# US 2013/0153790 A1 · Acoustic methods and systems for detecting terahertz radiation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0153790 A1 - Document ID: US20130153790A1 - Status: Published application - Kind: A1 - Application number: 13/643,871 - Filed: 2011-04-29 - Published: 2013-06-20 - Earliest claimed: 2010-04-29 - Assignees: Rensselaer Polytechnic Institute - Inventors: Benjamin Clough; Jingle Liu; Xi-Cheng Zhang - Web page: https://patentgrep.com/patent/US20130153790A1 ## CPC - G01N 21/63: optically excited - G01N 21/3504: for analysing gases, e.g. multi-gas analysis - G01N 21/3581: using far infrared light; using Terahertz radiation - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract Methods and systems for detecting radiation for example, terahertz radiation, with the aid of acoustic signal generation and detection include: directing an optical beam into a volume of gas; ionizing at least a portion of the volume of gas with the optical beam to produce a plasma; and detecting an acoustic signal produced from an interaction of a radiation wave with the plasma. The methods and systems are particularly adapted for remote detection of chemicals, biological substances, and explosives, among others. The capability of the methods and systems can be enhanced by employing multi-color laser excitation to produce the plasma and varying the time delay between the multi-color pulses. ## Claims ### Claim 1 A method of detecting radiation comprising: directing an optical beam into a volume of gas; ionizing at least a portion of the volume of gas with the optical beam to produce a plasma; and detecting an acoustic signal produced from an interaction of a radiation wave with the plasma. ### Claim 2 (depends on 1) The method as recited in claim 1, wherein the radiation wave comprises at least one of microwaves, terahertz radiation, infrared light, visible light, ultraviolet light, x-rays (soft and hard), gamma rays, and radio waves. ### Claim 3 (depends on 1) The method as recited in claim 1, wherein the acoustic signal comprises one or more of an infrasonic, a sonic, and an ultrasonic acoustic signal. ### Claim 4 (depends on 1) The method as recited in claim 1, wherein the acoustic signal comprises a pressure wave. ### Claim 5 (depends on 1) The method as recited in claim 1, wherein the acoustic signal comprises an omni-directional signal. ### Claim 6 (depends on 1) The method as recited in claim 1, wherein ionizing the at least a portion of the volume of the gas comprises at least one of single-color pulse excitation and multi-color pulse excitation. ### Claim 7 (depends on 6) The method as recited in claim 6, wherein ionizing the at least a portion of the volume of the ambient gas comprises dual-color pulse excitation. ### Claim 8 (depends on 7) The method as recited in claim 7, wherein the dual-color pulse excitation comprises a first pulse at a first frequency and a second pulse at a second frequency different from the first frequency, and wherein the first pulse and the second pulse are temporally separated by a time delay. ### Claim 9 (depends on 8) The method as recited in claim 8, wherein the method further comprises varying the time delay. ### Claim 10 (depends on 1) The method as recited in claim 1, wherein the method further comprises characterizing the radiation wave from the detected acoustic signal. ### Claim 11 (depends on 10) The method as recited in claim 10, wherein the characterizing comprises detecting at least one of an amplitude and a phase of the radiation wave. ### Claim 12 (depends on 1) The method as recited in claim 1, wherein the method comprises a method of remote sensing, and the radiation wave comprises a radiation wave transmitted through, emitted from, or reflected from a target. ### Claim 13 (depends on 12) The method as recited in claim 12, wherein the remote sensing is practiced at a distance of at least 1 meter from the target. ### Claim 14 (depends on 12) The method as recited in claim 12, wherein the remote sensing is practiced at a distance of at least 10 meters from the target. ### Claim 15 (depends on 12) The method as recited in claim 12, wherein the target comprises a chemical. ### Claim 16 (depends on 12) The method as recited in claim 12, wherein the target comprises a substance harmful to humans. ### Claim 17 (depends on 16) The method as recited in claim 16, wherein the substance harmful to humans comprises at least one of an explosive, a biological agent, and a chemical agent. ### Claim 18 (depends on 12) The method as recited in claim 12, wherein the volume of gas comprises a volume of gas in a vicinity of the target. ### Claim 19 (depends on 1) The method as recited in claim 1, wherein the method further comprises analyzing the detected acoustic signal. ### Claim 20 (depends on 1) The method as recited in claim 1, wherein the radiation wave comprises a terahertz radiation wave. ### Claim 21 A method of detecting a target, the method comprising: directing a first optical beam into a first volume of gas; ionizing at least a portion of the first volume of gas with the first optical beam to produce an emitter plasma and to emit terahertz radiation directed toward a target; directing a second optical beam into a second volume of gas; ionizing at least a portion of the second volume of gas with the second optical beam to produce a sensor plasma; and detecting an acoustic signal produced from an interaction of an incident terahertz wave with the sensor plasma, the incident terahertz