New immersed grating technology is needed particularly for use in imaging spectrometers that will be used in sensing the atmosphere O2A spectral band (750nm - 775 nm) at spectral resolution in the order of 0.1 nm whilst ensuring a high efficiency and maintaining low stray light. In this work, the efficiency, dispersion and stray light performance of an immersed grating are tested and compared to analytical models. The grating consists of an ion-beam etched grating in a fused-silica substrate of 120 mm x 120mm immersed on to a prism of the same material. It is designed to obtain dispersions > 0.30°/nm-1 in air and >70% efficiency. The optical performance of the immersed grating is modelled and methods to measure its wavefront, efficiency, dispersion and scattered radiance are described. The optical setup allows the measurement of an 80mm beam diameter to derive the bidirectional scatter distribution function (BSDF) from the immersed grating from a minimum angle of 0.1° from the diffracted beam with angular resolution of 0.05°. Different configurations of the setup allow the efficiency and dispersion measurements using a tuneable laser in the 750nm-775nm range. The results from the tests are discussed with the suitability of the immersed gratings in mind for future space based instruments for atmospheric monitoring.
New immersed grating technology is needed particularly for use in imaging spectrometers that will be used in sensing
the atmosphere O2A spectral band (750nm - 775 nm) at spectral resolution in the order of 0.1 nm whilst keeping a high
efficiency and low stray light. In this work, an Ion-beam etched grating in a fused-silica substrate of 100 mm 100mm
immersed on a prism of the same material is designed to obtain dispersions > 0.30°/nm-1 and 70% efficiency. The optical performance of the immersed grating is modelled and methods to measure its efficiency and scattered radiance are
described. The optical setup allows the measurement of an 80mm beam diameter to derive the bidirectional scatter
density function (BSDF) from the immersed grating from a minimum angle of 0.1° from the diffracted beam with
angular resolution of 0.05°.
Unlike other drive fusion class laser, Megajoule laser (LMJ) and its first prototype, the Laser Integration Line (LIL) are equiped with specific diffractive optical components. All these optics are situated in the final optic assembly.
An high efficiency diffraction focusing grating called 3w grating is used to focus the beam into the center of the target chamber instead of a classical focusing lens. Another large grating called 1w grating is used for optical path compensation purposes. Both gratings have a dimension of 420x470mm2 and are working at an incidence of 25°. Gratings are plano transmission holographic gratings directly engraved into fused silica substrates. The 1w grating is working at the wavelength of 1.053μm, its grooves are straight and equispaced. The 3w grating, is a focusing grating working at the wavelength of 0.351μm. Its grooves are curved and non equispaced.
Jobin Yvon was selected by CEA to manufacture these two types of diffraction graintgs. After processes developpements and facilitization, a complete batch of twelve 1w gratings and sixteen 3w gratings were delivered to CEA for integration.
After a brief presentation of CEA's specification for this diffractive components, we give some details on the manufacturing processes. We also demonstrate good agreement between specified and manufactured component. We give an overview of the global production performances
In Astronomy field, grisms or transmission gratings replicated on a prism are widely used to transmit in line the spectrum. To work in the infrared range, classical grisms present important limitations: the epoxy layer, necessary for replication, absorbs IR light, and in addition this layer constitutes a problem when instrument is used at low temperature.
Jobin-Yvon company, in collaboration with LAM in Marseille, France, designed and manufactured a transmission grating engraved directly into IR fused silica substrate. The transmission efficiency of the manufactured grating is 60% to 70% in natural light over the 1.5 to 2.5 microns wavelength range.
The number of grooves was 400 g/mm.
Other wavelength ranges are possible with similar efficiency, for example: 1.0 to 1.4 microns or 1.4 to 1.9 microns.
This grating made only only of fused silica, will survive without problem at any low or very low temperature, or vacuum environment.
High groove density reflection gratings placed at grazing incidence in the extreme off-plane mount offer increased performance over conventional in-plane mounts in the x-ray. We present initial off-plane efficiency test results from the grating evaluation facility at the University of Colorado. The test gratings are holographically ruled, ion-etched gratings with radial groove profiles that were developed and fabricated by Jobin-Yvon Inc.
The Megajoule laser (LMJ) and its first prototype, the Laser Integration Line (LIL), is equipped with a specific final optics assembly involving two diffraction gratings instead of a classical focusing lens. Both gratings have a dimension of 420 X 470 mm2 and are working at an incidence of 25 degree(s).. Gratings are plano transmission holographic gratings directly engraved into fused silica substrates. The 1(omega) grating is working at the wavelength of 1.053 micrometers , its grooves are straight and equispaced. The 3(omega) grating, is a focusing grating working at the wavelength of 0.351 micrometers . Its grooves are curved and non equispaced. The gratings were designed and manufactured to present efficiencies superior to 90% on the whole clear aperture and an improved damage threshold. After Jobin Yvon's selection by CEA in 1999, specific equipment and facilities were put in place to manufacture these large gratings. The aim of this contribution is to present the early results of the development of this 1(omega) and 3(omega) gratings. After a short introduction to the 1(omega) and 3(omega) gratings specifications, manufacturing process, efficiencies result and AFM profiles of the first manufactured gratings will be detailed.
To deviate and focus of the beams of the future Laser Integration Line (LIL) and Megajoule laser (LMJ), CEA has chosen an original setup using two large 420 x 470 mm2 transmission gratings. The first grating is an holographic plano transmission master grating with straight and equispaced ruling, 25 degree(s) incidence angle and working at 1.053 micrometers . The second one is an holographic plano transmission master grating, with curved and non equispaced ruling, 25 degree(s) incidence angle which combines both focusing and deviation properties. Groove profile of both gratings is deep laminar. High damage threshold, improved wavefront quality and high efficiencies are the main issues for those two gratings. Jobin Yvon's was selected by CEA in 1999 to develop, industrialize and manufacture gratings reaching LIL/LMJ specifications. A dedicated plant and facilities were built to manufacture the gratings directly engraved into the fused silica substrates provided by CEA. After process developments, Jobin Yvon manufactured the two first 1(omega) and 3(omega) gratings in mid 2001. After a short summary of the specification of these gratings, we present in this paper the production process and the performances of the 1(omega) and 3(omega) gratings manufactured. Wavefront data, efficiency measurements and damage threshold performances are detailed.
To focus the third harmonic of high energy neodymium glass laser, the usage of focusing transmissions diffractive gratings ion etched directly into fused silica blank brings major benefits in comparison with classical optical solutions using aspheric lenses. The damage threshold of such a diffractive component is the same as the damage threshold of a high grade, thin, fused silica plane window. The transmission efficiency reaches 94 percent for polarization s or p. The image quality is nearly perfect: this diffractive component acts as a stigmatic lens. It separates the remaining first and second harmonic from the third one and in addition it creates a focused reflective order with 0.5 percent efficiency which offers the possibility to get a well focused sampling beam.
Variable line space (VLS) diffraction gratings present interesting solutions to design high resolution monochromators for synchrotrons. The problem is to be able to record holographically the desired grooves distribution in order to take advantage of the holographic recording and ion etching process: low stray light, absence of ghosts and second order reduction. We will review the method of calculation of VLS diffraction gratings recorded holographically by using spherical and aspherical laser wavefronts. Then the manufacture of these gratings (accuracy of recording and ion etching process) will be described. We will give an example. And finally, the theory and the accuracy of a checking method will be presented.