Compressive sensing (CS) is an imaging method that enables the replacement of expensive matrix detectors by small and cheap detectors with one or a few detector elements. A high-resolution image is realized from a series of individual single-value measurements. Each measurement consists of capturing the image from an object or a scene after coding by a well-defined pattern. The reconstruction of the high-resolution image requires a number of measurements significantly smaller than the number of full-frame image pixels. This is because most natural images may be sparsely coded, i.e. we may find an appropriate basis for which most coefficients are close to zero. This paper reports CS experiments under pulse laser illumination at 1.55 μm. The light collected from the observed scene is spatially modulated using a digital micromirror device (DMD) and projected onto a single-pixel detector. The applied binary patterns are generated using a Hadamard matrix. Different approaches for pattern selection have been implemented and compared.
Conventional electro-optical and infrared (EO/IR) systems (i.e., active, passive, multiband and hyperspectral) capture an image by optically focusing the incident light at each of the millions of pixels in a focal plane array. The optics and the focal plane are designed to efficiently capture desired aspects (like spectral content, spatial resolution, depth of focus, polarization, etc.) of the scene. Computational imaging refers to image formation techniques that use digital computation to recover an image from an appropriately multiplexed or coded light intensity of the scene. In this case, the desired aspects of the scene can be selected at the time of image reconstruction which allows greater flexibility of the EO/IR system. Compressive sensing involves capturing a smaller number of specifically designed measurements from the scene to computationally recover the image or task specific scene information. Compressive sensing has the potential to acquire an image with equivalent information content to a large format array while using smaller, cheaper, and lower bandwidth components. More significantly, the data acquisition can be sequenced and designed to capture task specific and mission relevant information guided by the scene content with more flexibility. However, the benefits of compressive sensing and computational imaging do not come without compromise. NATO SET-232 has undertaken the task of investigating the promise of computational imaging and compressive sensing for EO/IR systems. This paper presents an overview of the ongoing joint activities by NATO SET-232, current computational imaging and compressive sensing technologies, limitations of the design trade space, algorithm and conceptual design considerations, and field performance assessment and modeling.
Remote detection of vibrational features from an object is important for many short range civil applications, but it is also of interest for long range applications in the defense and security area. The well-established laser Doppler vibrometry technique is widely used as a high-sensitivity, non-contact method. The development of camera technology in recent years made image-based methods reliable passive alternatives for vibration and dynamic measurements. Very sensitive applications have been demonstrated using high speed cameras in the visual spectral range. However, for long range applications, where turbulence becomes a limiting factor, image acquisition in the short- to mid-wave IR region would be desirable, as the atmospheric effects attenuate at longer wavelength.
In this paper, we investigate experimentally the vibration detection from short- and mid-wave IR image sequences using high speed imaging technique. Experiments on the extraction of vibration signature under strong local turbulence conditions are presented.
The development of camera technology in recent years has made high speed imaging a reliable method in vibration and dynamic measurements. The passive recovery of vibration information from high speed video recordings was reported in several recent papers. A highly developed technique, involving decomposition of the input video into spatial subframes to compute local motion signals, allowed an accurate sound reconstruction. A simpler technique based on image matching for vibration measurement was also reported as efficient in extracting audio information from a silent high speed video. In this paper we investigate and discuss the sensitivity and the limitations of the high speed imaging technique for vibration detection in comparison to the well-established Doppler vibrometry technique. Experiments on the extension of the high speed imaging method to longer range applications are presented.
As a consequence of the ongoing interest for deployment of laser systems into space, suitable optical components have to be
developed and must be extensively space qualified to ensure reliable, continuous, and autonomous operation. The exposure
to space environment can adversely affect the longevity of optics, mainly coatings, and lead to system degradation. An
increased operational risk is due to the air-vacuum effect, which can strongly reduce the laser damage resistance of optical
coatings. For this purpose, a vacuum laser damage test bench has been developed and is operated at DLR. In extensive test
campaigns, all damage-prone optics of the ALADIN laser system (being the laser source of the upcoming ESA ADM
Aeolus mission) were tested under operative conditions at the fundamental and at the harmonic wavelengths of Nd:YAG.
Further operational risks are due directly to operation under high vacuum. In the past, several space-based laser missions
have suffered from anomalous performance loss or even failure after short operation times. This degradation is due to
selective contamination of laser-exposed optical surfaces fed by outgassing constituents. These volatile components are
omnipresent in vacuum vessels. Various organic and inorganic species were tested at our facilities for their criticality on
deposit built-up. Finally, active optical components like Q-switch crystals or frequency converter crystals can also suffer
from bulk absorption induced by high-energy radiation (gray tracking) and dehydration. To analyze these effects, an ultrahigh
vacuum phase matching unit was set up to test various combinations of SHG and THG frequency converters.
We report the in situ characterization of a semiconductor saturable absorber mirror (SESAM) in an operating Yb:KGW mode-locked laser. The technique may be described as a pump-probe experiment in which the intracavity beam acts as a pump beam, while the output of the same laser is used as a test beam for the SESAM reflectivity. At zero delay, the probe pulse overlaps in time with the subsequent intracavity pulse. The method is an alternative to standard pump-probe measurements, in situations where the intracavity parameters such as energy fluence onto the SESAM, pulse length and center wavelength can not be simultaneously achieved with available lasers.
We have developed a mode-locked diode-pumped Yb:KGW laser generating 100-fs pulses with an output power of 126 mW. The corresponding optical spectrum has a 13.4 nm FWHM bandwidth and is centred at 1037.4 nm. In the multiple pulsing regime, bound states of solitons with rotating phase difference were observed. Consecutive solitons were separated by less than 1 ps.