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Mobile terawatt femtosecond laser system (mtfls) for long range spectral sensing and identification of bioaerosols and chemical agents in the atmosphere

Mobile terawatt femtosecond laser system (mtfls) for long range spectral sensing and identification of bioaerosols and chemical agents in the atmosphere description/claims

This patent application claims the benefit of U.S. Patent Application Ser. No. 60/458,757, filed Mar. 28, 2003 which is hereby fully incorporated by reference.

The present invention is related to detection and identification of airborne biological and chemical threats in real time at distances from a few meters to several kilometers. Advanced compact femtosecond terawatt laser technology is combined with state-of-the-art spectroscopic and computational methods. These methods are implemented in a unique mobile standoff detection system.

U.S. Pat. No. 5,175,664 to Diels et al. describes a method and arrangement for discharge of lightning using ultra-short laser pulses. This proposed method enables discharges of electricity transmitted via conductive ionized channels produced by one or more first laser pulses of wavelengths essentially within the ultraviolet (UV) range. The preferred wavelength of operation is about 248 nm and the pulse duration of the laser is of the order of 100 fs. In accordance with this invention, lightning is triggered by creating an ionized channel by one or more femtosecond UV pulses and simultaneously sending one or more laser pulses of longer wavelength and duration through the same path. In this way the conductivity of the laser induced channel can be maintained long enough for discharges and lightning to occur. However, this patent does not address applications associated with atmospheric spectral sensing of atmospheric gases, pollutants and biological agents using femtosecond terawatt laser generated filaments as light sources.

One other related reference is U.S. Pat. No. 5,726,855 to Mourou et al., entitled “Apparatus and Method for Enabling the Creation of Multiple Extended Conduction Paths in the Atmosphere” which claims an apparatus and method for the creation of multiple extended conduction paths in the atmosphere using high peak-power ultra-short laser pulses. Furthermore, the same group published addressing long range self-channeling of intense femtosecond pulses in air in 1994 by Mourou and co-workers. The focus of their patent is centered on an apparatus for controlling the discharge of lightning strikes and grounding means using a grounding tower. Also no claims are made regarding spectroscopic optical sensing and identification of bio-agents using multiple extended conduction paths in the atmosphere.

It will therefore be appreciated that there remains a need for an improved system and technique for determining whether certain molecules, such as bioaerosols and chemical agents, may be found within a sample.

Early warning of biological attack and plume prediction for biological aerosols require the capability to detect bio-agents over large distances. Thus, the present invention relates to a complex bio-agent sensing system based on the principle of using femtosecond terawatt lasers, preferentially titanium sapphire laser systems in conjunction with chirp-pulse amplification and compression. The propagation of such ultra-short laser pulses gives rise to strongly non-linear optical processes in the atmosphere, leading to filamentation of the laser pulse at a specific distance. Conducting plasma channel produce a white-light supercontinuum spanning the ultraviolet (UV), visible (VIS) and infrared (IR). Wavelength region. This novel atmospheric lamp can be used for spectroscopic analysis of bio-agents by means of a Lidar (Light Detection and Ranging) system. The supercontinuum can be generated directly in a particle cloud and hence is suitable for multi-spectral long-range detection and identification of bio-aerosols as well as chemical pollutants and radioactive isotopes. According to the invention, compact femtosecond terawatt laser technology is applied in combination of state-of-the-art spectroscopic and computational methods for spectral sensing of bio-aerosols with molecular specificity.

The current invention permits real time detection, discrimination, and identification of the full spectrum of threats including; toxins, spores, bacteria and virus. The sensing range spans up to 10,000 meters and can be applied to airborne versions together with stand alone trigger devices at strategically vital locations on sea, air or land.

