Lock-in stabilised externak cavity cw spin-flip Raman laser

A lock-in stabilised cw external-cavity spin-flip Raman laser has been operated in which a cavity mode resonant frequency is servo-controlled to the peak of the spontaneous gain as the magnetic field is swept. The design of the optical system eliminated additional undesired cavity interactions.     

Improved signal processing in pulsed and cw spin-flip Raman laser spectrometers

Double beam optical techniques which allow direct spectroscopic measurements using both pulsed and cw tunable spin-flip Raman lasers have been developed. The systems provide a high resolution spectrometer (spectral linewidths 0.03 cm^-1 pulsed and 0.003 cm^-1 cw) in the range 5.3–6μm. Line frequency measurements are accurate to 0.01 cm^-1 and intensity measurements to a few percent. Results of molecular spectroscopy provide a comparison of the relative performance of each system.     

Efficient cw sodium dimer Raman laser operation in a high-temperature sapphire cell

cw Raman lasing of Na₂ molecules generated in a heated, sealed-off, all-sapphire cell is demonstrated. Being not damaged by highly corrosive alkaline vapours, this type of cell enables operation without buffer gas in contrast to the normal heatpipe operation of these lasers. This allows us to study Raman lasers in alkaline vapours in new regimes and under ideal conditions. With an argon ion pump laser at 488 nm, Raman laser operation at 525 nm with more than 10% efficiency and thresholds below 0.2 mW for a cell without buffer gas (length 9 cm) have been obtained so far. The low thresholds, being a factor of 10 less than for comparable heatpipe operation, gives us the chance to use low-power diode lasers as pump sources and to realize compact reliable Raman laser systems. Received: 17 May 1999 / Published online: 25 August 1999     

Linearised tuning of a cw spin-flip Raman laser using anti-reflection coated cavities

By reducing the electron concentration of the InSb cavity and anti-reflection coating its ends, the frequency tuning of a cw spin-flip Raman laser has been linearised to ?99% of the spontaneous tuning rate, and the magnitude of mode jumps decreased to ? 30 MHz (0.001 cm^-1).     

Structure in the Stokes output of the InSb spin-flip Raman laser

Stokes output and threshold pump intensity of the InSb spin-flip Raman laser have been measured as a function of magnetic for various pump wavelenghts and crystal orientations. The observed structure is shown to arise from intraband absorptions of the pump and Stokes radiation and not from electron spin-phonon interactions.     

Characteristics of a hybridly mode-locked cw dye laser

We present experimental and theoretical results on the characteristics and random variations of subpicosecond pulses generated by a synchronously pumped cw dye laser with saturable absorber. The analysis of the power spectra indicates rapid fluctuations of the pulse duration of 40–50%, energy fluctuations of 3%, and a jitter of the repetition time of 0.1% corresponding to an absolute jitter of 12 ps. The latter is caused mainly by the temporal jitter of the pump laser. A mismatch of the lengths of the dye and the pump-laser cavity can result in a nonstationary mode-locking regime with a periodic change of the pulse parameters. The interpretation of the experimental results are supported by computer simulations of the pulse evolution process.     

Astigmatically compensated cw dye laser resonators using lenses

The compensation of the astigmatism of Brewster-angled dye cells can be performed with lenses as well as with spherical mirrors. The advantages of cw dye laser resonators using lenses lie in the linear configuration of the optics and the convenient adjustability of astigmatism compensation. An output efficiency of 30% already at 1.6W pumping power has been observed. In addition, ring laser resonators with lenses have been investigated and they delivered up to 400 mW single mode power in travelling wave operation at less than 2 W pumping power.     

The He/Cl2 laser at 258 nm

Lasing from e-beam pumped He/Cl₂ mixtures at 258 nm was investigated in a longitudinal pumping geometry. Time dependence, output powers and energies as well as the spectral composition of the laser pulses were determined for different experimental conditions. Optical gain was observed for eight transitions around 258 nm. The fine structure results from isotopic splitting and contributions from different vibrational states. No bottle-necking occurs. However, saturation and absorption by excited states limited the total output power to 6MW and the output energies to 200 mJ. A simple kinetic model is proposed that reproduces the larger number of experimental data quite sufficiently.     

On noise and fluctuations in a synchronously mode-locked cw laser system

A single-shot and synchronously-scanned streak camera, autocorrelation and noise spectrum analysing techniques are utilized to study the output characteristics of synchronously mode-locked cw lasers. Four main conclusions are drawn: (i) the pulse train from a synchronously-pumped dye laser reveals, besides phase jitter, considerable pulse shape fluctuations; (ii) autocorrelation measurements may be highly misleading when actual pulse shapes are considered; (iii) both the phase jitter and pulse shape fluctuations of the dye laser output are caused by the phase fluctuations of the pumping ion laser pulse train; (iv) the phase jitter of the ion laser proceeds from the fluctuations in the cavity roundtrip time with a characteristic time of about 5 s. Under optimum conditions the rms noise of the dye laser output was 2% and the phase jitter with respect to the rf sine drive of the acousto-optical mode-locker, 30 ps. A qualitative explanation fo the noise properties is given.     

Tunable UV-radiation by stimulated Raman scattering in hydrogen

We observed tunable UV radiation down to 175 nm by SRS of the output of a frequency-doubled dye laser in H₂. The high power output of the 4th anti-Stokes to 5th Stokes line generated by the frequency doubled dye laser and the 8th anti-Stokes to 3rd Stokes line generated by the undoubled dye laser represents a broadly tunable coherent radiation source between 189 nm and 2064 nm.     

