Göran Hansson

Bio: Göran Hansson is an academic researcher from Royal Institute of Technology. The author has contributed to research in topics: Lithium niobate & Optical parametric oscillator. The author has an hindex of 4, co-authored 5 publications receiving 204 citations.

Transmission measurements in KTP and isomorphic compounds

Abstract: The optical biaxial nature of crystals in the potassium titanyl phosphate (KTP) family result in anisotropic transmission that depends on the polarization direction of the transmitted radiation with respect to the fundamental crystal axes. Knowledge of the polarization-dependent crystal transmission is important for all wavelength-conversion applications and in particular is the only limitation on possible combinations of wavelengths when one uses the quasi-phase-matching techniques recently developed for the KTP family materials. In this study, polarized transmission spectra of KTiOPO4 (KTP), RbTiOPO4, RbTiOAsO4 (RTA), and KTiOAsO4 were measured over the 0.3–6-µm wavelength range with a spectrophotometer and a Fourier-transform infrared spectrometer. Seven crystal samples were studied, including four samples of KTP crystals of different origins. Variations in spectral transmission on the short- and long-wavelength edges, as well as visible-wavelength transmission and OH- absorption properties, are presented and discussed. The transmission of one sample of KTP and of RTA was also measured before and after periodic electric field poling.

Unstable resonator optical parametric oscillator based on quasi-phase-matched RbTiOAsO 4

Abstract: We demonstrate improved signal and idler-beam quality of a 3-mm-aperture quasi-phase-matched RbTiOAsO4 optical parametric oscillator through use of a confocal unstable resonator as compared with a plane-parallel resonator. Both oscillators were singly resonant, and the periodically poled RbTiOAsO4 crystal generated a signal at 1.56 µm and an idler at 3.33 µm when pumped at 1.064 µm. We compared the beam quality produced by the 1.2-magnification confocal unstable resonator with the beam quality produced by the plane-parallel resonator by measuring the signal and the idler beam M2 value. We also investigated the effect of pump-beam intensity distribution by comparing the result of a Gaussian and a top-hat intensity profile pump beam. We generated a signal beam of M2 ≈ 7 and an idler beam of M2 ≈ 2.5 through use of an unstable resonator and a Gaussian intensity profile pump beam. This corresponds to an increase of a factor of approximately 2 in beam quality for the signal and a factor of 3 for the idler, compared with the beam quality of the plane-parallel resonator optical parametric oscillator.

Mid-infrared-wavelength generation in 2-μm pumped periodically poled lithium niobate

Abstract: A periodically poled lithium niobate optical parametric oscillator pumped by a Tm:YAG laser at 2.0124-μm wavelength has been demonstrated. A pump pulse energy of 5.1 mJ generated 0.65 mJ of signal and idler pulse energy at a 50-Hz repetition frequency with a 27.8-μm domain-period-length grating. The lithium niobate crystal at a temperature of 180 °C yielded 3.61- and 4.55-μm signal and idler wavelengths, respectively. Wavelength tuning over a wide range was achieved with domain-period lengths from 25.5 to 28.2 μm and crystal temperature tuning from 50 to 180 °C. Signal wavelengths of 3.26–3.76 μm and idler wavelengths of 4.33–5.34 μm were generated.

Optical parametric generation in 2-mum-wavelength-pumped periodically poled LiNbO(3).

