Frédéric Lamontagne

Design and test results of the calibration unit for the MOAO demonstrator RAVEN

INO has designed, assembled and tested the Raven Multi-Object Adaptive Optics demonstrator calibration unit. This sub-system consists in a telescope simulator that will allow aligning Ravens components during its integration, testing its Adaptive Optics performances in the laboratory and at the telescope, and calibrating the Adaptive Optics system by building the interaction matrix and measuring the non-common path aberrations. The system is presented with the challenges that needed to be overcome during the design and integration phases. The system test results are also presented and compared to the model predictions.

Uncooled detector, optics, and camera development for THz imaging

A prototype THz imaging system based on modified uncooled microbolometer detector arrays, INO MIMICII camera electronics, and a custom f/1 THz optics has been assembled. A variety of new detector layouts and architectures have been designed; the detector THz absorption was optimized via several methods including integration of thin film metallic absorbers, thick film gold black absorbers, and antenna structures. The custom f/1 THz optics is based on high resistivity floatzone silicon with parylene anti-reflection coating matched to the wavelength region of interest. The integrated detector, camera electronics, and optics are combined with a 3 THz quantum cascade laser for initial testing and evaluation. Future work will include the integration of fully optimized detectors and packaging and the evaluation of the achievable NEP with an eye to future applications such as industrial inspection and stand-off detection.

Development of an optomechanical statistical tolerancing method for cost reduction

Optical systems generally require a high level of optical components positioning precision resulting in elevated manufacturing cost. The optomechanical tolerance analysis is usually performed by the optomechanical engineer using his personal knowledge of the manufacturing precision capability. Worst case or root sum square (RSS) tolerance calculation methods are frequently used for their simplicity. In most situations, the chance to encounter the worst case error is statistically almost impossible. On the other hand, RSS method is generally not an accurate representation of the reality since it assumes centered normal distributions. Moreover, the RSS method is not suitable for multidimensional tolerance analysis that combines translational and rotational variations. An optomechanical tolerance analysis method based on Monte Carlo simulation has been developed at INO to reduce overdesign caused by pessimist manufacturing and assembly error predictions. Manufacturing data errors have been compiled and computed to be used as input for the optomechanical Monte Carlo tolerance model. This is resulting in a more realistic prediction of the optical components positioning errors (decenter, tilt and air gap). Calculated errors probabilities were validated on a real lenses barrels assembly using a high precision centering machine. Results show that the statistical error prediction is more accurate and that can relax significantly the precision required in comparison to the worst case method. Manufacturing, inspection, adjustment mechanism and alignment cost can then be reduced considerably.

Evolution of INO Uncooled Infrared Cameras Towards Very High Resolution Imaging

Along the years INO has been involved in development of various uncooled infrared devices. Todays, the infrared imagers exhibit good resolutions and find their niche in numerous applications. Nevertheless, there is still a trend toward high resolution imaging for demanding applications. At the same time, low-resolution for mass market applications are sought for low-cost imaging solutions. These two opposite requirements reflect the evolution of infrared cameras from the origin, when only few pixel-count FPAs were available, to megapixel-count FPA of the recent years. This paper reviews the evolution of infrared camera technologies at INO from the uncooled bolometer detector capability up to the recent achievement of 1280×960 pixels infrared camera core using INOs patented microscan technology.

Disruptive advancement in precision lens mounting

Threaded rings are used to fix lenses in a large portion of opto-mechanical assemblies. This is the case for the low cost drop-in approach in which the lenses are dropped into cavities cut into a barrel and clamped with threaded rings. The walls of a cavity are generally used to constrain the lateral and axial position of the lens within the cavity. In general, the drop-in approach is low cost but imposes fundamental limitations especially on the optical performances. On the other hand, active alignment methods provide a high level of centering accuracy but increase the cost of the optical assembly. This paper first presents a review of the most common lens mounting techniques used to secure and center lenses in optical systems. Advantages and disadvantages of each mounting technique are discussed in terms of precision and cost. Then, the different contributors which affect the centering of a lens when using the drop-in approach, such as the threaded ring, friction, and manufacturing errors, are detailed. Finally, a patent pending lens mounting technique developed at INO that alleviates the drawbacks of the drop-in and the active alignment approaches is introduced. This innovative auto-centering method requires a very low assembly time, does not need tight manufacturing tolerances and offers a very high level of centering accuracy, usually less than 5 μm. Centering test results performed on real optical assemblies are also presented.

Lens auto-centering

In a typical optical system, optical elements usually need to be precisely positioned and aligned to perform the correct optical function. This positioning and alignment involves securing the optical element in a holder or mount. Proper centering of an optical element with respect to the holder is a delicate operation that generally requires tight manufacturing tolerances or active alignment, resulting in costly optical assemblies. To optimize optical performance and minimize manufacturing cost, there is a need for a lens mounting method that could relax manufacturing tolerance, reduce assembly time and provide high centering accuracy. This paper presents a patent pending lens mounting method developed at INO that can be compared to the drop-in technique for its simplicity while providing the level of accuracy close to that achievable with techniques using a centering machine (usually < 5 μm). This innovative auto-centering method is based on the use of geometrical relationship between the lens diameter, the lens radius of curvature and the thread angle of the retaining ring. The autocentering principle and centering test results performed on real optical assemblies are presented. In addition to the low assembly time, high centering accuracy, and environmental robustness, the INO auto-centering method has the advantage of relaxing lens and barrel bore diameter tolerances as well as lens wedge tolerances. The use of this novel lens mounting method significantly reduces manufacturing and assembly costs for high performance optical systems. Large volume productions would especially benefit from this advancement in precision lens mounting, potentially providing a drastic cost reduction.

