Browsing by Subject "Oscillators, Electric."

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    Femtosecond optical parametric oscillators based on potassium titanyl phosphate crystals
    (1996) Kartaloğlu, Tolga
    In this thesis, we describe our experiments to construct and characterize optical parametric oscillators (OPO) based on a potassium titanyl phosphate (KTP) crystals. The oscillator is synchronously pumped by a mode-locked Titanium:Sapphire laser at a wavelength of 745 nm, a pulse duration of 120 fs, and average power of 640 mW. The OPO converts the 745 nm pump beam to a signal beam at 1068 nm. The resonator is in the form of a ring cavity, with the KTP crystal positioned at the intracavity focus. The crystal is cut for type-II phase matching. We investigated the performance of the OPO with four different output coupler reflectivities. The 10% output coupler gives the best results with 170 mW of signal average power, corresponding to 27% conversion efficiency. The signal beam has an autocorrelation pulse width of 650 fs. In addition, we demonstrate phase-matched intracavity frequency doubling of the signal beam with the same KTP crystal, by placing a waveplate inside the resonator. The waveplate is used to rotate the polarization for type-II phase matching.
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    Laser wavelength upconversion with optical parametric oscillators using simultaneously phase-matched crystals
    (2002) Kartaloğlu, Tolga
    In this thesis, we present our work on optical parametric oscillators that employ a single nonlinear crystal that is simultaneously-phase-matched for second-harmonic or sum-frequency generation in order to obtain frequency upconversion of laser radiation. We achieved simultaneous phase matching of optical parametric amplification together with second harmonic generation or sum frequency generation in bulk KT10P04 and KTi0 As04 crystals, and in an aperiodically-poled LiNbOs crystal. We demonstrated very efficient frequency conversion of pulsed and continuous-wave lasers to higher frequencies with power conversion efficiencies reaching 40%. In addition, we present our work on an intracavity-doubled optical parametric oscillator that employs a periodicallypoled KT10P 04 crystal for optical parametric amplification and an intracavity (3- Ba2B04 crystal for second harmonic generation. In this thesis, we also introduce a method for designing aperiodic grating structures for simultaneous phase matching in poled nonlinear crystals. In contrast to periodic grating structures, a grating structure designed using our method allows one to achieve simultaneous quasi-phase matching of two arbitrarily chosen nonlinear interactions with freely adjustable coupling coefficients.
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    Nanosecond optical parametric oscillators generating eye-safe radiation
    (1998) Durak, Lütfiye
    In this thesis, construction and characterization of nanosecond optical parametric oscillators (OPO’s) generating eye-safe radiation are presented. These OPO’s convert the output of an Nd:YAG laser at 1.06 μ,\ι\ wavelength to 1.57 μη\ wavelength which is in the eye-safe band of the spectrum. A potassium titanyl phosphate (KTP) crystal is employed in these OPO’s. In the experiments, output signal energies, pulse durations, spectral characteristics, and divergence angles of the OPO outputs have been measured. We have obtained 35% conversion efficiency by using pump pulses having 15 rnJ energy and 7 ns pulse duration. These low energy OPO’s can be used in range finders. We have also constructed OPO’s that are pumped by 100 mJ pulses of 15 ns pulse duration, and 38% conversion efficiency was achieved. These high energy OPO’s can be used in target designators. The divergence angles of the low energy and the high energy OPO’s hav(' been measured as 4 rnrad and 3 mrad, respectively. A numerical model which takes into account the temporal and spatial beam profiles, diffraction, and absorptions in the crystal has been constructed. The model is in qualitative agreement with the experimental results.
