Optically pumped 13CD3OH: far infrared laserlines and assignment

Fourier transform and IR optoacoustic absorption data of ¹³ CD₃OH were used to search for new FIR laser lines. We have used a waveguide CO₂ laser of 300 MHz tunability as the optical pumping source. We report the observation and characterization of 13 new lines. Three of these lines are associated with absorbing transitions appertaining to the weak ¹³CD₃ asymmetric bending mode     

Spectroscopic Properties and Laser Performance of Er3+ and Yb3+ Co-Doped GdAl3(BO3)4 Crystal

An Er:Yb:GdAl₃(BO₃)₄ crystal was grown and room-temperature polarized absorption, emission, and gain spectra were investigated. Fluorescence decay curves of Er³⁺ at 1530 nm and Yb³⁺ at 1040 nm in the crystal were measured. Efficient laser operation of Er:Yb:GdAl₃(BO₃)₄ crystal at 1.5-1.6 mum was realized. Quasi-continuous-wave output powers of 1.8 W with slope efficiency of 19% and 0.78 W with slope efficiency of 14% were achieved in diode-pumped c-cut and c-cut and a-cut crystals, respectively. The output spectrum and polarization of Er:Yb:GdAl₃(BO₃)₄ laser were also investigated.     

New FIR laser lines from fully deuterated dichloromethane:completion of perpendicular/parallel emission pairs

We report 16 new far-infrared (FIR) laser emissions of CD₂ Cl₂. These lines are obtained by optically pumping the active molecule by means of a large-tunability waveguide CO₂ laser. Our tunability of 290 MHz around each CO₂ laser emission allows for the excitation of large-offset absorption transitions of CD₂Cl₂, not reachable by conventional CO₂ Lasers. While the overwhelming majority of the known FIR laser emissions of CD₂Cl₂ are polarized parallel to the polarization of the pump CO₂ line, 13 of the 16 new lines reported in this paper are polarized perpendicularly to the corresponding CO₂ pump line. The presence of both perpendicular and parallel lines is extremely important for the assignment of laser transitions     

13CD3OD optically pumped by a waveguide CO2 laser: new FIR laser lines

A waveguide CO₂ laser of wide tunability was used to pump infrared transitions of the ¹³CD₃OD C-O stretching vibrational mode. The optoacoustic signal associated with the absorbing transitions served as a guide to search for new laser lines. We could observe 36 new far-infrared laser lines ranging from 57 to 1192 μm. All lines were characterized in wavelength, relative polarization, intensity, optimum pressure of operation, and precise offset measurements     

Analysis of CH3OH far infrared laser lines optically pumped by sequence band and isotopic CO2lasers

Assignments are presented for seven far infrared (FIR) laser lines of CH3OH pumped by theS-9P(31),18-10R(24),13-9R(26), and13-9P(16)CO2laser lines, plus an interesting speculation for the FIR line pumped by the18-9P(12)CO2line. Frequencies have been deduced to a substantially improved accuracy of ±0.001 cm^-1from IR and FIR spectroscopic combination differences for most of the assigned lines as well as three other predicted transitions. In addition, accurate frequencies are given for 13 predicted FIR laser transitions which are expected from the IR spectrum to be pumped by three¹⁶O¹²C¹⁸O laser lines.     

High-Power Laser Performance of Yb:YAl3(BO3)4 Crystals Cut Along the Crystallographic Axes

High-power continuous-wave laser operation near 1 mum was demonstrated at room temperature with c-cut and a-cut Yb:YAl₃(BO₃)₄ crystals end-pumped by a fiber-coupled diode laser. Using a 2-mm-thick c-cut crystal, 10.6 W of output power was generated with an optical-to-optical efficiency of 65% and a slope efficiency of 72%. The complex polarization state of the generated laser radiation was also studied. With a 2-mm-thick a-cut crystal, sigma-polarized laser oscillation was obtained, producing a maximum output power of 8.1 W; the optical-to-optical and slope efficiencies were 56% and 61%, respectively. Complete absorption and emission cross section spectra of the Yb:YAl₃(BO₃) ₄ crystal were also derived, revealing very strong anisotropy of the spectroscopic properties     

The 13CH3OH optically pumped far-infraredlaser: new lines and frequency measurements

We report 18 new laser lines from ¹³CH₃OH generated in an optically pumped far-infrared laser; the laser lines are in the range of 54.2-420 μm and are all characterized in wavelength, polarization relative to the pumping CO₂ radiation, and pump offset relative to the CO₂ center frequency. The frequencies of seven of these new lines along with 10 previously reported lines were measured by an accurate heterodyne technique, mixing them in a metal-insulator-metal (MIM) point contact diode, with another laser line of known frequency     

