Apparatus and method for analyzing a sample
An apparatus and method for Crystal Anisotropy Terahertz Microscopy (“CATM”) is provided. The apparatus includes an emitter configured to emit a THz pulse and a detector configured to detect the THz pulse after the pulse is transmitted through a sample disposed on a sample surface of the detector. A pulsed radiation generator generates a probe beam to interrogate the detector. The detector may include an electro-optical (“EO”) crystal configured to change in birefringence according to the THz pulse. The sample surface of the detector may have a dielectric coating which is transmissive to THz and reflective to the probe beam. The sample is disposed on the dielectric coating.
1. An apparatus for Crystal Anisotropy Terahertz Microscopy (“CATM”), comprising:
an emitter configured to emit a THz pulse;
a detector configured to detect the THz pulse after the pulse is transmitted through a sample disposed on a sample surface of the detector; and
a pulsed radiation generator for generating a probe beam to interrogate the detector; and
a polarizer disposed in a path of the THz pulse between the emitter and the sample, wherein the polarizer is configured to polarize the THz pulse and is selectively rotatable; and
wherein the probe beam has a polarization configured to rotate as a function of a rotation of the polarizer to provide a constant detector sensitivity.
2. The apparatus of claim 1 , wherein the pulsed radiation generator is a laser configured to generate a probe beam in the infrared, near-infrared, or visible light regions of the spectrum.
3. The apparatus of claim 2 , wherein the pulsed radiation generator is a titanium-sapphire laser.
4. The apparatus of claim 1 , wherein the detector comprises an electro-optical (“EO”) crystal configured to change in birefringence according to the THz pulse.
5. The apparatus of claim 4 , wherein the EO crystal is a ZnTe crystal or a GaP crystal.
6. The apparatus of claim 4 , wherein the sample surface of the detector has a dielectric coating which is transmissive to THz and reflective to NIR, and the sample is disposed on the dielectric coating.
7. The apparatus of claim 6 , wherein the probe beam passes through the EO crystal and is reflected by the dielectric coating.
8. The apparatus of claim 7 , further comprising a polarization detector for measuring a difference in a polarization of the probe beam from a polarization of the reflected probe beam caused by the THz pulse in the EO crystal.
9. The apparatus of claim 1 , further comprising:
a beam splitter for splitting a pump beam from the probe beam; and
wherein the emitter is configured to be excited by the pump beam for emission of the THz pulse.
10. The apparatus of claim 1 , further comprising a sample plate for holding the sample, wherein the sample plate is configured to be selectively rotated with respect to the detector.
11. The apparatus of claim 1 , further comprising a hydration cell for maintaining hydration of the sample.
12. A method for CATM, comprising:
providing a sample disposed on an EO crystal, wherein a sample surface of the EO crystal has a dielectric coating which is transmissive to THz and reflective to NIR, and the sample is disposed on the dielectric coating;
transmitting a THz pulse through the sample and the EO crystal such that a birefringence of the EO crystal is changed according to the THz pulse; providing a probe beam to the EO crystal, wherein the probe beam reflects from the dielectric coating and co-propagates through the EO crystal with the THz pulse and wherein the probe beam has a polarization configured to rotate as a function of a rotation of the polarizer to provide a constant detector sensitivity; measuring a difference in a polarization of the probe beam from a polarization of the reflected probe beam, the difference caused by the THz pulse in the EO crystal.