Projects
Multilayer Dielectric gratings
Design, simulations, and thermal analysis of multilayer dielectric gratings for spectral beam combining applications.
Multilayer dielectric gratings are considered more suitable elements for high power laser applications like spectral beam combiner and laser pulse compressor due to its low power loss compared to metal gratings. It can offer nearly 98% diffraction efficiency to a particular order with no absorption and higher damage threshold compared to metal gratings. It would be desirable if these reflection gratings could be made entirely of dielectric, rather than metallic material, to minimize energy absorbed and the consequent damage. A reflection grating must incorporate two optical functions: It must combine high reflectivity with diffraction. Conventional metallic gratings combine these two functions in a single conducting surface. The conductivity of the metal forces reflection, while periodic grooves create diffraction. Because metallic gratings owe their reflectivity to conductivity, expressible as a complex-valued refractive index or permittivity, they have a disadvantage for applications that subject the grating to intense radiation: The absorption of radiation causes heating and damage. Transparent dielectric materials have much smaller absorption coefficients than do metals, and therefore optical devices based on dielectric materials have potential for withstanding more intense radiation. The grating created in a semi-infinite dielectric medium can place nearly all the incident light into one transmitted diffraction order. However, a single air–dielectric interface will not, by itself, produce a grating that has high reflection efficiency. A second optical element is required to produce high reflectivity. Multilayer stacks of thin (subwavelength-thickness) dielectric films are widely used in the optics industry as antireflection (AR) coatings, polarizers, beam splitters, filters, and highly reflecting mirrors. Rather than relying on conductivity or absorption to produce reflection, multilayer dielectric stacks rely on interference. A succession of (horizontal) planar layers are fabricated with thicknesses such that, for light of a specified wavelength and polarization and incident from above at a given angle, the phases of upward- and downward traveling waves within each layer reinforce the upward wave for high reflectivity mirror.
Spectral beam combination of low-power laser beams using a diffraction grating is a simple way of incoherently increasing the power of a laser system. In an SBC system, all the laser beams must be diffracted at a specific diffraction order, then combined to form a high-power laser beam. The combined beam needs to be diffraction limited, as well as having high radiance and high beam quality in the far field. In other words, the diffraction grating for an SBC system should have high diffraction efficiency and high beam quality. Furthermore, if many laser beams over a wide angle of incidence are combined, the angular dispersion should be large. We have followed basic principles to design the initial gratings and multilayer dielectric mirrors separately, then refine the parameters of the MLD grating system (grating + matching layer + multilayer mirror) using a matching layer to obtain high diffraction efficiency.
Combined diffractive optical elements (combo-DOE) are used store the phase information of multiple wavefronts together. It acts as a beam shaper for interferometric testing of aspheric / freeforms. Usually, one aspheric/ freeform wave front for the specimen under test, and another spherical wave front with a slight linear offset are Lithographically written together. The spherical wavefront provides the information at cat’s eye position.
Development of Interferometer For Testing of Optical Components For Academic and Industrial application
Visible-IR optics for ground and space applications
Optics for bio-medical and defence equipment
Optics for illumination systems for consumer products
This project seeks to develop a configuration of optical elements that manipulates the trajectory of light for the purpose of detecting very weak polarized signals. Under this project, IIT Delhi will provide support for optical design of the system. The optical design requirements pertain to the beam collimation optics for Vertical Cavity Surface Emitting Laser (VCSEL), beam expansion, use of polarizers, wave plates and polarizing cube beam splitter. Preliminary design inputs have been provided by the SSPL, DRDO.
Freeform surfaces in optical systems provide extra levels of design flexibility that can be used to minimize the size, weight, and/or performance of an optical system while retaining a comparable footprint.
The diffracto-freeform offers the opportunities of freeform for numerous improvements in their optical performance such as an improved control of aberrations, increased throughput and field-of-view at reduced system size, and cost
An end-to-end Shack-Hartmann wavefront sensing device is developed. It refers to the development on all fronts of any instrument – mechanical, electronics, optical and software.
