Nd doped crystals for medical laser applications

A simple formula is derived that gives the ratio of the maximum single-longitudinal-mode inversion density to the threshold inversion density for a standing-wave laser in terms of the cavity geometry and well-known material parameters. This formula can be used as a guideline in the design of single-frequency lasers.

Limits imposed by spatial hole burning on the single-mode operation of standing wave laser cavities

Opto-electronic measurement techniques are well established in fluid flow investigations. Their advantages are that they are non-intrusive, provide highly accurate measurement data and have fast response times. Laser Doppler velocimetry (LDV) is one of the most important methods for velocity measurements with high spatial and temporal resolution. Diode lasers and diode-pumped solid-state lasers as well as glass fibres and micro-optics are employed to an increasing extent. Particularly, the development of solid-state lasers proceeds rapidly. New lasers with improved properties such as high-power fundamental-mode emission make it possible to develop enhanced LDV sensor heads. This may open up new fields of application, for example in medicine and aerospace technology. The aim of this review is to describe the present state-of-the-art in LDV and to demonstrate how new laser concepts can still contribute to the development of new, improved LDV sensors. For that purpose, solid-state lasers such as diode lasers and diode-pumped solid-state lasers are introduced, and concepts of communication engineering for accomplishing directional multi-component velocity measurements are discussed. Also, velocity measurements with high spatial resolution are reported. A conclusive overview of applications and an outlook on future challenges are outlined.

https://iopscience.iop.org/article/10.1088/0957-0233/17/7/R01/pdf

Laser Doppler velocimetry using powerful solid-state light sources

Birefringent Nd:YAG microchip laser used in heterodyne vibrometry

The authors present, for the first time, the use of two orthogonal polarised axial modes of an Nd:YAG microchip laser in heterodyne interferometry. The realised heterodyne interferometer was used for direction sensitive velocity measurements.

Heterodyne interferometer using a novel two-frequency Nd:YAG laser

A theoretical model is derived by which the occurrence of the single and multiple emission line spectra of tunable microcrystal lasers is described. These spectra in general exhibit several emission lines, arising from the Stark-split atomic levels of the lasing ions in the crystal field. The model is based on the shift of the resonator frequencies due to the thermally induced shift of the optical resonator length and demonstrates that the coincidence of the resonator frequencies with the laser gain lines leads to the emission of single or multiple line spectra of microcrystal lasers. These spectra can be described by the model. The model is given as a set of criteria. In this way not only can predictions of the single emission-line tuning range be made but also resonator lengths can be optimized in order to obtain a maximum tuning range. Furthermore, Q-switched operation can be achieved for specific parameters by periodically shifting the resonator frequencies. The linewidth of the gain used in this model depends on the laser threshold and is folded with the thermal shift of the atomic transitions. Therefore the centre wavelength of the gain is assumed to be constant. The advantage is that this experimentally relevant linewidth can be measured easily with microcrystal lasers themselves, whereas spectroscopic data do not take laser threshold behaviour into account. It is shown that the results of the model are in good agreement with experimental data measured for two different Nd: YAG crystals. Simply by inserting other material and laser parameters, the model can easily be applied to other laser crystals and other wavelengths.

A model describing the single and multiple line spectra of tunable microcrystal lasers

Microcrystal lasers are characterized by a resonator mode separation that is of the order of the laser gain bandwidth of the active medium, which is responsible for several interesting laser physical phenomena that can be observed very pronouncedly. Especially by thermally tuning the resonator frequency with respect to the centre-of-gain not only broadly tunable single frequency lasers can be built: the measured data allow the simulation of the microcrystal laser behaviour by means of which optimisation of such lasers can be performed as well as laser performance can be understood better. Microcrystal lasers therefore are a good means to study relevant physical parameters by measuring the phenomena of stimulated emission themselves. This has been already suggested very early by Kamiskii [1] as ‘stimulated emission spectroscopy’, which up to now has been applied to macroscopic laser systems only.

Abstimmbare Mikrokristall-Laser

Optical pumping of laser crystals with new diode lasers provides an interesting potential for miniaturizing solid state lasers. This leads to small laser systems where a laserdiode, transfer optics and a laser crystal are integrated into a hybrid chassis. These lasers exhibit a high beam quality and stability.

Diode-Laser Pumped Miniature Solid State Lasers

Tests of Cr4+-doped garnets concerning their behavior as saturable absorbers have already been reported by several authors [1]. These materials show several well known good properties (high thermal conductivity, hardness, etc.) and especially for their high photostability they seem to be good candidates for passive Q-switching.

Passive Q-Switching of Diode-Pumped Solid-State Lasers with Cr4+:YAG Crystals

TEM/sub 00/ laser operation of a monolithic Nd:YAG crystal laser has been achieved on three transitions at 1.414 /spl mu/m, 1.444 /spl mu/m and at 1.431 /spl mu/m with laser diode pumping at 808 nm. The laser threshold was 1.5 W and the maximum output power 50 mW. The gain linewidths at 1.414 /spl mu/m and 1.444 /spl mu/m were determined by means of temperature tuning the microcrystal lasers. Calculations for designing tunable single frequency microcrystal lasers have been performed. >

N. P. Schmitt

Papers

A model describing the single and multiple line spectra of tunable microcrystal lasers

Abstimmbare Mikrokristall-Laser

Diode-Laser Pumped Miniature Solid State Lasers

Passive Q-Switching of Diode-Pumped Solid-State Lasers with Cr4+:YAG Crystals

Tunable laser-diode-pumped Nd:YAG microcrystal lasers at 1.4 /spl mu/m