Eugen Osiac

Diode pumping of a continuous-wave Pr 3+ -doped LiYF 4 laser

We report, for the first time to our knowledge, diode-pumped cw laser oscillation of Pr3+:LiYF4 in the red spectral range. The pump power is provided by a GaN laser diode emitting a maximum output power of 25 mW at a wavelength of approximately 442 nm. The Pr3+ laser emits 1.8 mW of output power at a 639.7-nm wavelength. Threshold pump power and slope efficiency in a nonoptimized setup are determined to be 5.5 mW and 24%, respectively.

The nature of nonequivalent Nd3+ centers in CNGG and CLNGG

Abstract Results on the spectroscopic investigations and modeling of Nd3+ nonequivalent center structure in calcium niobium gallium garnet (CNGG) and calcium lithium niobium gallium garnet (CLNGG) are presented. The low temperature absorption, emission under selective excitation and lifetimes on a large variety of samples with Nd3+ varying between 0.1 and 5 at.% are analyzed. At least five different types of centers have been separated. Based on spectral data along with previous reports on the composition of the crystals a model of Nd3+ five-center structure in CNGG and CLNGG disordered crystals is proposed. The relative intensities for all the centers can be explained consistently by the structural possibilities of occupation of the first cationic octahedral sphere around the Nd3+ site. Starting from an unique average composition of this sphere our modeling suggests a correlated placement of the cations in the first octahedral sphere around Nd3+: the larger charge of Nd3+ as compared to the substituted Ca2+ leads to a local depletion of Nb5+ ions, accompanied by a corresponding enhancement of the lower-charge cations ( Ga 3+ , Li + ) or vacancies as compared with the undoped crystals.

Spectroscopic characterisation of the upconversion avalanche mechanism in Pr3+,Yb3+:BaY2F8

Abstract The paper presents the spectroscopic investigation of Pr 3+ ,Yb 3+ :BaY 2 F 8 and the characteristics of the upconverted emission from the 3 P 0 level due to an avalanche mechanism under infrared excitation around 820 and 870 nm. Absorption and emission measurements at 12 K were performed in order to refine the Stark level scheme. Room temperature absorption, emission, excitation spectra, and excited state absorption measurements were performed and analysed in order to investigate the properties of the avalanche mechanism and to determine the spectroscopic parameters of this system. Based on the determined spectroscopic parameters a system of differential equations was established in order to describe the observed avalanche mechanism.

Optical pump-probe processes in Nd 3+ -doped KPb2Br5, RbPb2Br5, and KPb2Cl5

Recently, laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2}+{sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. In this paper we present cw pump-probe spectra in order to discuss excited state absorption, reabsorption processes due to the long lived lower laser levels as well as possible depopulation mechanisms feasible for more efficient laser operation in these crystals. The bromides will be compared with potassium lead chloride (Nd{sup 3+}:KPb{sub 2}Cl{sub 5}).

Spectroscopy and energy transfer characteristics of Nd3+ in CNGG

The garnets with disordered structure such as calcium niobium gallium garnet (CNGG) doped with Nd3+ are interesting materials for diode pumping. Spectroscopic investigations on Nd3+:CNGG have revealed a multisite structure and this is reflected in laser emission characteristics. The purpose of this paper is to present several new spectral aspects, a modeling for the main nonequivalent centers, energy transfer characteristics and an attempt to connect the laser characteristics to centers structure. Samples were grown by Czochralski method with Nd3+ from 0.1 to 5 at.% and the high resolution spectral and decay measurements were performed at 10 K. Similar considerations were made in the case of Nd3+ doped in calcium lithium niobium gallium garnet (CLNGG).

Inhomogeneous broadening effects in optical spectra Nd/sup 3+/ in CNGG and CLNGG

Summary form only given. Interesting classes of solid state hosts for diode pumped lasers or for short pulse emission could be those with broad spectral bands. Although rare earth ions in glasses satisfy this condition, their use in diode pumped lasers is limited by the small stimulated emission cross section and thermal conductivity. Therefore, a crystal that fulfils all these three requirements is expected to give better performances. These characteristics could be satisfied by crystals with disordered structure such as calcium niobium gallium garnet Ca/sub 3/Nb/sub 1.6875/Ga/sub 3.187/O/sub 12/ (CNGG) and calcium lithium niobium gallium garnet Ca/sub 3/Nb/sub 1.775/Ga/sub 2.95/Li/sub 0.275/O/sub 12/ (CLNGG). These crystals have several advantages compared with ordered garnet crystals, such as YAG: low melting point (smaller than 1500/spl deg/C), broad absorption and emission bands, larger doping level with ions such as Nd/sup 3+/, better thermal properties than glasses. Though laser emission was reported for Nd/sup 3+/ in CNGG and CLNGG, the growth conditions for homogeneous crystals or fibres, the spectroscopic characteristics, the nature of nonequivalent centers, and the energy transfer peculiarities are still problems to investigate. The paper attempts to elucidate the nature of non-equivalent Nd/sup 3+/ centers leading to Nd/sup 3+/ multisites in both crystals, CNGG and CLNGG, and to discuss the energy transfer processes.

Semiconductor laser pumping of a continuous-wave Pr/sup 3+/:LiYF/sub 4/ laser emitting at several wavelengths

We report continuous-wave laser operation of Pr/sup 3+/:LiYF/sub 4/ at 639.7 nm, 607.3 nm, and 522.6 nm using a frequency-doubled optically pumped semiconductor laser as pump source. Furthermore, a red continuous-wave Pr/sup 3+/:LiYF/sub 4/ laser was realized under GaN laser diode pumping.

Excited state absorption and gain measurements in Tm/sup 3+/ doped fluoride crystals

Tm/sup 3+/ is a very interesting ion for both realization of infrared lasers. We have measured the excited state absorption and gain for Tm/sup 3+/:BaYF crystals with the concentration of 5, 8, 12 and 18%, Tm/sup 3+/:YLF with the concentration of 6% and Tm/sup 3+/:KYF with the concentration of 15%. The investigations are based on pump and probe measurements using the double modulation technique with two lock-in amplifiers.

Determination of excited state absorption cross sections for spectrally overlapping transitions via phase sensitive detection

In this paper we show that in an excited state absorption (ESA) setup the phase sensitive detection features of the lock-in amplifier can be exploited for a complete discrimination of even spectrally overlapping transitions. In connection with Judd Ofelt calculations it allows the determination of the excited state absorption cross sections. The method of phase sensitive detection in the double modulation technique was described in detail for the example of excited state absorption measurements in Ho/sup 3+/,Yb/sup 3+/:YLiF/sub 4/ in the 720 nm - 860 nm spectral range.

Avalanche mechanism generating laser oscillation in Pr/sup 3+/,Yb/sup 3+/:BaY/sub 2/F/sub 8/

The avalanche excitation mechanism in the Pr/sup 3+/-Yb/sup 3+/-system is demonstrated in Pr,Yb:BaY/sub 2/F/sub 8/ (BYF). A nearly concentric resonator was used consisting of two mirrors with a radius of curvature of 50 mm. Two different output mirrors were used with transmissions of 1% and 6% in the 607.5 nm spectral range. Both orange (607.5 nm) and red (638.7 nm) laser oscillation were observed under 841 nm excitation.