Peter Lindblom

Optical studies of the influence of an intense ion beam on high-pressure gas targets

Abstract Optical studies of the penetration of protons, deuterons and α-particles (energy range 2–18 MeV) in helium, neon and argon gas targets have been made. The beam was photographed in the light emitted by atoms of the target gas. Through an interferometric arrangement, interferograms of the target gas were recorded showing variations in the refractive index of the gas caused by the particle beam. An asymmetric density reduction in the beam volume was seen in the form of an increased penetration range as a function of the vertical position in the beam. This density reduction was studied as a function of the beam current. The asymmetric density reduction is due to an upward gravitational transport of the heated gas in the target chamber. Estimates of the vertical temperature distributions were made from the recorded interferograms.

Blaze characteristics of echelle gratings

A new model for the blaze function of the two in-plane mountings of echelle gratings is described and extended to account for defects in the edges of the grooves. Expressions for the relative efficiency are given. The model shows that the wavelength for the maximum blaze intensity differs slightly from the wavelength lambda(0) satisfying mlambda(0) = d[sinalpha + sin(2theta - alpha)], the difference being a function of the spectral order. The off-blaze orders of the wavelengths diffracted at the central blaze for the mounting alpha < theta (alpha = angle of incidence, theta = blaze angle) lie at the minima of the blaze function for a perfect echelle. Results are given from measurements of the blaze angle and the groove edge defects of three echelles.

Multiechelle grating mountings with high spectral resolution and dispersion

This paper describes a new spectrometer mounting using several echelle gratings as dispersive elements. These gratings are mounted so that a resolution equal to the sum of the resolution of the individual gratings is obtained. In the mounting the dispersions from the gratings coact resulting in very high dispersion in the focal plane. The multiechelle grating mounting can be used to build compact spectrometers with higher resolutions than can be obtained with the widest gratings ever ruled. Results from an experimental verification of the multiechelle grating mounting are given.

MEGA spectrometer: a monochromator with supermillion resolution.

The multiechelle grating arrangement (MEGA) [ Appl. Opt.21, 4363 ( 1982)] is used in a 1.2-m pressure scanned monochromator. The spectral orders from the exit slit of the pressure vessel, containing four 160-mm wide echelle gratings together with a collimating and a focusing mirror, are separated by a prism order-sorter monochromator. Reading the intensities of the spectral orders while varying the pressure gives a read-off of the whole 330–700-nm spectral range (extendable down to 200 nm). A spectral resolution close to 2 × 106 at 632 nm was measured with a He–Ne laser. Operation of the spectrometer is described in detail.

Studies of emission-line profiles from ion-excited neon gas targets

Abstract The widths of some atomic emission lines from ion-beam-excited Ne-gas targets have been studied. The line width is a linear function of the pressure within the pressure region studied (20–500 kPa). The line broadening depends on the spectral line studied. A reduction in the line width was observed with increasing beam current. This was interpreted as being due to a density reduction caused by the beam. The results were applied to calculate the temperature of the gas at the point of light emission.

PIXE-Analysis With 6 MeV H2+-Ions

The use of 6 MeV H2+-ions for PIXE-analysis (PIXE = particle induced X-ray emission) with a cyclotron which has a lowest proton energy of 5 MeV, is described. The H2+-spectra obtained from organic material are similar to those found in the literature induced by 3 MeV protons. The H2+-spectra are compared to spectra taken with 5 MeV protons.

Premonochromator for stray light rejection in Raman spectroscopy

A new apparatus for attenuating the Rayleigh light is described. The main components are two concave gratings mounted in a special nondispersive way. By means of the first grating the entrance slit of the apparatus is focused as an intermediate spectrum upon a sharp-edged movable mirror. This mirror reflects all the spectrum except the Rayleigh light to the second grating, which collects the light to an image of the entrance slit. The result is a sharp cutting of the spectrum at any desired position. The rejection of the Rayleigh line has been measured to less than 10(-5) (optimally 10(-6)). Raman lines can be.measured about 10 cm(-1) from the exciting line. The instrument has been used as a preeliminating unit coupled to a conventional double monochromator. It is expected that a system consisting of the instrument and a good single monochromator can be used for Raman studies.

Tests performed with the improved MEGA spectrometer

In a previous paper [S. Engman and P. Lindblom, Appl. Opt. 23, 3341 (1984)] a new type of spectrometer, based on the multiechelle grating arrangement (MEGA) principle, was described. The expected resolution and principles of operation were verified. However, at that time the spectrometer was equipped with poor gratings that did not allow its testing in spectroscopic applications. Since then, new gratings have been obtained and improvements made to the system. This paper reports the spectroscopic tests made with the improved instrument. It is shown that the MEGA spectrometer is a useful new tool for optical spectroscopy.

Echelle gratings acting as one

A new device for producing order-sortable echelle spectra by use of consecutive diffactions in several echelle grating surfaces is described. This echelle emulating device (EED) comprises a prism placed in the path between a pair of echelle grating surfaces. The refractive angle of the prism is fixed through a simple relation. The device reproduces all the main properties of a single virtual echelle, obtained from a simple grating equation describing the combined action of the gratings and the prism. The spectral order of the EED is the sum of the spectral orders of the individual gratings. A spectrograph that utilizes the device is described, and several applications are discussed.

Pressure-dependent decay of the configuration in argon excited by alpha-particles and protons

The pressure dependence of the decay of the states excited by an energetic pulsed ion beam was studied in the pressure range 5-1600 kPa. All of the ten states have a fast build-up component and, with the exception of the state, two decay components: one fast (3-18 ns at 100 kPa) and one slow (20-300 ns at 100 kPa). Extrapolation of the fast decay rates to zero pressure yields the natural lifetimes of the states to values within the accuracy of the measurements. Most of the slow decays show nonlinear pressure dependencies. This nonlinearity is probably due to several competing processes. The slow decay of the - states can be associated with the fast decay of the state. The pressure dependency of the state is considerably different from the other states within the configuration. It is concluded that the build-up of the state is associated with dissociative recombination of and molecules.