In this thesis, analysis of thermal effects and various approaches for their mitigation in diode end pumped ultrafast lasers is presented. Experimental investigations were performed by employing Shack-Hartmann wavefront sensor which was adapted for measurements of thermal lens in diode end pumped lasers. During research, operation of high average power, diode-pumped, Nd:YVO4 laser with aspheric aberration corrector was investigated. Actual thermal lens measurements were conducted in order to design properly shaped aberration corrector that was manufactured using a thin film deposition technology. This allows us to conclude that employment of proper thermal lens aberration compensator allowed for laser threshold reducing and ensured improved output beam quality parameter M2 in wide pump power range. Prospects of output pulse energy scaling in diode end-pumped Yb:YAG laser by employing elliptical mode geometry was investigated. During our experiments, maximum average power in of ~ 5.5 W was obtained at repetition rates of 30-100 kHz, while in CW operation mode the 8 W output power was achieved. In spite of strongly astigmatic thermal lens due to optimized cavity design the output beam exhibits high spatial quality: beam quality parameter M2 in both vertical and horizontal plane was close to unity. Detailed comparative study of thermal effects in Yb doped KGW crystals with different orientation was performed. Measurements confirm, that anisotropic optical and thermal properties... [to full text] / Šios disertacijos tikslas – didelio tikslumo matuoklio, skirto šiluminio lęšio lazerių aktyviuosiuose elementuose matavimams sukūrimas, bei įvairių metodų, skirtų šiluminio lęšio įtakos mažinimui tyrimas. Matavimai buvo atliekami Shack‘o ir Hartmann‘o bangos fronto matuokliu, kuris buvo pritaikytas mažų skersinių matmenų (<1x1 mm) šiluminio lęšio matavimams. Pademonstruotas naujos konstrukcijos asferinis kompensatorius iš esmes mažinantis šiluminio lęšio aberacijų įtaką išilginio diodinio kaupinimo lazeriuose. Atlikti šiluminio lęšio aberacijų matavimai buvo panaudoti kompensatoriaus profilio skaičiavimams. Naudojant asferinį kompensatorių, pagamintą plonasienių dangų užgarinimo būdu, generacijos slenkstis sumažėjo daugiau kaip 3 kartus, taip pat ženkliai pagerėjo lazerio pluošto intensyvumo skirstinys. Darbe nagrinėjamas stiprinamų impulsų energijos didinimo būdas pasitelkiant eliptinę rezonatoriaus modą Yb:IAG lazeryje. Šis metodas leidžia kelis kartus padidinti stiprinamų impulsų energiją, išlaikant dirakciškai ribotus erdvinius pluošto parametrus. Taip pat, surasta lazerio rezonatoriaus konfigūracija, leidžianti palaikyti stipriai astigmatišką modą aktyviajame elemente, ir simetrišką modą lazerio išėjime. Pateikiami šiluminio lęšio matavimų rezultatai „atermalinės“ ir Ng orientacijos Yb:KGW kristaluose. Taip pat, parodėme, kad kristalo galų išsigaubimo įtaka Ng orientacijos Yb:KGW aktyviuosiuose elementuose gali siekti 50%. Atlikti tyrimai parodė, kad išbandyta... [toliau žr. visą tekstą]

Two-dimensional thermal, mechanical and optical simulations are carried out to investigate the effect of Nd3+ concentration on thermal, mechanical and optical behavior of Nd:YAG ceramic laser materials under continuous wave laser operation. In the analyses, rods are pumped longitudinally with laser diodes, in three, six, nine and twelve fold structures. Rods having diameters of 3 and 6 mm are pumped with 808 nm and 885 nm sources separately having Nd+3 concentrations of 0.6, 1, 2, 3, 4 and 6 at. %. Total absorbed pump power are kept constant for all rods. Absorbed pump power distribution are obtained for each rod using ray tracing method and Beer&amp / #8217 / s Law. In the analysis, temperature dependent material properties are incorporated. Nonlinear numerical solutions of thermal and stress equations have been performed. Temperature and stress results are obtained to investigate the effect of Nd concentration on the optical properties of ceramic YAG laser material. Analysis results reveal that, increase in Nd3+ concentration of YAG ceramic laser material, decreases the temperature and stress developed during optical pumping. Rods pumped with 808 nm source have large temperature and stress values compared to 885 nm pumped ones. Optical path difference (OPD) of each ray passed trough the material is calculated using thermal and elastic strain results together with photo-elastic constants of Nd:YAG material. Focal length and depolarization of each rod is calculated numerically from OPD results. Focal length of each rod is found to increase, in contrary depolarization is found to decrease with increase in the dopant concentration.

