Off plane conical dispersion monochromator for extreme UV and soft x-rays

SXR and EUV Off Plane Monochromator

The Off-Plane X-ray Czerny Turner (OP XCT) spectrometer design is for extreme and vacuum ultraviolet wavelengths, ~8 to 125nm (10 to 150eV). It is a monochromator with point to point imaging for high harmonic laser generation experiments like photoemission spectroscopy, pump probe ARPES. It has fixed entrance and exit slit positions. The grazing incidence off-plane optical system is very efficient, has low temporal broadening, good image formation and uses easy to obtain diffraction gratings. This monochromator is ideal for experiments with high harmonic lasers and other immobile sources (pinch, LPP, synchrotron).
The OP-XCT may optionally be built as a time compensating double monochromator. The imaging optics accomodate spectrograph applications. In this way, the OP-XCT can serve double duty; as diagnostic spectrograph studying formation HHG laser sources, and at the flip of a mirror, analytical monochromator illuminating samples.

OP-XCT PDF Data Sheet

Specifications & Additional Information:

Focal Length800 mm (others available when HHG source distances require)
Acceptance8 mrad
Angle of Incidence85 degrees (5 degrees grazing incidence)
Entrance & Exit Slits>Continuously variable micrometer actuated width AND height, 0.02 to 6mm
Grating Mount3-position, adjustable in vacuum
Vacuum Compatible10-6 torr (optional metal sealed UHV for 10E-10 torr)
Gratings80 x 30mm substrate
Wavelength Rangerefer to grating of interest for range

The XCT may be used for scanning applications with an exit slit or array detectors (eg. CCD or microchannel plate intensifiers.)

Performance with various diffraction gratings:

Grating groove density (g/mm) (others available) 1800 1200 600 300
Resolution (nm, FWHM) 0.06 0.08* 0.16 0.32
Grating Range (nm) 0 to 25 0 to 35 0 to 75 0 to 140
1st Order Blaze (nm) 44 27 84 113
19 30 81
5 14

*measured value with 0.05 mm pinhole at entrance

Outline Drawing

Off-plane x-ray Czerny Turner Monochromator

Select Publications

Abstract: Presenting means for spectral analysis in the extreme and vacuum ultraviolet, of single or multi-shot plasmas or plasma plumes and their strata, via multi-dimensional view chords. We describe a novel grazing incidence off-plane optical system, related efficiency, and image formation at two dimensional detectors. Method and means of surveying low and high-resolution events and their visualization and recording thereof are illuminated. Our goal is to acquainting investigators with a unique spectrometer (spectrograph) configuration, which with help of state of the art detectors may be useful for plasma diagnostics.
D. Schoeffel, E. Schoeffel, and L. Krupa
Abstract: The design and the characterization of a monochromator for the spectral selection of ultrashort high-order laser harmonics in the extreme ultraviolet are presented. The instrument adopts the double-grating configuration to preserve the length of the optical paths of different diffracted rays, without altering the extremely short duration of the pulse. The gratings are used in the off-plane mount to have high efficiency. The performances of the monochromator have been characterized in terms of spectral response, efficiency, photon flux, imaging properties, and temporal response. In particular, the temporal characterization of the harmonic pulses has been obtained using a cross-correlation method: Pulses as short as 8 fs have been measured at the output of the monochromators, confirming the effectiveness of the time-delay compensated configuration.
Luca Poletto, Paolo Villoresi, Fabio Frassetto, Francesca Calegari, Federico Ferrari, Matteo Lucchini, Giuseppe Sansone, and Mauro Nisoli
Abstract: The conical diffraction mounting in which the direction of incident light belongs to a plane parallel to the direction of the grooves has the unique property of maintaining high diffraction efficiency, even in the extreme-ultraviolet (EUV) region. This property is useful for designing high-throughput time-delay compensated monochromators for the spectral selection of ultrashort EUV pulses as the high-order harmonics generated by the interaction between an ultrashort laser pulse and a gas jet. The time compensation allows one to exploit the femtosecond scale duration of the harmonics both to have high intensity and to reach an unprecedented temporal resolution for pump and probe experiments. Because two gratings have to be used for time compensation, the high diffraction efficiency becomes an essential requirement, which can be fulfilled by the conical diffraction mounting. Measurements recently accomplished at the Bending Magnet for Emission Absorption and Reflectivity (BEAR) beam line (ELETTRA Synchrotron, Trieste, Italy) for three gratings in the 10–90 nm region are reported here that show a peak efficiency of as much as 0.7 in the first order. A model computing the electromagnetic propagation and the grating efficiency, implemented and tested with the experimental data, permits the study and design of rather complex systems operating in the conical mounting. Basic physical principles and mathematical aspects of the model are discussed here.
M. Pascolini, S. Bonora, A. Giglia, N. Mahne, S. Nannarone, and L. Poletto
Chapter 18 opening paragraph: We discuss the use of diffraction gratings to perform the spectral selection of ultrashort pulses in the extreme-ultraviolet and soft X-ray spectral regions, ranging in the 3-100 nm wavelength range. The main application of such a technique is the spectral selection of highorder laser harmonics and free-electron-laser pulses in the femtosecond time scale. We present the design and realization of both single- and double-grating monochromators using an innovative grating geometry, namely the off-plane mount. The performances of existing instruments are shown. The use of diffraction gratings to change the phase properties of the pulse, e.g. to compress it to shorter temporal duration close to the Fourier limit, is also discussed.
Luca Poletto, Paolo Villoresi and Fabio Frassetto [Source: Advances in Solid-State Lasers: Development and Applications, Book edited by: Mikhail Grishin, ISBN 978-953-7619-80-0, pp. 630, February 2010, INTECH, Croatia, downloaded from SCIYO.COM]

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