Abstract: An optical parametric generator based on periodically poled LiNbO(3) and pumped by a 2051-mum-wavelength laser has been demonstrated Pump pulses of 50-ns duration of 50-Hz repetition frequency were converted into signal and idler pulses in the 34-52-mum wavelength range in a double-pass pump configuration by a 5-cm-long quasi-phase-matched crystal An average pump power of 180 mW generated 30-mW average signal power at 364-mum wavelength, corresponding to 167% signal conversion efficiency

2 µm Wavelength Pumped Optical Parametric Oscillator using Periodically-Poled LiNbO3

Abstract: A 2 μm wavelength pumped Optical Parametric Oscillator (OPO) using the new nonlinear material Periodically Poled Lithium Niobate (PPLN) has been demonstrated. The OPO was pumped by a Tm:YAG laser at 2.013 μm wavelength and operated doubly resonant close to degeneracy at 3.8 to 4 pm and 4 to 4.3 μm signal and idler wavelengths respectively. Pumping at 9.2 mJ pulse energy produced a combined signal and idler pulse energy of 0.82 mJ, corresponding to 8.9% efficiency. The experiments showed a difference between calculated and observed domain period length close to degeneracy caused by deviations in the dispersion data for Lithium Niobate in the 3 to 5 μm wavelength range.

Mid-infrared optical parametric oscillators and frequency combs for molecular spectroscopy

Abstract: Nonlinear optical frequency conversion is one of the most versatile methods to generate wavelength-tunable laser light in the mid-infrared region. This spectral region is particularly important for trace gas detection and other applications of molecular spectroscopy, because it accommodates the fundamental vibrational bands of several interesting molecules. In this article, we review the progress of the most significant nonlinear optics instruments for widely tunable, high-resolution mid-infrared spectroscopy: continuous-wave optical parametric oscillators and difference frequency generators. We extend our discussion to mid-infrared optical frequency combs, which are becoming increasingly important spectroscopic tools, owing to their capability of highly sensitive and selective parallel detection of several molecular species. To illustrate the potential and limitations of mid-infrared sources based on nonlinear optics, we also review typical uses of these instruments in both applied and fundamental spectroscopy.

Photostable second-harmonic generation from a single KTiOPO4 nanocrystal for nonlinear microscopy.

Abstract: Nonlinear second-harmonic generation (SHG) microscopy has become a commonly used technique for investigating interfacial phenomena and imaging biological samples. Different non-centrosymmetric nanometric light sources have been recently studied in this context, for example, organic nanocrystals. For those systems, resonant optical interaction leads to an enhancement of the nonlinear response but also to a parasitic effect that is detrimental for practical applications, namely photobleaching due to two-photon residual absorption. Conversely, inorganic non-centrosymmetric materials with far-off resonance interaction avoid this limitation. Recent achievements have been obtained using KNbO3 nanowires as a tunable source for subwavelength optical microscopy and Fe(IO3)3 nanocrystallites as promising new SHG-active particles with potential applications in biology. However, either the dimensions of the used crystals are still of the order of the micrometer along one axis or the corresponding bulk material is not easily grown, so that the crystal characteristics are not directly available. A complementary approach consists of considering a well-known SHG-active bulk material and investigating its properties in nanoparticle form. Potassium titanyl phosphate (KTiOPO4, KTP) is a widely used nonlinear crystal. [11] Studies of this material have focused on the optimized growth of largesize single crystals, which have found numerous applications in

Generation of high-power femtosecond light pulses at 1 kHz in the mid-infrared spectral range between 3 and 12 µm by second-order nonlinear processes in optical crystals

Abstract: We review methods for frequency conversion of amplified femtosecond laser pulses from the near- to the mid-infrared. The potential of all commercially available optical crystals is evaluated on the basis of the specific requirements in the high-power femtosecond regime. A comparative experimental study of a number of materials (birefringent and quasi-phase-matched) employed in a seeded optical parametric amplifier pumped near 800 nm is presented, where the generated idler is tunable between 3 and 4 µm. Internal conversion efficiencies as high as 40% and pulse energies as high as 20 µJ are achieved in this spectral range. Wavelength tunability up to 12 µm with energies exceeding 1 µJ is demonstrated by pumping optical parametric amplifiers and generators near 1.25 and 2 µm, as well as by difference frequency generation with a quantum efficiency of 40-80%. In all cases the generated mid-infrared pulses are almost bandwidth limited with a duration of 100-200 fs.