H. M. von Bergmann

A compact streak camera for 150 fs time resolved measurement of bright pulses in ultrafast electron diffraction

We have developed a compact streak camera suitable for measuring the duration of highly charged subrelativistic femtosecond electron bunches with an energy bandwidth in the order of 0.1%, as frequently used in ultrafast electron diffraction (UED) experiments for the investigation of ultrafast structural dynamics. The device operates in accumulation mode with 50 fs shot-to-shot timing jitter, and at a 30 keV electron energy, the full width at half maximum temporal resolution is 150 fs. Measured durations of pulses from our UED gun agree well with the predictions from the detailed charged particle trajectory simulations.

Ionization and shielding of interface states in native p+-Si/SiO2 probed by electric field induced second harmonic generation

Electric field induced second harmonic measurements applying femtosecond laser pulses (1.59 eV, 80±5 fs, 80 MHz) to substantially boron doped p+-Si/SiO2 interfaces reveal a temporal evolution of the second harmonic (SH) signal, which differs drastically from that of weakly doped samples. A significant initial SH signal is observed in native p+-Si/SiO2 interfaces for boron doping concentrations >7.5×1017 cm−3. This SH signal is attributed to a built-in interfacial electric field E0 generated by the doping induced accumulation of charges at the Si/SiO2 interface following the ionization of interface defect states. A sign reversal is observed in the azimuthal SH anisotropy pattern of the initial SH signal relative to that of the saturated SH signal in p+-Si/SiO2 indicating that the doping related and electron induced interfacial field components oppose each other. Furthermore, the intensity dependence of the initial SH signal in p+-Si/SiO2 is found to be nonquadratic and, in particular, shows a nonmonotonic ...

High average power 1314 nm Nd:YLF laser, passively Q-switched with V:YAG

A 1314 nm Nd:YLF laser was designed and operated both CW and passively Q-switched. Maximum CW output of 10.4 W resulted from 45.2 W of incident pump power. Passive Q-switching was obtained by inserting a V:YAG saturable absorber in the cavity. The oscillator delivered a maximum of 825 μJ energy per pulse, with a pulse duration of 135 ns at a pulse repetition frequency of 6.3 kHz, effectively delivering 5.2 W of average power.

Traveling‐wave corona excitation of high‐power uv nitrogen lasers operating at gas pressures ranging from 0 to 3 bar

The authors use a novel 60‐cm traveling‐wave pulsing system to investigate the properties of corona‐excited uv nitrogen lasers operating at pressures ranging from 0 to 3 bar. The device will provide subnanosecond pulses at megawatt power levels. The lasing output at 337 nm can be enhanced by the addition of sulphur hexafluoride at total pressures of ≲1.5 bar.

Optical second-harmonic imaging of PbxCd1−xTe ternary alloys

We employ femtosecond laser pulses (80 fs, 1.59 eV, and 80 MHz) to study the optical second-harmonic (SH) response of PbxCd1−xTe ternary alloys (x about 0.2) grown by the vertical Bridgman method. The alloy segregates into a Pb-rich and a Cd-rich phase, the latter dominating the SH response of the ternary alloy by at least two orders of magnitude. Several sample regions show a regular layer-by-layer accommodation of the Pb-rich and Cd-rich phases as seen by a periodic alternation of the alloy’s SH response on a ∼10‐μm length scale. Furthermore, we employ polarization-resolved SH imaging as well as SH imaging at different azimuthal angles to obtain spatially resolved mappings of the sample, which are sensitive to the composition as well as the growth orientation of the PbxCd1−xTe material system. We observe an azimuthal phase shift of approximately 30° between coherent macroscopic regions (several mm2) in the Cd-rich phase of the ternary alloy. We interpret these regions as large area crystalline grains of...

High average power Q-switched 1314 nm two-crystal Nd:YLF laser

A 1314 nm two-crystal Nd:YLF laser was designed and operated in both CW and actively Q-switched modes. Maximum CW output of 26.5 W resulted from 125 W of combined incident pump power. Active Q-switching was obtained by inserting a Brewster-cut acousto optic modulator. This setup delivered an average power of 18.6 W, with a maximum of 5.6 mJ energy per pulse with a pulse duration of 36 ns at a pulse repetition frequency of 500 Hz.

Comparative study of thermal lensing in low-doped Nd:YVO 4 and Nd:GdVO 4 of equal doping concentration

Nd:GdVO4 is a relatively new laser material with spectral properties very similar to those of Nd:YVO4. It was initially reported that it had almost twice the thermal conductivity of Nd:YVO4, and therefore was said to reduce negative thermal effects. Sato and Taira [1] recently re-measured the thermal conductivity and its temperature dependency and found that it was significantly lower than that of Nd:YVO4. They also reported that dn/dT in the higher gain π-polarisation of Nd:YVO4 is 7.92 at 1064 nm, compared to 10.1 for Nd:GdVO4. One would therefore expect that Nd:YVO4 would have weaker thermal lensing, since it is influenced by both the thermal conductivity and dn/dT. To our knowledge, a direct comparison of the thermal lens of the two materials has never been performed with equal doping concentrations and dimensions. Therefore, we aimed to compare the two materials directly under diode-end-pumping by performing thermal lens measurements during lasing with a HeNe probe beam using identical low-doped (0.15%), 4×4×18 mm3 crystals. Our setup was such that we could separately analyse the dioptric powers in the σ and π polarisations.

High-power end-pumped Nd:YLF laser without lifetime quenching

In this paper, we demonstrate the power scaling of an end-pumped Nd:YLF laser to compensate for the astigmatic thermal lens and Q-switched laser performance without any sign of lifetime quenching is presented.

The effect of normalization for depth profiling LIPS experiment

Laser‐induced Plasma spectroscopy (LIPS) is a useful method for determining the elemental composition of various materials but for long time it have been mainly restricted to qualitative and quantitative determination of samples. Recently LIPS is applied to depth‐profile analysis. The lines used in depth profiling are always chosen with great care. The lines chosen should be of nearly of the same height and in the same spectral window. These conditions should be in addition to the general conditions for the lines used in the LIPS as being isolated, non resonant and symmetric lines. All these conditions made it very hard to select a suitable line for depth profiling. In this paper we are trying to investigate the differences that may occur on changing the spectral lines obtained from Ti thin film deposited on a Si (100) substrate and to see the effect of normalization on the depth profiling experiment. It was found that after making normalization, the values of the Average Ablation Rate per pulse and the d...

The effect of spectral lines choice for depth profiling LIPS experiment

Laser‐induced Plasma spectroscopy (LIPS) is a useful method for determining the elemental composition of various materials but for long time it have been mainly restricted to qualitative and quantitative analysis of samples material. Recently LIPS is applied in addition to depth‐profile analysis. In this paper we were trying to investigate the differences in the depth profile, obtained adopting femtosecond LIPS, that may occur on changing the spectral lines chosen for the analysis. The used femtosecond laser has pulse duration of 130 fs, wave length of 795 nm and pulse energy 200 μJ. It was found that the differences observed were not significant as long as the spectral lines chosen are fulfilling the LIPS spectral lines conditions.