H. Scheife

High-power continuous-wave upconversion fiber laser at room temperature.

We report cw laser emission of a Pr, Yb-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF fiber in the red spectral region. Laser emission was achieved on the transition P(0)(3)?F(2)(3)(lambda(L)=635 nm) with a Ti:sapphire pump laser tuned to lambda(p)=850 nm . A maximum output power of P(out)=675 mW was obtained at an incident pump power of P(in)=3.37 W . The output power was increased to P(out)=1020 mW when pumping with P(in)=5.51 W was provided by two Ti:sapphire lasers. A photon avalanche process was found to contribute strongly to the population of the upper laser level.

Nondestructive measurement of the propagation losses in active planar waveguides

A nondestructive loss-measurement method for active planar waveguides has been developed. It is based on the determination of the longitudinal distribution of fluorescence light along the waveguiding direction, obtained at different excitation wavelengths. First measurements have been performed on a 10 μm thick Nd:Sc2O3 waveguiding film, deposited on a sapphire substrate by pulsed laser deposition, and on a 35 μm thick diffusion-bonded Nd:YAG waveguide between sapphire layers. Their scattering losses have been determined to be (11.6±0.9) and (6.9±0.9) dB/cm, respectively.

Compact diode pumped cw solid-state lasers in the visible spectral region

This paper reviews recent advances in diode pumped cw solid-state lasers in the visible spectral region. Such lasers are based on rare earth doped materials. Visible wavelengths can be generated by frequency conversion of near IR-lasers or by up-conversion pumped rare earth ion lasers.

Epitaxial growth by pulsed laser deposition of Er-doped Sc2O3 films on sesquioxides monitored in situ by reflection high energy electron diffraction

In this letter, the authors report on the epitaxial growth by pulsed laser deposition of Sc2O3 and Er(5%):Sc2O3 films on {100} and {111} oriented Sc2O3. They observed layer-by-layer growth in the orientation defined by the substrate. This was indicated by reflection high energy electron diffraction as intensity oscillations of the specularly reflected electron beam. A monolayer-smooth film surface was observed by atomic force microscopy. Such a growth behavior was also achieved during initial growth of Sc2O3 on {100} oriented Y2O3. Additional x-ray diffraction analysis shows good agreement with the growth behavior mentioned above.

Continuous-wave laser action of an Er:Sc 2 O 3 bulk crystal at 1.58 μm

This paper reports on a Er:Sc₂O₃ laser emitting a CW output power of 16.1 mW at 1583.7 nm for 890 mW of absorbed pump power, and with slope efficiency 4.2%. The Er:Sc₂O₃ of 4.75 mm length was grown by the Nacken-Kyropoulos method. Ti:Al₂O₃ laser emitting at 975 nm was used as the pump source.

PLD-grown Yb-doped Sesquioxide Films on Sapphire and Quartz Substrates

This paper focuses on the fabrication and characterization of crystalline Yb-doped sesquioxide films (Yb2O3, Yb:Lu2O3, Yb:Sc2O3) grown by pulsed laser deposition on single crystal sapphire (α-Al2O3) and quartz (α-SiO2) substrates as well as on lutetia (Lu2O3) and scandia (Sc2O3) substrates. Such ytterbium doped active films can be promising for use in a thin-disk laser setup. X-Ray diffraction measurements show that the films grow highly textured along direction. The ω-scan (rocking curve) shows deviation of the crystallite orientation ~4° in case of Lu2O3 and Yb2O3 films and <1° for Sc2O3 films. Yb2O3 films reveal no luminescence at room temperature and the well known Yb3+ emission in the 975-980 nm region (zero-phonon line) can only be observed at temperatures below 20 K. A similar effect is observed in a bulk Yb2O3 crystal. Ytterbium emission and excitation spectra measured at room temperature for Yb(5%):Lu2O3 and Yb(4%):Sc2O3 films resemble those of the bulk crystal very closely. Luminescence decay lifetimes are also comparable to those measured in a bulk crystal. This indicates a high quantum efficiency of the Yb3+-emission and allows application of such films as active media for thin disk lasers.

