We present a cavity ring-down spectroscopy apparatus suitable for high-resolution absorption spectroscopy. The central feature of the spectrometer is a ring-down cavity whose comb of eigenfrequencies is actively stabilized with respect to a tuneable, frequency-stabilized reference laser. By using dichroic ring-down cavity mirrors that are designed to have relatively high losses and low losses at the respective wavelengths of the reference laser and probe laser, the cavity stabilization dynamics are decoupled from frequency jitter of the probe laser. We use the cavity eigenfrequencies as markers in spectral scans and achieve a frequency resolution of ≈1 MHz. Five rovibrational transitions in the (2,0,1) vibrational band of water vapor near 0.935 μm are probed with a continuous-wave external-cavity diode laser, and their line strengths are determined and compared to literature values. Collisional narrowing effects and pressure shifting are observed, illustrating the applicability of the method for quantitative line shape studies of weakly absorbing systems.

No abstract

The absolute frequency of the 473-THz He-Ne laser (633 nm), stabilized on the g or i hyperfine component of the (127)I(2) 11-5 R(127) transition, was measured by comparing its frequency with a known frequency synthesized by summing the radiation from three lasers in a He-Ne plasma. The three lasers were (1) the 88-THz CH(4)-stabilized He-Ne laser (3.39 microm), (2) a 125-THz color-center laser (2.39 microm) with its frequency referenced to the R(II)(26) (13)C(18)O(2)laser, and (3) the 260-THz He-Ne laser (1.15 microm) referenced to an I(2)-stabilized dye laser at 520 THz (576 nm). The measured frequencies are 473 612 340.492 and 473 612 214.789 MHz for the g and i hyperfine components, respectively, with a total uncertainty of 1.6 parts in 10(10). The frequency of the i component adjusted to the operating conditions recommended by the Bureau International des Poids et Mesures is 473 612 214.830 +/- 0.074 MHz.

We measure the proton gyromagnetic ratio in H 2 0 by the low field method, $,(low). The result $,(low) = 2.67 513 376 loss-' 7 & (0.11 ppm), leads to a value of the fine structure constant of a-' = 137.0 359 840 (0.037 ppm) and a value for the quantized Hall resistance in SI units of RH = 25 812.80460 Q (0.037 ppm). To achieve this result, we measured the dimensions of a 2.1-m solenoid with an accuracy of 0.04 pm, and then measured the NMR frequency of a water sample in the field of the solenoid.

Abstrct-A newly designed iodine stabilized belium-neon (He-Ne) laser is described wbich is stable to 3 x 10-13 (1000-s sample time) but which exhibits an intensity dependent shift of about 8 kHz/W Cm2. ChieS agreement between dissimilar asers is atained wben the internal power densities are approximately equal. INTRODUCTION THE GENERAL acceptance by the standards community Tof the intracavity iodine stabilized helium-neon (He-Ne) laser operating at 633 nm as the defacto standard of length, and the demand by the metrological and scientific communities for a length reference whose stability exceeds that of currently available commercial lasers, prompted the National Bureau of Standards (NBS) to develop a portable stabilized laser system. The primary purpose of this effort was to promote the use of the iodine stabilized laser in applications remote from the laser laboratory by technicians or scientists who have neither the resources nor the time to develop their own instruments. This system was designed to be compact and lightweight and therefore easily transportable. The controls were designed to facilitate operation by people who have not had prior laser experience. In consequence of this, performance compromises were made relative to systems which are used as standards in national laboratories. THE SYSTEMThe stabilized laser system consists of two units as shown in Fig. I-the laser head and the electronic controller-the latter being completely contained in a commercial oscilloscope mainframe. Printed on the faces of the plug-in modules are the instructions for operation and the BIPM [1] vacuum wavelengths for the seven central iodine (127) hyperfine components coincident with the (He-Ne) gain curve. A drawing of the laser head is shown in Fig. 2; it is of standard configuration using four INVAR rods to separate the mirrors and secure the optical elements. The cavity length is 30 cm and is formed by a flat total reflector, which is placed at the absorption end of the cavity, and a 60-cm radius of curvature spherical output coupler which has a transmittance of 0.07. The laser tube is approximately 20 cm long, has a 1-mm bore diameter, and is filled with an 11:1 mixture of He4 and natural neon at a total pressure of 3.5 torr. Both the laser tube and the absorption cell are mounted in collets for ease of alignment and mainte- The iodine cell is mounted in a finned housing which is the heat sink for the thermoelectric cooler which maintains the iodine at a prescribed pressure. The contrast of the peaks due to the saturated absorption of the iodine relative to the laser intensity is approximately 0.15 percent. The tilt plates, to which the mirrors are attached, are kinematically mounted and can be removed and replaced without requiring realignment. Five flexible multiconductor shielded cables connect the laser head to the servo plug-in modules in the oscilloscope mainframe. The laser tube is powered by a high-efficiency current feedback switching power supply; and, while the laser tube is normally operated in sat...