Abstract: A light frequency standard for use as an optical clock is disclosed that is improved by optical pumping. Optical pumping is utilized to change the ground states of the atomic vapor from transition forbidden to transition allowed ground states involved in two-photon absorption process. The added element of an optical pump increases the absorbers available in the two-photon process and creates a stronger absorption line signal used for locking the laser to an absolute frequency. An optical spectrometer based upon two-photon absorption is disclosed that is improved by optical pumping. In this case, two optical pumps are used, One optical pump provides photons for two-photon absorption, but it also depletes absorbing atoms that are in ground states where two-photon absorption is allowed. The other optical pump replenishes the supply of absorbing atoms into ground states allowing two-photon absorption. The spectrometer is useful for measuring Doppler shift with LIDAR.

Abstract: An apparatus is disclosed for filtering of probe light and measurement of probe light frequency. The apparatus includes an optical filter comprised of a medium of rapidly changing circular birefringence. The circular birefringent medium changes the polarization of probe light such that light within a certain frequency bandwidth is rotated between crossed polarizers so it will be transmitted through the second polarizer. The spectrometer rotates the polarization of probe light an amount that is dependent upon probe light frequency. Probe light frequency is deduced by analyzing probe light polarization after it propagates through the birefringent medium. The birefringent medium is constructed from a gaseous substance and a magnetic field, where the gaseous substance has one or more absorption lines near the probe light frequency. The magnetic field permeates the gaseous substance and shifts the frequency of the absorption line(s) by the Zeeman effect.

Abstract: An apparatus is disclosed for filtering of probe light and measurement of probe light frequency. The apparatus includes an optical filter comprised of a medium of rapidly changing circular birefringence. The circular birefringent medium changes the polarization of probe light such that light within a certain frequency bandwidth is rotated between crossed polarizers so it will be transmitted through the second polarizer. The spectrometer rotates the polarization of probe light an amount that is dependent upon probe light frequency. Probe light frequency is deduced by analyzing probe light polarization after it propagates through the birefringent medium. The birefringent medium is constructed from a gaseous substance and a magnetic field, where the gaseous substance has one or more absorption lines near the probe light frequency. The magnetic field permeates the gaseous substance and shifts the frequency of the absorption line(s) by the Zeeman effect.

Abstract: A method and apparatus is disclosed for measurement of probe light frequency. The apparatus includes an optical spectrometer comprised of a medium of rapidly changing circular birefringence. The circular birefringent medium changes the polarization of probe light an amount that is dependent upon probe light frequency. Thus probe light frequency is deduced by analyzing probe light polarization after it propagates through the birefringent medium. The birefringent medium is constructed from a gaseous substance and a magnetic field, where the gaseous substance has one or more absorption lines near the probe light frequency. The magnetic field permeates the gaseous substance and shifts the frequency of the absorption line(s) by the Zeeman effect. The method includes probe light emitted from a transmitter, which scatters off of a target, then the scattered probe light is collected and transmitted through the optical spectrometer where frequency is measured.

Abstract: An apparatus is disclosed for filtering of probe light. The apparatus includes an optical filter comprised of a medium circular birefringence between crossed polarizers. The circular birefringent medium changes the polarization of light of a particular frequency bandwidth. So that after passing through the first polarizer, the polarization of a particular frequency bandwidth probe light is rotated between crossed polarizers so it will be transmitted through the second polarizer. The birefringent medium is constructed from a gaseous substance such as atomic vapor and two pump lasers in resonance with absorption lines of the absorbing substance by the process of two-photon absorption. A magnetic field is utilized in some embodiments that permeates the absorbing substance and separates absorption lines for excited state transitions by the Zeeman effect.

Abstract: A method and apparatus is disclosed for measurement of probe light frequency. The apparatus includes an optical spectrometer comprised of a medium of rapidly changing circular birefringence. The circular birefringent medium changes the polarization of probe light an amount that is dependent upon probe light frequency. Thus probe light frequency is deduced by analyzing probe light polarization after it propagates through the birefringent medium. The birefringent medium is constructed from a gaseous substance and a magnetic field, where the gaseous substance has one or more absorption lines near the probe light frequency. The magnetic field permeates the gaseous substance and shifts the frequency of the absorption line(s) by the Zeeman effect. The method includes probe light emitted from a transmitter, which scatters off of a target, then the scattered probe light is collected and transmitted through the optical spectrometer where frequency is measured.

Abstract: A tunable optical spectrometer is disclosed that includes a medium configured to perform polarization rotation within a frequency band on a linearly polarized test beam, wherein the medium is circularly birefringent, and wherein the polarization rotation is achieved based on two-photon-absorption. The medium includes a gaseous substance, a reference laser beam of circular polarization and a longitudinal magnetic field. The test beam propagates through the medium twice, once in the same direction as the magnetic field, and once in the opposite direction of the magnetic field. The test beam undergoes polarization rotation an amount that depends upon the frequency of the test beam.

Abstract: A tunable optical filter includes a medium configured to perform polarization rotation on a portion of a linearly polarized signal beam having a frequency within a selected frequency band, wherein the medium is circularly birefringent within the frequency band, and wherein the polarization rotation is achieved based on two-photon-absorption. The first stage of the filter transmits a dual transmission line, and a subsequent portion of the filter partions the output of the first stage into two separate transmission channels.

Abstract: A tunable optical spectrometer is disclosed that includes a medium configured to perform polarization rotation within a frequency band on a linearly polarized test beam, wherein the medium is circularly birefringent, and wherein the polarization rotation is achieved based on two-photon-absorption. The medium includes a gaseous substance, a reference laser beam of circular polarization and a longitudinal magnetic field. The test beam propagates through the medium twice, once in the same direction as the magnetic field, and once in the opposite direction of the magnetic field. The test beam undergoes polarization rotation an amount that depends upon the frequency of the test beam.