Spectrometer system

Abstract

A wobbling single slit is provided as the entrance slit of a spectrometer which rectilinearly reciprocates at a constant amplitude, such amplitude being selectively adjustable. A control signal is obtained from a circuit that oscillates the slit for controlling the frequency and phase of the ac signal component detected and amplified from the detector after the superposed dc detected signal component is separated from the ac signal component.

What is claimed as new and what it is desired to secure by Letters Patent of the United States is: 
     
       1. In a spectrometer system including a radiant energy source, a scanning spectrometer, only a single entrance slit disposed between said source and said spectrometer, said source producing a focused radiant energy beam passing through said entrance slit and into said spectrometer, said spectrometer having a single fixed exit slit whereby a radiant energy path is established from said source through said entrance slit and through said spectrometer and out said exit slit, said system including a photomultiplier detector in said radiant energy path aft of and spaced from said exit slit, an absorption cell adapted to contain a medium to be investigated, said cell communicating with said radiant energy path between said exit slit and said detector, said system having no correlation mask corresponding to a medium to be investigated in said cell, the improvement comprising means for movably mounting said entrance slit, said means including means for rectilinearly reciprocating said entrance slit at a constant and rapid frequency to modulate the wavelength of the radiant energy beam detected in a sinusoidal manner. 
     
     
       2. In the system as defined in claim 1 wherein said detector includes a photomultiplier tube having grid wires, said movable entrance slit being located in the radiant energy path between said source and spectrometer whereby radiant energy interference on said grid wire is non-existent. 
     
     
       3. In the system as defined in claim 1 wherein said detector receives the radiant energy after passage through an absorbing medium to be investigated in said cell and converts the received energy into a modulated signal, a tuned phase lock-in amplifier means for receiving said signal and converting said signal into a first signal of selected frequency and a dc signal, said amplifier means being tuned to the same frequency as the frequency at which said entrance slit is reciprocating. 
     
     
       4. In the system as defined in claim 1 wherein said detector receives the radiant energy after passage through an absorbing medium to be investigated in said cell and converts the received energy into a modulated signal, a tuned phase lock-in amplifier means for receiving said signal and converting said signal into a first signal of selected frequency and a dc signal, said amplifier means being tuned to twice the frequency as the frequency at which said entrance slit is reciprocating. 
     
     
       5. In the system as defined in claim 1 wherein said means for rectilinearly reciprocating said entrance slit includes circuit means for maintaining constant the amplitude of the reciprocating motion of said entrance slit. 
     
     
       6. In the system as defined in claim 5 wherein said circuit means includes a selectively adjustable means for altering the amplitude of the reciprocating motion of said entrance slit. 
     
     
       7. In the system as defined in claim 1 wherein said detector receives the radiant energy after passage through an absorbing medium to be investigated in said cell and converts the received radiant energy into a modulated signal, a potentiometric recorder, a tuned phase lock-in amplifier means for receiving said signal and converting said signal into a first signal of selected frequency and a dc signal, said first and dc signals being coupled to said recorder to record the ratio of said first signal to said dc signal. 
     
     
       8. In the system as defined in claim 7 wherein said means for rectilinearly reciprocating said entrance slit includes means for providing a control signal representative of the frequency and phase of the reciprocating motion of said entrance slit to said amplifier for use in rectifying said first signal. 
     
     
       9. In the system as defined in claim 8 wherein said amplifier means is tuned to the same frequency at which said entrance slit is reciprocating. 
     
     
       10. In the system as defined in claim 8 wherein said amplifier means is tuned to twice the frequency at which said entrance slit is reciprocating. 
     
     
       11. In a spectrometer system including a radiant energy source, a spectrometer, only a single entrance slit disposed between said source and said spectrometer, said source producing a focused radiant energy beam passing through said entrance slit and into said spectrometer, said spectrometer having a single fixed exit slit whereby a radiant energy path is established from said source through said entrance slit and through said spectrometer and out said exit slit, said system including a photomultiplier detector, an absorption cell adapted to contain a medium to be investigated, said cell communicating with said radiant energy path between said exit slit and said detector, said detector receiving said radiant energy after passage thereof through said cell and producing an output signal, the improvement comprising means for rectiliearly reciprocating said entrance slit at a constant and rapid frequency to modulate the wavelength of radiant energy beam detected in a sinusoidal manner, a potentiometric recorder for producing a ratio of two signals both derived from said output signal of said detector whereby said ratio is invariant with changes in the intensity of said source. 
     