Energy transfer processes in crystalline Er 3+ ,Yb 3 +:Sc 2 O 3

Using Yb³⁺ as a sensitizer for Er³⁺ doped laser materials is a common technique [1] in glass host materials because of the high Yb³⁺ absorption cross sections. The Yb³⁺ ions absorb the pump light and transfer the energy to the Er³⁺ ions. Due to the energy match between the 4I11/2 level of Er³⁺ and the ²F<inf>5/2</inf> level of Yb³⁺, the energy transfer process is resonant. Er³⁺ doped crystalline sesquioxides have a higher thermal conductivity, a higher hardness, higher peak emission cross sections and narrower emission peaks compared to Er³⁺:glass. These advantages make crystalline Er³⁺:Sc<inf>2</inf>O<inf>3</inf> a promising laser material. In this work the energy transfer from Yb³⁺ to Er³⁺ in crystalline Sc<inf>2</inf>O<inf>3</inf> is studied. For the spectroscopic characterization, crystalline Sc<inf>2</inf>O<inf>3</inf> films with different Er³⁺,Yb³⁺ concentrations have been grown on a-Al<inf>2</inf>O<inf>3</inf> substrates by Pulsed Laser Deposition (PLD).

Energy migration governs upconversion losses in Er 3+ -doped integrated amplifiers

Energy-transfer upconversion (ETU) is a detrimental effect in many rare-earth-ion-doped infrared amplifiers and lasers [1], among them Er³⁺-doped waveguide amplifiers [2]. Er³⁺ concentrations in the order of 10²⁰ cm⁻³ are usually necessary to attain high gain values on the centimeter length scale of an integrated optical device. At such high Er³⁺ doping, electric dipole-dipole interactions between neighboring ions such as energy migration and ETU take place, thereby reducing the population inversion and negatively affecting the gain performance of the amplifier. We investigated these effects by lifetime and gain measurements, see Figs. 1 (a) and (c), respectively, in Al<inf>2</inf>O<inf>3</inf>:Er³⁺ waveguides and analyzed the results in the frame of the microscopic model developed by Zubenko et al. [3]. The luminescent decay from the ⁴I<inf>13/2</inf> first excited level of Er³⁺ can be described by the equation in a given equation is the error function, n(t = 0) = n(0) is the initial excitation density of the ⁴I<inf>13/2</inf> level, τ<inf>D</inf> is its intrinsic lifetime, C<inf>DA</inf> is the microparameter of ETU from the ⁴I<inf>13/2</inf> level, and τ<inf>0</inf> is the mean time of a migration hop. By fitting the experimental decay curves measured in samples with 7 different Er³⁺ concentrations, out of which only 4 are shown in Fig. 1 (a) for simplicity, we find τD = 7.6 ms and C<inf>DA</inf> = (6.1±0.6)×10⁻⁴¹ cm⁶/s, while τ<inf>0</inf> decreases from 65 ms down to 1 ms with increasing Er³⁺ concentration, see Fig. 1(b). This behavior is due to decreasing distance among Er³⁺ ions with increasing concentration, which enhances the probability of the energy-migration process.

Growth, micro-structuring, spectroscopy, and optical gain in as-deposited

PCT No. PCT/EP93/02622 Sec. 371 Date May 27, 1994 Sec. 102(e) Date May 27, 1994 PCT Filed Sep. 27, 1993 PCT Pub. No. WO94/08169 PCT Pub. Date Apr. 14, 1994.In a flexible connection arrangement for two pipe portions having a metallic bellows which is connected axially on either side in a gastight manner with connection pieces, the sides of the connection pieces facing the bellows are provided with radially widened end portions. Also provided are a damping insert, which extends coaxially relative to the bellows a along its length and is in a working connection therewith, and heat protection device for the bellows acting in the radially inward direction. The damping insert encloses the bellows radially outwardly such that the turns of the bellows contact the damping insert. The lateral end regions of the damping insert are held in the widened end portions without being fastened thereto and are supported radially outwardly by the latter. The connection pieces are connected with one another via a spring which surrounds the damping insert radially outwardly. The heat protection means are formed by a pipe segment which extends within the bellows coaxially relative to the bellows at a radial distance from the latter and which is fastened to the connection piece located in the front as viewed in the direction of flow.

Al_2O_3:Er

This study reports on the 2-dimensional growth of Yb:YAG and YbAG pulsed laser deposited (PLD)-films on YAG, which is monitored by RHEED measurements in situ during growth. The properties of the films after growth are investigated by means of XRD, AFM and optical spectroscopy. Films highly textured in the orientation defined by the substrate are obtained.