Vasilii A. Konyushkin

First ceramic laser in the visible spectral range

Results for new fluoride ceramics doped with praseodymium ions in which, to the best of our knowledge, for the first time a laser in the visible spectral range (639 nm) was obtained under GaInN blue laser diode optical pumping. In our experiments, CW operation with lasing threshold less than 100 mW of absorbed pump power and slope efficiency exceeding 9% was realized.

Tunability of laser based on Yb-doped hot-pressed CaF 2 ceramics

The aim of presented study was an investigation of tunability of diode pumped laser based on hot-pressed Yb:CaF2 ceramics. The tested Yb:CaF2 sample was in the form of 3.5mm thick plane-parallel face-polished plate (without AR coatings). The Yb3+ concentration was 5.5 %. A fiber (core diameter 200 μm, NA= 0.22) coupled laser diode (LIMO, HLU25F200-980) with emission at wavelength 976 nm, was used for longitudinal Yb:CaF2 pumping. The laser diode was operating in the pulsed regime (4 ms pulse length, 20 Hz repetition rate). The duty-cycle 8% ensured a low thermal load even under the maximum diode pumping power amplitude 10W (crystal sample was only air-cooled). This radiation was focused into the crystal (pumping beam waist diameter ~ 170 μm). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.01 − 1.09 μm, HT @ 0.97 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 98% @ 1.01 − 1.09 μm. Tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and the laser active medium. The extremely broad and smooth tuning was obtained. The laser was continuously tunable over ~ 66nm (from 1015nm to 1081 nm) and the tuning band was mostly limited by free spectral range of used birefringent filter. The tunability FWHM was 40 nm corresponding bandwidth 10 THz results in Fourier limited gaussian pulse width ~ 40 fs (FWHM). The maximum output power amplitude 0.68W was obtained at wavelength 1054nm for absorbed pump power amplitude 6W. The laser slope efficiency was 15%.

New Visible SrF2:Pr3+ Ceramic Laser at 639 nm

For the first time to our knowledge SrF2:Pr3+ fluoride ceramics was developed and visible 639 nm wavelength oscillations were obtained in diode pumped CW mode with slope efficiency above 9%.

Spectroscopic and Oscillation Properties of Yb 3+ Ions in BaF 2 -SrF 2 -CaF 2 Crystals and Ceramics

Absorption and emission cross sections of Yb3+ions in SrF2crystal and CaF2-SrF2and BaF2-SrF2solid solutions were determined. Tuning in 1000-1080 nm region was observed. Physicochemical and oscillation properties of CaF2ceramic were investigated.

Fluoride Ceramics for Mid IR Lasing (2-3 μm) and Planar Waveguides

Fluoride ceramics doped with Er3+, Tm3+, Ho3+ ions was developed and its spectroscopic and laser properties in 2-3 μm spectral region were investigated. Slope efficiency about 20% was demonstrated in 2 μm spectral region.

First visible 639 nm SrF 2 :Pr 3+ ceramic laser

During the last years the interest for RE doped fluoride ceramics has arisen due to its improved thermo mechanical properties compared to analogous single crystal. Within short period of time number of fluoride nanoceramics were developed and rather efficient diode pumped lasing was demonstrated for LiF:F<inf>2</inf>⁻ [1], CaF<inf>2</inf>-SrF<inf>2</inf>:Yb³⁺ [2], CaF<inf>2</inf>:Yb³⁺ [3], SrF<inf>2</inf>:Nd³⁺ [4]. The common feature for all these ceramics was that laser oscillations in near IR spectral region 1–1.2 µm were obtained. It is well known that the optical losses in ceramic host material (scattering on grain boundaries, pores and inclusions) should strongly increase at shorter wavelengths. From this point of view the development and the investigation of laser ceramics which can oscillate at visible wavelengths is of great important. The recent success in visible light generation with Pr³⁺ ions [5] has become possible due to development of efficient blue GaInN diodes. In this work the results on oscillation properties of new Pr³⁺ doped SrF<inf>2</inf> ceramics are firstly presented.

Cryogenically cooled tunable Tm, Y:CaF 2 laser

The goal of this work was an investigation of the temperature influence (80–300 K) on laser properties of thulium doped CaF<inf>2</inf>, co-doped by yttrium (Tm, Y:CaF<inf>2</inf>), which could serve as gain medium for generation of radiation at 1.8–2 μm. CaF<inf>2</inf> single crystal and ceramic belong to promising laser hosts.[1, 2] Its doping by trivalent ions, like Tm³⁺, leads to forming of complex structures necessary for charge-compensation.[3] The variety of these centers broaden the absorption and emission spectra, which is favorable to diode pumping and laser tunability. Co-doping by optically inactive Y³⁺ ions could further increase the variety of optical centers without negative effect of upper laser level concentration quenching. Here we report the first results obtained with Tm, Y:CaF<inf>2</inf>.

InGaN diode pumped Pr:SrF2 laser at 639 nm wavelength

We report on Pr:SrF2 single crystal laser operation at 639nm wavelength under blue laser diode pumping. The laser system was operated in the pulsed regime at 100 Hz repetition rate and 2 ms pulse duration. Using 3.5W InGaN laser diode as a pump source, 6mW of the mean output power at 639nm was extracted from the Pr:SrF2 sample. The corresponding slope efficiency related to the absorbed mean power was 16.4 %.

Temperature influence on diode-pumped Tm:SrF2-CaF2 laser properties

The goal of this work was an investigation of the temperature influence (in range 77 - 300 K) on laser properties of Tm:SrF2-CaF2 solid-solution, which is suitable as a gain medium for generation of radiation at 1.8-2 μm. The tested Tm:SrF2-CaF2 sample (60 mol% CaF2, 38 mol% SrF2) was doped with 2 mol% of TmF3. The diameter of the grown boule was 10 mm. The sample was cut and optically polished parallel to growing axis. The polished sample thickness was 8.5 mm. It was fixed in temperature controlled cupreous holder, placed inside vacuum chamber of the liquid nitrogen cryostat. A fiber coupled laser diode, operating in pulsed regime (10 ms pulse length, 10 Hz repetition rate) at wavelength 764 nm, was used for longitudinal sample pumping. The 142mm long semi-hemispherical laser cavity consisted of at pumping mirror (HR @ 1:8 - 2:0 μm, HT @ 0.77 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 92% @ 1:8 - 2:0 μm. From the results it follows that the temperature of the active medium has a strong infkuence on laser slope efficiency. The highest slope efficiency (42% in respect to absorbed power), obtained for temperature 77 K, was more than five times higher than slope efficiency for 300 K. The threshold decreased twice with the temperature lowering from 300 to 77 K. Laser output power amplitude 5.5W at wavelength 1856nm was reached for absorbed power 15.8W at 77 K.

Spectroscopic and oscillation properties of Nd 3+ and Yb 3+ ions optical centers in BaF 2 -SrF 2 -CaF 2 crystals and ceramics

Trivalent rare-earth ions in fluorides are known to form different optical centers due to non isovalent substitution of divalent cations and different forms of charge compensation. The set of optical centers usually depends on the type of rare-earth ions, their concentration and fluoride host. Existence of wide range of fluoride solid-solutions also allows to influence the process of optical centers formation and thus manipulate the spectroscopic and oscillation properties of rare-earth ions [1].