We report on fabrication, structure, spectroscopic and nonlinear properties of a new functional optical material – transparent glass-ceramics (GCs) based on Co2+,Ga3+-codoped ZnO (Co2+:GZO) nanocrystals. The introduction of Ga3+ cations that are smaller than Zn2+ ones and have a different valence state, is expected to modify the crystal field around the Co2+ ions leading to broadband absorption at the 4A2(4F) → 4T1(4F) transition. The glass of the ZnO – K2O – Al2O3 – SiO2 system was doped with 3 mol% Ga2O3 and 0.05 mol% CoO. Transparent GCs were produced by secondary heattreatments at 680 – 860 °C. They contained one crystalline phase - nanosized (8 – 26 nm) hexagonal GZO crystals, Ga3+ ions being distributed between the ZnO nanocrystals and the residual glass. The absorption spectra of GCs contained an intense band at 1.3-1.65 μm related to the 4A2(4F) → 4T1(4F) Co2+ transition in Td sites. A rise of IR losses due to the free charge carrier scattering in GZO was observed. Absorption saturation of transparent GCs was studied at ~1.54 μm. They exhibited low saturation fluence, 0.7–1.3 ± 0.2 J/cm2, and high laser-induced damage threshold, ~25 J/cm2. Co2+,Ga3+- codoped ZnO-based transparent GCs are promising for passive Q-switching of eye-safe erbium lasers emitting at ~1.5- 1.7 μm.
We introduce a Raman scattering based detector of carbon isotopes in gaseous mixtures. A solid state 532 nm 5 W CW laser focused into a gaseoussample by a custom-built diffraction-limited objective was used for excitation of Raman signal. Raman signal was collected by an f-matcher with edge filter at excitation wavelength of 532 nm. A Czerny-Turner scheme based spectrometer and a cooled down to -40°C CMOS camera were used to register the signal.
Natural carbon isotopes (carbon-12 (12C) and carbon-13 (13C)) contained in human respiration can be used to detect various diseases (cachexia, helicobacter pylori). Isotope mass spectrometry (IRMS), which is widely used to determine carbon isotopes in human respiration has a high level of accuracy and sensitivity, but is a very complex and expensive technique. There is a less expensive way to detect carbon isotopes using an isotope-selective non-dispersive infrared spectrometer (NDIRS), but it is only suitable for simple breath tests when a small number of samples is required. Raman spectroscopy is well suited for the simultaneous detection of various gases in the analysis of human respiration, but the Raman signal from the carbon isotopes has a very low intensity, what makes their detection difficult. In this work, we demonstrate an effective system for detecting carbon isotopes 12CO2 and 13CO2 in human breath with an extremely low concentration level of ~ 0.01%. The Raman detector consists of a 5 W CW narrow-linewidth single-frequency solid-state laser at 532 nm, a focusing system with compensation for a spherical aberration, a gas cell which can withstand pressures up to 100 atmospheres and a high-resolution Czerny-Turner based spectrometer with a matrix, cooled by a Peltier element down to -40 °C. Such a system has a lower cost in comparison with analogues and can be used the medical diagnosis of various diseases.
We model output characteristics of the 1645 nm 8 mJ 10 ns 100 Hz Q-switched Er:YAG DPSSL. The laser is end pumped at a wavelength of 1532 nm. Fiber-coupled diode laser module was 10 nm FWHM, 12 W CW, 200 μm, NA 0.22. Various tapering of the active rod has been considered for 1 mm diameter, 20 mm long and 0.5% Er doping. We discuss the heat deposition process, the energy storage efficiency and the average power limitations for Q-switched regime of generation and amplification, and find the system scalable for the high power operation.