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    Nanosecond upconversion optical parametric oscillators
    (2005) Figen, Ziya Gürkan
    In this thesis, we demonstrate a technique for highly efficient red beam generation using nanosecond upconversion optical parametric oscillators based on KTiOAsO4 crystals that are simultaneously phase matched for optical parametric generation and sum-frequency generation. Pumped at a wavelength of 1064 nm by a Qswitched Nd:YAG laser, these devices produce red output beams at 627 nm with 1064-nm-to-627-nm energy conversion efficiencies reaching 20% for the singlepass pumping and 30% for the double-pass pumping. Our devices are simpler in architecture compared to other devices converting nanosecond Nd:YAG laser radiation into red wavelengths. A typical nanosecond upconversion optical parametric oscillator is comprised of three cavity mirrors which are all high reflectors at the signal wavelength (1525 nm), a 2-cm-long KTiOAsO4 crystal, and an intracavity retarder plate for rotating the polarization of the signal beam. The total cavity length is under 5 cm. With its small size, the device can be shaped into a module to be placed in front of Nd:YAG lasers for highly efficient red beam generation. The single-pass sum-frequency generating optical parametric oscillator is the first demonstration of a nanosecond optical parametric oscillator using simultaneous phase matching. We have fully characterized these devices in terms of their energy output as functions of polarization rotation angle and input pump energy, time profiles, spatial beam profiles, and spectra of the output. In this thesis, we also present our work on modelling continuous-wave intracavity optical parametric oscillators.
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    A numerical solution for nanosecond single crystal upconversion optical parametric oscillators
    (2005) Yalabık Ateş
    A model of single-crystal upconversion optical parametric oscillators (OPO’s) is a valuable tool for design and optimization. In these devices, a single nonlinear crystal is used both for optical parametric amplification (OPA) and sumfrequency/second-harmonic generation (SFG/SHG). This thesis presents a computational model for single-crystal upconversion OPO’s with pump pulse durations on the order of few nanoseconds. When the duration of the pump pulse is longer than the round trip time of the cavity used in the OPO, the transient nature of the problem must be taken into consideration. Besides the evolutions of the interacting light beams in time, the beam profiles and effects due to diffraction are incorporated into the model. Besides the model, incorporating nonlinear interaction and diffraction inside the crystal, solutions for different cavity components are given in detail. Computational results for a class-D sum-frequency OPO are presented, which are in good agreement with experimental measurements.
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    Plane-wave dynamics of single crystal upconversion optical parametric oscillators
    (1999) Akgün, Gülbin
    This thesis presents our investigation of the dynamics of single crystal up- conversion optical parametric oscillators (OPO’s). In these devices, parametric generation and sum frequency generation or second harmonic generation processes are simultaneously phase matched in a single crystal for the same direction of propagation. These devices can be categorized depending on the polarization geometries of the interacting fields leading to simultaneous phase matching of the two processes. The dynamics of these OPO’s are analyzed using a discrete dynamical system representation. The dependence of the dynamics of the system on various parameters is investigated by forming bifurcation diagrams. Regions of stable steady state, multistable, periodic and chaotic operation are identified on these diagrams.
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    Plane-wave theory of single-crystal upconversion optical parametric oscillators
    (1998) Dikmelik, Yamaç
    'rhis thesis pi'('s('nts a theoi'etical analysis of single-crystal upconversion optical parametric oscillators (OPO’s) where a single nonlinear crystal is used for both the OPO and sum-frequency generation (SPG) or second-harmonic generation (SHG). In these devices, the OPO and SFG/SHG processes are both phase matched for the same direction of propagation inside the crystal. Different polarization geometries for which this simultaneous phase matching condition can potentially be satisfied are identified and categorized, for both biréfringent. a.nd quasi-phcise matching methods. This categorization results in four classes of sumfrequency generating OPO’s (SF-OPO’s) and three classes of self-doubling OPO’s (SD-OPO’s). Plane-wa.ve coupled mode equations a.re presented for each of these seven classes. Solutions of these coupled mode equations, and calculation of the single-pass saturated signal gain are outlined. The dependence of the photon conversion efficiency on various design parameters are investigated. .Λ pulsed plane-wave model that takes into account the temporal profiles of the fields and the group velocity mismatch between pulses is constructed. This model is in good qualitative agreement with experimental measurements of a class-G SF-OPO.