Conical Diffraction Mounting Research Articles

Cr/C lamellar multilayer grating in conical diffraction mounting for beam splitter used in X-ray free-electron lasers.

A lamellar multilayer grating in a conical diffraction mounting was proposed as a beam splitter for X-ray free-electron lasers. Theoretical calculations demonstrated that the distribution of diffraction efficiency can be adjusted by optimizing the groove depth or d-spacing. A Cr/C multilayer lamellar grating with a line density of approximately 2500 L/mm was fabricated. The performance of the element was measured in the Optics Beamline PM-1 (BESSY-II) at an energy of 1500 eV. A five-order diffraction pattern was recognized, and the diffraction efficiencies of the -/+first-order were approximately 12.6 and 4.4%, respectively. The asymmetric distribution of diffraction efficiency can be caused by the different sidewall angles of the grating groove.

Coupled-mode theory and Fano resonances in guided-mode resonant gratings: the conical diffraction mounting.

We study resonances of guided-mode resonant gratings in conical mounting. By developing 2D time-dependent coupled-mode theory we obtain simple approximations of the transmission and reflection coefficients. Being functions of the incident light's frequency and in-plane wave vector components, the obtained approximations can be considered as multi-variable generalizations of the Fano line shape. We show that the approximations are in good agreement with the rigorously calculated transmission and reflection spectra. We use the developed theory to investigate angular tolerances of the considered structures and to obtain mode excitation conditions. In particular, we obtain the cross-polarization mode excitation conditions in the case of conical mounting.

Temporal characterization of a time-compensated monochromator for high-efficiency selection of extreme-ultraviolet pulses generated by high-order harmonics

Ultrafast extreme-ultraviolet pulses are spectrally selected by a time-delay-compensated grating monochromator. The intrinsic very short duration of the pulses is obtained by exploiting the high-order harmonic generation process. The temporal characterization of the harmonic pulses is obtained using a cross-correlation method: pulses as short as 8 fs are measured at the output of the monochromator in the case of the 23rd harmonic. This value is in agreement with the expected duration of such pulses, indicating that the influence of the monochromator is negligible. The photon flux has been measured with a calibrated photodiode, pointing out the good efficiency of the monochromator, derived by the exploitation for the two gratings of the conical diffraction mounting.

Angle‐resolved Mueller polarimeter using a microscope objective

AbstractA new Mueller polarimeter based on liquid crystals and a microscope objective is presented for the characterization of diffraction gratings in a conical diffraction mounting. Fast measurements of complete Mueller matrices over a range of polar angles ϑ (0–60°) and azimuthal angles φ (0–360°) are achieved without mechanical movements. The polarization states generator and analyzer are based on nematic liquid crystals. The angular range is achieved through focalization of light over the measured sample with a microscope objective of high numerical aperture and imaging of the objective's back Fourier plane on a CCD. Results on isotropic samples and diffraction gratings are shown. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Gratings in a conical diffraction mounting for an extreme-ultraviolet time-delay-compensated monochromator

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.

Time-compensated grazing-incidence monochromator for extreme-ultraviolet and soft X-ray high-order harmonics

The use of a grating monochromator for the selection of one or more high-order laser harmonics produced by a femtosecond pulse interacting with a gas jet may alter the duration of the pulse itself. This is due to the differences in the optical paths of the rays caused by ordinary diffraction when a grating is used. The time stretching can be almost eliminated by using two gratings in time-compensated configurations. Unfortunately, the classical diffraction mounting has low efficiency, overall in the extreme-ultraviolet region. High broadband efficiency can be obtained by using the conical diffraction mounting. A time-compensated monochromator with toroidal gratings used in conical diffraction is here presented. It is shown that the time compensation is very effective in a broad spectral region, ranging from VUV to soft X-rays, with much higher efficiency than the classical diffraction mounting.

The second kind angular dispersion and the analysis of characteristics of diffraction grating

The first and second kind formulas of angular dispersion, corresponding respectively to the polar angle and azimuthal angle of diffraction grating, are presented based on the generalized grating equation produced on the basis of vector diffraction theory under the condition of conical diffraction mounting; at the same time, by making theoretical and numerical analysis of the condition in which the second kind formula of angular dispersion changes evidently and the corresponding mathematical expression is obtained.

Creation of an optical xyz coordinate system using bidirectional blazing from a symmetric triangular-groove grating in a conical diffraction mount

An xyz beam splitter is described that uses a diffraction grating upon which light is incident in a plane parallel to the grating grooves to produce symmetric conical diffraction into the ±1 orders, with all higher orders being suppressed or evanescent. The ±1 orders are mutually orthogonal when the wavelength/grating period ratio λ/Λ=1/2, independent of the angle of incidence ϕ. Orthogonality of, the ±1 orders with the direction of incidence occurs at ϕ=arctan(1/2)=35.264°. By choice of a symmetric triangular-groove profile (isoceles with a 120° apex angle), bidirectional blazing occurs into the desired ±1 orders, with little or no light appearing in the vestigial 0 order.

