Deformable Grating Research Articles

Realization of a Cost-Effective Deformable Grating for the Extreme-Ultraviolet

The application of a deformable grating to the realization of a time delay compensated monochromator is presented. The grating is realized as a replica on a thin glass substrate and the deformation is realized with a mechanical bender. The monochromator is conceived for the spectral selection of a single harmonic in the spectral range 20-80 nm in beamlines exploiting the high harmonic generation process. A possible optical design requiring only two deformable gratings, a mirror and an intermediate slit is presented.

Modified rigorous coupled-wave analysis for multi-layer deformable gratings with arbitrary profiles and materials.

In this paper, the rigorous coupled-wave analysis (RCWA) is extended for general multi-layer deformable gratings with arbitrary numbers of layers, surface profiles, layer offsets, and materials. The contribution from the offset between grating layers and/or due to the movement of the deformable grating layer is included in the expansion of the relative permittivity by the Fourier series, enabling the calculations of deformable gratings commonly used in many optical-based displacement sensing devices. The accuracy and efficiency of the extended RCWA are verified by a number of grating models. It is found that the numerical results are in excellent agreement with those from the finite element method, while the RCWA method costs only ∼1/10 in computation time when compared to its counterpart. Our approach can be used for fast calculation and optimization of multi-layer deformable gratings for optical displacement sensing applications.

Active optics in astronomy – modeling of deformable substrates: freeform surfaces for FIREBall and MESSIER

Abstract Active optics techniques on large telescopes and astronomical instrumentations provide high imaging quality. For ground-based astronomy, the co-addition of adaptive optics again increases angular resolution up to providing diffraction-limited imaging at least in the infrared. Active and adaptive optics marked milestone progress in the detection of exoplanets, super-massive black holes, and large-scale structure of galaxies. This paper is dedicated to highly deformable active optics that can generate non-axisymmetric aspheric surfaces – or freeform surfaces – by use of a minimum number of actuators: a single uniform load acts over the surface of a vase-form substrate whilst under reaction to its elliptical perimeter ring. Two such instruments are presented: (1) the Faint Intergalactic Redshifted Emission Balloon (FIREBall) telescope and multi object spectrograph (MOS) where the freeform reflective diffraction grating is generated by replication of a deformable master grating, and (2) the MESSIER wide-field low-central-obstruction three-mirror-anastigmat (TMA) telescope proposal where the freeform mirror is generated by stress figuring and elastic relaxation. Freeform surfaces were obtained by plane super-polishing. Preliminary analysis required use of the optics theory of 3rd-order aberrations and elasticity theory of thin elliptical plates. Final cross-optimizations were carried out with Zemax raytracing code and Nastran FEA elasticity code in order to determine geometry of the deformable substrates.

Hyperspectral imaging with deformable gratings fabricated with metal-elastomer nanocomposites.

We report the fabrication and characterization of a simple and compact hyperspectral imaging setup based on a stretchable diffraction grating made with a metal-polymer nanocomposite. The nanocomposite is produced by implanting Ag clusters in a poly(dimethylsiloxane) film by supersonic cluster beam implantation. The deformable grating has curved grooves and is imposed on a concave cylindrical surface, thus obtaining optical power in two orthogonal directions. Both diffractive and optical powers are obtained by reflection, thus realizing a diffractive-catoptric optical device. This makes it easier to minimize aberrations. We prove that, despite the extended spectral range and the simplified optical scheme, it is actually possible to work with a traditional CCD sensor and achieve a good spectral and spatial resolution.

Fluid-enhanced tunable diffraction with an elastomeric grating

We replicate a diffraction grating by soft lithography. Tunable diffraction is accomplished by modifying groove spacing through the application of strain on the elastomeric replica. The range of strain-variable diffraction angles is extended by adding a refracting liquid layer to the grating. Using a water layer, the diffraction angle is tuned from 38 to 33.4 deg with an applied strain of 17.7%. With an equal amount of strain, employing a glycerol layer results in the diffraction angle varying from 38.8 to 34.4 deg. Our experimental results are accurately described by the combined effects of diffraction by a deformable grating and refraction by a fluid with a curved surface.

Spatio-temporal modeling and optimization of a deformable-grating compressor for short high-energy laser pulses.

