The spectral and laser characteristics of two anti-reflection (AR) coated Cr:ZnSe single crystals 3 mm and 5 mm long were investigated under ~1.7 μm laser diode pumping. The crystals were assembled in a copper holder actively cooled by circulating water. Room temperature absorption and fluorescence spectra were measured, together with the fluorescence lifetime of Cr2+ ions were measured. The influence of the pump pulse durations on the output laser power was investigated. The mean output power of ~2.7 W in CW mode at the wavelength of ~2.4 μm (~24% slope efficiency) was obtained with the 5 mm thick AR coated sample. In this case the M2 beam parameter of ~1.1±0.1 and the beam waist diameter of ~42±4 μm which corresponds to the maximum (in the beam waist) laser power density of ~200 kW/cm2. Furthermore, using a MgF2 birefringent plate, the laser output was tuned from ~2.05 μm up to ~2.65 μm with a spectral linewidth of ~5-10 nm and a Gaussian beam profile. The mean laser output power in the broad mid-infrared range of ~2.1-2.52 μm exceeded 1 W, which corresponds to a power density of at least ~73.5 kW/cm2.
In this work the results of research of an optimal concentration ratio of Cr2+ and Fe2+ co-doped active ions for more efficient Cr2+ → Fe2+ ions energy transfer in a chosen Zn1-xMnxSe (x ≈ 0.15) host material are presented. Three cryogenically cooled Cr2+,Fe2+:Zn1-xMnxSe (x ≈ 0.15) single crystals with the same thickness of ~2.7 mm and with different doping ratios of Cr2+ and Fe2+ ions of ~1:1, ~2:1, and ∼3:1 were investigated under Q-switched Er:YLF laser excitation (wavelength: ∼1.73 μm, pulse energy: ∼10 mJ, pulse duration: ∼150 ns). The temperature dependence of the absorption and fluorescence spectra, the fluorescence decay time as well as the laser output characteristics were measured. The Fe2+ ions maximum laser output of ~50 μJ at the wavelength range of ~4.25-4.42 μm was obtained with the crystal sample for which the active ions ratio was ~2:1. A further increase of the chromium ions amount (Cr2+:Fe2+ ≈ 3:1) led to worse results. Using appropriate resonator cavity mirrors, the samples were also able to generate the ~2.35-2.45 μm laser radiation from Cr2+ ions. The laser output beam spatial profiles were close to Gaussian in all cases. In summary, an optimized compact source of mid-infrared ~4.25-4.42 μm (Fe2+) and ~2.35-2.45 μm (Cr2+) of Cr,Fe:Zn1-xMnxSe (x ≈ 0.15) crystal pumped via Cr2+ ions by the ~1.73 μm radiation is described.
The spectroscopic and laser characteristics of optically polished Cr:ZnSe single crystals in four different lengths of 2, 3, 5, and 10 mm were investigated when pumping with a laser diode generating radiation at the wavelength of ~1.69 μm. The optimization from the point of laser efficiency was done in dependence on the crystal samples active length, effect of antireflection (AR) coatings, pumping pulse duration, and repetition rate. As a result, a 3 mm thick anti-reflection coated Cr:ZnSe crystal pumped by a laser diode with a pulse length of 20 ms and repetition rate of 10 Hz was chosen as the optimal. Using a 0.8 mm thick MgF2 birefringent filter the laser oscillations were continuously tunable from 2.1 μm up to 2.7 μm with the narrow spectral linewidth of ~5 nm and Gaussian beam profile. Maximum mean output power of ~0.35 W and maximum optical-to-optical slope efficiency of ~39% was obtained for 3 mm thick AR-coated sample which was ~28% and ~10% higher than that for uncoated sample of the same thickness, respectively. Continuously tunable laser oscillation wavelength was measured in the range of ∼2.1-2.7 µm with the mean output power of P ≥ 150 mW within a ∼5 nm linewidth. The absorption and fluorescence spectra as well as fluorescence lifetime were also measured. The Cr2+ fluorescence lifetime of ∼7.2 µs measured for the 1 ns pulse excitation at room temperature (RT) was constant within the whole absorption band of 1.35–2.25 µm.
