vacuum-ultraviolet grade windows to high-temperature, bakable vacuum systems has been developed. Both 7.5-cm-diam MgF2 and CaF2 windows were found to be He leak tight to temperatures exceeding 330 °C. Smaller 4-cm-diam windows seal at temperatures exceeding 400 °C. The seals do not appear to be adversely affected by temperature cycling and they do not distort the optical quality of the window. The sealing technique has been used without failures in a Hg vapor four-wave-mixing cell that is used to produce high-power 130-nm coherent radiation.

Ultraviolet converter transients induced by electrons

The output of ultraviolet converters typically used in satellite astronomy was monitored during irradiation with electrons from a sealed 90Sr source which approximated the peak flux in earth’s outer electron belt. The signal induced by irradiation was attributed to two mechanisms: (1) photoelectrons resulting from photons created in the MgF2 window and (2) the direct impact of electrons on the phosphor. For irradiation the at ~1 × 107 e/cm2 sec, these two effects produced signals which were, in order of magnitude, the same as those produced by an incident UV flux (254 nm) of 108 and 107 photons/cm2 sec, respectively. In addition, the induced signal was investigated as a function of electron energy by irradiating another converter with 0.4–1.8-MeV electrons from a Van de Graaff. These results suggest that the dominant contribution to the electron-induced signal is Cerenkov photon production in the MgF2 window.

Lyman-alpha detector with MgF2 window

Ion chambers having a polished MgF2 window and filled with nitric oxide gas have been developed for the measurements of absolute intensities of solar and geocoronal hydrogen Lyman-α radiation. The area sensitivities of the detectors and the effects of moisture on the transmittances of MgF2 single crystals were measured and compared with those in the cleaved LiF cases. The results indicate that an ion chamber with a polished MgF2 window has a superior suitability for the reliable measurement in rocket and satellite experiments as well as in laboratory work.

Azimuth Angle Dependence of Equatorial Ultraviolet Airglow

AN ionization chamber and an EUV solar blind photomultiplier were flown to an altitude of 103 km on a Dauphin rocket launched from Kourou, French Guiana (5° N; 35° E), on September 14,1971, at 0020 (local time). The ionization chamber had a 15° field of view and was filled with Cs2 with an MgF2 window; the resulting bandpass is 1150 Å–1250 Å. The photomultiplier, field of view 5°, was enclosed in a sealed box filled with O2 which transmits UV radiation only through 3 windows between 1150 Å and 1250 Å (ref. 1).