New FIR laser lines from optically pumped methanol analogues

Several new laser lines using optically pumped deuterated methanol molecules have been discovered. These not only increase the spectral coverage of pumped methanol isotopes but may assist in the assignment of a molecular structure.     

Measurement and assignment of new FIR laser lines in12CH3OH and13CH3OH

We have found twelve new FIR laser lines in¹²CH₃OH and thirty three in¹³CH₃OH. Both molecules were pumped by a regular cw CO₂ laser. We have also assigned 20¹³CH₃OH laser lines to specific rotational energy levels in the excited C-O stretchhindered rotation combined states     

Photophysical properties and laser performance of photostable UV laser dyes

The photophysical properties such as singlet absorption and fluorescence spectra, the fluorescence quantum yield and fluorescence decay time as well as the laser performance data such as the tuning range, the conversion efficiency, and the photochemical stability of 12 sterically hinderedp-quaterphenyls have been measured in ethanol and/or dioxane at room temperature. The sterically hinderedp-quaterphenyls exhibit shorter laser dye emissions in the 330–380 nm range than the parent compoundp-quaterphenyl. The conversion efficiencies of the sterically hinderedp-quaterphenyls range between 1 and 21%. The photochemical stability of the sterically hinderedp-quaterphenyls is by a factor of 10 to 20 better in dioxane than in ethanol. 2-Methyl-5-tert. butyl-p-quaterphenyl and 2,5,2,5-tetramethyl-p-quaterphenyl are among the most stable UV laser dyes known today.     

Resonant pumping far-infrared NH3 laser

A far-infrared (FIR) NH₃ laser was resonantly pumped with a line-tunable infrared (IR) NH₃ laser. The number of the observed FIR laser lines amounted to 33. Most of them belonged toaR(J,K) rotation-inversion transition in (0, 1, 0, 0) vibrational state. The line tunability of sealed-off FIR NH₃ laser was almost achieved in 90, 115, 150, and 220 m wavelength regions by the selective line tuning of the pumping IR NH₃ laser.     

Sub-nanosecond microchip laser with intracavity Raman conversion

Efficient sub-nanosecond pulse operation of microchip lasers with intracavity Raman conversion and pulse compression is presented for the first time. The microchip lasers were composed of Nd:LSB or Nd:YAG laser crystals, Cr⁴⁺:YAG saturable absorber, and Ba(NO₃)₂ Raman medium. The pulse duration obtained at the Stokes wavelength (1196 nm) was as short as 118 ps. Optical conversion efficiency of laser-diode pump power to the Stokes power of 8% was reached. Pulse energy and peak power of Stokes emission were 1.2 μJ and 5.4 kW, correspondingly. Numerical calculations are in good agreement with obtained experimental results. Received: 20 December 2002 / Revised version: 6 March 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-716/645-6945, E-mail: ankuzmin@acsu.buffalo.edu RID="**" ID="**"Present address: University at Buffalo, SUNY, The Institute for Lasers, Photonics, and Biophotonics, 458 NSC, Buffalo, NY 14 260-3000, USA     

Investigation of 13CH3OH methanol: new laser lines and assignments

We have reinvestigated ¹³CH₃OH as a source of far-infrared (FIR) laser emission using a CO₂ laser as a pumping source. Thirty new FIR laser lines in the range 36.5 μm to 202.6 μm were observed and characterized. Five of them have wavelengths between 36.5 and 75 μm and have sufficient intensity to be used in LMR spectroscopy. Using Fourier-transform spectroscopic data in the infrared (IR) and FIR regions we have determined the assignment for 10 FIR laser transitions and predict nine frequencies for laser lines which have yet to be observed. Received: 17 July 2000 / Published online: 6 December 2000     

Spectral investigation of cw rf-pumped atomic Xe laser with a slab geometry

A radiofrequency excited atomic Xe slab laser with an active volume of 2 × 10 × 300 mm³ using a quartz envelope containing the laser-gas mixture shows a stable cw performance with an output power of almost 1 W. The free-running system oscillates, depending on gas composition and density, on several lines between 1.73 and 3.51 m. Line competition phenomena are observed. Single-line oscillation yields more than 500 mW.     

Further investigations on ir pumping of CH3OD and CD3OD by a cw CO2 laser

Respectively, 41 and 36 new cw far-infrared lasing lines have been observed using a waveguide resonator in CH₃OD and CD₃OD pumped by a low-pressure CO₂ laser emitting in the 9.4, 10.4 m regular bands and in the 10.8 m hot band. The wavelength range was 46.6 m–1.67 mm in CH₃OD and 53.6 m–1 mm in CD₃OD.     

Study of simultaneous oscillation on several transitions in cw CO laser

Received: 13 September 1995/Revised version: 5 August 1996     

Polarization-resolved analysis of the characteristics of a Raman laser made with a polarization maintaining fiber

We derive a simple model describing steady characteristics of Raman fiber lasers made with polarization maintaining fibers. We show both theoretically and experimentally that this kind of laser simply consists of two independent Raman lasers linearly polarized along the fiber birefringence axes. The output power characteristics of the laser are shown not to be influenced by optical Kerr effect. Finally, we use our model to propose answers to questions recently raised about efficiency of Raman lasers made with polarization maintaining fibers.