Departemt of Applied Physics

High-power continuous-wave generation at 533 nm is demonstrated in bulk periodically poled KTiOAsO 4 (KTA) by single-pass frequency doubling of a VBG-locked Yb-doped fiber laser. Absorption characteristic and second harmonic generation (SHG) performance of different KTA samples are studied and compared. The best performing sample catered for 25%-efficient SHG of 13.6 W green light with high spatial beam quality M 2 <1.2.

Tids nog se vår onda tid Och hennes galla smaka. Verlden är en sorge-ö, Bäst man andas, skall man dö Och bli mull tillbaka. En gång, där en källa flöt Förbi en skyl i rågen, Stod en liten gosse söt Och spegla sig i vågen: Bäst sin bild han såg så skön Uti böljan, klar och grön, Straxt han inte såg'en. Så är med vår lifs-tid fatt, Och så försvinna åren: Bäst man andas godt och gladt, Så ligger man på båren.

In this master thesis project, a pulsed UV laser was designed and constructed. Also, the effects of absorption in a volume Bragg grating were investigated. The laser was diode pumped and constructed with Yb:KYW as gain medium. The lasing was at a wavelength of 1029.2 nm with a spectral bandwidth of 0.23 nm, locked by a volume Bragg grating that was used as input coupler for spectral control. Passive Q-switching was used to generate pulses by placing a Cr:YAG saturable absorber inside the cavity. The laser generated radiation with a maximum peak power of 3.8 kW at an average power of 0.35 W, a repetition rate of 4 kHz and a pulse width of 16 ns. The maximum average power was 1.3 W with a peak power of 2 kW at a repetition rate of 20 kHz and with a pulse width of 20 ns. Through extra-cavity second harmonic generation using an LBO crystal, green light at a wavelength of 514.7 nm was generated. The maximum average power was 130 mW with an optical conversion efficiency from the fundamental of around 10 %. Then, the second harmonic and the fundamental wave were mixed to generate UV light, at a wavelength of about 343 nm, by using a second LBO crystal. The maximum average power of UV was about 23 mW with an optical efficiency, with respect to the green, of approximately 20 %. One limitation of the laser was that the Cr:YAG was bleached not only by the circulating laser field, but also by remaining pump light. This resulted in decreasing peak power with increasing pump power, thus limiting the nonlinear conversion efficiencies. Thermal fracture of the Cr:YAG was a limiting factor for the intra-cavity average power, while burning of the coating on the Yb:KYW crystal limited the maximum peak power.

Picosecond blue-light induced infrared absorption (BLIIRA) was investigated in periodically poled KTiOPO 4 , Rb:KTiOPO 4 , RbTiOPO 4 , KTiOAsO 4 and RbTiOAsO 4. The dependence of BLIIRA on blue light average power and intensity as well as on crystal temperature was studied. The results show the presence of at least two different types of color centers. A higher level of remnant absorption was observed in the phosphates compared to the arsenates. We attribute the largest portion of the induced absorption to photo-generated electrons and holes self-trapped in the proximity to Ti 4+ and O 2ions, respectively, forming polaron color centers. Stabilization of these centers is aided by the presence of mobile alkali metal vacancies in the crystal. The lower level of remnant absorption in arsenates is related to higher population of thermal phonons related to TiO 6 group vibrations in arsenates.

This thesis describes the work at the Royal Institute of Technology on the conception and construction of a multi-wavelength laser, to be used in digital holography experiments at Luleå Technical University. The stated goal was to create a system that could simultaneously deliver several laser beams at different wavelengths without the need for wavelength tuning or other manipulation that could at the same time be used in a harsh industrial environment. The first part describes the creation and discussion of several ideas and theoretically possible systems. These ideas were evaluated in several rounds of discussions after which a decision to construct a specific prototype was made. The second part describes the practical work from constructing the first miniature test beds to the finalization of a working and tested system.