Dual circular polarization modulation spectrometer

A dual circular polarization modulator spectrometer comprising, in combination:

• a light source;
• a wavelength selection device;
• a polarizer;
• a first polarization modulator vibrated to modulate the incoming light between left and right circular polarized light at a selected frequency;
• a sample chamber;
• a second polarization modulator vibrated to modulate the incoming light between left and right circular polarized light at a frequency that is not the same frequency as the selected frequency for the first polarization modulator whereby strength of the first polarization modulator and strength of the second polarization modulator can be manipulated to eliminate unwanted background signal;
• a light detector;
• a first lock-in amplifier whereby a signal corresponding to the selected frequency of the first polarization modulator is isolated;
• a second lock-in amplifier whereby a signal corresponding to the selected frequency of the second polarization modulator is isolated;
• an electronic manipulator to combine the signals from the first and the second lock-in amplifiers can be combined by mathematical operations.

A method for obtaining a circular dichroism spectra of a substance free of linear birefringence interference comprising:

• adding a second polarization modulator to a circular dichroism spectrometer, said circular dichroism spectrometer having a light source, a wavelength selection device, a first linear polarizer, a first polarization modulator vibrated at a selected frequency, a sample chamber, a light detector, and a lock-in amplifier to detect the signal corresponding to the selected frequency of the first polarization modulator;
• vibrating the second polarization modulator at a selected frequency that is not the same as the selected frequency of first polarization modulator, whereby the strength of the first polarization modulator and the strength of the second polarization modulator can be manipulated to eliminate unwanted background signal;
• adding a second lock-in amplifier whereby the signal corresponding to the selected frequency of the second polarization modulator is isolated;
• electronically manipulating the signals obtained from the first and the second lock-in amplifiers whereby the resulting signal is the circular dichroism spectra of the substance in the sample chamber free from linear birefringence interference.

A method for obtaining the circular dichroism spectra of a substance free of linear birefringence interference comprising:

• adding a first and a second polarization modulator and a polarizer to an absorption spectrometer, said absorption spectrometer having a light source, a wavelength selection device, a sample chamber and a light detector;
• vibrating the first polarization modulator at a selected frequency;
• vibrating the second polarization modulator at a selected frequency that is not the same selected frequency at which the first polarization modulator vibrates;
• selecting the strength of the modulation of the first and the second polarization modulators so that unwanted background signal will be eliminated;
• locating the sample chamber between the first and the second polarization modulators;
• adding a first lock-in amplifier and a second lock-in amplifier whereby a signal corresponding to the selected frequency of the first polarization modulator and a signal corresponding to the selected frequency of the second polarization modulator are obtained;
• electronically manipulating the signal from the first lock-in amplifier and the signal from the second lock-in amplifier whereby a circular dichroism spectra is obtained that is free from linear birefringent interference.

A circular polarization spectrometer comprising, in combination:

• a light source;
• a wavelength selection device;
• a first polarizer;
• a plurality of polarization modulators vibrating at selected frequencies whereby the strength of each polarization modulator can be manipulated to minimize unwanted background interference;
• a sample chamber;
• a light detector;
• a plurality of lock-in amplifiers whereby each polarization modulator may have a corresponding lock-in amplifier and the signal corresponding to each lock-in amplifier can be isolated;
• an electronic manipulator to combine the signals from the plurality of lock-in amplifiers whereby the signals can be combined by mathematical operations.