Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radioastronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is ± 5 parts in 107. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH2F2, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO2 pump laser, and strength

The rotational spectrum of the FeD radical in its X4Δ state, measured by far-infrared laser magnetic resonance

Transitions between the spin-rotational levels of the FeD radical in the v = 0level of the X 4Δ ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. Pure-rotational transitions have been observed for the three lowest spin components. Lambda-type doubling is resolved on all the observed transitions; nuclear hyperfine structure is not observed. The energy levels of FeD are strongly affected by the breakdown of the Born–Oppenheimer approximation and cannot be modeled accurately by an effective Hamiltonian. The data are therefore fitted to an empirical formula to yield term values and g-factors for the various spin-rotational levels involved

Frequencies and Wavelengths From a New Far-Infrared Lasing Gas: 13CHD2OH

The first laser action produced by the partially deuterated isotopic form of methanol, 13CHD2OH, has been observed. With this laser medium, eight far-infrared laser emissions were discovered having wavelengths ranging from 33.8 to 80.9 mum. A three-laser heterodyne system was used to measure the frequencies for these newly discovered laser lines and are reported with fractional uncertainties of plusmn3 times 10 -7. The offset frequency of the CO2 pump laser was measured with respect to its center frequency for each 13CHD2OH laser emission

Measurement of Optically Pumped CH3 18OH Laser Frequencies Between 3 and 9 THz

The CH 3 18 OH isotopic form of methanol has been reinvestigated as a source of far-infrared (FIR) radiation using an optically pumped molecular laser system designed for wavelengths below 100 μm. With this system, four FIR laser emissions have been discovered, ranging in wavelength from 33.15 to 51.97 μm. The 33.15-μm line is the shortest known laser wavelength generated by optically pumped CH 3 18 OH. These lines are reported with their operating pressure, polarization relative to the CO 2 pump laser, and their relative strength. The frequencies of these new laser emissions, along with eight previously reported lines, were measured using heterodyne techniques and are reported with fractional uncertainties up to ±2 × 10 -7 . The offset frequency of the CO 2 pump laser was measured with respect to its center frequency for each FIR laser emission

First Laser Action Observed From Optically Pumped CH317OH

The CH 3 17 OH isotopic form of methanol has been investigated as a far-infrared laser medium for the first time. Using two distinct experimental systems, this investigation has resulted in the discovery of twelve far-infrared laser emissions that range in wavelength from 69.7 to 642.9 μm. Along with the wavelength, each laser emission is reported with its optimal operating pressure and relative intensity. The frequency for the 69.7 μm line was measured to be 4 302 957.7 ± 1.0 MHz and is reported with the CO 2 pump laser\u27s offset frequency relative to its center frequency

The far-infrared and microwave spectra of the CH radical in the v = 1 level of the X2Π state

Transitions between the spin–rotational levels of the 12CH radical in the v = 1 level of the X2Π state have been studied by the technique of laser magnetic resonance at far-infrared wavelengths. The data have been combined with a measurement of lambda-doubling transition frequencies at 7 GHz to determine an improved set of molecular parameters for CH in the v = 1 level. The parameters provide information on the effects of vibrational excitation on the structural properties of CH. Accurate predictions of the transition frequencies between the low-lying levels of the radical in the absence of a magnetic field have also been made. Small inconsistencies in the least-squares fit of the laser magnetic resonance data prompted re-measurement of three far-infrared laser frequencies, the 122.5 μm line of CH2F2 pumped by 9R(22), the 122.5 μm line of CH2F2 pumped by 9P(8) and the 554.4 μm line of CH2CF2 pumped by 10P(14). The new measurements differ by as much as 3.8 MHz from those made previously and are more accurate; they also remove the inconsistencies in the fit. The re-measured frequencies of the two 122.5 μm lines are identical within experimental error which suggests that the far-infrared lasing transition is the same, namely the rR23(32) transition in the v9=1 level of CH2F2