Measurements and assignments of new large offset CD3OH FIR laser lines

By using an acoustooptic modulator we extend the 300 MHz tunability of a waveguide CO₂ laser to 480 MHz. The CD₃OH was optically pumped by the 10R(32), 10R(34), and 10R(36) CO₂ laser lines, and 17 new FIR laser lines were discovered. The Stark effect on previously known FIR laser lines was investigated, and some tentative FIR laser lines assignments are suggested.     

Acoustooptic extension of the frequency tunability of CW CO2 lasers: New FIR lasers emissions from CH3OH and13CH3OH

We have increased the frequency tunability of our CW waveguide CO₂ lasers by means of an acoustooptic amplitude modulator, operating at the fixed frequency of 90 MHz. The up-shifted, or down-shifted, laser optical sideband can be generated independently by adjusting the orientation of the modulator. The efficiency is larger than 50%. The frequency tunability of the CO₂ laser around each laser line is thus increased by 180 MHz. To demonstrate the possibilities of this method, a source composed of the above modulator and of a CW, 300 MHz tunable waveguide CO₂ laser has been used for the search of new large offset FIR laser lines from optically pumped CH₃OH and¹³CH₃OH molecules. As a result 15 and 10 new large offset laser lines were discovered respectively. New assignments of some laser lines are also proposed. We have also measured the Stark effect, the offset, and the polarization of other already known lines. In particular a Stark effect frequency tuning of about 1 GHz is demonstrated for a laser line at 208.399 m.     

IR absorption measurements and new FIR emission lines in CH3OH by use of a frequency-tunable CW waveguide CO2 laser

The IR absorption in CH₃OH in the vicinity of CO₂ laser lines has been measured quantitatively by use of a 300 MHz tunable waveguide CO₂ laser with output powers of about 3 W. Information on frequency offsets from the CO₂ line centers, small signal and saturated absorption coefficients of FIR laser pump transitions is obtained. Some stronger pump transitions with frequency offsets larger than 50 MHz gave rise to the observation of 8 new FIR emission lines with wavelengths from 43 to 125 μm.     

High-resolution spectroscopy with and frequency stabilization of a cw dye laser

The hyperfine splittings of the Na D₁ and D₂ lines were investigated using a single mode cw dye laser. The light of the laser was scattered by the atoms of an atomic beam and the fluorescent light was observed as the frequency of the laser was tuned across the D lines. The Doppler width of the atomic beam was reduced to about 2.5 MHz so that the absorption width of the atoms of the beam was essentially determined by the natural width of the 3²P_1/2 and 3²P_3/2 levels, which is about 10 MHz. Since the linewidth observed for the hyperfine transitions was 30 MHz, most of the hyperfine components of the D₁ and D₂ lines could be resolved. In another experiment the frequency of the dye laser was locked to a hyperfine transition of the D₁ line. The observed variation of the output frequency of the dye laser was less than ±1.5 MHz. In addition, the intensity of the dye laser was controlled to about 10⁻³, using an electro-optically variable transmission filter.     

New large offset far-infrared laser lines from CD3OH

The CD₃OH molecule has been investigated for new far-infrared laser lines by optically pumping with a cw waveguide CO₂ laser. The increased tunability (300 MHz) with respect to a conventional CO₂ laser permits to pump many new CD₃OH lines. As a consequence 108 new laser lines have been discovered, ranging from 42.9 to 1155 m in wavelength. On some lines the effect of an electric Stark field has been investigated demonstrating a laser frequency tuning. The total number of known FIR laser lines from CD₃OH is increased to about 340 making this molecule the most prolific together with CH₃OH.     

New fir laser lines and frequency measurements from optically pumped13CD3OH3

We report the discovery of 57 new fir laser lines from¹³CD₃OH molecule optically pumped by a waveguide CO₂ laser of 300 MHz tunability. For all lines, precise frequency offset measurements between the CO₂ line center and the center of the absorbing¹³CD₃OH line were performed using the transferred Lamb-Dip technique. We have also measured directly the frequency of seven FIR laser lines by heterodyning with already known laser lines. We present a complete list of all known laser lines (134) and frequency measurements (24) for this molecule.Work supported by CNPq, FAPESP, FAEP-Brasil, and CNR-Italia     

CH<Subscript>3</Subscript>OH optically pumped by a <Superscript>13</Superscript>CO<Subscript>2</Subscript> laser: new laser lines and assignments

