High-resolution spectrometer using combined dispersive and interferometric wavelength separation for raman and laser-induced breakdown spectroscopy (LIBS).

In this paper the concept of a compact high-resolution spectrometer based on the combination of dispersive and interferometric elements is presented. Dispersive elements are used to spectrally resolve the light in one direction with coarse resolution (Δλ < 0.5 nm), while perpendicular to that direction an etalon provides high spectral resolution (Δλ < 50 pm). This concept for two-dimensional spectroscopy has been implemented for the wavelength range λ = 350-650 nm. Appropriate algorithms for reconstructing spectra from the two-dimensional raw data and for wavelength calibration were established in an analysis software. Potential applications for this new spectrometer are Raman and laser-induced breakdown spectroscopy (LIBS). Resolutions down to 28 pm (routinely 54 pm) could be realized for these applications.

Tunable 6.8 W narrow bandwidth emission from a single-stripe continuous-wave broad-area laser diode in a simple external cavity.

An antireflection-coated broad-area laser diode with an emitter size of 400 microm x 1 microm and a chip length of 1500 microm is operated in a simple external cavity. For wavelength stabilization and to narrow the bandwidth a diffraction grating in a Littrow configuration is used. At an injection current of 9 A up to 6.8 W of optical output power and a resulting slope efficiency of 0.8 W/A could be achieved. Further, the bandwidth could be narrowed to 100 pm (FWHM), and a tuning range of 40 nm around 976 nm was obtained.

Tunable diffraction-limited light at 488 nm by single-pass frequency doubling of a broad area diode laser.

A laser system that is based on second-harmonic generation of a broad area laser diode and provides 23.2 mW of diffraction-limited light with narrow bandwidth is described. It is tunable from 487.4 to 489 nm. The broad area laser diode is frequency stabilized in an external cavity that yields 800 mW of diffraction-limited light. This infrared light is converted into the visible by use of a 1 cm periodically poled MgO:LiNbO(3) bulk crystal with a measured single-pass conversion efficiency of up to 3.6%/W x cm.

High cw power using an external cavity for spectral beam combining of diode laser-bar emission.

In extension to known concepts of wavelength-multiplexing diode laser arrays, a new external cavity is presented. The setup simultaneously improves the beam quality of each single emitter of a standard 25 emitter broad-area stripe laser bar and spectrally superimposes the 25 beams into one. By using this external resonator in an "off-axis" arrangement, beam qualities of Mslow2<14 and Mfast2<3 with optical powers in excess of 10 W in cw operation are obtained.

1,8-Bis(hexamethyltriaminophosphazenyl)naphthalene, HMPN: a superbasic bisphosphazene "proton sponge".

It is shown that a combination of Schwesinger's phosphazene base concept and the idea of the disubstituted 1,8-naphthalene spacer, first introduced by Alder in paradigmatic 1,8-bis(dimethylamino)naphthalene (DMAN), yields a new superbase, HMPN, which represents the up to date most basic representative of this class of "proton sponges", as evidenced by the theoretically estimated proton affinity PA = 274 kcal/mol and the measured pK(BH+) (MeCN) 29.9 +/- 0.2. HMPN is by nearly 12 orders of magnitude more basic than Alder's classical 1,8-bis(dimethylamino)naphthalene (DMAN). The title compound, HMPN, is prepared and fully characterized. The spatial structure of HMPN and its conjugate acid is determined by X-ray technique and theoretical DFT calculations. It is found that monoprotonated HMPN has an unsymmetrical intramolecular hydrogen bridge (IHB). This cooperative proton chelating effect renders the bisphosphazene more basic than Schwesinger's set of "monodentate" P1 phosphazene bases. The density functional calculations are in good accordance with the experimental results, providing some complementary information. They conclusively show that the high basicity of HMPN is a consequence of the high energy content of the base in its initial neutral state and the intramolecular hydrogen bonding in the resulting conjugate acid with contributions to proton affinity of 14.1 and 9.5 kcal/mol, respectively.

1,8-bis(dimethylethyleneguanidino)naphthalene: tailoring the basicity of bisguanidine "proton sponges" by experiment and theory.

1,8-bis(dimethylethyleneguanidino)naphthalene (DMEGN), the second example of a peralkyl guanidine "proton sponge" based on the 1,8-naphthalene backbone, was prepared and fully characterized. The crystal structure analysis of monoprotonated DMEGN reveals an unsymmetrical intramolecular hydrogen bridge. A decrease in the basicity with respect to the noncyclic parent 1,8-bis(tetramethylguanidino)naphthalene was found. Nevertheless, a new proton sponge provides a new crossbar in the ladder of highly basic neutral organic compounds. A detailed theoretical study of DMEGN and related cyclic guanidines explains this surprising experimental result. Homodesmotic reactions reveal that the intramolecular hydrogen bond contributes effectively 10 kcal/mol to proton affinity of DMEGN.

1,8-bis(tetramethylguanidino)naphthalene (TMGN): a new, superbasic and kinetically active "proton sponge".

1,8-Bis(tetramethylguanidino)naphthalene (TMGN, 1) is a new, readily accessible, and stable "proton sponge" with an experimental pK(BH(+)) value of 25.1 in MeCN, which is nearly seven orders of magnitude higher in basicity than the classical proton sponge 1,8-bis(dimethylamino)-naphthalene (DMAN). Because of the sterically less crowded character of the proton-accepting sp(2)-nitrogen atoms, TMGN also has a higher kinetic basicity than DMAN, which is shown by time-resolved proton self-exchange reactions. TMGN is more resistant to hydrolysis and is a weaker nucleophile towards the alkylating agent EtI in comparison to the commercially available guanidine 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD). Crystal structures of the free base, of the mono- and bisprotonated base were determined. The dynamic behavior of all three species in solution was investigated by variable-temperature (1)H NMR experiments. DeltaG (++) values obtained by spectra simulation reveal a concerted mechanism of rotation about the C-N bonds of the protonated forms of TMGN.

External resonator design for high-power laser diodes that yields 400mW of TEM(00) power.

Normal diode lasers with average output powers of 1 W or more exhibit bad beam quality and therefore cannot be applied for high-precision applications or nonlinear optics. Therefore an external output coupling mirror was used in our experiments. Diffraction-limited operation was achieved, which yielded 400 mW of power and a factor-of-12 improvement in brightness. With this resonator type 1.1 W of average output power was also obtained, with a beam propagation factor of 2.6 in the slow axis; fast axis emission is always diffraction limited.

Tuning high-power laser diodes with as much as 0.38 W of power and M(2) = 1.2 over a range of 32 nm with 3-GHz bandwidth.

Gain-guided diode lasers usually have emission wavelengths determined by the manufacturing process, with typically 0.5-1-nm bandwidth. Furthermore, their beam quality is rather poor. We show that external cavities allow for tunable narrow-bandwidth operation of gain-guided diode lasers. At the same time the beam quality is drastically improved; almost diffraction-limited light of more than 200 mW has been achieved over the whole tuning range from 910 to 942 nm with narrow bandwidth.