     
       12. In a spectrometer system including a radiant energy source, a scanning spectrometer, said source producing a focused energy beam passing into said spectrometer, said system including a photomultiplier detector, an absorption cell adapted to contain a medium to be investigated, means for sinusoidally varying the wavelength of the radiant energy beam from said source into said spectrometer at a constant and rapid frequency, said means including a single rectilinearly reciprocating entrance slit between said source and said spectrometer, said sinusoidally varying beam passing from said spectrometer through said absorption cell onto said detector, means to receive the output signal from said detector and provide an indication of the existence and concentration of the medium to be investigated. .Iadd. 13. In a spectrometer system including a radiant energy source for producing a focused energy beam, a scanning spectrometer having a single entrance slit for receiving the focused energy beam and a single exit slit for passing the radiant energy beam from said spectrometer, said system including a single photomultiplier detector, an absorption cell adapted to contain a medium to be investigated and receiving the radiant energy beam from said spectrometer, said system having no correlation mask corresponding to a medium to be investigated in said cell, means for sinusoidally varying the wavelength of the radiant energy beam from said source into said spectrometer at a constant and rapid frequency, said sinusoidally varying beam passing from said spectrometer through said absorption cell onto said detector and, means to receive the output signal from said detector and provide an indication of the existence and concentration of the medium to be investigated..Iaddend..Iadd. 14. In the system as defined in claim 13 wherein said exit slit is fixed in its location in said system..Iaddend..Iadd. 15. In the system as defined in claim 13 wherein said detector includes a photomultiplier tube having grid wires, said means for generally sinusoidally varying the wavelength of the radiant energy beam being located in the radiant energy path between said source and said exit slit of said spectrometer whereby radiant energy interference on said grid wire is non-existent..Iaddend. .Iadd. 16. In the system as defined in claim 13 wherein said detector receives the radiant energy after passage through an absorbing medium to be investigated in said cell and converts the received energy into a modulated signal, a tuned phase lock-in amplifier means for receiving said signal and converting said signal into a first signal of selected frequency and a dc signal, said amplifier means being tuned to said frequency..Iaddend..Iadd. 17. In the system as defined in claim 13 wherein said detector receives the radiant energy after passage through an absorbing medium to be investigated in said cell and converts the received energy into a modulated signal, a tuned phase lock-in amplifier means for receiving said signal and converting said signal into a first signal of selected frequency and a dc signal, said amplifier means being tuned to twice said frequency..Iaddend..Iadd. 18. In the system as defined in claim 13 wherein said means for generally sinusoidally varying the wavelength includes circuit means for maintaining constant the amplitude of the wavelength variation. .Iaddend..Iadd. 19. In the system as defined in claim 18 wherein said circuit means includes a selectively adjustable means for altering the amplitude of the wavelength variation..Iaddend. .Iadd. 20. The system as defined in claim 13 wherein said detector provides a modulated output signal and wherein said means to receive said output signal from said detector and provide an indication of the existence and concentration of the medium comprises a tuned phase lock-in amplifier means for converting said modulated output signal into an ac signal component and a dc signal component and an indicator responsive to the ratio between said components. .Iaddend..Iadd. 21. In the system as defined in claim 20 wherein said means for sinusoidally varying the wavelength includes means for providing a control signal representative of the frequency and phase of the wavelength variation of said amplifier for use in rectifying said first signal..Iaddend..Iadd. 22. In the system as defined in claim 21 wherein said amplifier means is tuned to said frequency..Iaddend..Iadd. 23. In the system as defined in claim 21 wherein said amplifier means is tuned to twice said frequency..Iaddend.