Fredrik Kullander

Development of a fluorescence-based point detector for biological sensing

This paper presents the status of an ongoing development of a point detector for biological warfare agent sensing based on ultraviolet laser-induced fluorescence from single particles in air. The detector will measure the fluorescence spectra of single particles in a sheath flow air beam. The spectral detection part of the system consists of a grating and a photomultiplier tube array with 32 channels, which measure fluorescence spectra in the wavelength band from 300 nm to 650 nm. The detector is designed to measure laser induced fluorescence from single laser pulses and has been tested by measuring fluorescence from simulants of biological warfare agents in aqueous solution. The solutions were excited with laser pulses at the wavelengths of 293 nm and 337 nm. The paper also presents preliminary results on the sheath flow particle injector and time-resolved measurements of fluorescence from biological warfare agent simulants in solution.

Evaluation of biological aerosol stand-off detection at a field trial

We have performed a field trial to evaluate technologies for stand-off detection of biological aerosols, both in daytime and at night. Several lidar (light detection and ranging) systems were tested in parallel. We present the results from three different lidar systems; one system for detection and localization of aerosol clouds using elastic backscattering at 1.57 μm, and two systems for detection and classification of aerosol using spectral detection of ultraviolet laser-induced fluorescence (UV LIF) excited at 355 nm. The UV lidar systems were utilizing different technologies for the spectral detection, a photomultiplier tube (PMT) array and an intensified charge-coupled device (ICCD), respectively. During the first week of the field trial, the lidar systems were measuring towards a semi-closed chamber at a distance of 230 m. The chamber was built from two docked standard 20-feet containers with air curtains in the short sides to contain the aerosol inside the chamber. Aerosol was generated inside the semi-closed chamber and monitored by reference equipments, e.g. slit sampler and particle counters. Signatures from several biological warfare agent simulants and interferents were measured at different aerosol concentrations. During the second week the aerosol was released in the air and the reference equipments were located in the centre of the test site. The lidar systems were measuring towards the test site centre at distances of either 230 m or approximately 1 km. In this paper we are presenting results and some preliminary signal processing for discrimination between different types of simulants and interference aerosols.

Spectral detection of ultraviolet laser induced fluorescence from individual bioaerosol particles

We present results of a measurement system designed for detecting the fluorescence spectrum of individual aerosol particles of biological warfare agents excited with laser pulses at wavelengths around 290 or 340 nm. The biological aerosol is prepared and directed into a narrow air beam. A red laser is focused on the aerosol beam and a trigger photomultiplier tube monitor the presence of individual particles by measuring the scattered light. When a particle is present in the detection volume, a laser pulse is triggered from an ultraviolet laser and the fluorescence spectrum is acquired with a spectrometer based on a diffraction grating and a 32 channels photomultiplier tube array with single-photon sensitivity. The spectrometer measures the fluorescence spectra in the wavelength region from 300 to 800 nm. In the experiment we used different simulants of biological warfare agents. These bioaerosol particles were excited by a commercial available gas laser (337 nm), or a laser (290 nm) that we have developed based on an optical parametric oscillator with intracavity sum-frequency mixing. In the analysis of the experiments we compare the measured signals (fluorescence spectra, total fluorescence energy and the scattered energy) from the individual bioaerosol particles excited with the two different ultraviolet wavelengths.

Development of fluorescence-based LIDAR technology for biological sensing

Results of our on-going development of biological warfare agents (BWA) detection systems based on spectral detection of ultraviolet (UV) laser induced fluorescence (LIF) are presented. A compact optical parametric oscillator (OPO) with intracavity sum-frequency mixing (SFM) to generate 293 nm UV laser irradiation was developed. The OPO/SFM device was pumped by a diode-pumped Nd:YAG laser (1064 nm), including subsequent second-harmonic generation (SHG) in an external periodically poled KTiOPO4 (PPKTP) crystal. The laser generated 1.8 ns pulses at 100 Hz with an average power of 44 mW at 532 nm. The whole system could be used to deliver approximately 30 µJ laser irradiation per pulse (100 Hz) at 293 nm. The spectral detection part of the system consists of a grating and a photomultiplier tube (PMT) array with 32 channels, which can measure fluorescence spectra in the wavelength band from 250 nm to 800 nm. The detector system was designed along with a trigger laser to enable measurement of fluorescence spectra from an individual aerosol particle of simulants for BWA upon excitation with a single nanosecond laser pulse. We demonstrate the successful detection and spectral characterization of simulants for BWA, i.e., Bacillus atrophaeus (BG), Bacillus thuringiensis (BT), and Ovalbumin (OA).

