Reducing scattering related features in terhertz time domain spectroscopy bz averaging the impulse waveform over a plurality of sample points

Abstract

A method of investigating an object, comprising the steps of: (a) irradiating the object with an optically-generated pulse of electromagnetic radiation, said pulse having a plurality of frequencies in the range from 100 GHz to 100 THz; (b) detecting radiation transmitted and/or reflected from the object to obtain a time domain waveform; (c) repeating steps (a) and (b) for a plurality of points on the object and (d) combining data from step (c) to produce a time domain waveform for the object which has been averaged over the plurality of points.

1 . A method of investigating an object, comprising the steps of:
 (a) irradiating the object with an optically-generated pulse of electromagnetic radiation, said pulse having a plurality of frequencies in the range from 100 GHz to 100 THz;   (b) detecting radiation transmitted and/or reflected from the object to obtain a time domain waveform;   (c) repeating steps (a) and (b) for a plurality of points on the object and   (d) sequentially combining data from step (c) to produce a time domain waveform for the object which has been averaged over the plurality of points, said sequential combining and averaging continuing until the effect of scattering in the produced time domain waveform has been reduced.   
   
   
       2 . The method of  claim 1  further comprising the steps of:
 (b)(i) obtaining a reference measurement taken in the absence of an object;   (b)(ii) detecting radiation in the absence of an object; and   (b)(iii) subtracting the signal measured by the detector during step (b)(ii) from the signal measured by the detector during step (b).   
   
   
       3 . The method of  claim 1  wherein the Fourier transform of the averaged time domain waveform from step (d) is calculated. 
   
   
       4 . The method of  claim 3  further comprising obtaining a first derivative of the obtained spectra. 
   
   
       5 . The method of  claim 1  wherein the plurality of points in step (c) is iteratively increased until the waveform from step (d) is substantially unchanging. 
   
   
       6 . (canceled) 
   
   
       7 . (canceled) 
   
   
       8 . An apparatus for investigating an object comprising:
 a source of electromagnetic radiation for irradiating a point on the object with an optically-generated pulse of electromagnetic radiation, said pulse having a plurality of frequencies in the range from 100 GHz to 100 THz;   a detector for detecting radiation transmitted and/or reflected from the object to obtain a time domain waveform;   scanning means for sequentially irradiating a plurality of points on the object and   means for sequentially combining time domain waveforms from each of the plurality of points to produce a time domain waveform for the object which has been averaged over the plurality of points, said sequential combining and averaging continuing until the effect of scattering in the produced time domain waveform has been reduced.   
   
   
       9 . A method of imaging a sample comprising the steps of:
 (a) investigating the sample according to a method as claimed in  claim 1 ;   (b) deriving a spectral waveform from the time domain waveform obtained in step (a);   (c) identifying the components of the sample from the spectral waveform in step (b);   (d) re-irradiating the sample with an optically-generated pulse of electromagnetic radiation, said pulse having a plurality of frequencies in the range from 100 GHz to 100 THz;   (e) detecting radiation transmitted and/or reflected from the object to obtain a time domain waveform, the detected radiation having first passed through at least one bandpass filter corresponding to at least one component of the sample; and   (f) generating an image from the radiation detected in step (e).   
   
   
       10 - 12 . (canceled)