Acoustic and Optical Illumination Technique for Underwater Characterization of Objects/Environment

Abstract

The invention provides a method for acoustically and optically characterizing an immersed object of interest by generating a serial plurality of acoustic and optical illumination pulses through a liquid. In addition to the spectral analyses/imaging of objects/environment made possible by the white-light illumination, a target material can be ablated, generating an ionized plume to spectrally identify the target's constituent atoms.

What is claimed is: 
     
         1 . A method for acoustically and optically characterizing an immersed object of interest by generating a serial plurality of acoustic and optical illumination sources in a liquid, the method comprising: transmitting a serial plurality of laser-generated optical pulses through the liquid; the optical pulses reaching I.sub.LIB at optically specified locations, through pulse compression and ionizing a liquid volume, thereby generating a serial plurality of acoustic and optical illumination source pulses, wherein the pulse compression is achieved through at least one of a) optical group velocity dispersion induced longitudinal compression of a frequency chirped optical pulse and b) transverse self focusing via a nonlinear optical Kerr effect; and then measuring and analysing the returned acoustic and optical signals. 
     
     
         2 . The method according to  claim 1 , wherein the liquid is water. 
     
     
         3 . The method according to  claim 1 , wherein the liquid is seawater. 
     
     
         4 . The method according to  claim 1 , wherein the pulse compression includes both optical group velocity dispersion induced longitudinal compression of a frequency chirped optical pulse and transverse self focusing via a nonlinear optical Kerr effect. 
     
     
         5 . The method according to  claim 1 , without lens focusing of the optical pulses. 
     
     
         6 . The method according to  claim 1 , with lens focusing of the optical pulses. 
     
     
         7 . The method according to  claim 1 , wherein the optical pulses have a wavelength between 300 and 500 nanometers. 
     
     
         8 . The method according to  claim 1 , wherein the optical pulses have a wavelength less than 11 microns. 
     
     
         9 . The method according to  claim 1 , wherein the optical pulses travel through the liquid for distances of at least one meter. 
     
     
         10 . The method according to  claim 9 , wherein the distances are between 1 and 50 meters. 
     
     
         11 . The method according to  claim 1 , wherein the optical pulses are negatively chirped optical pulses. 
     
     
         12 . The method according to  claim 1 , wherein the optical pulses are negatively chirped optical pulses, and the liquid has a positive optical group velocity dispersion parameter .beta..sub.2. 
     
     
         13 . The method according to  claim 1 , wherein the optical pulses are positively chirped optical pulses. 
     
     
         14 . The method according to  claim 1 , wherein the optical pulses are positively chirped optical pulses, and the liquid has a negative optical group velocity dispersion parameter .beta..sub.2. 
     
     
         15 . The method according to  claim 1 , wherein the optical pulses are monochromatic optical pulses. 
     
     
         16 . The method according to  claim 1 , wherein the optical pulses are broadband optical pulses without chirp. 
     
     
         17 . The method according to  claim 1 , wherein the optical pulses have a wavelength varying effectively linearly with time. 
     
     
         18 . The method according to  claim 1 , wherein the liquid is water, including sea water, and the optical pulses are generated under water. 
     
     
         19 . The method according to  claim 1 , wherein the liquid is water, including sea water, and the optical pulses are generated in air and are transmitted into the water. 
     
     
         20 . A method for acoustically and optically characterizing an immersed object of interest by generating a serial plurality of acoustic and optical illumination sources in a liquid, the method comprising: transmitting a serial plurality of laser-generated optical pulses through the liquid; the optical pulses reaching I.sub.LIB at optically specified locations, through pulse compression and ionizing a liquid volume, thereby generating a serial plurality of acoustic and optical illumination source pulses, wherein the pulse compression is achieved through at least one of a) optical group velocity dispersion induced longitudinal compression of a frequency chirped optical pulse and b) transverse self focusing via a nonlinear optical Kerr effect; acoustically locating the object of interest; and then measuring and analysing the returned optical signals. 
     
     
         21 . The method according to  claim 20 , wherein the optical signal analysis consists of manipulating different polarization states of the returned optical signals, in the form of comparing and differencing them. 
     
     
         22 . The method according to  claim 20 , wherein the optical signal analysis consists of manipulating different spectral bands of the returned white light optical signals, in the form of comparing and adding them. 
     
     
         23 . The method according to  claim 20 , wherein the optical signal analysis consists of time-gating the images in order to compare and add them in order to generate a 3D image of the target of interest. 
     
     
         24 . The method according to  claim 20 , wherein the optical signal analysis consists of measuring the laser induced breakdown spectrum of the object's laser-ionized material surface, ionized by one or more shots at each ionized position to assess the object's surface material composition at that position. 
     
     
         25 . A method for characterizing a volume of liquid by generating a serial plurality of acoustic and optical illumination sources in a liquid, the method comprising: transmitting a serial plurality of laser-generated optical pulses through the liquid; the optical pulses reaching I.sub.LIB at optically specified locations, through pulse compression and ionizing a liquid volume, thereby generating a serial plurality of acoustic and optical illumination source pulses, wherein the pulse compression is achieved through at least one of a) optical group velocity dispersion induced longitudinal compression of a frequency chirped optical pulse and b) transverse self focusing via a nonlinear optical Kerr effect; rastering throughout the volume; and then measuring and analysing the returned line spectra of the laser induced breakdown to verify the composition of the water and analysing the returned acoustic signals to verify the location of the optical sources. 
     
     
         26 . A method for characterizing a volume of liquid by generating a serial plurality of acoustic and optical illumination sources in a liquid, the method comprising: transmitting a serial plurality of laser-generated optical pulses through the liquid; the optical pulses reaching I.sub.LIB at optically specified locations, through pulse compression and ionizing a liquid volume, thereby generating a serial plurality of acoustic and optical illumination source pulses, wherein the pulse compression is achieved through at least one of a) optical group velocity dispersion induced longitudinal compression of a frequency chirped optical pulse and b) transverse self focusing via a nonlinear optical Kerr effect; rastering throughout the volume; and then measuring and analysing the returned absorption spectra of the conical emission of white light to verify the composition of the water and analysing the returned acoustic signals to verify the location of the optical sources. 
     
     
         27 . A method for acoustically and optically imaging living tissue by generating a serial plurality of acoustic and optical illumination sources at the surface of the body, capable of penetrating the tissue, allowing for optical and acoustic return signals to be gated and read to reconstruct the tissue geometry.