We demonstrate a pulse-bursting phenomenon in Yb:Er glass laser operating at 1.54 μm. Glass-ceramic material with a low value of saturation threshold based on Co2+:β-ZnSiO4 nanocrystals was used as a passive gate for pulse-burst operation. The bursts of pulses were 1.5 ms long, each burst consisted of 40-55 pulses with 9-30 μJ energy per pulse and 0.2-3 μs pulse width. Bursting outputs arise via a coupling between slow switching arising via a slow pump modulation and fast pulsations resulting from Q-switch mechanism. We show that absorption cross-section strongly affects the mode of laser operation ranging from relaxation oscillations corresponding to low cross-section values to bursting and conventional Q-switch operation in the case of their higher values.
We report on the passive Q-switching of a compact diode-side-pumped Er,Yb:glass laser by a novel saturable absorber (SA) based on transparent glass-ceramics (GC) containing Co2+Mg(Al,Ga)2O4 nanocrystals. To prepare the GC, an initial magnesium aluminosilicate glass doped with Ga2O3 containing 0.1 mol% CoO was synthesized by a conventional melt-quenching technique and heat-treated at 850–950 °C. The X-ray diffraction analysis of the GC confirmed the precipitation of Co2+Mg(Al,Ga)2O4 crystals with spinel structure (6-7 nm in size). Depending on the heat-treatment temperature, the saturation intensity for the GC measured at 1540 nm was in the 0.5...0.7 J/cm2 range and the recovery time was in the 240...335 ns range. Using the SA based on GC prepared by the heat-treatment at 950 °C with an initial transmission of 84.7%, we generated stable Q-switched pulses 1.14 mJ in energy and 7.2 ns in duration. The peak power reached 160 kW, the repetition rate was 1 Hz and the laser wavelength was 1535 nm. The developed GCs are promising for Q-switching of erbium lasers emitting at 1.5-1.7 μm.
We demonstrate a durable and efficient 3 mJ 10 ns 100 Hz Nd:YAG laser developed with a view to the space borne operation. We discuss the cavity construction design principle, the approach to high efficiency and the smooth pulse operation. The experimental investigation for the best pair of Q-switch transmission and output coupler reflection coefficient is considered. The factors influencing the pulse shape are analyzed. The 100 Hz operation with good beam quality is demonstrated.
We demonstrate side pumped ultra-compact Q-switched Er:glass laser for rangefinding with 1.4 mJ energy at 1.54 um. Laser diode with 75 W power and 5 ms pulse duration was used. Active medium was enveloped with diffuse reflector. Output pulse energy in free-running mode was 27 mJ with a slope efficiency of 12%. Transparent glass-ceramics containing Co2+:MgAl2O4 nanocrystals were used as a passive gate to ensure Q-switching in an operation temperature range and transverse mode selection. The Q-switch mode had steady operation at 1 Hz repetition rate with thermal effects playing no visible role.
We demonstrate a compact Er:glass single-rod fiber laser for rangefinding with 1 mJ energy Q-switched at 1.54μm.
Double-pass pumping with 16 W power and 5 ms pulse duration was used. Active medium was enveloped with diffuse
reflector. Thus efficient output power operation achieved. Free-running mode output pulse energy was 12 mJ with a
slope efficiency of 16%. Transparent glass-ceramics containing Co2+:MgAl2O4 nanocrystals were selected as the optimal
passive gate to ensure Q-switching in a temperature range and transverse mode selection. The Q-switch mode had steady
operation at 1 Hz repetition rate with thermal effects playing no visible role.
We experimentally study passive mode-locking in Nd:YVO4 laser based on second harmonic generation in KTP crystal.
We characterized RF spectra and optical spectra versus pump power, the KTP crystal temperature and position, the
output coupler reflectivity, and the intracavity polarizer. We discuss the device performance considering cascaded χ(2)
lensing in KTP, frequency doubling nonlinearity, and Kerr lens formed in Nd:YVO4. Implementing an intracavity Lyot
filter and cavity length modulation via PZT does not affect mode-locking capability. These results and ultra-low noise
mode beat signal open a new perspective for stable RF signal generation by transferring optical reference stability
(iodine absorption lines) into RF domain.