wave produced by an interaction of the terahertz radiation with the target. ### Claim 22 (depends on 21) The method as recited in claim 21, further comprising focusing the incident terahertz wave in the sensor plasma. ### Claim 23 (depends on 21) The method as recited in claim 21, wherein the target comprises a remote target. ### Claim 24 (depends on 21) The method as recited in claim 21 wherein detecting comprises focusing the acoustic signal from the interaction of the incident terahertz wave and the sensor plasma. ### Claim 25 (depends on 21) The method as recited in claim 21, wherein the target comprises a substance harmful to humans. ### Claim 26 (depends on 21) The method as recited in claim 21, wherein the detecting is performed more than 10 meters from the target. ### Claim 27 (depends on 21) The method as recited in claim 21, wherein the first volume and the second volume at least partially overlap. ### Claim 28 (depends on 21) The method as recited in claim 21, further comprising processing the acoustic signal detected with spectroscopic analysis. ### Claim 29 (depends on 21) The method as recited in claim 21, wherein at least one of the first optical beam and the second optical beam comprises a dual-color laser pulse comprising a first pulse at a first frequency and a second pulse at a second frequency different from the first frequency, and wherein the first pulse and the second pulse are temporally separated by a time delay. ### Claim 30 (depends on 29) The method as recited in claim 29, further comprises varying the time delay. ### Claim 31 A system for detecting radiation comprising: an optical beam directed into a volume of a gas wherein at least a portion of the volume of the gas is ionized and a plasma is produced; and a detector for detecting an acoustic signal emitted from an interaction of an incident radiation wave with the plasma. ### Claim 32 (depends on 31) The system as recited in claim 31, wherein the radiation wave comprises at least one of microwaves, terahertz radiation, infrared light, visible light, ultraviolet light, x-rays (soft and hard), gamma rays, and radio waves. ### Claim 33 (depends on 31) The system as recited in claim 31, wherein the acoustic signal comprises one or more of a infrasonic, a sonic, and an ultrasonic acoustic signal. ### Claim 34 (depends on 31) The system as recited in claim 31, wherein the acoustic signal comprises a pressure wave. ### Claim 35 (depends on 31) The system as recited in claim 31, wherein the acoustic signal comprises an omni-directional signal. ### Claim 36 (depends on 31) The system as recited in claim 31, wherein ionizing the at least a portion of the volume of the gas comprises at least one of single-color pulse excitation and multi-color pulse excitation. ### Claim 37 (depends on 31) The system as recited in claim 31, wherein ionizing the at least a portion of the volume of the ambient gas comprises dual-color pulse excitation ionization. ### Claim 38 (depends on 37) The system as recited in claim 37, wherein the dual-color pulse excitation ionization comprises a first pulse at a first frequency and a second pulse at a second frequency different from the first frequency, and wherein the first pulse and the second pulse are temporally separated by a time delay. ### Claim 39 (depends on 38) The system as recited in claim 38, wherein the system further comprises means for varying the time delay. ### Claim 40 (depends on 31) The system as recited in claim 31, wherein the system further comprises means for characterizing the radiation wave from the detected acoustic signal. ### Claim 41 (depends on 31) The system as recited in claim 31, wherein the optical beam comprise a first optical beam and the volume of gas comprises a first volume of gas; wherein the system further comprises a second optical beam directed into a second volume of gas wherein at least a portion of the second volume of the gas is ionized and a terahertz wave is produced; and wherein the terahertz wave comprises the source of the incident radiation wave. ### Claim 42 (depends on 41) The system as recited in claim 41, wherein the incident radiation wave comprises a terahertz wave resulting from interaction of the terahertz wave from the second volume of gas and a target. ### Claim 43 (depends on 42) The system as recited in claim 42, wherein the system comprises a remote sensing system, wherein remote sensing is practiced at a distance of at least 1 meter from the target. ### Claim 44 (depends on 43) The system as recited in claim 43, wherein the remote sensing is practiced at a distance of at least 10 meters from the target. ### Claim 45 (depends on 42) The system as recited in claim 42, wherein the target comprises a chemical. ### Claim 46 (depends on 42) The system as recited in claim 42, wherein the target comprises a substance harmful to humans. ### Claim 47 (depends on 46) The system as recited in claim 46, wherein the substance harmful to humans comprises at least one of an explosive, a biological agent, and a chemical agent. ### Claim 48 (depends on 42) The system as recited in claim 42, wherein the first volume of gas and the second volume of gas are in a vicinity of the target. ### Claim 49 (depends on 31) The system as recited in claim 31, wherein the system further comprises a detected acoustic signal analyzer. ### Claim 50 (depends on 40) The system as recited in claim 40, wherein the analyzer is adapted to detect at least one of an amplitude and a phase of the radiation wave.