Remote sensing using coherent sonic wave photoacoustic detection and methods

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.