New short-wavelength laser emissions from optically pumped 13CD3OD

We report the discovery of 15 new laser emissions from ¹³ CD₃OD when optically pumped with a CW CO₂ laser. The wavelengths of these lines, ranging from 57.5 to 135.2 μm, are reported along with their polarization relative to the CO₂ pump laser, operating pressure and relative intensity. A three-laser heterodyne system was then used to measure the frequencies of 12 optically pumped laser emissions from this methanol isotope. These emissions range from 65.7 to 151.8 μm and are reported with fractional uncertainties up to 2·10^-7     

Frequency stabilization of laser diodes using 1.51-1.55 μmabsorption lines of 12C2H2 and 13C2

Frequency stabilization of a 1.55 μm DFB laser diode is demonstrated using vibrational-rotational absorption of ¹²C ₂H₂ and ¹³C₂H₂ molecules (named VRAM). Frequency stability within 2 MHz peak to peak fluctuation can be achieved in the wavelength region of 1.51-1.55 μm. Frequency-stabilized DFB laser compact modules have been constructed. Frequency stabilities are evaluated by measuring the beat spectrum of the two lasers. In addition, the temperature and pressure dependences of the acetylene absorption lines are characterized     

Small-frequency-difference stabilization of laser diodes using12C2H2 and 13C2H2 absorption lines for transmitter and local oscillator ofoptical heterodyne systems

Small-frequency-difference stabilization of distributed Bragg reflector (DBR) laser diodes has been demonstrated for the first time by using vibrational-rotational absorption of ¹²C₂H ₂ and ¹³C₂H₂ molecules. Frequency stabilization of two DBR laser diodes has been carried out at a wavelength of about 1.536 μm. The frequency difference between the two stabilized lasers was evaluated to be 9 GHz by the beat spectrum measurement. The experimental results suggest that such a pair of frequency-stabilized laser diodes with a small frequency difference could be used as the transmitter and local oscillator of optical heterodyne systems     

Characterization of new FIR laser lines from CHD/sub 2/OH

In this work, we report new optically pumped far-infrared (FIR) laser lines from CHD/sub 2/OH. A waveguide CO/sub 2/ laser of wide tunability (290 MHz) was used as pump source, and a Fabry-Pe/spl acute/rot open cavity was used as a FIR laser resonator. Optoacoustic absorption spectra were used as a guide to search for new FIR laser lines. We could observe 15 new laser lines in the range from 116.4 to 401.4 /spl mu/m. The lines were characterized according to wavelength, relative polarization, relative intensity, and optimum working pressure. The transferred Lamb-dip technique was used to measure the frequency absorption transition both for the new and previously reported laser lines.     

Study on spectral characteristics and operating parameters ofoptically pumped NH3 FIR cavity laser

By solving the density matrix equations of a quantum system and taking into account the multibeam interference characteristics of a Fabry-Perot cavity, the output power density of an optically pumped NH ₃ far-infrared (FIR) cavity laser was calculated by means of the iteration method. Based on the calculations, the spectral characteristics and operating parameters of the laser were studied. Experimentally, by using inductive metallic meshes as reflectors and couplers, a series of FIR cavity lasers with a sample tube of 10, 20, and 100 cm in length were designed and constructed, and the emissions of the NH₃ cavity lasers pumped by a TEA-CO₂ laser with a 10R(8) or 9R(16) line were measured. The experimental results were in good agreement with theoretical calculations     

Theoretical and experimental investigations of a diode-pumpedquasi-three-level laser: the Yb3+-doped Ca4GdO(BO3)3 (Yb:GdCOB) laser

We present a theoretical and experimental analysis of a diode-pumped Yb³⁺-doped Ca₄GdO(BO₃)₃ (Yb:GdCOB) laser. A new model for a diode-pumped quasi-three-level laser is described. The effects of absorption saturation, temperature profile, and the beam quality M² factor of the pump diode have been taken into account, for the first time to our knowledge. We have obtained a good agreement between experimental measurements and theoretical calculations with two different pump wavelengths, 902 and 976 nm. Our model has given good predictions of the laser performances for different crystal temperatures and different M² factors of the pump beam. As much as 440 mW of output power (at 1082 nm) have been achieved for 640 mW of absorbed pump power at 976 nm, corresponding to one of the highest slope efficiencies (81%) ever obtained with Yb-doped lasers     