Measuring ice clouds with an airborne far-IR radiometer

In recent years, i.e., since the International Polar Year of 2007– 2008, thin ice clouds (TICs) that are unique to polar regions have been revealed as standing features of the polar atmosphere during the dark season.1 Such discoveries have also been made possible by two highly successful satellites launched in April 2006—NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation2 (CALIPSO) and CloudSat3—which include active instruments (a lidar and radar, respectively) used to probe clouds and aerosols for the first time. Over the past few years, it has thus become a prime scientific objective to monitor the formation of TICs and light precipitation in the Earth’s coldest regions (i.e., at high latitudes and near the tropopause). Despite this recent work, new far-IR data is still required to improve medium-range weather forecasting during the winter months, and which is essential for populations living at farnorthern latitudes. In our work (as part of a collaboration between the National Optics Institute, Canada, and the Canadian Space Agency), we have thus built a new aircraft-certified far-IR radiometer (FIRR).4 Our ultimate aim is for the instrument to be a future microsatellite payload. At present, however, we have designed the FIRR for use on the Alfred Wegener Institute’s (Germany) Polar 6 aircraft, i.e., for unattended airborne measurements of ice clouds over the Arctic. Our ground tests show that when used as a non-imaging radiometer, the FIRR exhibits a noise equivalent radiance in the range of 10–20mW/(m2sr). In addition, we have found that the dynamic range and detector vacuum integrity of the instrument are suited to the conditions of airborne experiments. In the design of the FIRR, we had to meet a number of specific requirements, i.e., those of a pan-arctic airborne mission. First, it is necessary that the system enables cloud radiance Figure 1. (a) Photograph of the far-IR radiometer instrument, showing the two stand-alone units of the instrument: the optomechanical device (OMD) and instrument control device (ICD). (b) Schematic illustration of the instrument’s mirrors, camera, and filter wheel (inside the enclosure under the ICD rack). The radiometer has a footprint (excluding the ICD) of 887 813mm, and the OMD has a height of 570mm. FPA: Focal plane array.

Optomechanical design of TMT NFIRAOS Subsystems at INO

The adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). Recently, INO has been involved in the optomechanical design of several subsystems of NFIRAOS, including the Instrument Selection Mirror (ISM), the NFIRAOS Beamsplitters (NBS), and the NFIRAOS Source Simulator system (NSS) comprising the Focal Plane Mask (FPM), the Laser Guide Star (LGS) sources, and the Natural Guide Star (NGS) sources. This paper presents an overview of these subsystems and the optomechanical design approaches used to meet the optical performance requirements under environmental constraints.

Design and instrumentation of an airborne far infrared radiometer for in-situ measurements of ice clouds

We report on the design and instrumentation of an aircraft-certified far infrared radiometer (FIRR) and the resulting instrument characteristics. FIRR was designed to perform unattended airborne measurements of ice clouds in the arctic in support of a microsatellite payload study. It provides radiometrically calibrated data in nine spectral channels in the range of 8-50 μm with the use of a rotating wheel of bandpass filters and reference blackbodies. Measurements in this spectral range are enabled with the use of a far infrared detector based on microbolometers of 104-μm pitch. The microbolometers have a new design because of the large structure and are coated with gold black to maintain uniform responsivity over the working spectral range. The vacuum sealed detector package is placed at the focal plane of a reflective telescope based on a Schwarschild configuration with two on-axis spherical mirrors. The telescope field-of-view is of ~6° and illuminates an area of ~2.1-mm diameter at the focal plane. In operation, FIRR was used as a nonimaging radiometer and exhibited a noise equivalent radiance in the range of 10-20 mW/m2-sr. The dynamic range and the detector vacuum integrity of FIRR were found to be suited for the conditions of the airborne experiments.

NFIRAOS beamsplitters subsystems optomechanical design

The early-light facility adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). The science beam splitter changer mechanism and the visible light beam splitter are subsystems of NFIRAOS. This paper presents the opto-mechanical design of the NFIRAOS beam splitters subsystems (NBS). In addition to the modal and the structural analyses, the beam splitters surface deformations are computed considering the environmental constraints during operation. Surface deformations are fit to Zernike polynomials using SigFit software. Rigid body motion as well as residual RMS and peak-to-valley surface deformations are calculated. Finally, deformed surfaces are exported to Zemax to evaluate the transmitted and reflected wave front error. The simulation results of this integrated opto-mechanical analysis have shown compliance with all optical requirements.