Christian Eisele

• Dr. rer. nat.
• Senior Researcher at Fraunhofer Institute of Optronics, System Technologies and Image Exploitation

A novel apparatus for a sensitive test of the independence of the speed of optical waves from the propagation direction has been developed. It employs a monolithic ULE glass structure containing two orthogonal, crossing Fabry–Perot cavities which enable common mode rejection of certain disturbances. Highly accurate locking and cavity frequency read...

We demonstrate a diode laser system which is suitable for high-resolution spectroscopy in the 1.2μm and yellow spectral ranges. It is based on a two-facet quantum dot chip in a Littrow-type external cavity configuration. The laser is tunable in the range 1125–1280nm, with an output power of more than 200mW, and exhibits a free-running line width of...

Im Zuge der vorliegenden Arbeit wurde eine Apparatur für die Überprüfung einer Grundaussage der Speziellen Relativitätstheorie, der Isotropie der Lichtgeschwindigkeit, entwickelt. Abweichungen von der Isotropie bedeuten eine Verletzung der Lorentz Invarianz, eine von allen etablierten Theorien der Grundkräfte angenommenen Symmetrie, und würden auf...

We report on the results of a strongly improved test of local Lorentz invariance, consisting of a search for an anisotropy of the resonance frequencies of electromagnetic cavities. The apparatus comprises two orthogonal standing-wave optical cavities interrogated by a laser, which were rotated approximately 175 000 times over the duration of 13 mon...

Guided, semi-guided or un-guided missiles constitute a permanent threat for military platforms. Survivability could be increased by novel methods that allow the detection of threats before launch. New methods have to be identified and their realisations with passive and/or active electro-optical (EO) sensors have to be shown. Fraunhofer IOSB (Germ...

In the framework of a NATO research group Fraunhofer IOSB and partners conducted a field trial in an arid shrub land environment in southern New Mexico (USA). The group investigates environmental limitations of fielded EO-TDAs (Electro-Optical Tactical Decision Aids). Main objective of the trial was to study the impact of the atmosphere on imagin...

Compressed Sensing provides an innovative imaging technique with fundamental differences to conventional imaging. A collection of low-resolution measurements is taken to reconstruct a picture with higher resolution computationally. The significant advantage is the small number of measurements and reduced number of measured pixels compared to the nu...

We report on first findings of a field trial, which has been carried out in a desert-like shrub land environment in New Mexico (USA) to acquire data for the improvement of electro-optical tactical decisions aids.

The problem deals with an exact calculation of the intersection area of a circle arbitrary placed on a grid of square shaped elements with gaps between them (finite fill factor). Usually an approximation is used for the calculation of the intersection area of the circle and the squares of the grid. We analyze the geometry of the problem and derive...

Considerable efforts were made in the last decade to develop devices for the detection of hostile shooters immediately after or even before the shot. This development was strongly driven by the changed threat situation soldiers have to cope with. In the assymetric conflicts of our days, ambushs and sniper attacks are not the exception, but the rule...

We report on propagation measurements performed during the MINOTAUROS (Maritime INvestigations On Targets & Atmosphere Under Reduction of Optical Signatures) experiment on Crete, Greece, in late summer of 2016. The field trial has been organized by NATO STO Task Group SET-211 on Naval Platform Protection in the EO/IR Domain with strong support of t...

Localizing a shooter in a complex scenario is a difficult task. Acoustic sensors can be used to detect blast waves. Radar technology permits detection of the projectile. A third method is to detect the muzzle flash using electro-optical devices. Detection of muzzle flash events is possible with focal plane arrays, line and single element detectors....

A long term field trial called FESTER (First European South African Transmission Experiment) has been conducted by an international collaboration of research institutes over the course of almost one year at False Bay, South Africa. Main objectives of the experiment are a better insight into atmospherical effects on propagation of infrared radi...

The First European South African Experiment (FESTER) was conducted over about a 10 month period at the Institute of Maritime Technology (IMT) in False Bay, South Africa. One of the principal goals was recording of static and dynamic thermal infrared signatures under different environmental conditions for both validation of existing thermal equ...