This paper have investigated the dual polarization oscillations (DPO) and associated dynamical behaviors in laser-diode-pumped microchip Nd:GdVO4 laser. Some optical properties of Nd:YAG, Nd:YVO4, and Nd:GdVO4 laser materials are compared. The higher thermal conductivity of Nd:YAG makes it suitable for higher-power applications. The larger stimulated-emission coefficient of Nd:YVO4 material makes it favorable for increasing light-light conversion efficiency. However, Nd:GdVO4 material has high thermal conductivity and large stimulated-emission coefficient. Many experiments done to study Nd:GdVO4 crystal¡¦s properties focused on the efficiency of high power generation. Orthogonal linearly-polarized emissions could be obtained in fluorescence spectrum of Nd:GdVO4, but DPO did not be observed in Nd:GdVO4 laser possessing a large fluorescence anisotropy with laser-diode pumping. In this paper, DPO on different transitions in laser-diode-pumped microchip Nd:GdVO4 are obtained for the first time. Furthermore, more effective generation of dual polarization oscillations is affected by the pumping conditions associated with different temperature gradient than different pumping power density. The results imply that DPO can be generated without having to use additional optical elements and Nd:GdVO4 material is suitable for the construction of compact DPO lasers. Laser properties including oscillation spectra, input-output characteristics, pump-dependent pattern formations and noise power spectra are studied experimentally. A poor mode matching between the pump beam and lasing beam results in the generation of high order transverse modes. The observed anti-phase dynamics have been explained in terms of the reduced three-dimensional cross-saturation of population inversions among orthogonally-polarized modes. The study of dynamics of microchip Nd:GdVO4 lasers under pump modulation has also been reported in this paper. Different phase correlations among laser modes are obtained by tuning the modulation frequency and amplitude. The observed dynamical states are reproduced theoretically by rate equations of multimode class-B lasers including the cross-saturation among individual modes and the pump modulation.

Darbo tikslas – ištirti puslaidininkiniais lazeriais kaupinamos Yb:KGW femtosekundinės sistemos, susidedančios iš osciliatoriaus ir regeneratyvinio stiprintuvo, veikos dinamiką ir panaudojant gautus rezultatus optimizuoti spinduliuotės parametrus. Darbe nagrinėta termo-lęšio bei netiesinio Kerro elemento poveikis rezonatoriaus stabilumui. Panaudojus gautus rezultatus sukurtas trumpiausius impulsus (31 fs) generuojantis iterbio jonais legiruotą strypinį aktyvųjį elementą turintis lazeris. Taip pat pasiūlytas ir eksperimentiškai realizuotas pakreiptų impulsų stiprinimo metodas, kurį taikant optinio plėstuvo plėtimo mastas priklauso tik nuo pluošto matmenų ir gardelės rėžių skaičiaus ir nepriklauso nuo impulso spektro pločio. Impulsų spūdai optimizuoti pasiūlytas ir eksperimentiškai pademonstruotas naujos konstrukcijos vienašūvis autokoreliatorius, kuriame tiriamojo impulso spektrą paskleidžiant kampine dispersija pasižyminčiu optiniu elementu, gaunama informacija apie įvairių spektrinių komponenčių išsidėstymą laike su skiriamąja geba, kuri priklauso tik nuo panaudoto elemento kampinės dispersijos. Šis metodas yra tinkamas vienareikšmiškai charakterizuoti femtosekundinių impulsų spūdą ir tuo yra paprastesnis už plačiai naudojamus FROG, GRENOUILLI ir SPIDER metodus. Tiriant puslaidininkiniais lazeriais kaupinamo Yb:KGW regeneratyvinio stiprintuvo dinamika nustatyti reiškiniai ribojantys maksimalią impulso energiją ir maksimalią išvadinę galią. Panaudojus tyrimo rezultatus... [toliau žr. visą tekstą] / The objective of the present work is to examine the dynamics diode pumped femtosecond Yb:KGW laser consisting of an oscillator and a regenerative amplifier and to optimize its radiation parameters using the results obtained. The thermal-lens and nonlinear Kerr medium effect on the stability of the resonator has been studied. On the basis of the results obtained an oscillator which generates 31 fs pulses has been developed. To our knowledge they are the shortest pulses reported from the laser with a bulk ytterbium doped gain medium. We have also proposed and experimentally demonstrated the tilted pulse amplification method. Applying this method the scale of pulse stretching in the optical stretcher depends only on the beam size and the diffraction grating grooves density and does not depend on the bandwidth of the pulse. In order to optimized the compression of amplified pulses we have also proposed and experimentally tested a new design of single shot autocorrelator which disperses the given pulse spectrum by help of optical component with the angular dispersion. It this way the information is obtained about the distribution of various time-dependent spectral components with the resolution which depends only on the angular dispersion of the optical component used. The present method gives unambiguous characterization of the pulse compression which makes it less complex than widely used FROG, GRENOUILLI and SPIDER methods. The maximum pulse energy and the maximum output power... [to full text]