We report 12 new THz (far-infrared) laser lines from methanol (CH₃OH), ranging from 58.1 μm (5.2 THz) to 624.6 μm (0.5 THz). A ¹³CO₂ laser of wide tunability (110 MHz) has been used for optical pumping, allowing access to previously unexplored spectral regions. Optoacoustic absorption spectra were used as a guide to search for new THz laser lines, which have been characterized in wavelength, polarization, offset, relative intensity, and optimum operation pressure. For 20 laser lines previously observed, we have measured the absorption offset with respect to the ¹³CO₂ laser line center. PACS 33.20.Ea; 33.20.Vq; 33.80.-b     

Spectroscopy of the excited C-O stretching Q branch of 13CD3OH: Measurement and assignment of new FIR laser lines

The Q branch of the C-O stretching fundamental band of ¹³CD₃OH has been investigated. Starting from a high resolution (4 × 10⁻³cm⁻¹) infrared Fourier transform spectrum and using a waveguide CO₂ laser of 300 MHz tunability and an acoustooptic modulator for an extension of ±90 MHz, 31 new FIR laser lines have been observed. The related absorptions have been measured by means of optoacoustic detection. The frequency of one new FIR laser line was also measured. Eight tentative assignments are proposed for the IR absorption and FIR laser emissions.     

Assignments of methanol laser lines by frequency measurements and Fourier transform spectroscopy

We have measured the frequencies of four CH₃OH far-infrared laser lines that were previously known only by wavelength measurement. Two of these lines turned out to be doublets, bringing the total number of measured lines to six. We can now confirm the assignments of five of them and definitely disprove the assignments proposed for the sixth.In particular we confirm the assignments for the four strong laser lines at 205 and 208 µm pumped by the 9-P(34) CO₂ laser line. These lines share a common upper level in the first excited CO-stretch state, and terminate in the upper and lower levels of a hybrid state with J=5. Heterodyne frequency measurements and conventional microwave spectroscopy show that both lines are split into two components approximately 3.5 MHz apart. The origin of this further splitting is interpreted as a perturbed K-splitting.Work supported by Consiglio Nazionale delle Ricerche -Italia     

Saturated absorption Stark spectroscopy of CH3OH with CO2 lasers

The vibration-torsion-rotation spectrum of CH₃OH has been studied by saturated absorption spectroscopy in applied electric fields up to 20 kV/cm, using ¹²C¹⁶O₂ and ¹²C¹⁶O₂ lasers. Frequency offsets for 129 absorption lines were measured relative to the frequency of a fluorescence stabilized reference laser with an accuracy of ±0.5 MHz for 75 lines inside the ±40 MHz tuning range and 2–5% for lines located up to 1.2 GHz outside the tuning range, but Stark tuned into resonance. For 36 lines we obtained fully-resolved Stark spectra, allowing determination of both lower and upper state K. Using this information in combination with information available from optically-pumped FIR laser emission, a total of 44 lines were completely assigned as transitions involving torsional n = 0, 1, 2 and 3 states of the CO stretch. Certain states belonging to n = 1 displayed an anomalous Stark effect which is at present not understood.     

New far-infrared laser lines from CH3Cl and CH3Br optically pumped with a continuously tunable high pressure CO2 laser

In this paper we report on the detection of new far-infrared laser lines from CH₃Cl and CH₃Br optically pumped with a continuously tunable high pressure CO₂ laser. We found 80 new lines for CH₃Cl and 9 new lines for CH₃Br in the frequency region between 16 cm^–1 and 41 cm^–1, all due to stimulated Raman scattering. For the Raman gain regions bandwidths up to about 700 MHz were found. We also observed high intensity short far-infrared laser pulses of durations in the nanosecond regime.Permanent address: Physics Department, State Pedagogical University, SU-119435 Moscow, USSR     

New far infrared laser lines from 13CH2F2 and frequency measurements

We report new FIR laser lines from ¹³CH₂F₂ molecules optically pumped by a waveguide CO₂ laser. The increased tunability (300 MHz) with respect to a conventional CO₂ laser allows the pumping of ¹³CH₂F₂ vibrational transitions of large offset. 34 new laser lines have been discovered, ranging from 113.1 m to 491.4 m in wavelength, thus increasing the number of known FIR laser lines from this important molecule to 99. For all the new lines and many (36) of those known previously, precise offset measurements through the transferred Lamb-dip technique were performed. The frequency of six new laser lines was also directly measured by heterodyne detection with known laser lines.     

Optically pumped CW fir laser: New submillimeter laser emissions from CH2DOH, CH3I, CD3I, and trioxymethylene

We obtained twelve new far infrared laser transitions by optically pumping the CH₂DOH, CH₃I, CD₃I and Trioxymethylene molecules with a CW CO₂ laser having a tunability range of 280 MHz. We measured the wavelength, polarization, relative intensity and pump offset relative to the CO₂ center frequency for all the new lines.     