Development of scanning Shack-Hartmann Wavefront Sensor for In-situ measurement of aspheric and freeform optical surface
This indigenously developed wavefront sensing device brings together the Shack-Hartmann technique and highly optimized processing algorithm to deliver a very large dynamic range of wavefront measurements. This device can serve a vast spectrum of applications such as laser, microscopy, biomedical, astronomy, spectroscopy etc. The in-house developed product is highly capable in terms of accuracy, dynamic range, spatial resolution, and stability along with various tools to ease the process and visualization of measurement. Optical machining industry has a huge demand for small and sleek metrology equipment which could be mounted over the machine platform itself i.e., in-situ optical metrology.
A set of devices (Model T and Model R) that measures wavefront from optical components having complex geometries such as aspheric or freeform surfaces has been developed. An algorithm is indigenously developed for the reconstruction of wavefront along with the motion control program. The whole optics of the device is developed in-house.
A large-sized optical surface could also be measured using a scanning feature of this device. In this mode, the device scans the optical surface under machining in a square grid of size m x m. It stitches the captured sub-apertures data to compute the highly accurate wavefront of the order of fraction of lambda. This wavefront is traced back to define the measured surface profile. The difference of the desired and the measured surface profile is then fed to the machine for corrective feedback machining. This process does not require the removal of the component from the machining platform for metrology. While it measures keeping the component in place, it also provides the feedback to repeat the corrective machining process. Thus, with the help of this device, the machining time is significantly reduced and made accurate by reducing alignment errors introduced otherwise in moving the component.
Design and development of diffractive optical element as spectral beam combiner for high power laser application
A planar DOE was designed by ray tracing and fabricated with grayscale lithography technique. A polarization-based phase shifting Twyman-green interferometric setup was developed in the laboratory.
In case of aspheric, the departure of the aspheric surface from its best fitting spherical surface is large in many cases. When the aspheric is measured interferometrically, this large departure from the spherical reference surface results in too many interference fringes for interpretation. This makes it difficult to measure the aspheric surface. To overcome this problem, null corrector optics has been introduced in the standard interferometers. The null element converts a spherical or plane wave front into one that precisely matches the aspheric surface under test. Null elements are in general lithographically written diffractive optical elements (DOE).
Polarization based phase shifting enabled Twyman-Green interferometer has been developed to test the surface profile of rotationally invariant aspheric surface. The combo- DOE, with aspheric and spherical wavefronts is used as null elements. With help of polarization optics interference pattern with better fringe contrast and different reflectivity surfaces are tested. The developed setup is also extended to for quasi-absolute testing of Aspheric surface.
This event provide insights about the field of optics which covered almost every aspect in entirety of this field from optical design, fabrication and characterization. Along with it, there was a workshop conducted to provide hands on experience for the participants from Stellar Optics, IRDE, Dehradun and CSIR-CSIO, Chandigarh.
SPION-based nano-abrasives have been developed via a simple hydrothermal route.
The developed SPION nano-abrasives have been explored for superfinish optical polishing to achieve the surface finishing to Angstrom level.
- Highly efficient polishing abrasive
- Suitable for generating superfinish optical substrates
- Can provide surface roughness (RMS) up to 2 Å
- Can polish optical and laser-grade glasses like Fused Silica (FS), Anhydrous FS, BK-7, and Zerodur
- Recyclable and reusable
The development of optical measurement techniques for monitoring slow land mass displacement to predict landslides is a critical advancement in geotechnical and environmental engineering. Landslides can have devastating consequences, leading to loss of life and property, and early detection is essential for mitigating these risks. Landslides are geological phenomena that involve the movement of rock, soil, and debris down a slope under the influence of gravity. They can occur suddenly or gradually, with slow-moving landslides often exhibiting subtle signs before catastrophic failure. Predicting and monitoring these slow land mass displacements can help prevent disasters.
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