Laser speckle reduction and photo-thermal speckle spectroscopy

Abstract

A method of reducing laser speckle by reflecting an infrared laser off a rotating diffuser and coupling the diffused light into a multi-mode optical fiber. Also disclosed is a photo-thermal speckle spectroscopy device having an infrared laser, a visible laser, a foam, and a camera. The infrared and visible lasers are focused on the foam, which causes the visible laser to scatter. A camera records the speckle pattern, which shifts when the IR laser is turned on. The related method of photo-thermal speckle spectroscopy is also disclosed.

What is claimed as new and desired to be protected by Letters Patent of the United States is: 
     
         1 . A method of reducing speckle, comprising:
 focusing an infrared (IR) laser input beam onto a rotating diffuser; and   coupling diffused laser light into a multi-mode optical fiber.   
     
     
         2 . The method of  claim 1 , additionally comprising illuminating a sample with light from the multi-mode optical fiber that covers a portion of a field view of a reflecting objective, wherein the reflected light is sent to a micro-bolometer. 
     
     
         3 . The method of  claim 1 , additionally comprising illuminating a sample at a distance from the multi-mode optical fiber with light from the multi-mode optical fiber. 
     
     
         4 . A photo-thermal speckle spectroscopy device, comprising:
 an infrared (IR) laser that is toggled on and off;   a visible laser that is always on;   a substrate, wherein the substrate comprises an analyte to be tested; and   a camera;   wherein the IR laser and the visible laser are directed to the substrate causing the visible laser to scatter, wherein the camera records a speckle pattern, and wherein the speckle pattern changes when the IR laser is turned on.   
     
     
         5 . The photo-thermal speckle spectroscopy device of  claim 4 , wherein the substrate is a foam. 
     
     
         6 . The photo-thermal speckle spectroscopy device of  claim 4 , wherein the substrate is a polyethylene foam. 
     
     
         7 . The photo-thermal speckle spectroscopy device of  claim 4 , wherein the substrate is a meta-material or other structure that is engineered to suppress IR absorption. 
     
     
         8 . The photo-thermal speckle spectroscopy device of  claim 4 , wherein the change in speckle pattern between IR laser-illuminated frames and non-illuminated frames is determined by correlating images recorded by the camera. 
     
     
         9 . The photo-thermal speckle spectroscopy device of  claim 4 , wherein the IR laser is split such that a portion of it is directed to the substrate and the other part interferes with the reflected speckle pattern before being recorded by the camera. 
     
     
         10 . The photo-thermal speckle spectroscopy device of  claim 4 , wherein photo-thermal speckle spectroscopy can be performed at different wavelengths by discrete stepping or continuous tuning the IR laser wavelength. 
     
     
         11 . The photo-thermal speckle spectroscopy device of  claim 4 , wherein the IR laser stays on and the IR laser wavelength is either step-wise or continuously changed. 
     
     
         12 . A method of photo-thermal speckle spectroscopy, comprising:
 directing an infrared (IR) laser that is toggled on and off and a visible laser that is always on to a substrate causing the visible laser to scatter, wherein the substrate comprises an analyte to be tested; and   recording a speckle pattern with a camera, wherein the speckle pattern changes when the IR laser is turned on.   
     
     
         13 . The method of  claim 12 , wherein the substrate is a foam. 
     
     
         14 . The method of  claim 12 , wherein the substrate is a polyethylene foam. 
     
     
         15 . The method of  claim 12 , wherein the substrate is a meta-material or other structure that is engineered to suppress IR absorption. 
     
     
         16 . The method of  claim 12 , wherein the change in speckle pattern between IR laser-illuminated frames and non-illuminated frames is determined by correlating images recorded by the camera. 
     
     
         17 . The method of  claim 12 , wherein the IR laser is split such that a portion of it is directed to the substrate and the other part interferes with the reflected speckle pattern before being recorded by the camera. 
     
     
         18 . The method of  claim 12 , wherein the method is repeated at different wavelengths of the IR laser either by discrete stepping or continuous tuning the IR laser wavelength. 
     
     
         19 . The method of  claim 12 , wherein the IR laser is stays on and the IR laser wavelength is either step-wise or continuously changed.