Matthias Lenzner

Generic incubation law for laser damage and ablation thresholds

In multi-pulse laser damage and ablation experiments, the laser-induced damage threshold (LIDT) usually changes with the number of pulses in the train, a phenomenon known as incubation. We introduce a general incubation model based on two physical mechanisms—pulse induced change of (i) absorption and (ii) critical energy that must be deposited to cause ablation. The model is applicable to a broad class of materials and we apply it to fit data for dielectrics and metals. It also explains observed changes of the LIDT as a function of the laser repetition rate. We discuss under which conditions the crater-size method to determine LIDTs can be applied in multi-pulse experiments.

Concerning the Spatial Heterodyne Spectrometer.

A modified Spatial Heterodyne Spectrometer (SHS) is used for measuring atomic emission spectra with high resolution. This device is basically a Fourier Transform Spectrometer, but the Fourier transform is taken in the directions perpendicular to the optical propagation and heterodyned around one preset wavelength. In recent descriptions of this device, one specific phenomenon - the tilt of the energy front of wave packets when diffracted from a grating - was neglected. This led to an overestimate of the resolving power of this spectrograph, especially in situations when the coherence length of the radiation under test is in the order of the effective aperture of the device. The limits of usability are shown here together with some measurements of known spectral lines.

Impact of resonant dispersion on the sensitivity of intracavity phase interferometry and laser gyros.

Intracavity phase interferometry is a phase sensing technique using mode-locked lasers in which two intracavity pulses circulate. The beat frequency between the two output frequency combs is proportional to a phase shift to be measured. A laser gyro is a particular implementation of this device. The demonstrated sensitivity of 10-8 of these devices could be manipulated by applying a giant dispersion to each tooth of the comb. It is shown that the resonant dispersion of a Fabry-Perot inserted in the cavity couples to the modes of the frequency comb, resulting in a large change in phase response.

A Sagnac Fourier spectrometer

When a transmission grating is placed in a Sagnac interferometer, two diffracted wavefronts propagate in opposite directions and interfere at the output, forming a Fizeau fringe pattern. This interferogram contains spectral information heterodyned around a center wavelength. By changing the design, high resolving power or broad spectral range can be accomplished.

A Sagnac fourier spectrometer

When a transmission grating is placed in a Sagnac interferometer, two diffracted wavefronts propagate in opposite directions and interfere at the output, forming a Fizeau fringe pattern. This interferogram contains spectral information heterodyned around a center wavelength. By changing the design, high resolving power or broad spectral range can be accomplished.

Exploiting shock wave and self-absorption for high resolution laser induced breakdown spectroscopy

The shock wave created by a high energy UV filament is sufficient create a low pressure absorber enabling higher resolution laser induced breakdown spectroscopy, through reduction or pressure broadening. Isotopic selectivity is demonstrated.

Resolving isotopic emission lines using a spatial heterodyne spectrometer

A modified Spatial Heterodyne Spectrometer (SHS) is used for measuring atomic emission spectra for instance in LIBS experiments. This device is basically a Fourier Transform Spectrometer, but the Fourier transform is taken in the directions perpendicular to the optical propagation and heterodyned around one specific wavelength. Therefore, this device uses no movable parts. The resolution of the device is sufficient to distinguish common isotopic lines.