Monolithic large-scale diffraction gratings are desired to improve the performance of high-energy laser systems and scale them to higher energy, but the surface deformation of these diffraction gratings induce spatio-temporal coupling that is detrimental to the focusability and compressibility of the output pulse. A new deformable-grating-based pulse compressor architecture with optimized actuator positions has been designed to correct the spatial and temporal aberrations induced by grating wavefront errors. An integrated optical model has been built to analyze the effect of grating wavefront errors on the spatio-temporal performance of a compressor based on four deformable gratings. A 1.5-meter deformable grating has been optimized using an integrated finite-element-analysis and genetic-optimization model, leading to spatio-temporal performance similar to the baseline design with ideal gratings.

Mechanics of dielectric elastomer-activated deformable transmission grating

Laminating a thin layer of elastomeric grating on the surface of a prestretched dielectric elastomer (DE) membrane forms a basic design of electrically tunable transmission grating. We analyze the inhomogeneous deformation of a circular multiple-region configuration. Variation of the geometric and material parameters, as well as of the critical condition determined by loss of tension instability, is probed to aid the design of a DE-based deformable grating. The predicted changes in the grating period agree substantially with the experimental results reported by Aschwanden et al (Aschwanden et al 2007 IEEE Photon. Technol. Lett. 19 1090).

Characterization of a micromachined vertically deformable varying-pitch grating for a spectrometer

A new type of micromachined vertically deformable varying-pitch grating is designed and fabricated. Its characterization and its feasibility as a spectrometer are presented. The deformable grating shows a 0.7 µm working range and 3.6 kHz bandwidth. Its characterization and its feasibility as a spectrometer are presented. The varying-pitch grating has the ability to detect an individual wavelength with a single detector by physical scanning. Its deformable capability can increase intensity and resolution at a specific wavelength. Those two capabilities are experimentally demonstrated.

Reconfigurable Optical Wavelength Multiplexer Using a MEMS Tunable Blazed Grating

This paper describes a free-space 1 timesP cyclically tunable optical multiplexer based on a stationary tunable blazed grating (TBG). An analytical model is used in deriving a closed- form expression for the transmission of the deformable grating, given an actuation scheme that requires only (P -1) control signals. A 1 times3 demultiplexer is implemented using a six-element TBG, and tuning over a free spectral range of 13.5 nm in C-band is demonstrated.

A micromachined scanning grating interferometer for the out-of-plane vibration measurement of MEMS

A micromachined scanning grating interferometer (µSGI) is presented for use in measuring the out-of-plane vibration of microelectromechanical systems (MEMS). The µSGI uses a phase sensitive deformable diffraction grating to achieve interferometric axial resolution and a microfabricated lens to improve lateral resolution of the measurement. The grating is intended to be actuated to control diffraction patterns while measuring the MEMS vibration to increase measurement sensitivity. The deformable grating and the microlens are fabricated by surface micromachining techniques on separate wafers which are then precisely aligned and assembled. The fabricated deformable grating shows an actuation range of 0.54 µm and an operating voltage of under 31 V. An assembled grating and lens chip are successfully integrated with a silicon photodiode in less than 2 cm3. The integrated µSGI has been demonstrated by measuring 4.4 nm, 900 kHz vibration of a MEMS device while actuating the deformable grating in the measurement.

Scanning Grating Microinterferometer for MEMS Metrology

Quality control and metrology are critical to improved productivity and yield in MEMS design and production. This paper presents a micrograting interferometer for use in measuring MEMS devices. The sensor is also capable of making dynamic measurements, qualifying the functionality of the MEMS devices. The system employs a phase sensitive diffraction grating for interferometric axial resolution and a microfabricated lens for improved lateral resolution. The microinterferometer is capable of array implementation and can be used to increase the yield of MEMS manufacturing processes. The results generated by a single microinterferometer show good correlation with both analytic models and measurements of the MEMS devices by other metrology tools. The microinterferometer enables measurement of steady state vibration of MEMS devices as well as the development of surface vibration profiles. Initial results presented in this paper also demonstrate the ability to measure quantities such as part surface curvature, as well as reduce low frequency vibrational noise. The use of a deformable diffraction grating is proposed to further enhance the sensor’s capabilities.