CaF2 Laser Crystals Research Articles

10-mJ 300-fs 1-kHz cryogenically cooled Yb:CaF2 regenerative amplifier

In this paper, we report on a cw-pumped cryogenically cooled Yb:CaF2 laser crystal regenerative amplifier that can produce >10.3 mJ, <285 fs laser pulses at 1034-nm and repetition rate of 1-kHz. We achieve record high optical pump to optical amplified compressed output efficiency at >14%. Using a symmetric cavity design to compensate thermal lensing effect, we were able to achieve excellent beam quality with measured M2 at 1.19 and 1.16 at horizontal and vertical directions, respectively.

High-power 2.8 μm lasing in a lightly-doped Er:CaF2 crystal

Er3+-doped crystals pumped by laser diode (LD) is an effective way to obtain near 3 μm laser, which has advantages of low cost and compact structure. CaF2 and SrF2 crystals have the fluorite structure makes Er3+ ions easy to form “clusters”, this effect shortens the space between Er3+ ions, then bring intense interionic energy transfer inside the lightly-doped crystal. Due to the existence of “clusters”, not only the self-termination process was solved, but also the severe thermal damage during the Er3+ 2.8 μm laser generation was avoided. In this work, high quality 1.7 at.% Er:CaF2 laser crystals have been successfully grown by temperature gradient method. LD pumped 2756.6 nm laser with maximum output power of 2.32 W was achieved. It is the highest laser output power generated by LD-pumped Er3+-doped fluoride crystals in recent years. Furthermore, we also demonstrated the 1532 nm LD pumped 1.7 at.% Er:CaF2 laser performance, which proved the strongly energy transfer inside the lightly-doped Er:CaF2 crystal. These results are valuable to the development of the mid-infrared laser towards the direction of compact structure and low cost.

Near-infrared lasing and tunable upconversion from femtosecond laser inscribed Nd,Gd:CaF2 waveguides

Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd:CaF2 laser crystals by using ultrafast laser inscription. Waveguide properties are investigated in terms of guiding behaviors and localized laser-induced lattice damages. Under an optical pump of 808 nm light, continuous-wave waveguide lasing at 1.06 µm is achieved, with a single-mode operation and a minimum lasing threshold of 98.8 mW. Furthermore, the visible emissions of Nd3+ with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process. The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.

Thermally-induced-anisotropy issues in oriented cubic laser crystals, the cryogenically cooled Yb:CaF2 case

Cubic crystals are often favored due to their interesting isotropic properties -such as the refractive index, the dilatation, etc-that simplify their use in laser systems. Among all Yb-doped high-symmetry materials, Yb:CaF2 is a very attractive one for high-energy high-power lasers. However, in such systems, thermal loads become important and thermal anisotropic effects can occur even for simple cubic crystals impacting severely the laser system design. In this context, we report here, a study of thermally induced polarization anisotropy in Yb-doped CaF2 laser crystals. Both thermal lens and thermally induced depolarization are precisely studied for different crystal orientations, namely the [110] and the [111] orientation. The study is performed with a pump/probe setup adapted to improve the signal-to-noise ratio under high power pumping. We observed both, classical-thermally induced depolarization and thermal lensing in accordance with previous work, but also, for certain configurations, atypical depolarization figures and astigmatic lenses. These results were also confronted with numerical simulations. The comparison between the [110] and the [111] oriented crystals represents a crucial study to determine the origins of these unusual effects and to allow a better understanding of thermal anisotropy in cubic laser-crystals.

Switchable single-dual-wavelength Yb,Na:CaF2 waveguide lasers operating in continuous-wave and pulsed regimes

Depressed-cladding waveguides are produced in Yb,Na:CaF2 laser crystal by applying ultrafast laser inscription. Under pumping at 946 nm, continuous-wave (CW) and Q-switched laser oscillations with low thresholds are realized in these waveguide structures. With the variation of pumping power, switchable single- and dual-wavelength laser emissions peaking at 1013.9 nm and 1027.9 nm are generated. The maximum output power achieved for CW lasing is about 170 mW, corresponding to an optical-to-optical conversion efficiency as high as 45.3%. A pulse energy of 0.13 μJ is obtained for the waveguide laser operating in the pulsed regime.

Correction: Site selective analysis of Nd3+–Lu3+ codoped CaF2 laser crystals

Correction for ‘Site selective analysis of Nd3+–Lu3+ codoped CaF2 laser crystals’ by S. Normani et al., CrystEngComm, 2016, 18, 9016–9025.

Role of monovalent alkali ions in the Yb3+ centers of CaF2 laser crystals

Abstract Yb 3+ and M + monovalent alkali ions (M + = Li + , Na + , K + )-co-doped CaF 2 cubic laser crystals were grown by the micro-pulling-down method (μ-PD) under CF 4 atmosphere. Structural and spectroscopic characterizations of Yb 3+ in substitution of Ca 2+ (absorption, emission and decay curves) were carried out to study the effect of M + ions as charge compensators.

Spectroscopy and lasing of cryogenically cooled Yb, Na:CaF2

Absorption, photoluminescence spectra and CW lasing parameters of an Yb3+- and Na+-codoped CaF2 laser crystal are measured in the temperature range from 5 K to 290 K. The crystal appears to be a promising host for broadband multi-mJ kHz CW-pumped regenerative amplification.

Codoping Na^+ to modulate the spectroscopy and photoluminescence properties of Yb^3+ in CaF_2 laser crystal

Three kinds of Yb3+ - and Na+-codoped CaF2 laser crystal with different Na:Yb ratios of 0, 1.5, and 10 are grown by the temperature gradient technique. Room-temperature absorption, photoluminescence spectra, and fluorescence lifetimes belonging to the transitions between ground state 2F7/2 and excited state 2F5/2 of Yb3+ ions in the three crystals are measured to study the effect of Na+. Experimental results show that codoping Na+ ions in different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in a CaF2 lattice in a large scope.