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We report on the absolute frequency stabilization of Yb-Er:glass lasers against different acetylene absorption lines in the 1.5 /spl mu/m spectral region. An external frequency modulation technique was adopted to independently stabilize two diode-pumped erbium microlasers against the P(15) rovibrational line at 1534.099 nm. A long-term frequency stability below 10/sup -9/ (200 kHz) was measured on both the closed-loop error signal and on the beat note frequency. From the beat signal analysis, a 1 ms laser linewidth of 50 kHz was observed. The Allan standard deviation of the beat frequency was below 10/sup -10/ for integration times between 10 ms and 1 s and as low as 4/spl times/10/sup -11/ around 0.1 s.

An External-Cavity Laser Diode was frequency locked on molecular absorption line R(3) of hydrogen iodide at 1.541 μm using the wavelength modulation technique. This molecular reference is very important in many fields like HD-WDW telecommunication system and interferometry. Preliminary measurements of the closed-loop error signal provided a relative frequency stability of 9.5 times 10-10 in a 160 Hz acquisition bandwidth.

The first results of optical pumping of the /sup 3/P/sub 1/ level in the excited metastable triplet of Mg are reported. A nearly total depletion of the above level has been achieved in a metastable atomic beam through resonant interaction with the /sup 3/S/sub 1/ (3s4s) level. For this purpose, a cavity-stabilized coumarin 6 ring dye laser has been used. The outlook for an optically pumped Mg frequency standard is also discussed on the basis of the results reported. >

In the first part of this paper the characteristics of frequency deviation and modulation bandwidth required for phase-locking optically pumped far infrared lasers to reference synthesized signals are examined. Then different fast modulation techniques suitable for this purpose are discussed pointing out their particular features. Experimental results concerning laser frequency modulation by Stark effect, injection locking and electrically variable reactances (e.g Schottky diodes, plasma cell) are reported and compared.

An analysis of abrupt-junction millimetric varactor doublers using Schottky diodes is performed and numerically implemented to evaluate conditions of maximum output power. This power level, the efficiency, and the circuit parameters have been derived as a function of the geometrical and physical parameters of the junction. Physical phenomena which allow the application of the model up to the plasma resonance frequency in epilayer are taken into account. Comparison of available experimental data with the theory developed is repotted.

Experimental results of harmonic generation in the submillimetric wavelength region using carcinotrons as fundamental sources are reported. The multiplier is a commercial cross-waveguide structure equipped with a Schottky barrier diode operating as a non-linear resistance. Power levels useful for many spectroscopic applications can be obtained with these wideband tunable sources.

A direct frequency measurement of the 496 μm, K = 2 line from a CH 3 F laser is reported. Our laser is a metallic wave-guide device pumped by a frequency stabilized CO 2 laser; its output is mixed in a CaAs-Au Schottky barrier diode with a 100 GHz klystron and the beat note is observed on a spectrum analyzer. The result is f CH 3 F (496 μm, K = 2) = 604 297.5 ± 0.2 MHz.

The realization of a primary frequency standard at 10 μm on an OsO4 molecular beam is here examined and the possibility of reaching a high stability level and an accuracy better than 10−14 is discussed.

We report the absolute frequency measurement of the 81.5 μm rotational transition and of the 263.4 μm inversion transition in the ν2 vibrational state of 14NH3. A very low-phase noise frequency multiplication chain has been used in the experiments allowing a phase-coherent synthesis up to the frequency of 3.7 THz.

The isotopic frequency shift for the3P1–3P0 ΔmJ=0 fine structure transition in the metastable triplet of24Mg and26Mg is reported. The transitions corresponding to the two even isotopes of Mg (λ≃498 µm) are observed in a metastable atomic beam through a two-zones Ramsey interaction technique with a transit time limited full width at half maximum of 1.2 kHz (Q=5×108). The isotopic shift turned out to be 1712.5±0.2 kHz.

The performances of metal-semiconductor point-contact diodes as mixers in the near-infrared region were tested. Preliminary experiments were performed in order to phase-lock two diode lasers at 850 nm a few hundred gigahertz apart. GaSb, InAs, and InSb as semiconductor layers were used. The frequency bridge between the two lasers was covered by a Gunn diode frequency locked to a 1-GHz oscillator. A novel phase-lock circuit was tested on two diode lasers 72 GHz apart.