The objective of the present work is to examine the dynamics diode pumped femtosecond Yb:KGW laser consisting of an oscillator and a regenerative amplifier and to optimize its radiation parameters using the results obtained. The thermal-lens and nonlinear Kerr medium effect on the stability of the resonator has been studied. On the basis of the results obtained an oscillator which generates 31 fs pulses has been developed. To our knowledge they are the shortest pulses reported from the laser with a bulk ytterbium doped gain medium. We have also proposed and experimentally demonstrated the tilted pulse amplification method. Applying this method the scale of pulse stretching in the optical stretcher depends only on the beam size and the diffraction grating grooves density and does not depend on the bandwidth of the pulse. In order to optimized the compression of amplified pulses we have also proposed and experimentally tested a new design of single shot autocorrelator which disperses the given pulse spectrum by help of optical component with the angular dispersion. It this way the information is obtained about the distribution of various time-dependent spectral components with the resolution which depends only on the angular dispersion of the optical component used. The present method gives unambiguous characterization of the pulse compression which makes it less complex than widely used FROG, GRENOUILLI and SPIDER methods. The maximum pulse energy and the maximum output power... [to full text] / Darbo tikslas – ištirti puslaidininkiniais lazeriais kaupinamos Yb:KGW femtosekundinės sistemos, susidedančios iš osciliatoriaus ir regeneratyvinio stiprintuvo, veikos dinamiką ir panaudojant gautus rezultatus optimizuoti spinduliuotės parametrus. Darbe nagrinėta termo-lęšio bei netiesinio Kerro elemento poveikis rezonatoriaus stabilumui. Panaudojus gautus rezultatus sukurtas trumpiausius impulsus (31 fs) generuojantis iterbio jonais legiruotą strypinį aktyvųjį elementą turintis lazeris. Taip pat pasiūlytas ir eksperimentiškai realizuotas pakreiptų impulsų stiprinimo metodas, kurį taikant optinio plėstuvo plėtimo mastas priklauso tik nuo pluošto matmenų ir gardelės rėžių skaičiaus ir nepriklauso nuo impulso spektro pločio. Impulsų spūdai optimizuoti pasiūlytas ir eksperimentiškai pademonstruotas naujos konstrukcijos vienašūvis autokoreliatorius, kuriame tiriamojo impulso spektrą paskleidžiant kampine dispersija pasižyminčiu optiniu elementu, gaunama informacija apie įvairių spektrinių komponenčių išsidėstymą laike su skiriamąja geba, kuri priklauso tik nuo panaudoto elemento kampinės dispersijos. Šis metodas yra tinkamas vienareikšmiškai charakterizuoti femtosekundinių impulsų spūdą ir tuo yra paprastesnis už plačiai naudojamus FROG, GRENOUILLI ir SPIDER metodus. Tiriant puslaidininkiniais lazeriais kaupinamo Yb:KGW regeneratyvinio stiprintuvo dinamika nustatyti reiškiniai ribojantys maksimalią impulso energiją ir maksimalią išvadinę galią. Panaudojus tyrimo rezultatus... [toliau žr. visą tekstą]

Yb-ion doped gain media have become the material of choice for reliable generation of ultrashort pulses at wavelength around 1 μm. At present, however, operation at high average power (>1 W) with sub-100 fs pulses still remains challenging. The efforts of developing an Yb-ion oscillator towards this goal, therefore, are the main focus of this thesis. In this work, the Yb:KGd(WO4)2 (Yb:KGW) crystals were chosen to serve as the gain media. To achieve high power operation, two fundamental issues have been carefully considered: 1) a new pumping scheme was proposed to alleviate the thermal issues in the Yb:KGW crystals; 2) a new method was introduced to characterize intracavity losses in the broadband Yb-ion oscillators. As a side effect observed during the optimization of the CW operation, simultaneous two-wavelength emission was also discussed. With the knowledge and experimental understanding of the fundamental issues in laser oscillators operated in the continuous-wave regime, the next step of this work demonstrated their operation in a pulsed regime. The dual action of the Kerr-lens and saturable absorber (KLAS) mode locking was proposed in this work and resulted in greatly enhanced laser performance. The laser delivered pulses with 67 fs duration at a repetition rate of 77 MHz. The average output power reached 3 W, which, to the best of our knowledge, is the highest average output power produced to date from the Yb-ion based bulk lasers with such a short pulse duration. The scalability of pulse energy and peak power was also demonstrated by reducing the repetition rate to either 36 MHz or 18 MHz. The cavity with the latter repetition rate produced 85 fs pulses with the pulse energy up to 83 nJ, which corresponds to a peak power as high as 1 MW. As required by many biomedical applications, the wavelength of the generated pulses (~1 μm) can be tuned in the near-infrared region by coupling them into an optical parametric oscillator (OPO). The feasibility of this approach was demonstrated in the last part of this thesis, through a thorough theoretical analysis of two OPO materials suitable for excitation at 1.04 μm.

Made available in DSpace on 2014-10-09T12:28:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:45Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Made available in DSpace on 2014-10-09T12:51:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:17Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:03/10164-9