Localised temperature dynamics of GaAlAs laser facets investigated by Raman microprobe measurements

Raman micro-probe studies of diode laser facet temperatures in CW operation show a significant linear temperature rise below the laser threshold and a rapid nonlinear heating above the threshold. Dynamical measurements using current injection pulses show fast heating of the laser facet with a sub-microsecond risetime and much slower cooling within several micro-seconds.<>     

Quasi-cw laser action in K5Nd(MoO4)4

We report on room temperature quasi-cw laser action in K₅Nd(MoO₄)₄ at a wavelength of 1.067 μm. The crystal was pumped with the 5140 Å line of an argon ion laser. Due to thermal effects actual cw lasing was not possible. Chopping the pump light with a low duty cycle of 1∶1000 leads to quasi-cw laser action and stable output power. We have determined the fundamental laser parameters: threshold pump powerA _T=15 mW, slope efficiency η=22%, and internal lossesL=2.5%. In order to explain the measured relaxation oscillations, diffusion of the excited 4f-excitons is considered. According to a recently developed theory, a diffusion constant ofD=2×10^?6cm²/s explains the observed results.     

High frequency heterodyne spectroscopy with current-modulated diode lasers

The use of current-modulated semiconductor lasers for optical heterodyne spectroscopy has been investigated at modulation frequencies up to 2.6 GHz. The current modulation produces a simultaneous frequency and amplitude modulation of the laser output. A characteristic heterodyne spectrum occurs when the modulated laser probes a narrow absorption line. In order to analyze the measured spectra, a complete line shape theory has been derived for heterodyne spectroscopy with frequency- and amplitude-modulated laser light. The results show how the obtained signals depend on the modulation frequency and the phase difference between the frequency and the amplitude modulation. The measurement technique permits investigation of the FM-AM phase difference of current-modulated semiconductor lasers.     

Blue, green and yellow upconversion lasing in Er:YLiF/sub 4/ using 1.5 mu m pumping

The authors report blue, green and yellow upconversion laser action in Er/sup 3+/:YLiF/sub 4/ following pumping at 1.500 mu m below 80 K. For the blue transition the ratio of the output frequency to the input frequency is 3.3, the highest yet reported for an upconversion laser. In spite of the multiple upconversion steps, the thresholds for laser action were less than 80 mW. It is proposed that the nonlinear upconversion pumping proceeds via a sequence of several pairwise cross-relaxation steps.<>     

Linear concentration quenching of luminescence in rare earth laser materials

Assuming fast spatial energy diffusion among the donor ions, the rate equations are shown to yield the linear concentration dependence of the quenching rate observed in highly concentrated rare earth compounds, such as NdP₅O₁₄. This concentration dependence is not related to the particular form of the interionic interaction responsible for the quenching. We also supply new experimental data confirming the linear behavior in Nd_xRE_1?xP₅O₁₄ (RE = La, Eu, Tb) for 0.01 ? x ?1.     

Frequency modulation (FM) spectroscopy

Frequency modulation (FM) spectroscopy is a new method of optical heterodyne spectroscopy capable of sensitive and rapid measurement of the absorption or dispersion associated with narrow spectral features. The absorption or dispersion is measured by detecting the heterodyne beat signal that occurs when the FM optical spectrum of the probe wave is distorted by the spectral feature of interest. A short historical perspective and survey of the FM spectroscopy work performed to date is presented. Expressions describing the nature of the beat signal are derived. Theoretical lineshapes for a variety of experimental conditions are given. A signal-to-noise analysis is carried out to determine the ultimate sensitivity limits.     

Thin-film aggregate color centers as media for frequency domain optical storage

Thin films of aggregate color centers have been produced by electron and ion irradiation of bulk alkali halide crystals. The transverse spatial distribution of the centers was controlled on a submicron scale using electron lithography. Photochemical hole burning has been accomplished for the first time in a thin film of color centers, using the 6070 Å zero-phononN ₁ line produced by ion and electron irradiation of NaF crystals.     

Determination of formaldehyde release from wood-based panels using SPME-GC-FAIMS

Several standardized methods exist to determine formaldehyde (HCHO) release from wood-based panels (WBPs). These methods were developed decades ago to be used in manufacturers laboratories to provide a mean of production control. They are robust and take several hours to yield results. Modern WBP panel production, however, is a continuous process. Therefore the established methods are too time-consuming for process control and process optimization with respect to HCHO release. Moreover, there is a strong trend of lowering the regulatory HCHO emission limits. Thus, there is a need for a comparatively fast and precise method which is suitable for the use on-site in a WBP manufacturers laboratory. In this work, an optimization of the solid phase micro extraction gas chromatography high field asymmetric waveform ion mobility spectrometry (SPME-GC-FAIMS) method is presented with respect to GC-FAIMS settings and the calibration procedure. It is also shown that, in addition to WBP block samples, also particles can be used for the measurement. The industrial applicability of SPME-GC-FAIMS system was demonstrated by testing the HCHO release of freshly produced WBPs on-site in the manufacturers laboratory.     

Electric dipole transition cross sections and effective site symmetry of Eu3+ in pseudocentric K5Eu(MoO4)4

The fluorescence and absorption spectra of Eu³⁺ in K₅Eu(MoO₄)₄ have been measured at 300 K and 77 K. The fluorescence lifetime of the ⁵D₀ state is 1.4 ms at 300 K. The largest cross section $\text{σ(}{}^5\text{D}{}_0\text{→}{}^7\text{F}{}_2\text{(4)) = 1.3 × 10}{}^{\mathrm{?21}}\text{cm}{}^2$ and the removal of degeneracies require to replace the nearest neighbour D_3d symmetry of Eu³⁺ by the effective symmetries C₁, C₂ and C_s of the whole unit cell. It is shown that C₁ dominates because of the statistical distribution of K⁺ and Eu³⁺. The corresponding inhomogeneous broadening is observed at 77 K.