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A CO2 sensor for capnography, based on a hollow waveguide (HWG) and tunable diode laser absorption spectroscopy (TDLAS), is presented; the sensor uses direct absorption spectroscopy and requires neither frequent calibration nor optical filters, giving it a significant advantage over existing techniques. Because of the HWG, the CO2 measurement achieved a concentration resolution of 60 ppm at a measurement rate of 25 Hz, as characterized by Allan variance. The length of the HWG was selected to efficiently suppress the optical fringes. This setup is perfectly suited for the detection of CO2 by capnography, and shows promise for the potential detection of other breath gases.

A simple and robust technique is reported to offset lock a single semiconductor laser to the atom resonance line with a frequency difference easily adjustable from a few tens of megahertz up to tens of gigahertz. The proposed scheme makes use of the frequency modulation spectroscopy by modulating sidebands of a fiber electro-optic modulator output. The short-term performances of a frequency offset locked semiconductor laser are experimentally demonstrated with the Allan variance of around 3.9×10?11 at a 2 s integration time. This method may have many applications, such as in Raman optics for an atom interferometer.

A high-performance transportable fountain clock is attractive for use in laboratories with high-precision time-frequency measurement requirements. This Letter reports the improvement of the stability of a transportable rubidium-87 fountain clock because of an optimization of temperature characteristics. This clock integrates its physical packaging, optical benches, microwave frequency synthesizers, and electronic controls onto an easily movable wheeled plate. Two optical benches with a high-vibration resistance are realized in this work. No additional adjustment is required after moving them several times. The Allan deviation of the fountain clock frequency was measured by comparing it with that of the hydrogen maser. The fountain clock got a short-term stability of 2.3×10−13 at 1 s and long-term stability on the order of 10−16 at 100,000 s.

A clock laser based on a 30-cm-long ultrahigh finesse optical cavity was developed to improve the frequency stability of the Sr optical lattice clock at the National Institute of Metrology. Using this clock laser to probe the spin-polarized Sr87 atoms, a Rabi transition linewidth of 1.8 Hz was obtained with 500 ms interrogation time. Two independent digital servos are used to alternatively lock the clock laser to the S01 (mF=+9/2)→P03 (mF=+9/2) transition. The Allan deviation shows that the short-term frequency stability is better than 3.2×10−16 and averages down followed by 1.8×10−15/τ.

We demonstrate a proposal for making an ultrastable laser referenced to a multi-cavity, enabling a lower thermal noise limit due to the averaging effect. In comparison with a single-cavity system, relative frequency instability of the synthesized laser can be improved by a factor of the square root of the cavity number. We perform an experiment to simulate a two-cavity system with two independent ultrastable lasers. Experimental results show that the relative frequency instability (Allan deviation) of the synthesized laser is 5 × 10−16, improved by a factor of √2 from a single-cavity-stabilized laser.

A quantum cascade (QC) laser-based spectrometer is developed to measure trace gases in air. The proposed spectrometer is tested for N2O, and the results presented in this letter. This system takes advantage of recent technology in QC lasers by utilizing intra-pulse scan spectroscopy, which allows high sensitive measurement. Without calibration gases, the gas concentration can be calculated with scan integration and the corresponding values from the HITRAN04 database. By analyzing the Allan variance, a detection limit of 2 ppb is obtained. Continuous measurement of N2O sampled from ambient air shows the applicability of the proposed system for the field measurements of gases of environmental concern.