Compact diode-pumped solid-state lasers (DPSSL) arecontinuously replacing traditional gas lasers as well asenabling completely new technology. However, compact and costefficient designs are required to satisfy end-user demands. Theaim of this thesis was therefore to investigate novel laserdesigns for given applications considering these demands. In alarge part of the thesis work, nonlinear optics were employedto realize laser wavelengths where there was no appropriatelaser transition available. Besides other nonlinear crystals such as BBO, LBO and KTP,periodically poled KTP played an important role in this thesiswork. Its unique properties regarding up conversion processeswere exploited, thus supplying a broadened view over itspotential and limitations. This thesis places emphasis on practical concerns, mainlyrelated to real applications. It gives solutions to the beamshaping of laser diodes, covers the simulation and the designof laser dynamics as well as laser performance and describesthe sources of laser output degradation and damage mechanisms.Novel infrared lasers were designed and multiple intra-cavity,external cavity and non-resonant multi-pass frequencyconversion schemes were successfully employed and optimized.These produced red, orange, green, blue and ultraviolet outputfor various applications like spectroscopy, micro machining andwriting of fiber Bragg gratings. Keywords:diode-pumped solid-state lasers, nonlinearoptics, frequency conversion,

<p>Compact diode-pumped solid-state lasers (DPSSL) arecontinuously replacing traditional gas lasers as well asenabling completely new technology. However, compact and costefficient designs are required to satisfy end-user demands. Theaim of this thesis was therefore to investigate novel laserdesigns for given applications considering these demands. In alarge part of the thesis work, nonlinear optics were employedto realize laser wavelengths where there was no appropriatelaser transition available.</p><p>Besides other nonlinear crystals such as BBO, LBO and KTP,periodically poled KTP played an important role in this thesiswork. Its unique properties regarding up conversion processeswere exploited, thus supplying a broadened view over itspotential and limitations.</p><p>This thesis places emphasis on practical concerns, mainlyrelated to real applications. It gives solutions to the beamshaping of laser diodes, covers the simulation and the designof laser dynamics as well as laser performance and describesthe sources of laser output degradation and damage mechanisms.Novel infrared lasers were designed and multiple intra-cavity,external cavity and non-resonant multi-pass frequencyconversion schemes were successfully employed and optimized.These produced red, orange, green, blue and ultraviolet outputfor various applications like spectroscopy, micro machining andwriting of fiber Bragg gratings.</p><p><b>Keywords:</b>diode-pumped solid-state lasers, nonlinearoptics, frequency conversion,</p>

In many fields, scientific or industrial, optical devices that can be tailored in terms of spectral qualities and output power depending on the application in question are attractive. Nonlinear optics in combination with powerful laser sources provide a tool to achieve essentially any wavelength in the electromagnetic spectrum, and the advancement of material technology during the last decade has opened up new possibilities in terms of realising such devices. The main part of the thesis deals with the development of compact functional lasers based on nonlinear interaction utilising diode-pumped solid-state lasers and also laser diodes. Efficient frequency conversion into the visible and ultraviolet part of the electromagnetic spectrum has been achieved, using both Nd:YAG and Nd:YVO4 lasers as well as a semiconductor laser as the fundamental light sources. For the nonlinear conversion, periodically poled potassium titanyl phosphate (PPKTP), bismuth triborate (BiBO) and beta barium borate (BBO) have been employed. In the search for compact and reliable light sources emitting in the visible part of the spectrum, two different approaches have been explored. First, a scheme based on sum-frequency mixing of a diode-pumped solid-state laser and a laser diode of good beam quality. The idea of this approach is to take advantage of the individual strength of each device, which would be the flexibility in terms of wavelength for the laser diode and the possibility to reach high output power from the diode-pumped solid-state laser. Second, by mixing two different solid-state lasers substantially more output power could be generated albeit at a cost of less freedom in the choice of spectral output. As these two light sources had their central wavelength at 492 nm and 593 nm, respectively, they are highly interesting in biomedical applications since they correspond to the peak absorption of several popular fluorophores. In applications such as lithography, material synthesis and fibre grating fabrication, laser sources emitting in the deep-UV spectrum are desired. An all solid-state 236 nm laser source with 20 mW of average power have been designed and constructed, by frequency-quadrupling a passively Q-switched Nd:YAG laser lasing on a quasi-three level transition. Also, a novel concept for miniaturising solid-state lasers has been examined. Using a heat-conductive polymer carrier, a generic approach especially suited for mass-production of functional laser devices is presented. Finally, it has been proven that GRIN lenses can provide a very compact beam shaping solution to standard laser diodes based on the beam twisting approach. This method offers several advantages such as compactness of the beam shaping system, automated assembly in solid-state laser manufacturing due to the shape of these lenses and polarisation preservation of the laser diode output. / QC 20100903

Short optical pulses and engineered nonlinear media is a powerful combination. Mode locked pulses exhibit high peak powers and short pulse duration and the engineered ferro-electric KTiOPO4 facilitates several different nonlinear processes. In this work we investigate the use of structured, second-order materials for generation, characterization and frequency conversion of short optical pulses. By cascading second harmonic generation and difference frequency generation the optical Kerr effect was emulated and two different Nd-based laser cavities were mode locked by the cascaded Kerr lensing effect. In one of the cavities 2.8 ps short pulses were generated and a strong pulse shortening took place through the interplay of the cavity design and the group velocity mismatch in the nonlinear crystal. The other laser had a hybrid mode locking scheme with active electro-optic modulation and passive cascaded Kerr lensing incorporated in a single partially poled KTP crystal. The long pulses from the active modulation were shortened when the passive mode locking started and 6.9 ps short pulses were generated. High-efficiency frequency conversion is not a trivial task in periodically poled materials for short pulses due to the large group velocity mismatch. Optimization of parameters such as the focussing condition and the crystal temperature allowed us to demonstrate 64% conversion efficiency by frequency doubling the fs pulses from a Yb:KYW laser in a single pass configuration. Quasi phase matching also offers new possibilities for nonlinear interactions. We demonstrated that it is possible to simultaneously utilize several phase matched second harmonic interactions, resulting in a dual-polarization second harmonic beam. Short pulse duration of the fundamental wave is a key parameter in the novel method that we demonstrated for characterization of the nonlinearity of periodically poled crystals. The method utilizes the group velocity mismatch between the two polarizations in a type II second harmonic generation configuration. The domain walls of PPKTP exhibit second order nonlinearities that are forbidden in the bulk material. This we used in a single shot frequency resolved optical gating arrangement. The spectral resolution came from Čerenkov phase matching, a non-collinear phase matching scheme that exhibits a substantial angular dispersion. The second harmonic light was imaged upon a CCD camera and with the spectral distribution on one axis and the temporal autocorrelation on the other. From this image we retrieved the full temporal profile of the fundamental pulse, as well as the phase. The spectral dispersion provided by the Čerenkov phase matching was large enough to characterize optical pulses as long as ~200 fs in a compact setup. The Čerenkov frequency resolved optical gating method samples a thin stripe of the beam, i.e. the area close to the domain wall. This provides the means for high spatial resolution measurements of the spectral-temporal characteristics of ultrafast optical fields. / QC 20100831