In this paper some constructions and test results of new detection modules for Free Space Optics (FSO) operated in the 8-12μm wavelength range are presented. In this spectrum, FSO communication is less sensitive to atmosphere features. The main requirements for detectors construction applied in FSO receiver correspond to both operational and functional parameters. These devices should be characterized by high detectivity and operation speed. It is necessary to achieve low value of error rate in the case of high attenuation of laser beam and small-aperture receiving optics. In this way, the design of the FSO transceiver is simplified. In practice, detection performance close to fundamental limits are required. Additionally, for the present optical links, subnanosecond response time is also very important. This can be achieved using of HgCdTe photodiode in the form of modified N+pP+ heterostructure with immersion lens, reverse biasing and TEC cooling. Immersion lens enables optimization of the detector physical dimensions, decreasing detector capacity and time constant detector. The high detectivity of the detection module was achieved by both matching the photodiode to the preamp and minimizing noises. The paper is review of designing and investigation process of the detection modules for FSO application. Some results of the performed simulations and experiments are also discussed. Finally, further refinements will be conducted taking into account parameters of FSO receiver.
The paper presents some aspects of approach to construct an optical detection system for laser absorption sensing. These aspects concern a designing procedure of the system, starting with a photodetector, preamplifier, and ending with a signal processing. There is also discussed a project of integrated preamplifier which can be applied in Cavity Enhanced Absorption Spectroscopy (CEAS). In the preamplifier, boxcar method was implemented using integrated circuit (IC) of switched integrator and a special synchronous block. Taking into account an idea of CEAS operation, selected methods of the exponential signal analyzing are described and tested. The main task of the methods is to determine decay time of this signal. The results of these tests make it possible to define some virtues of the designed boxcar technique that could be useful in CEAS sensing instrument.
A laboratory demonstrator of the optoelectronic sensor employing cavity enhanced spectroscopy has been designed to detect the trace amounts of carbon monoxide. High sensitivity of this sensor is provided by the use of optical cavity consisted of dielectric mirrors with extremely high reflectance. The instrument concept was taking into consideration the latest achievement of optoelectronic technology as a part of the ‘EDEN’ project, funded by the Polish National Centre for Research and Development. Preliminary tests using the sensor concept have shown that detection of carbon monoxide is possible using the developed devices. In this configuration, the sensor is characterized by high linear sensitivity in the concentration range of 10 ppb to 2.5 ppm.
The aim of this paper is to address some of the aspects of thermal management of QCLs. Results include electrical and spectral characterization of the devices. Results show shift of QCL emission mode towards lower wavenumbers during the pulse. Characteristics were registered at different temperatures of operation and driving conditions. Registered shift rates depend on operating temperature, being the highest at room temperature. Based on spectral tuning results, temperature increase rates for different modes of operations were evaluated, delivering information on thermal dynamics of investigated devices.
The article describes an application one of the most sensitive optoelectronic method – Cavity Enhanced Absorption
Spectroscopy in investigation of nitric oxide in exhaled breath. Measurement of nitric oxide concentration in exhaled
breath is a quantitative, non-invasive, simple, and safe method of respiratory inflammation and asthma diagnosis. For
detection of nitric oxide by developed optoelectronic sensor the vibronic molecular transitions were used. The
wavelength ranges of these transitions are situated in the infrared spectral region. A setup consists of the optoelectronic
nitric oxide sensor integrated with sampling and sample conditioning unit. The constructed detection system provides to
measure nitric oxide in a sample of 0-97% relative humidity.
The article describes application of cavity enhanced absorption spectroscopy (CEAS) for detection of nitrogen oxides and vapours of explosives. The oxides are important greenhouse gases that are of large influence on environment, living organisms and human health. These compounds are also markers of some human diseases as well as they are emitted by commonly used explosives. Therefore sensitive nitrogen oxides sensors are of great importance for many applications, e. g. for environment protection (air monitoring), for medicine investigation (analyzing of exhaled air) and finally for explosives detection. In the Institute of Optoelectronics MUT different types of optoelectronic sensors employing CEAS were developed. They were designed to measure trace concentration of nitrogen dioxide, nitric oxide, and nitrous oxide. The sensors provide opportunity for simultaneous measurement of these gases concentration at ppb level. Their sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or mass spectrometry. Our sensors were used for some explosives detection as well. The experiment showed that the sensors provide possibility to detect explosive devices consisting of nitroglycerine, ammonium nitrate, TNT, PETN, RDX and HMX.
The paper presents the new infrared detection module developed at the VIGO System Ltd. Its high sensitivity of was
achieved by both matching the IR detector to the preamp and minimizing noises. High sensitivity of the detector was
achieved by using photodiodes with immersion lens. Immersion lens enables optimization of the detector area,
decreasing detector capacity and time constant. Detector noise was reduced as a result of photodiode cooling by means
of a thermoelectric cooler and reverse biasing. Developed module is dedicated to NOx optoelectronic sensors operates
basing on Cavity Enhanced Absorption Spectroscopy technique.
The article describes an application of cavity enhanced absorption spectroscopy for nitric oxide and nitrous oxide
detection. Both oxides are important greenhouse gases that are of large influence on environment, living organisms and
human health. These compounds are also biomarkers of some human diseases. They determine the level of acid rain, and
can be used for characterization of specific explosive materials. Therefore the sensitive detectors of these gases are of
great importance for many applications: from routine air monitoring in industrial and intensive traffic areas, to detection
of explosives in airports, finally for medicine investigation, for health care, etc.