The cryogenically cooled Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.4) single crystal with the thickness of ~3.6 mm was investigated under two different excitation wavelengths of the Q-switched Er:YAG laser (λ ≈ 2.94 μm, Eout ≈ 50 mJ) and by the gain-switched Fe:ZnSe laser (λ ≈ 4.05 μm, Eout ≈ 9 mJ). Because of relatively low Fe2+ ions concentration, the absorption coefficients at 78 K and 300 K ranged between 3 cm-1 and 2 cm-1 for both excitation wavelengths used. Absorption and fluorescence spectra, fluorescence lifetime as well as laser output characteristics were measured at low temperatures (78–180 K). The Cr,Fe:Zn1-xMgxSe (x ≈ 0.4) laser system was able to generate laser radiation at ~5 μm at liquid nitrogen (LN2) temperature of 78 K under both ~2.94 μm and ~4.05 μm laser excitation. The laser oscillation wavelength was shifted up to ~5 μm compared with a typical Fe:ZnSe output (~4.0–4.1 μm at LN2 temperature) due to the high amount of magnesium in the host material. Moreover, the oscillation wavelength was shifted even farther by increasing temperature of the active medium. The laser output energy was ~1.34 mJ and ~0.14 mJ for the ~2.94 μm and ~4.05 μm laser excitation, respectively. The beam profile structure was approximately fundamental for both excitation wavelengths used. The results present a novel mid-infrared 4.7–5.1 μm coherent laser source based on cubic AIIBVI matrix using direct excitation at wavelengths of ~2.94 μm or ~4.05 μm.
Two different mid-infrared (mid-IR) crystalline laser active media of Zn1-xMnxSe and Zn1-xMgxSe with similar manganese or magnesium ions amount of x ≈ 0.3 co-doped by divalent chromium (Cr2+) and iron (Fe2+) ions were investigated at cryogenic temperatures and compared for different excitation wavelengths used. Both single crystals were synthesized by high pressure Bridgman method and their thickness were 2.6 mm and 5 mm, respectively. Crystals were investigated under three excitation wavelengths of the Q-switched Er3+:YLF laser at ~1.73 μm, Q-switched Er3+:YAG laser at ~2.94 μm, and the gain-switched Fe2+:ZnSe laser operated at liquid nitrogen temperature of 78 K at a wavelength of ~4.05 μm. Spectroscopic and laser output characteristics were measured: absorption and fluorescence spectra, laser output pulse duration, mean output energy, and laser oscillation spectra. Both laser systems were able to generate radiation by Cr2+ or by Fe2+ ions under direct excitation, or by Fe2+ ions via the Cr2+ → Fe2+ energy transfer depending on the excitation wavelength and the output coupler conditions. Fe2+ ions in Cr2+,Fe2+:Zn1-xMnxSe and Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.3) laser systems at 78 K pumped by Er3+:YLF laser radiation at ~1.73 μm via the energy transfer mechanism generated laser radiation at the wavelengths of ~4.4 μm and ~4.8 μm at 78 K, respectively. Obtained results have shown a possibility of developing novel coherent laser systems in mid-IR region (~2.3 – 2.5 μm and ~4.4 – 4.9 μm) based on AIIBVI matrices. Thus, possibility to excite the Fe2+ active ions in both samples directly by ~2.94 μm as well as ~4.05 μm radiation or eventually in a compact way through the Cr2+ → Fe2+ ions energy transfer-based mechanism by ~1.73 μm radiation was demonstrated.
Two novel cryogenically cooled non-cubic wurtzite structure Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.2 and x ≈ 0.3) single crystals co-doped with Cr2+ and Fe2+ ions with thickness of 2.5 and 5 mm, respectively, were investigated under two excitation wavelengths of the Q-switched Er3+:YLF (λ ≈ 1.73 μm) and Er3+:YAG (λ ≈ 2.94 μm) lasers. Absorption and fluorescence spectra, fluorescence lifetimes as well as laser output characteristics for both Cr2+ and Fe2+ doping ions were measured at 78 K. Both Cr2+,Fe2+:Zn1-xMgxSe laser systems were able to generate radiation from Cr2+ as well as Fe2+ active ions depending on appropriate pumping wavelength and a set of laser cavity mirrors. Moreover, Fe2+ ions mid-IR lasing using the Cr2+ → Fe2+ ions energy transfer at ~4.57 μm and ~4.8 μm for magnesium content of x ≈ 0.2 and x ≈ 0.3, respectively were realized for ~1.73 μm Q-switched Er3+:YLF laser pumping. The results present an opportunity to develop novel mid-IR 4.4 – 4.9 μm coherent laser sources based on non-cubic AIIBVI matrices using direct Fe2+ ions pumping at ~2.94 μm as well as excitation via co-doped Cr2+ ions at ~1.73 μm.