The experiment FESTER (First European South African Transmission ExpeRiment) took place in 2015 to investigate the atmospheric influence on electro-optical systems across False Bay / South Africa on a long term basis. Several permanent stations for monitoring electro-optical propagation and atmospheric parameters were set up around the Bay. A...

Optical turbulence for over-water conditions was investigated in a long-term experiment over False Bay near Cape Town, South Africa. A sonic anemometer and two boundary-layer scintillometers were deployed to access in-situ turbulence as well as the integrated turbulence over two 1.8 and 8.7 km paths. Statistical analysis reveals spatial-temporal va...

An overview is given of the First European – South African Transmission ExpeRiment (FESTER), which took place in South Africa, over the False Bay area, centered around Simon’s Town. The experiment lasted from April 2015 through February 2016 and involved continuous observations as well as periodic observations that took place during four Intensive...

The performance of electro-optical platform protection systems can be degraded significantly by the propagation environment around the platform. This includes aero-optical effects and zones of severe turbulence generated by engine exhausts. For helicopters rotor tip vortices and engine exhaust gases that are pressed down by the rotor airflow form t...

We have performed a series of experiments in order to simultaneously validate several devices and methods for measurement of the path-averaged refractive index structure constant ( 𝐶𝑛 2). The experiments were carried out along a horizontal urban path near the ground. Measuring turbulence in this layer is particularly important because of the prospe...

A simple grid of 10×10 white-light LEDs allows for simultaneous measurement of several characteristics of atmospheric turbulence. With this device, an imaging sensor and the model of tilt anisoplanatism one can determine turbulence strength, anisotropy, outer scale and spectral slope of turbulence. We describe the theory and present preliminary res...

Article taken from the annual report 2013-2014 of the Fraunhofer Institute of Optronics, System Technologies and Image Exploitation - IOSB

Decorrelation of tip/tilt is important in imaging and laser propagation through the atmosphere without a cooperative beacon. Applications include laser-guide-star AO and multi-laser-beam communications. We compute gradient-tilt anisoplanatism for spherical-wave propagation. The model is to be validated against experiments over a 110-m path.

We report on the results of a strongly improved test of local Lorentz invariance, consisting of a search for an anisotropy of the resonance frequencies of electromagnetic cavities. The apparatus comprises two orthogonal standing-wave optical cavities interrogated by a laser, which were rotated approximately 175 000 times over the duration of 13 mon...

The isotropy of the speed of light is one of the best known invariance principles in physics. It is one aspect of Lorentz Invariance, which is a basic assumption of all theories of the fundamental forces. In the course of the past 120 years the isotropy has been tested with ever increasing precision. We have developed a highly sensitive laser Mich...

Modern Michelson-Morley-type experiments with ultra-stable res- onators are aiming to measure a possible violation of Lorentz invariance for electromagnetic waves. We will report about the latest results of our measurements using optical high finesse resonators (F = 190000) orthogonally embedded in a rectangular ULE (ultra low expansion coefficient...

Over the past years several Michelson-Morley-type experiments have been performed [1-4], utilising either optical or microwave resonators, which lead to strong constraints on possible violations of Local Lorentz Invariance (LLI) for electromagnetic waves. We will report on the development of a new apparatus for an im- proved test of LLI. Our experi...

Recently, three high-precision Michelson-Morley-type experiments have been performed using lasers [1,2,3]. They led to strong tests of Local Lorentz Invariance for electromagnetic waves by comparing the resonance frequencies of two orthogonal resonators as a function of orientation in space. We are currently developing a new apparatus for such a te...

We describe an experiment in which Rb-atoms are precooled in a 2-D MOT at high Rb-pressure and are then transferred in to a UHV chamber where they are first captured in a conventional MOT, compressed at field gradients above 50 G per cm and then loaded into a CO2 laser trap. Storage times of 10 seconds are achieved in a single beam CO2 laser trap....