Detection of nano-scale particles with a self-referenced and self-heterodyned raman micro-laser

Abstract

A system and method for is a micro-laser based nano-scale object detection system and method using frequency shift and/or mode splitting techniques. The system and method can provide highly sensitive detection of nanoparticles with a self-referenced and self-heterodyned whispering-gallery Raman micro-laser. The system and method also provides for nano-particle size measurement.

What is claimed is: 
     
         1 . A particle detection system comprising:
 a mode-splitting based micro-resonator implemented micro-laser, where the micro-resonator is constructed to effect a Raman scattering based Raman gain;   a pump laser having a light emission coupled into the micro-resonator, where said light emission is sufficient to effect Raman scattering based Raman gain of the micro-resonator to emit a Raman laser light transmission.   
     
     
         2 . The particle detection system as recited in  claim 1 , further comprising:
 a wavelength division multiplexer adapted to separate the polarization controlled light emission of the pump laser and the Raman laser light transmission; and   a photodetector optically coupled to the wavelength division multiplexer to sense the Raman laser light transmission and said photodetector having a signal output representative of the Raman laser light transmission.   
     
     
         3 . The particle detection system as recited in  claim 2 , where said micro-resonator is placed in one or more of a free air, gas or liquid environment containing a nano-particle such that the nano-particle is introduced to the micro-resonator. 
     
     
         4 . The particle detection system as recited in  claim 3 , further comprising:
 a frequency analyzer coupled to the signal output of the photo detectors for detecting mode splitting.   
     
     
         5 . The particle detection system as recited in  claim 4 , further comprising:
 a computer coupled to the frequency analyzer configured to determine if the signal output of the photo detector is indicative of a presence of the nano-particle by resolving mode-splitting.   
     
     
         6 . The particle detection system as recited in  claim 1 , further comprising a three dimensional nano-positioning stage having the micro-resonator placed thereon and having a range of motion to precisely tune the distance between the fiber coupled waveguide and the micro-resonator. 
     
     
         7 . The particle detection system as recited in  claim 1 , further comprising:
 a broad band pump configured with various frequency components, which can couple into the micro-resonator to thereby effect Raman gain, where the broad band pump is tunable to one or more of the various frequency components if a Raman laser at a specific spectral band is desired.   
     
     
         8 . A method for particle detection comprising:
 pumping a light emission and coupling the light emission to the micro-resonator constructed to effect a Raman scattering based Raman gain, where said light emission is sufficient to effect Raman scattering based Raman gain of the micro-resonator to emit a Raman laser light transmission;   inducing mode-splitting when a nanoparticle is detected; and   resolving mode splitting with Raman gain assisted loss compensation.   
     
     
         9 . The method for particle detection as recited in  claim 8 , further comprising:
 introducing a nano-particle to the micro-resonator by placing the micro-resonator in an environment containing nano-particles.   
     
     
         10 . The method for particle detection as recited in  claim 9 , further comprising:
 heterodyning of split laser lines; and   monitoring beat frequency for detecting the nano-particle.   
     
     
         11 . The method for particle detection as recited in  claim 9 , further comprising:
 nanoparticle-induced splitting of a Raman lasing line creating a doublet; and   detecting the splitting of the Raman lasing line with a photodetector, which generates a beat note signal whose frequency corresponds to the amount of mode splitting.   
     
     
         12 . The method for particle detection as recited in  claim 11 , further comprising:
 changing the wavelength of the controlled light emission into different spectral bands.   
     
     
         13 . The method for particle detection as recited in  claim 11 , further comprising:
 scanning repeatedly the pump laser a frequency to obtain a transmission spectra of the micro-resonator; and   measuring the transmitted power.   
     
     
         14 . The method for particle detection as recited in  claim 13 , further comprising:
 increasing the power of the pumping of the light emission through a fiber coupled waveguide thereby narrowing the resonance linewidth to thereby render mode-splitting as detectable.   
     
     
         15 . The method for particle detection as recited in  claim 9 , further comprising:
 adjusting the micro-resonator from a first position to a second position with a three dimensional nano-positioning stage having the micro-resonator placed thereon and having a range of motion to precisely tune the distance between the fiber coupled waveguide and the micro-resonator.   
     
     
         16 . The method for particle detection as recited in  claim 8 , further comprising:
 introducing one or more of a plurality of nano-particles to the micro-resonator by placing the micro-resonator in an area proximate to the plurality of nano-particles and positioned to effect introduction of the one or more of the plurality of nano-particles to the micro-resonator.   
     
     
         17 . The method for particle detection as recited in  claim 16 , further comprising:
 measuring the one or more of the plurality of nanoparticles by monitoring a scatterer induced width of distribution of a beat-note frequency change of the micro-resonator, where larger particles induce larger changes with wider distribution;   calculating the route-mean-square of the beat-note frequency changes that are above a threshold value, where for different particle sizes and the distributions of the beat-frequency changes follow a same statistical model; and   plotting the width of distribution of beat-note frequency changes to estimate an effective width of respective jump distributions;   estimating a size ratio between a reference plurality of nano-particles and the plurality of the particles of interest.   
     
     
         18 . The method for particle detection as recited in  claim 17 , further comprising:
 monitoring the changes in the beat-note frequency and counting the number of particles binding; and   taking multiple measurements and assigning an average polarizability to a plurality of detected particles.