# US 2014/0150529 A1 · Remote sensing using coherent sonic wave photoacoustic detection and methods > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0150529 A1 - Document ID: US20140150529A1 - Status: Published application - Kind: A1 - Application number: 13/693,367 - Filed: 2012-12-04 - Published: 2014-06-05 - Earliest claimed: 2012-12-04 - Assignees: U.S. Army Research Laboratory ATTN: RDRL-LOC-I - Applicants: U.S. Army Research Laboratory Attn: - Inventors: KRISTAN PETER GURTON; YONGLE PAN - Web page: https://patentgrep.com/patent/US20140150529A1 ## CPC - G01S 17/86: Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders - G01S 15/74: Systems using reradiation of acoustic waves, e.g. IFF, i.e. identification of friend or foe - G01N 21/1702: {with opto-acoustic detection, e.g. for gases or analysing solids} - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES - 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 A method and system for detecting composition of a physical space comprising: a laser beam source; an acoustic sensor; a beam focusing mechanism for focusing the laser beam at predetermined points in the physical space to generate a thermal inhomogeneity which results in the propagation of a pressure wave that propagates outward from the predetermined excitation point at a propagation velocity approximating the speed of sound for the particular composition of the media; at least one processor for controlling the timing for the laser beam focusing to generate thermal inhomogeneities; whereby the laser focal point is moved sequentially along the light-of-sight at various excitation points by the beam focusing mechanism approximately at the phase front velocity to define a series of predetermined excitation points and pressure wave propagations such that the series of pressure wave propagations combine to produce a coherent pressure wave detectable by the acoustic sensor. ## Claims ### Claim 1 A method for detecting the composition of a physical space comprising; at a first predetermined time focusing a laser at a first predetermined excitation point along the line of sight of the laser to create rapid localized heating of the gases to produce a thermal inhomogeneity which results in the propagation of a first pressure wave; the first pressure-wave propagating outward from the predetermined excitation point at a propagation velocity approximating the speed of sound that is defined for the particular composition of the media; at a second predetermine time focusing a laser to a second predetermined excitation point along the line of sight of the laser to produce a second pressure wave; the velocity from the first predetermined excitation point to the second predetermined excitation point being selected to approximate the propagation velocity of the pressure wave which creates an effective superposition of the first and second pressure-waves at the second predetermined excitation point; and moving the laser focal point sequentially along the light-of-sight at various excitation points approximately at the phase front velocity to define a series of predetermined excitation points and pressure wave propagations; whereby the series of pressure wave propagations combine to produce a coherent pressure wave that can be detected at a predetermined distance by an appropriate acoustic sensor. ### Claim 2 (depends on 1) The method of claim 1 further including returning the laser focus to the first predetermined excitation point whereupon the process is then repeated along the laser beam line-of-sight until a coherent pressure wave is produced that can be detected at a predetermined distance by an appropriate acoustic sensor. ### Claim 3 (depends on 2) The method of claim 2 wherein the repetition of each sweep from the first predetermined excitation point to the last predetermined excitation point is conducted at a fixed frequency F, defined by the mere of the tune period needed to move from the first predetermined excitation point to the last in the series of excitation points at the propagation velocity. ### Claim 4 (depends on 1) The method of claim 1 wherein the pressure wave is detected by an acoustic receiving sensor mounted in the proximity of the laser beam source ### Claim 5 (depends on 1) The method of claim 1 wherein the absorption spectra for localized regions of the atmosphere are detected by an acoustical sensor and measured by at least one processor. ### Claim 6 (depends on 1) The method of claim 1 wherein the method is utilized for the detection of hazardous chemical/biological airborne materials and/or gases in the atmosphere. ### Claim 7 The method of clam 1 wherein the coherent pressure wave is detected using a Cassegrain telescope configuration. ### Claim 8 (depends on 7) The method of claim 7 wherein the coherent pressure wave is received by a sensor positioned approximately on the central axis of the laser beam. ### Claim 9 (depends on 1) The method of claim 1 wherein the method is used in conjunction with a lidar system. ### Claim 10 (depends on 1) The method of claim 1 wherein the method is capable of remotely measuring atmospheric absorption related parameters for identifying the biological/chemical composition of the atmosphere at the physical space. ### Claim 11 A system for detecting the composition of a physical space comprising: a laser beam source; an acoustic sensor; a beam focusing mechanism for focusing the laser beam at predetermined points in the physical space to generate a thermal inhomogeneity which results in the propagation of a pressure wave; the pressure-wave propagating outward from the predetermined excitation point at a propagation velocity approximating the speed of sound that is defined for the particular composition of the media; at least one processor for controlling the timing for the laser beam focusing to generate thermal inhomogeneities; whereby the laser focal point is moved sequentially along the light-of-sight at various excitation points by the beam focusing mechanism approximately at the phase front velocity to define a series of predetermined excitation points and pressure wave propagations such that the series of pressure wave propagations combine to produce a coherent pressure wave that can be detected at a predetermined distance by the acoustic sensor. ### Claim 12 (depends on 10) The system of claim 10 wherein the laser can be dynamically focused at any point within the physical space by the beam focusing mechanism under the control of the at least one processor. ### Claim 13 (depends on 10) The system of claim 10 wherein the beam focusing mechanism comprises a Cassegrain telescope configuration. ### Claim 14 (depends on 10) The system of claim 10 wherein the at least one processor operates to generate the thermal inhomogeneities at time intervals such that at a first predetermined time the laser beam is focused at a first predetermined excitation point along the line of sight of the laser to create rapid localized heating of the gases to produce a thermal inhomogeneity which results in the propagation of a first pressure wave; the first pressure-wave propagating outward from the predetermined excitation point at a propagation velocity approximating the speed of sound that is defined for the particular composition of the media; and at a second predetermine time the laser beam is focused to a second predetermined excitation point along the line of sight of the laser to produce a second pressure wave; the velocity from the first predetermined excitation point to the second predetermined excitation point being selected to approximate the propagation velocity of the pressure wave which creates an effective superposition of the first and second pressure-waves at the second predetermined excitation point; and wherein the laser focal point is moved sequentially along the light-of-sight at various excitation points approximately at the phase front: velocity to define a series of predetermined excitation points and pressure wave propagations such that the summation of the pressure waves produces a coherent pressure wave that is detected by the acoustic sensor. ### Claim 15 (depends on 10) The system of claim 10 wherein the at least one processor operates to repeat each cycle from the first predetermined excitation point to the last predetermined excitation point at a fixed frequency F, defined by the inverse of the time period needed to move from the first predetermined excitation point to the last in the series of excitation points at the propagation velocity. ### Claim 16 (depends on 10) The system of claim 10 further comprising a Lidar system. ### Claim 17 (depends on 10) The system of claim 10 wherein the coherent pressure wave is received by a sensor positioned approximately on the central axis of the laser beam. ### Claim 18 (depends on 10) The system of claim 10 wherein the laser beam is emitted in the direction of the line-of-sight along an axis and the propagation and sensing of the acoustic waves are conducted along the axis.