Image of sample using terahertz time domain spectroscopy in reflection mode to identify in a first material like normal breast tissue a second material like cancerous tissue by evaluating the phase change at the interface between the sample and a window like a quartz window, against which the sample is pressed

1. A method of investigating a sample, the sample comprising at least a first material in order to determine the presence of at least one further material, the method comprising the steps of:

a) irradiating the sample with electromagnetic radiation in the range from 25 GHz to 100 THz;

b) detecting radiation reflected from the sample;

c) determining a parameter related to the amplitude of the radiation, which is reflected from the sample, in the time domain;

d) analysing the parameter derived in step (c) in order to determine if there has been a 180° change in phase of the reflected radiation relative to the radiation irradiating the sample in order to determine if the sample further comprises the at least one further material;

wherein the irradiating and reflected radiation passes through a window member having a refractive index that falls between the refractive indices of the at least first and at least one further materials such that the irradiating radiation undergoes no change in chase upon being reflected at an interface between the window member and the at least a first material and undergoes a 180° change in phase upon being reflected at an interface with between the window member and the at least one further material.

2. A method of imaging a samples the sample, comprising at least a first material and at least one further material, the method comprising the steps of:

a) irradiating the sample with electromagnetic radiation in the range from 25 GHz to 100 THz;

b) detecting radiation reflected from the sample;

c) determining a parameter related to the amplitude of the radiation, which is reflected from the sample, in the time domain;

d) generating an image by plotting the value of the parameter calculated in step (c) for different points of the sample to show if there has been a 180° change in phase of the reflected radiation relative to the radiation irradiating the sample,

wherein the irradiating and reflected radiation passes through a window member having a refractive index that falls between the refractive indices of the at least a first and at least one further materials such that the irradiating radiation undergoes no change in phase upon being reflected at an interface between the window member and the at least a first material and undergoes a 180° change in phase upon being reflected at an interface between the window member and the at least one further material.

3. A method as claimed in claims 1 or 2 wherein the parameter determined in step (c) coincides with a maxima or minima in the detected radiation.

4. A method as claimed in claims 1 or 2 wherein the parameter determined in step (c) corresponds to a ratio of the detected radiation calculated at two separate time values.

5. A method as claimed in claim 4 wherein the ratio is of a maxima to a minima in the detected radiation.

6. A method as claimed in claims 1 or 2 wherein the window member is constructed from one of the following materials: high resistivity silicon, z-cut quartz, TPX, polystyrene or polythene.

7. A method as claimed in claims 1 or 2 wherein the window member has a refractive index which substantially does not vary with frequency.

8. A method of investigating a sample as claimed in claim 1 wherein the at least a first material is normal breast tissue and the at least one further material is cancerous tissue.

9. A method as claimed in claims 1 or 2 wherein the method further comprises the step of:

obtaining a baseline signal by irradiating the member in the absence of the sample and

detecting the amplitude of the reflected radiation, and

wherein in step (c):

the first parameter is determined by subtracting the baseline signal from the detected amplitude of the radiation reflected from both the member and the sample.

10. An apparatus for imaging a sample comprising at least a first material and at least one further material, the apparatus comprising

a source for irradiating a sample with a pulse of electro-magnetic radiation, said pulse having a plurality of frequencies in the range 25 GHz to 100 Thz;

detector means for detecting the amplitude of radiation reflected from the sample;

calculating means for determining a parameter related to the amplitude of the radiation, which is reflected from the sample, in the time domain and configured to determine if there has been a 180° change in phase of the reflected radiation relative to the radiation irradiating the sample;

imaging means for generating an image by plotting the value calculated by the calculating means for different points of the sample;

wherein the apparatus further comprises a window member through which the irradiating and reflected radiation passes, the window member arranged to have a refractive index that falls between the refractive indices of the at least a first and at least one further material of the sample to be imaged such that the irradiating radiation undergoes no change in phase upon being reflected at an interface between the window member and the at least a first material and undergoes a 180° change in phase upon being reflected at an interface between the window member and the at least one further material.

11. The use of quartz in a THz medical scanning apparatus wherein the apparatus comprises

a source for irradiating a sample with a pulse of electro-magnetic radiation, said pulse having a plurality of frequencies in the range 25 GHz to 100 Thz;

detector means for detecting the amplitude of radiation reflected from the sample;

a quartz window member; and

calculating means for determining a parameter related to the amplitude of the radiation, which is reflected from the sample, in the time domain and configured to determine if there has been a 180° change in phase of the reflected radiation relative to the radiation irradiating the sample,

wherein the irradiating and reflected radiation passes through the quartz window member such that the irradiating radiation undergoes no change in phase upon being reflected at an interface between the quartz window member and at least a first material of the sample and undergoes a 180° change in phase upon being reflected at an interface between the quartz window member and at least one further material of the sample.