Kinetics of excitation transfer from Cr2+ to Fe2+ ions in co-doped ZnSe.

The transfer of electronic excitations from Cr2+ to Fe2+ ions in co-doped epitaxially grown ZnSe is studied by time-resolved photoluminescence (PL) spectroscopy with unprecedented sub-10 ns time resolution. Upon excitation of Cr2+ ions by a picosecond pulse at 2.05 µm wavelength, PL from Fe2+ ions displays a delayed onset and a retarded decay in comparison to Fe2+ PL directly excited at 3.24 µm. We measure an extremely rapid 60 ns buildup of the Fe2+ luminescence, which is followed by a slower relaxation on the few micrometer scale. The experimental results are analyzed in the framework of Förster radiationless resonant energy transfer. Directly connecting to the work of Fedorov et al. [Opt. Mater. Express9, 2340 (2019)10.1364/OME.9.002340], the 60-ns buildup time of energy transfer is found to correspond to a Cr2+-Fe2+ distance of 0.95 nm, close to the length of the space diagonal of the ZnSe unit cell. This result demonstrates a significant density of spatially correlated Cr2+-Fe2+ ion pairs at short distance, in parallel to ions with a random distribution at a larger mutual separation.

Thermo-Optical Studies of Laser Ceramics.

A cycle of works on manufacturing and studying laser and magnetooptical ceramics with a focus on their thermo-optical characteristics performed by the research team is analyzed. Original results that have not been published before such as measurements of the Verdet constant in the Zr:TAG, Re:MgAl2O4, and ZnAl2O4 ceramics are also presented.

High-purity CVD-ZnSe polycrystal as a magneto-active medium for a multikilowatt Faraday isolator.

Prospects for using ZnSe polycrystals synthesized by the chemical vapor deposition (CVD) method for the development of Faraday isolators for high-power radiation at a wavelength of 1076 nm are investigated. A Faraday isolator was built by a conventional scheme for room temperature operation. No thermally induced depolarization was observed in the device for the laser power range up to 1270 W, which is the main limiting factor for powerful isolators. It was demonstrated experimentally that thermally induced depolarization is not expected at powers up to 2.5 kW.

High power simultaneous dual-wavelength CW and passively-Q-switched laser operation of LD pumped Tm:YLF at 1.9 and 2.3 µm.

Simultaneous dual-wavelength laser oscillation of Tm:YLF at 1.9 and 2.3 µm were successfully realized. The three-mirror cavity was exploited to study dual-wavelength laser performance, which is formed by a shared input mirror and two independent output couplers for the two laser wavelengths. Under an absorbed pump power of 15.2 W, the maximum CW output powers of 5.49 W around 1908nm and 1.12 W around 2305 nm were simultaneously obtained, corresponding to a total optical-to-optical conversion efficiency of 43.5%. A Cr2+:ZnSe was further used to passively Q-switch the dual-wavelength laser, generating pulses with pulse widths of 554 ns at 1.9 µm and 4 µs at 2.3 µm. To the best of our knowledge, this is the first report on the dual-wavelength laser operation of Tm3+-single-doped solid-state laser at 1.9 and 2.3 µm. The higher optical conversion efficiency, smaller wavelength competition effect and simultaneous dual-wavelength output make this Tm-doped solid-state laser have potential application in medical surgery.