Our compact detection system provides opportunity for simultaneous measure of both NO and N<sub>2</sub>O concentration at ppb
level. Its sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or
The paper presents a model of a free space optical transmitter operating in the wavelength range of 8-12 μm. In the
transmitter, a quantum cascade laser controlled by a special driver was applied. The driver provides the control of the
energy, repetition rate and duration of radiation pulses. In the described transmitter, generation of pulses with high duty
cycle is also provided, making it possible to use the data link with either RZ or NRZ coding. In the frame of the study,
the impact of laser working conditions on the data link operation was determined.
The paper presents a construction and some investigations results of a new driver for quantum cascade (QC) lasers.
The driver is designed to control pulse and CW mode QC lasers. For both laser mode operations, there is the possibility
to set a laser current in the range of 0.1 A - 3 A and pulse duration of 30 ns at the frequencies to the level of 25 MHz.
The stabilization of the temperature in the range of 50°C ÷ -30°C with accuracy of 1.5 K is also achieved. A full
synchronization with external pulses makes the driver very useful in a construction of a free space optical transmission
system and of a laser spectroscopy setup.
The paper presents an application of an optical parametric generator (OPG) for cavity enhanced absorption spectroscopy
(CEAS) technique to nitric oxide (NO) detection. The principle of this method is based on an injection of a radiation
beam into an optical cavity at a very small angle. The radiation is multiple reflected inside the resonator equipped with
spherical and high reflectance mirrors. After each reflection a part of the radiation leaves the optical cavity due to
residual transmission of mirrors. In the case of NO detection the laser emitting at around 5.26 μm was applied. During
investigation of CEAS system with OPG, two-lenses collimator was required to improve OPG beam divergence. The Ge
and ZnSe lenses were used. Thanks to this decrease of about three times in beam diameter was achieved (at the distance
of 1 m from source). It make it possible to measure output signal from the CEAS optical cavity.
The paper presents construction of broadband optical system devoted to free space optical communication using long
wavelength quantum cascade laser and a heterostructural thermally cooled HgCdTe photodetector. This system should
characterize with lower sensitivity to adverse meteorological conditions when compared with the systems operating
in near IR.
We present the study of potential application of Cavity Enhanced Absorption Spectroscopy (CEAS) for
construction of fully optoelectronic and portable NO<sub>2</sub> detector which could replace the commonly used chemical
detectors. We demonstrate an experiment on detection of NO<sub>2</sub> in the ambient air. The concentration of investigated
absorber was found by determination of decay time of pulse radiation trapped in the optical cavity constructed with two
mirrors of a very high reflectivity coefficient (R > 99,99%). As a light source a blue pulsed diode laser was applied. The
output signal was detected by a photomultiplier and analysed by a digital oscilloscope. For this construction the detection
limit better than 1 ppb was obtained. The cavity parameters and it's adjustment were controlled by a beam from a red
laser that is not absorbed by NO<sub>2</sub>. In order to perform the measurements in two spectral regions the special mirrors have
been developed. Study of influence of another NO<sub>x</sub> compounds (especially NO<sub>3</sub>) on final result was investigated as well.
The paper presents a measuring system of extreme ultraviolet radiation pulses (13.5 nm). The system is used for
monitoring a gas-puff laser-plasma source constructed at the Institute of Optoelectronics. The radiation source and the
system are used in metrology of EUV optics. The system consists of a detection head and a system of optical filters,
which are housing in a special construction. Additional element of the measuring system is a special processing unit.
The measuring system was used during investigations of the plasma-laser optimization. The results were comparable
with the ones from a spectrograph and an Emon energy meter.
This paper presents application of Cavity Ring-Down Spectroscopy (CRDS) and Cavity Enhanced Spectroscopic (CEAS) techniques with blue laser diodes-based system for nitrogen dioxide (NO2) detection. CES technique bases on integration of the light from a resonator. Since the integrated intensity is proportional to the decay time, the experimental signal can be related to the absorption process. The minimum detectable concentration of the absorber for a specific transition is inversely proportional to the effective sample-path length, and directly proportional to the minimum intensity fluctuation detected by a receiving system. In the presented system, the blue laser diode was mounted in a temperature-controlled housing. The light transmitted through the cavity was focused onto a PMT of H5783-03 type. The detector signal enters a lock-in amplifier and next a computer with a 16-bit data acquisition board.
The paper presents analyses of a testing system of extreme ultraviolet detectors. The testing procedure concerns determination of a quantum efficiency of photodiode detectors. The testing method is based on a comparison of the detected signals from the model detector and the tested one The system consists of a gas-puff laser plasma source, a metrology chamber with an optical system, and a model energy detector. Theoretical and experimental investigations, including optimisation of efficiency and stability of the radiation source, calculation of a charge measurement accuracy of the model detector, determination of mirrors reflectivity and its angle dependence are discussed.
We present an experiment on detection of nitrogen dioxide in free air using cavity enhanced spectroscopy. As a light source a blue pulsed diode laser was applied, while the output signal was detected with a photomultiplier. The absorber concentration was found by investigation of the optical resonator quality. It was done by determination of decay time of radiation pulse trapped in the cavity. Also the measurement of the phase shift between the output signal and modulation signal was used as the alternative method. The detection limit better than 1 ppb was demonstrated. The aim of this experiment was to study potential application of cavity enhanced absorption spectroscopy for construction of fully optoelectronic NO<sub>2</sub> detector which could replace the commonly used chemical detectors.
In the paper, we present UV-detection system and it¢s noise model. It consist of GaN photodiode produced by ITME in Warsaw, and low noise preamplifier. The Schotttky barrier MSM and p-π-n visible blind detectors on gallium nitride were used. The main purpose was to analyse the first stage of UV receiver (photodetector plus low noise preamplifier) to optimise them providing maximal value of signal-to-noise ratio.