A signal beam is generated in three and four level-atomic system in hot Rb vapors with N2 buffer in electromagnetically induced transparency (EIT) conditions by adding a pump-beam deflected within a small angle to the coupling and probe beams. Linewidth below 200 Hz and time delay above 1 msec are reported. It is suggested that the generated signal proprieties offer several advantages over the transmitted ones that are used traditionally in EIT applications.
The introduction of periodically poled crystals with high non-linear coefficients has lowered significantly the threshold for parametric processes. This progress enables pumping frequency conversion devices with low pulse energy, Q-switched, diode-pumped, solid-state lasers.
New non-linear optical ferroelectric materials, such as KTP and Stoichiometric Lithium Tantalate (SLT) were proven to exhibit adequate deff, higher optical damage resistance and lower photo-refractivity in comparison to well-known periodically poled Lithium Niobate. Advances in poling technology have enabled the production of relatively thick periodically poled crystals from those materials. Thus, in principal much higher average power levels can be converted.
We have investigated the effects that limit frequency conversion efficiency as power levels are increased. Average power induced thermal lensing and thermal phase mismatching were considered. The resulting power limitations are discussed, and under some assumptions quantitative expressions for these limits were formulated.
Thermal lensing imposes a limit on the local power density. Thermal phase mismatching imposes a limit on the overall power.
Near stoichiometric LiTaO3 is investigated for high power quasi-phase-matched optical frequency conversion applications due to its high optical damage threshold and low coercive field. In this work, near stoichiometric undoped and MgO-doped LiTaO3 wafers were characterized by transmission through cross-polarizes, x-ray diffraction and microscope inspection. Periodically inverted domain structures were fabricated in 1 to 4mm thick wafers, by electric field poling in vacuum. Efficiency values between 10% and 16% were obtained for direct frequency conversion of 1 μm to 4 μm light using optical parametric oscillations scheme. The resulting periodically poled structure quality and frequency conversion efficiency seems to be limited by crystalline imperfections of the wafers.
Yb doped fiber lasers are of importance due to their potential applications as efficient pumps for erbium doped fiber amplifiers, as well as for achieving the argon ion-laser line of 488nm through frequency doubling. An efficient high power fiber laser operating at 980nm is presented. The fiber laser consists of an all-silica air clad fiber with an Yb doped core. The double-clad fiber configuration has a single-mode (SM) core and a small diameter inner silica clad. The inner clad is surrounded by air filled capillaries within a standard sized outer silica cladding. The air cladding provides the fiber with high numerical aperture (NA), greater than 0.6. This high NA is essential for efficient pump coupling into the small inner clad, as well as for the fiber laser saturation and its resulted efficient operation at a three level scheme. Fiber Bragg gratings were written on the core, thus forming an all-fiber cavity. We have achieved over 1W of 980nm laser emission in SM, with a threshold of 285mW and a slope-efficiency of 30%. Furthermore, a very narrow line-width of the laser emission enabled its efficient frequency doubling using an extra-cavity doubling configuration with PPKTP crystals, developed by Soreq NRC. Output power of 19mW at 490nm in transverse SM has been achieved using a single polarization component of the fiber laser emission, with a conversion efficiency of 14%/W. All fiber cavity design within an all-silica air-clad fiber, and emission suitable for efficient frequency doubling makes this source highly suitable and cost-effective for various applications, such as telecommunication and diagnostics.
We present a temperature-dependent Sellmeier equation for congruent and stoichiometric LiTaO3. The refractive indices in the range of 0.39-4.1 micrometers were determined by scanning the pump lasers wavelength and finding the QPM second harmonic wavelength for a series of period- temperature pairs, and from QPM OPO measurements. The obtained new Sellmeier coefficients were used to calculate the QPM wavelengths of the idler and signal for a PPSLT OPO pumped at 1064 nm. An OPO based on PPSLT was demonstrated. The idler-tuning range was 4.1828-3.9898 micrometers for temperatures of 40-200 degree(s)C. The obtained wavelengths were in good agreement with our predictions.
Frequency conversion efficiency limiting factors in PPKTP crystals and segmented waveguides have been investigated. It was found that at high intensity, back conversion effects related to the spectral and spatial properties of the laser beam, limit the conversion efficiency. High conversion efficiencies in PPKTP are demonstrated by selecting proper laser conditions. A parametric study of the influence of geometrical parameters on conversion efficiency in periodically segmented waveguides has been carried out and an optimal design parameter range has been defined. An improved waveguide structure in which higher efficiencies can be obtained is suggested.
Periodically poled KTiOPO4 (KTP) wafers with short period length are required for generation of green and blue coherent light. Electric field poling processes developed for producing inverted micrometer scale domain structures in other ferro-electric materials cannot be directly applied to flux-grown KTP due to its relatively high (super ionic) conductivity at room temperature. In this paper we describe the low temperature method developed by us for poling flux- grown KTP crystals without modifying their composition. High voltage switching pulses were applied to KTP samples at a temperature below the superionic insulating transition and the switching charge was continuously monitored. This way, high quality domain gratings of 3.8 - 10 micrometers periods were fabricated in 0.5 - 1.0 mm thick flux-grown KTP plates. Second harmonic generation in the range of 400 - 530 nm light by these samples were tested with different types of IR lasers including diode, diode pumped solid state and fiber lasers. The results demonstrate that the low temperature poling technique can provide high quality, short period periodically poled KTP for blue and green coherent light generation.
The formation of anodic oxides on HgZnTe has been studied and characterized by XPS technique. The physical properties of anodized p-type layers have been investigated by the differential Hall effect, photoconductivity, and photoluminescence measurements. It was found that the tendency to form surface inversion layers on HgZnTe by anodization is considerably lower than that for HgCdTe. There is a considerable increase in effective lifetime values and in photoluminescence intensities. In addition, significant differences between the voltametric analysis curves of HgZnTe and HgCdTe were observed. The results are discussed in view of the bonding characteristics of the two materials.
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