This invention presents a promising new trigger sensor and a standoff detection system that can identify airborne biological, chemical, and nuclear agents within a few seconds at distances from a few meters to several kilometers. The biological agent-sensing device is based on the principle of remote differential time resolved monitoring of the atmosphere using ultrashort terawatt laser pulses. According to this invention, concept of advanced compact femtosecond Terawatt (fs-TW) laser technology is combined with state-of-the-art spectroscopic and computational methods. The stand off sensing technology permits real time detection, discrimination, and identification of the full spectrum of threats including; toxins, spores, bacteria and virus. The sensing range spans up to 10,000 meters and can be applied to airborne versions together with stand alone devices at strategically vital locations on sea, air or land. This system would reduce the probability of false alarm and time for detection by more than one order of magnitude. The minimum anticipated range would be of the order of 5-10 spores per liter of air.

In one embodiment, the invention is provided in a system for determining the constituents of a sample, the system comprising, a femtosecond terawatt laser radiation source configured to emit laser radiation through a sample, an optical unit configured to receive light backscattered from the sample, and a detection and analysis unit coupled to the optical unit for analyzing a spectral signature of the sample. The system may also an optical fiber cable coupling the optical unit to the detection and analysis unit.

In some variations, the detection and analysis unit comprises an integrated diagnostic unit having one or more infrared and UV/VIS spectrometers with gated detection capability, two photo-multipliers attached to an air transient digitizer, and a data acquisition control unit. In addition, or in the alternative, the detection and analysis unit may further comprise a real-time computing system for identification and discrimination of at least one of the group comprising aerosols, airborne bacteria, viruses, toxins, dust particles, pollen, water droplets, gaseous agents, and pollutants.

The femtosecond terawatt laser radiation source may be amplified by a variety of techniques such as chirped pulse amplification. It may also be, in some examples, a laser such as a Ti:Sapphire laser that is configured to emit energy of approximately 300 mJ per pulse. The femtosecond terawatt laser radiation source may have a pulse power of about approximately 3 and 4 TW with a pulse duration approximately of the order of 80 to 100 fs and a repetition rate of approximately 10 Hz. It may emit light within a spectral range approximately centered at 800 nm or 267 nm with a spectral width of approximately 20 nm. In addition, the femtosecond laser radiation source may emits laser pulses at a center wavelength of approximately 800 nm and spectral width of 20 nm to create plasma filaments as well as at a wavelength of approximately 267 nm.

The detection and analysis unit may configured to detect airborne biological, chemical agents and water droplets by at least one technique chosen from the group comprising: differential absorption, Raman Raleigh and Mie scattering, fluorescence, flourescence LIDAR measurements, ground-based LIDAR measurements, air-based LIDAR measurements, and Raman LIDAR measurements. The detection and analysis unit may also be configured to provided 3D maps or other representations of detected molecules to further assist with their identification.

In another variation, the invention is embodied in a method for determining the constituents within a sample, the method comprising the steps of providing a femtosecond terawatt laser radiation source configured to emit laser radiation through a sample, capturing light backscattered from the sample, and analyzing a spectral signature of the sample to determine its constituents.

The analyzing step may determine whether the constituents include least one of the group comprising: aerosols, airborne bacteria, viruses, toxins, dust particles, pollen, water droplets, gaseous agents, and pollutants.

The method may also include the step of amplifying the femtosecond terawatt laser radiation source using chirped pulse amplification.

In some variations, the femtosecond terawatt laser radiation source is a laser such as a Ti:Sapphire laser configured to emit energy of approximately 300 mJ per pulse. The method may also include the step of pulsing the femtosecond terawatt laser radiation source at a power of about approximately 3 and 4 TW with a pulse duration approximately of the order of 80 to 100 fs and a repetition rate of approximately 10 Hz. The femtosecond terawatt laser radiation source may emit light within a spectral range approximately centered at 800 nm or 267 nm with a spectral width of approximately 20 nm.

Optionally, the femtosecond laser radiation source may emit laser pulses at a center wavelength of approximately 800 nm and spectral width of 20 nm to create plasma filaments as well as at a wavelength of approximately 267 nm.

Depending on the desired implementation, the analyzing step may use at least one technique chosen from the group comprising: differential absorption, Raman Raleigh and Mie scattering, fluorescence, flourescence LIDAR measurements, ground-based LIDAR measurements, air-based LIDAR measurements, and Raman LIDAR measurements for determining which constituents are present within a sample.

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