Frequency standards, infrared

Infrared spectroscopy of adsorbed CO is a useful characterization tool for dendrimer-templated supported nanoparticles, because it directly probes particle surface features. In these experiments, which are performed in a standard infrared spectrometer using an in-situ transmission or DRIFTS cell, a sample of supported DENs is first treated to remove the organic dendrimer. Samples are often reduced under H2 at elevated temperature, flushed with He, and cooled to room temperature. Dosing with CO followed by flushing to remove the gas-phase CO allows for the spectrum of surface-bound CO to be collected and evaluated. Because adsorbed CO stretching frequencies are sensitive to surface geometric and electronic effects, it is potentially possible to evaluate the relative effects of each on nanoparticle properties. 

In order for a detector to follow the intensity modulation of the sample in the frequency range of 50 kHz, it must have a response time on the order of a few microseconds or less. Standard infrared detectors are thermal detectors which... 

The first frequency measurement of the 15 — 25 resonance made use of a transportable ClU-stabilized HeNe infrared frequency standard at 88 THz [24], built at the Institute of Laser Physics in Novosibirsk/Russia. For calibration it was transported repeatedly to the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig/Germany where it could be compared with a Cs atomic clock using the PTB frequency chain [25]. 

The lack of accurate and stable frequency standards in the near-infrared spectral range, and in particular at 1083 nm, is a serious inconvenient to improve the present frequency stability of the He-locked master laser. On the other hand, hyperfine transitions of the iodine molecule has been defined as secondary frequency standard at different visible wavelengths, and in particular at 532 nm, the doubled frequency of the 1064 nm Nd YAG laser. Likewise, our idea has been to lock the master laser frequency to I2 hyperfine transitions at its doubled frequency, 541 nm. 

One interesting reference standard may be the methane stabilized helium neon laser at 3.39 pm. Its infrared frequency can be compared directly with the microwave cesium frequency standard with the help of a relatively short frequency chain [32], An accuracy of 1 part in 1012 or better appears feasible for a transportable secondary standard. 

Primary length measurements are these days based on optical frequency standards. If one needs a unit of length, for example, a wave-length for interferometric measurement, then one divides the optical frequency by the value of the speed of light (299 792 458 m.s ) as defined in the SI metre. The mise en pratique of the metre [44] lists a number of frequency-stabilised lasers at various wavelengths in the visible and near infrared spectral regions. 

INFRARED AND FAR-INFRARED ABSORPTION FREQUENCY STANDARDS (continued)... 

This frequency mixing in suitable nonlinear mixing elements is the basis for building up a frequency chain from the Cs atomic beam frequency standard to the optical frequency of visible lasers. The optimum choice for the mixer depends on the spectral range covered by the mixed frequencies. When the output beams of two infrared lasers with known frequencies v and V2 are focused together with... 

PROGRAMMABLE, SECONDARY FREQUENCY STANDARDS BASED INFRARED SYNTHESIZERS FOR HIGH RESOLUTION SPECTROSCOPY... 

The intent of this paper is to give a brief overview of salient components and techniques which led to the development of programmable infrared synthesizers absolute frequency accuracy, reproducibility and resettability with standard deviations of about 5 WIz (1.7 x 10 cm ) relative to the primary Cesium frequency standard at the National Bureau of Standards in Boulder, Colorado, has been achieved. 

C. Freed, J. W. Biellnskl, and W. Lo, "Programmable, Secondary Frequency Standard Based Infrared Synthesizer using Tunable Lead-Salt Diode Lasers," Proceedings of Tunable Diode Laser Development and Spectroscopy Applications," SPIE 438, (1983). 

In addition, other frequency chains have been developed that start from stabilized CO2 lasers locked to the cesium frequency standard in a similar way, but then use infrared color-center lasers to bridge the gap to the l2-stabilized HeNe laser [14.155a]. 

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