A high-dynamic-range reflectivity measurement instrument has been developed with a dynamic range in excess of 100 dB and sensitivity below 1 pW. It can measure the angle-dependent back-scattered reflectivity of static surfaces up to 80º incidence angle over any orientation without the need for physical contact with the part. It has been designed to operate at both 800 nm and 1550 nm. The system operates through lock-in detection of amplitude-modulated laser light in a bi-static probe architecture, specially designed to minimise the effects of unwanted scattering and stray light. This development has been designed for on-site characterisation of the reflectivity of components of the ITER nuclear fusion reactor whose size, radioactivity or toxicity are inappropriate for insertion in traditional BRDF measurement instrumentation. Measuring the reflectivity of these components is critical for the development of tools for in-service inspection of ITER’s reaction chamber, a key element for the safety of the machine. The reflectivity of beryllium blanket module components and tungsten divertor components has been measured to vary over a range of up to 50 dB from normal to 80º incidence angle, to values below 10-5 /sr. Strong anisotropy of the reflectivity is also observed. This data has been matched with the inspection system performance in a custom simulator to confirm that inspection is possible over < 95 % of the ITER reactor plasma facing components.
This paper describes the design of a 3-5microns 26:1 zoom with a focal length extender capability that increases NFOV
focal length by 1.75x. Mechanical restrictions for a payload envelope will be considered as well as cold stop efficiency
Lately the short-wave infrared (SWIR) has become very important due to the recent appearance on the market of
the small detectors with a large focal plane array. Military applications for SWIR cameras include handheld and
airborne systems with long range detection requirements, but where volume and weight restrictions must be
considered. In this paper we present three different designs of telephoto objectives that have been designed
according to three different methods. Firstly the conventional method where the starting point of the design is an
existing design. Secondly we will face design starting from the design of an aplanatic system. And finally the
simultaneous multiple surfaces (SMS) method, where the starting point is the input wavefronts that we choose.
The designs are compared in terms of optical performance, volume, weight and manufacturability. Because the
objectives have been designed for the SWIR waveband, the color correction has important implications in the
choice of glass that will be discussed in detail.
Two new optical structures are designed using the Simultaneous Multiple Surfaces (SMS) method, comprised of 2
reflecting surfaces and 2 refracting surfaces, 800mm focal length, f/8 (aperture diameter 100 mm) and 1.180 diagonal
field of view in the SWIR band. The lens surfaces are rotational symmetric and calculated to have good control of
non-paraxial rays. We have achieved designs with excellent performance, and with total system length of less than 60 mm.
While multichannel configurations are well established for non-imaging applications, they have not been used yet
for imaging applications. In this paper we present for the first time some of multichannel designs for imaging
systems. The multichannel comprises discontinuous optical sections which are called channels. The phase-space
representation of the bundle of rays going from the object to the image is discontinuous between channels. This
phase-space ray-bundle flow is divided in as many paths as channels there are but it is a single wavefront both at the
source and the target. Typically, these multichannel systems are at least formed by three optical surfaces: two of
them have discontinuities (either in the shape or in the shape derivative) while the last is a smooth one. Optical
surfaces discontinuities cause at the phase space the wave front split in separate paths. The number of discontinuities
is the same in the two first surfaces: Each channel is defined by the smooth surfaces in between discontinuities, so
the surfaces forming each separate channel are all smooth. Aplanatic multichannel designs are also shown and used
to explain the design procedure.
In this work, we propose two new optical structures, using the Simultaneous Multiple Surfaces (SMS) method,
comprised of 2 reflecting surfaces and 2 refracting surfaces, 800mm focal length, f/8 (aperture diameter 100 mm)
and 1.18° diagonal field of view in the SWIR band. The lens surfaces are rotational symmetric and calculated to have
good control of non-paraxial rays. We have achieved designs with excellent performance, and with total system
length of less than 60 mm.
Using the Simultaneous Multiple Surface method in 2D (SMS2D), we present a
fast catadioptric objective with a wide field of view (125°×96°designed for a microbolometer
detector with 640×480 pixels and 25 microns pixel pitch.