Optically pumped submillimeter laser lines from CD2Cl2 using a large tunability CW CO2 laser

Twenty-five new laser lines have been obtained in the wavelength region from 155 to 830 μm by optically pumping the CD₂Cl₂ (deuterated dichloromethane) molecule with a CW CO₂ laser having a tunability range of 300 MHz. The wavelength, polarization relative to that of CO₂ pumping radiation, and offset relative to the CO₂ center frequency were determined for all of the new lines and some other already known laser emissions. For all of them we give also the relative intensity and the optimum pressure of operation. Permanent address: Depto de Física e Química da FEIS — UNESP 15.378-000 Ilha Solteira-SP, Brazil     

Laser spectroscopy of ethylene with waveguide CO2 and N2O lasers

Fifty Doppler-broadened absorption lines of ethylene have been measured within large profiles CO₂ or N₂O lase lines. These laser lines are produced by a high pressure waveguide laser and have a full width between 200 and 900 MHz. Eleven absorption lines, the more intense ones, have been assigned to the ν₇ band of C₂H₄. The other absorption lines must belong to hot bands or to the ν₇ band of H₂¹²C¹³CH₂.     

Pressure broadening by argon in the hyperfine resolved P(10) and P(70) (17,1) transitions of I2 XΣ(0g)→BΠ(0u) using sub-Doppler laser saturation spectroscopy

The dependence of pressure broadening upon hyperfine component in the P(10) and P(70) lines of the (17,1) band of the I₂ X¹Σ(0_g⁺)→B³Π(0_u⁺) has been studied using laser saturation spectroscopy. By limiting absorption to the zero velocity group, Doppler broadening is removed, lineshapes with widths (FWHM) <9 MHz are detectable, and collision-induced broadening is measured at pressures of 0.2-1.2 Torr. The rates for broadening by argon are 8.3±0.3 and 10.7±0.4 MHz/Torr for the P(70) and P(10) lines, respectively. No significant variation in broadening rates is observed for the 15 hyperfine components of these even rotational lines. The effects of velocity cross-relaxation introduce a broad baseline into the spectra, which is strongly dependent on rotational state, pressure, and laser modulation frequency. The observed broadening rates correlate well with prior measurements and the polarizability of the collision partner.     

Optoacoustic laser Stark spectroscopy in the ν2 band of 14NH3

Laser Stark spectroscopy of the R(5, K) transitions in the ν₂ band of ammonia was carried out using coincidences with the 9-μm band CO₂ laser lines. We observed 22 Doppler-free resonances by using an optoacoustic detector and a Lamb-dip stabilized CO₂ laser. A simultaneous analysis of sa, aa, and ss lines yields zero-field transition frequencies with an absolute accuracy of 1 ～ 2 MHz.     

New FIR laser lines from CD3OD optically pumped by a CO2 waveguide laser

In this work we report new FIR laser lines from CD₃OD optically pumped by a CO₂ waveguide laser. The wide tunability of this laser (290 MHz) makes it possible to pump absorption lines with large frequency offset relative to the CO₂ laser line center, which are not possible by using conventional CO₂ lasers. As a consequence 19 new laser lines have been discovered, ranging from 38.0 m to 455.2 m in wavelength. For all lines, precise frequency offset measurements between the CO₂ line center and the center of the absorber CD₃OD line were performed using the transferred Lamb-dip technique. We also present direct Doppler-free offset measurements of infrared absorption, obtained within the FIR laser cavity itself, using optoacoustic detection.Work supported by FAPESP, CNPq, FAP-Brasil and CNR-Italy     

Frequency stabilization of an InGaAsP DFB laser using a molecular absorption line at 1.54308 μm

Molecular absorption lines due to vibrational-rotational transitions in¹⁴NH₃ are observed near 1.5 m. An InGaAsP DFB laser is frequency stabilized to a linear absorption line within 500 MHz at 1543.08 nm. Such an absolute frequency-stabilized DFB laser is useful for coherent optical system applications owing to its long-term frequency stability and for residual gas detectors.     

A new efficient far-infrared optically pumped laser gas: CH3 18OH

The¹²CH₃ ¹⁸OH molecule has been investigated for new far-infrared laser lines by optically pumping it with a cw waveguide CO₂ laser. The larger tunability (318 MHz) with respect to a conventional CO₂ laser permits the pumping of many¹²CH₃ ¹⁸OH lines. As a consequence 100 new laser lines have been discovered, ranging from 34.6 m to 653.2 m in wavelength. The infrared spectrum of¹²CH₃ ¹⁸OH has been observed and all the fundamental vibration energies measured.