A high-speed modulated retro-reflector communication link with a transmissive modulator in a cat's eye optics arrangement

An optical communication link with a modulated retro-reflector in a cats eye optics arrangement has been evaluated. A transmissive multiple quantum well modulator with a modulation bandwidth in excess of 10 MHz was placed in a wide field-of-view cats eye optic system. A laser transceiver with one line and one broadband source around 1550 nm was used to interrogate the modulated retro-reflector and detect the reflected and modulated signal. Multi-level digital encoding was evaluated as a way to increase the information transfer rate in conditions with relatively high signal-to-noise ratio. The links were evaluated in indoor as well as outdoor conditions.

Performance analysis for standoff biological warfare agent detection lidar

Lidar has been identified as a promising sensor for remote detection of biological warfare agents. Elastic lidar can be used for cloud detection at long ranges and UV laser induced fluorescence can be used for discrimination of bioaerosols against naturally occurring aerosols. This paper analyzes the performance of elastic lidar such as sensitivity, range and angular coverage rate vs. atmospheric visibility, laser and receiver parameters. The analysis of the UV fluorescence lidar is concentrated on estimating the signal strength as a function of range, concentration and optical background level. The performance analysis supports the goal for a practical lidar system to detect 1000 particles/liter at 2-3 km using elastic backscatter and to verify the bioaerosol using fluorescence characterization at 1 km. Some examples of test results with an elastic lidar and a range gated imaging system both at 1.5 μm wavelength are presented together with fluorescence spectra of biological warfare agent simulants measured at an excitation wavelength of 355 nm.

Detection of fluorescence spectra of individual bioaerosol particles

We present initial results of a measurement system designed for detecting the fluorescence spectrum of individual particles of biological warfare agent (BWA). A compact optical parametric oscillator with intracavity sum-frequency mixing and a commercial Nitrogen gas laser was used as excitation sources to generate 293 nm or 337 nm UV laser irradiation. The pulsed lasers and a photomultiplier tube (PMT) array based spectrometer were triggered by a red laser-diode and a PMT detector that sensed the presence of a particle typical of size 5-20 μm in diameter. The spectral detection part of the system consisted of a grating and a PMT array with 32 channels, which measured fluorescence in the wavelength from 280 nm to 800 nm. The detector system was used to demonstrate the measurement of laser induced fluorescence spectra of individual BWA simulant particles by excitation of single UV laser pulses. The spectrum obtained by averaging spectra from several BWA aerosol simulant particles were found generally similar, but not identical, to the fluorescence spectrum obtained from water solutions containing the same particles dissolved.

System trials with modulated retro-reflective optical communication

Retro-reflective optical communication was investigated in field trials set up in urban and maritime environments. A 1550 nm laser transceiver with an output power ranging from 1 mW to 2 W and liquid crystal polarisation modulators in conjunction with corner cube reflectors were used in different experimental arrangements. The emphasis in this work was on system performance issues in tactical application such as the effects of platform vibrations and beam distortion induced by the atmospheric turbulence. In particular, the conditions for counteraction of communication interrupts, caused by line of sight jitter, using a dynamic tip-tilt mirror in the laser transceiver were tested. We report on the results from field trials wherein these issues have been addressed.

Coordinated multi-wavelength laser system propagation experiments

Atmospheric propagation degradation effects including attenuation, aerosol scattering and turbulence have a great impact on the performance of optical systems. Relevant military optical systems include active and passive imaging for target recognition, free-space optical communication and DIRCM/EOCM. This paper will report on experimental work including measurement of retro signals at 1.5 and in the 3-5 μm wavelength regions for evaluation of retro communication links and DIRCM performance. Imaging experiments using a range-gated system both in the active and passive mode at 1.5 μm, will also be carried along the same paths. A dedicated target box and test targets have been fabricated for mounting on a mast at 8 km from our laboratory. The box contains reflectors and receivers in different slots each of which can be opened by a telephone call. A heated target on top simulates a point target in the IR region. The test targets are aimed for the range-gated imaging system. Preliminary experimental data will be presented and discussed.

Code division multiplexing in interferometric optical fiber sensor networks

Code division multiplexing (CDM) is a useful method to address optical fiber sensors in remote networks by means of a single optical carrier. Our past studies of CDM for fiber optic networks of intensity modulating devices revealed that sensor-sensor crosstalk levels in the range of -60 dB are within reach and that a large number of sensor signals can be multiplexed. Our current effort aims to analyse the noise properties of interferometric networks interrogated using this scheme. Typical targeted figures of merits are; noise < 10 /spl mu/rad//spl radic/Hz, dynamic range > 80 dB, sensor bandwidth > 5 kHz, sensor to sensor crosstalk < 40 dB, number of sensors in each subarray > 30.