Abstract: A method of measuring a quantity or characteristic of a qualified air, e.g., clean air or prefiltered air, present in an environment, e.g., a chamber or a cleanroom, includes freely placing a measurement apparatus with an open multipass cell in the environment, and allowing a qualified air, such as clean air or prefiltered air, present in the environment to move freely into and out of an optical cavity of the open multipass cell. The method further includes obtaining a measurement of a quantity or a characteristic based on the qualified air in the optical cavity.

Abstract: An optical cavity includes a cell having at least one structure with a first end and a second end, a first end-cap configured to removably receive a first mirror, and a second end-cap configured to removably receive a second mirror. The first end-cap is attached to the structure at the first end and has an opening with a center axis. The second end-cap is attached to the structure at the second end and has an opening with a center axis that is axially aligned with the center axis of the first end-cap. The cell can be a closed cell, wherein the structure is a tube axially aligned with the center axis. The cell can be an open cell, wherein the structure is a tube that includes one or more openings through its wall. The cell can be an open cell, wherein the structure includes one or more rods, each off axis from the center axis.

Abstract: A cell for an optical cavity includes a tube with a first open-end and a second open-end, a first end-cap, and a second end-cap. The first end-cap is fixedly attached to the tube at the first open-end and has an opening with a center axis. The second end-cap is fixedly attached to the tube at the second open-end and has an opening with a center axis that is axially aligned with the center axis of the first end-cap.

Abstract: Certain aspects of the present disclosure provide techniques and apparatus for generating oscillating signals and for wireless communication, such as a frequency synthesizer architecture using a step-symmetric inductor. An example frequency synthesizer generally includes an oscillator and a frequency adjustment circuit, an output of the oscillator being coupled to an input of the frequency adjustment circuit, the frequency adjustment circuit comprising a step-symmetric inductive element. An example transceiver generally includes the frequency synthesizer described herein, as well as a mixer having a local-oscillator (LO) input coupled to an output of the frequency adjustment circuit; and an amplifier coupled to the mixer.

Abstract: An optical system for performing an absorption measurement of a medium sample includes a laser source configured to output a laser beam having a wavelength corresponding to an absorption region of interest; a ringdown cavity comprising a chamber configured to receive the medium sample, an input mirror at an input end, an output mirror at an output end, and an optical axis that extends through the centers of the input mirror and the output mirror; a coupling device configured to couple the laser beam through the input mirror into the chamber; and a detector optically coupled with the cavity, and configured to detect an intensity of light of the wavelength corresponding to the absorption region of interest that extends through the output mirror, wherein a cavity geometry of the cavity increases the re-entrant condition of the cavity relative to a conventional cavity comprised of two spherical mirrors.

Abstract: An optical system for performing an absorption measurement of a medium sample includes a laser source configured to output a laser beam having a wavelength corresponding to an absorption region of interest; a ringdown cavity comprising a chamber configured to receive the medium sample, an input mirror at an input end, an output mirror at an output end, and an optical axis that extends through the centers of the input mirror and the output mirror; a coupling device configured to couple the laser beam through the input mirror into the chamber; and a detector optically coupled with the cavity, and configured to detect an intensity of light of the wavelength corresponding to the absorption region of interest that extends through the output mirror, wherein a cavity geometry of the cavity increases the re-entrant condition of the cavity relative to a conventional cavity comprised of two spherical mirrors.

Abstract: An optical system for performing an absorption measurement of a medium sample includes a laser source configured to output a laser beam having a wavelength corresponding to an absorption region of interest; a ringdown cavity comprising a chamber configured to receive the medium sample, an input mirror at an input end, an output mirror at an output end, and an optical axis that extends through the centers of the input mirror and the output mirror; a coupling device configured to couple the laser beam through the input mirror into the chamber; and a detector optically coupled with the cavity, and configured to detect an intensity of light of the wavelength corresponding to the absorption region of interest that extends through the output mirror, wherein a cavity geometry of the cavity increases the re-entrant condition of the cavity relative to a conventional cavity comprised of two spherical mirrors.

Abstract: An optical system for performing an absorption measurement of a medium sample includes a laser source configured to output a laser beam having a wavelength corresponding to an absorption region of interest; a ringdown cavity comprising a chamber configured to receive the medium sample, an input mirror at an input end, an output mirror at an output end, and an optical axis that extends through the centers of the input mirror and the output mirror; a coupling device configured to couple the laser beam through the input mirror into the chamber; and a detector optically coupled with the cavity, and configured to detect an intensity of light of the wavelength corresponding to the absorption region of interest that extends through the output mirror, wherein a cavity geometry of the cavity increases the re-entrant condition of the cavity relative to a conventional cavity comprised of two spherical mirrors.