Narrow bandwidth emission from a mirrorless, far infrared, 13CH3F laser

Frequency tuning and linewidth measurements are reported for a pulsed, mirrorless, kilowatt-power-level, far-infrared (FIR) ¹³ CH₃F laser operating at 245 GHz. The pump laser is an etalon tunable, single-mode CO₂ TEA laser. The FIR frequency spectrum was measured with 2.5-MHz resolution on individual 100-ns laser output pulses using harmonic mixing techniques. The linewidth of the amplified spontaneous emission was found to be surprisingly narrow, about 15 MHz. Frequency tuning of the FIR laser, as the pump laser frequency is tuned, is nonlinear, possibly due to inhomogeneous broadening of the gain by the K-level substructure of the rotational states. These results indicate that heterodyne receivers capable of single-shot frequency measurements can be important tools for investigating the properties of Raman FIR lasers     

Evaluation of absorption and emission properties of Yb3+doped crystals for laser applications

The emission and absorption properties of numerous host crystals doped with Yb³⁺ ions have been studied. The hosts which have been selected include LiYF₄, LaF₃, SrF₂, BaF₂, KCaF₃, KY₃F₁₀, Rb₂NaYF₆, BaY₂ F₈, Y₂SiO₅, Y₃Al₅ O₁₂, YAlO₃, LuPO₄, Ca₅(PO₄)₃F, LiYO₂, and ScBO ₃. Spectral determinations have been made of the resonant absorption and emission cross sections between 850 and 1100 nm, and the emission decay times of the upper laser level have been measured. The emission cross sections have been evaluated using the absorption cross section and principle of reciprocity, and again using the Fuchtbauer-Ladenberg formula. Agreement between the two methods is within 20% for most materials. The results are discussed in the framework of requirements for an effective diode-pumped Yb³⁺ laser system. Ca₅(PO₄)₃F:Yb is predicted to exhibit the most useful laser properties and is expected to be far superior to Y₃Al₅O₁₂:Yb in many key microscopic parameter values     

Raman Scattering and Nd3+ Laser Operation in NaLa(WO 4)2

The continuous-wave laser operation of Nd-doped tetragonal NaLa(WO ₄)₂ crystal is studied at room temperature by optical pumping in the spectral region overlapping AlGaAs diode laser emission. This crystal has inhomogeneously broadened optical bands. From the room-temperature spectroscopic parameters determined it is found that the optimum Nd concentration for the ⁴F_3/2rarr⁴I_J laser channels must be in the 3-5 at.% range. For J=11/2 and 13/2 channels (lambdaap1.06 and 1.3 mum) the most favourable polarization configuration is parallel to the crystallographic c axis, while for J=9/2 little polarization dependence of the laser efficiency is predicted. Laser operation was achieved with a 3.35 at.% Nd-doped sample grown by the Czochralski method. The laser operation was tested in an hemispherical optical cavity pumped by a Ti:sapphire laser. Stimulated emission at lambda=1056 nm was achieved for a wide spectral pumping range, lambda=790-820 nm. Stimulated Raman scattering was achieved in the picosecond regime with an efficiency similar to that of monoclinic KY(WO₄)₂ reference compound     

Observation and assignment of D218O FIR laserlines optically pumped by a waveguide CO2 laser

By means of a detailed analysis of the v₂ infrared band of D₂¹⁸O, it has been possible to assign most of the FIR emissions reported in the literature. Moreover, two FIR laser lines which fall in the range of tunability of the CW waveguide CO₂ laser have been predicted and observed. The frequency of the stronger line was measured and found to be 2611.4185(10) GHz, thus filling a gap in the presently available comb of FIR laser lines whose frequencies have been measured. The wavelength precision of the assigned lines was improved by about two orders of magnitude     

Narrow-band CO2-TEA laser for efficient FIR laser pumping

To reduce the linewidth mismatch between the emission lines of a CO2-TEA laser and the absorption lines of a low-pressure FIR gain medium a tiltable Ge etalon has been introduced into the TEA resonator. The resulting spectral compression and tunability increase the energy conversion efficiency in a TEA laser pumped CH3OH laser by as much as a factor of 37 and has led to the observation of 14 new FIR laser lines.     

Observation and characterization of new FIR laser lines from formicacid

We report the observation and characterization of seven new far-infrared (FIR) laser lines from H¹²COOH and H¹³COOH in the range 232.2 to 746.6 μm optically pumped by a wide-tunability waveguide CO₂ laser. Their absorption frequency is outside of the tuning range of a conventional CO₂ pump laser     

Far infrared laser frequencies of 13CD3OH

We have measured 30 far-infrared laser frequencies of optically pumped ¹³CD₃OH, 13 of which are new lines. The frequencies range from 0.5 to 4.9 THz with the majority between 0.75 and 1.5 THz. Two frequency stabilized CO₂ lasers were used as standards for the heterodyne measurements