Using the Simultaneous Multiple Surface method in 2D (SMS2D), we present a fast catadioptric objective with a wide
field of view (125°×96°) designed for a microbolometer detector with 640×480 pixels and 25 microns pixel pitch
Keywords: Infrared lens design, thermal imaging, Schwarzschild configuration, SMS2D, wide field of view, driving
cameras, panoramic systems
Using the Simultaneous Multiple Surface method in 2D (SMS2D), we present a fast catadioptric objective with a wide
field of view (125°×96°) designed for a microbolometer detector with 640×480 pixels and 25 microns pixel pitch.
In this contribution we present a compact system to create an illumination distribution with a constant aspect ratio 3:4
and FOV from 0.4 to 1 degree. Besides, the system must delivery 40 W from 170 individual laser diodes placed in a
regular 2-D array distribution of 10 x 20 mm.
The main problem that must be solved is the high asymmetry of the individual sources; emission divergence's ratio 3:73
(0.3 vs. 7.4 degree) combined with the flux holes due to the laser's heat drain. In one axis (divergence of 0.3º) the best
design strategy approach is a Galileo telescope but in the other axis a collimator configuration is the best solution. To
manage both solutions at the same time is the aim of this contribution.
Unfortunately for the Galileo strategy, source dimensions are too large so aspheric surfaces are needed, and the
collimator configuration requires an EFL that must change from 573 to 1432 mm. The presented solution uses a set of
three fixed anamorphic lenses, two of them pure cylinders, combined with a wheel of anamorphic lenses that have the
function to change the FOV of the system. The most important contribution of the design is to obtain a constant final
ratio 3:4 from an initial ratio of 3:73 with no losses of energy.
The proposed solution produces an illumination pattern with peaks and valleys lower than 40%. This pattern distribution
might be unacceptable for a standard illumination solution. However, the actual FOV is used to illuminate far away
targets thus air turbulence is enough to homogenize the distribution on the target.
The Schmidt-Cassegrain configuration has advantages from the point of view of the packaging constraint but doesn't
provide enough optical quality through the full field of view when a larger F-number (3.6) and a FOV of 1° are necessary
to reach the minimum illumination threshold in the sensor. Moreover, to improve the global performance the telescope's
window must be spherical instead of flat. All these factors produce a poor image optical quality that must be increased.
We had overcome those problems introducing two changes in the traditional Schimdt-Cassegrain configuration. First, we
had changed the spherical primary mirror to a Mangin mirror. This introduces a second surface and an extra thickness
that can be used to optimize the system without adding new elements. Secondly, as the Mangin mirror is the entrance
pupil of the system with a 200 mm diameter, the use of aspherical surfaces on it is too expensive. Instead we have aspherized the telescope's secondary mirror to obtain the required image quality.
This aspheric coefficient of the secondary mirror, introduced in an element with a diameter not larger than 50 mm, replaces the third order coefficient of the second surface of the telescope window.
Wavefront coding (WFC) is a powerful hybrid optical-numerical technique for increasing the depth of
focus of imaging systems. There is a low cost solution that uses decentred lenses inducing coma as an
adjustable and removable phase element. This coding has been proven useful for IR systems. However
these systems usually have several configurations with multiple fields of view. Unless the detector is
uncooled, the f/number of the system is maintained for all configurations thus entrance pupil size changes
for each one. As a result, the coding coma changes accordingly. This paper presents an approach to
maintain the same amount of coma for dual field of view (DFOV) systems.