Ultraviolet conical diffraction: a near-stigmatic tandem grating mounting spectrometer

Conical diffraction grating mounts (gratings used off-plane) offer many new possibilities in the ultraviolet and extreme ultraviolet wavelength domain. Up to now, single conical diffraction gratings, whether coupled or not to grazing incidence gratings, have had limited spectral resolution and disadvantages owing to the simultaneous monochromatic slit image rotation with the grating rotation during the wavelength scan. Here we propose a tandem conical diffraction mount that improves the spectral resolution and nearly eliminates the monochromatic slit image rotation. This results in the improvement of spectral image quality. Through the example of a complete solar telescope-spectrometer instrumentation, the qualities (spectral and angular resolution-2 pm and 1 sec of arc) and limits (lower efficiency) of the mounting are compared to other recent solar instrumentations proposed in the 30-135-nm wavelength range.

Reflection gratings in conical diffraction mounting

An experimental study of light diffraction from an aluminium holographic grating is carried out in conical diffraction mounting. Angular dependences of the efficiency and ellipticity of the first diffraction order are measured and some peculiar features are pointed out. The results are in good agreement with the calculations based on the rigorous electromagnetic theory. The ellipticity of the diffracted wave changes strongly in the presence of an oxidised layer.

Diffraction anomalies of coated dielectric gratings in conical diffraction mounting

A theoritical study of the anomaly in the zero-order efficiency caused by waveguide mode excitation is carried out for the case of conical diffraction mounting. The influence of the incident light polarization on the mode excitation is discussed. In particular it is shown that the coupling into the guided wave vanishes at a given polarization. A generalization of the phenomenological approach is presented for conical diffraction mounting.

Conical diffraction mounting generalization of a rigorous differential method

A generalization of the method of J. Chandezon et al. (1982) is presented for conical diffraction mounting. The applicability of the invariance theorem for real metal and dielectric gratings is discussed and the existence of some polarization effects is demonstrated. A formulation of the reciprocity theorem in conical diffraction mounting is proposed, valid not only for the efficiencies of the diffracted orders but for the amplitudes, too.

X-ray spectrographs using radial groove gratings

A high efficiency spectrograph design for the EUV and soft X rays is presented. This grazing incidence system uses a plane surface reflection grating with rulings that are radial, like the spokes of a wheel. The grating is placed in a beam of light that is converging to a focus. The single reflection off the grating is in the conical diffraction mount ensuring maximum performance from the system. Aberrations and performance levels are discussed. The gratings can be manufactured with existing ruling engines. Sample applications to an X-ray monochromator and an EUV stellar spectrograph are discussed.

High Efficiency Spectrographs for the EUV and Soft X-Rays

A basic need of modern UV and x-ray astronomy is the capability to perform high resolution spectroscopy of faint stars. The use of modern grazing incidence optics can be coupled to high blaze angle reflection gratings used in the conical diffraction mount to offer a versatile, efficient approach to the design problem. We discuss two designs of interest: an echelle spectrograph for use longward of 100 A, and an Objective Reflection Grating Spectrograph for use in the soft x-rays. General design considerations and measurements of grating efficiencies are also presented.

Echelle spectrographs at grazing incidence

It is shown that by using the conical diffraction mount existing echelle gratings can be used at grazing incidence to achieve high spectral resolution in the extreme UV and soft x rays. Design considerations for grazing incidence echelle spectrographs are examined, and two sample designs are discussed. The first, for use in the extreme UV has a primary mirror and an entrance slit to the spectrograph. The system has resolution of 10(4), operates at any wavelength longward of 100 A, and covers 30% of the spectrum at a single setting. The x-ray spectrograph uses objective gratings to obtain spectral resolution of 2.8 x 10(4) over any factor of 2 in wavelength. It operates to wavelengths as short as 4 A.

Very high x-ray efficiency from a blazed grating

The efficiency of X-ray diffraction from reflection gratings has been investigated experimentally using a gold-coated plane grating of 25 x 120 mm with a nominal blaze angle of 21 deg in a conical diffraction mount. Results show that conical diffraction is capable of producing very high dispersion efficiencies. The peak of first order at 13.3 A is 40%; at 44 A, the peak is 34%. The most immediate application of this result is to X-ray astronomy where sources are weak.

Diffraction gratings for the vacuum ultraviolet spectral region

A technique has been developed to measure the efficiency of diffraction gratings in the vacuum ultraviolet spectral region at any angle of incidence which will be discussed briefly. The measurements show that concave gratings do not have a uniform efficiency over their surfaces, primarily because of the change in blaze angle across the surface. Examples will be shown of results obtained using both conventionally ruled, and holographically recorded, gratings. A short discussion of stray light will be given, followed by a description of the conical diffraction mounting that promises to be useful in synchroton radiation monochromators.