Wavefront coding (WFC) is a powerful hybrid optical-numerical technique for increasing the depth of focus of imaging
systems. It is based on two components: (1) an optical phase element that codifies the wavefront, and (2) a numerical
deconvolution algorithm that reconstructs the image. Traditionally, some sophisticated optical WFC designs have been
used to obtain approximate focus-invariant point spread functions (PSFs). Instead, we present a simple and low cost
solution, implemented on infrared (IR) cameras, which uses a decentred lens inducing coma as an adjustable and
removable phase element. We have used an advanced deconvolution algorithm for the image reconstruction, which is
very robust against high noise levels. These features allow its application to low cost imaging systems. We show
encouraging preliminary results based on realistic simulations using optical PSFs and noise power spectral density (PSD)
laboratory models of two IR imaging systems. Without induced optical phase, the reconstruction algorithm improves the
image quality in all cases, but it performs poorly when there are both in and out-of-focus objects in the scene. When
using our coding/decoding scheme with low-noise detectors, the proposed solution provides high quality and robust
recovery even for severe defocus. As sensor noise increases, the image suffers a graceful degradation, its quality being
still acceptable even when using highly noisy sensors, such as microbolometers. We have experienced that the amount of
induced coma is a key design parameter: while it only slightly affects the in-focus image quality, it is determinant for the
final depth of focus.
The performance of bi-spectral diffractive lenses for MWIR and LWIR is shown. The effect of ghost light produced by
third order will enhance the importance of the reference wavelength (λ0) in the design of the diffractive surface.
The effect of the 2D structured noise on the post-processing of images in hybrid optical-digital imaging systems is studied on the basis of the Wiener restoration filter. 2D structured noise is modeled as an additive noise that has the same random value along a row or a column in the image. The restoration is carried out with the Wiener filter in an unsupervised way by the use of well established procedures to determine the filter constant as a function of the noise power. We show that the classical Wiener filter is not satisfactory for the case of systems affected by 2D noise and we conclude that this is caused by an overdetermantion of the 2D noise in the procedure to find the filter constant. From this conclusion we propose a new filter based on the separability of the Optical Transfer Function of the optical system that depends on two constants, one for each principal direction of the 2D noise. Furthermore, we define a procedure for the unsupervised determination of these constants and we evaluate the quality of the restoration obtained by this procedure.
The use of several materials (Ge, ZnSe and GASIR1) and bi-spectral diffractive surfaces are evaluated for the design of dual waveband optical systems, MWIR and LWIR. The design of a complex objective is described.
We analyze the performances of the most known phase filter design (the cubic phase plate) in wavefront coding systems with respect to on- and off-axis imaging. To this end, the PSF will be calculated at different off-axis positions and the contribution of coma and astigmatism aberration terms to its spatial variation will be evaluated. The study will include the subsequent digital image processing procedure as well, so that a clear idea of the overall system performance will be drawn.
Optical design for fish-eye lenses usually includes a front meniscus lens that reduces the angles of incidence of chief rays towards the rest of the optics. However it also introduces distortion of the pupil, both shape and position. Thus, pupil aberration are one of the most relevant problems when designing this type of lenses. This paper shows the relationships between image and pupil aberrations and describes the design of MWIR fish-eye lenses that include diffractive surfaces in order to properly control entrance pupil size. The design goal is to achieve a constant pupil area over the field of view.
This paper describes the configuration of a DFOV objective intended for use with a linear detector in the LIR band. The implications of the presence of the scanner are evaluated, including a definition of distortion in the scanning direction and a study of cold stop efficiency. The rear part of the objective is redesigned to deal with a focal pane array. Criteria such as the improvement of the cold stop efficiency are kept in mind. The new arrangement introduces a binary surface to control pupil aberrations maintain the volume envelope as in the previous case.
This paper describes the design of a DFOV objective intended for use with a focal plane array in the MIR waveband. The seven-elements' arrangement with binary and aspheric surfaces yields a low distortion, high quality and lightweight objective. Focusing and athermalization mechanisms are evaluated. In addition, the implications of different configurations for the detector calibration subassembly are discussed.
The need of coma at the exit pupil of a telescope for a scanning IR camera is well known. However, in some cases it is impossible to introduce the required pupil coma if there are not enough degrees of freedom. This paper describes the use of a binary surface in a DFOV telescope so that pupil aberrations are properly controlled. The design has been performed on an already existing telescope, maintaining design philosophy. Several positions of the surface are considered. Comparison among all possible configurations is evaluated in terms of image and radiometric quality as well as weight and cost savings. The effect of the binary surface on the system performance over the operative temperature range is also studied.