Iron doped II-VI binary and ternary semiconductor materials are developed for mid-infrared (mid-IR) laser applications and some of them (ZnSe, ZnMnSe, ZnMgSe, CdMnTe) were already proven as laser active materials. In this article, the spectroscopic and laser properties of novel Fe2+ doped Zn1-xMnxTe (x ≈ 0.3) active material synthesized using Bridgman technique is presented. This active material was pumped by an Er:YAG laser at ~3 μm as well as Fe:ZnSe laser at 4.1 μm and has demonstrated various spectroscopic and laser output characteristics within the temperature range from 78 up to 300 K. At ~3 μm pumping, the central oscillation wavelength was ~4.8 μm at 78 K and shifted to 5.15 μm at 160 K. At 4.1 μm pumping, the central oscillation wavelength was red-shifted to ~4.9 μm at 78 K and shifted to 5.25 μm at 160 K. The output energy at 10 μJ level was achieved. These results present a great potential of the Fe2+:Zn1-xMnxTe (x ≈ 0.3) crystal for mid-IR laser radiation generation.
New laser applications as medicine treatment, air pollutants measurement, free-space communications, target illumination, and industrial technologies require laser radiation in the mid-infrared region of 4–6 μm where Fe2+-based lasers can generate. Pumping of Fe2+-doped active material is usually provided by sources generating near 3 μm (as YAG:Er, Er-fiber, or ZnSe:Cr) fitting the Fe2+ absorption maximum. Other promising pumping way is the energy transfer from Cr2+ to Fe2+ in co-doped materials. This energy transfer process in gain-switched operation under 200 ns, 1.73 μm pulse excitation was reported recently. In this paper we would like to present 1 ms, 10 Hz laser operation of the Zn1-xMnxSe:Fe2+,Cr2+ (x = 0.3) crystal within the 78–110 K temperature range under 1.94 μm commercial Tm:fiber laser pumping. The active crystal was placed in the cryostat and the cavity was formed by a curved dichroic pumping mirror and a curved output coupler. The slope efficiency of 1 % was achieved for 1.94 μm pumping at 78 K. The central laser output wavelength at 78 K was ~4.45 μm and the output spectrum temperature shift was about 2 nm/K. Furthermore, tunability range over 300 nm (4.35–4.67 μm) obtained at 78 K using intracavity tuning element. The results will be compared to an analogous Zn1-xMnxSe:Fe2+ (x = 0.3) crystal in a gain-switched mode under Q-switched YAG:Er3+ 2.94 μm laser pumping. Moreover, laser generation of crystals with different Mn concentration and CW generation will be also presented.
KEYWORDS: Teeth, Semiconductor lasers, Diodes, Temperature metrology, Infrared lasers, 3D modeling, Laser dentistry, Scanning electron microscopy, Hydrogen, Electron microscopes
The study describes a diode system which activates a home-bleaching agent for discolored teeth. The techniques involve pastes utilizing 16 % hydrogen and carbamide peroxide. Two different laser diodes operating at 445 nm and 1.7 um were used. The exposition power densities used were up to 10 W/cm2. For bleaching, stereolithographic models and trays were prepared. Bleaching technique was activated laser irradiation lasting for 100 s, bleaching. After the bleaching process, the enamel surface was with the scanning electron microscope. This process resulted in a 2-3 shade change measurement in one treatment.
The interest in the development of coherent mid-infrared radiation sources is caused by its potential application in medicine, spectroscopy, laser remote sensing of the atmosphere, metrology, and in many other fields of interest. This study presents temperature dependence of spectral properties of Cr:ZnSe laser active medium in range of 78-380 K. The temperature influence on the absorption, fluorescence and oscillation spectra were investigated in detail. While heating the Cr:ZnSe crystal from 78K to 380 K, the absorption peak maximum has shifted for 65nm toward a shorter wavelength from 1813nm to 1748nm together with the absorption spectrum broadening from 262nm to 373nm and decreasing the absorption coefficient. The FWHM of the fluorescence spectrum was broadened from 280nm (2030-2310 nm) to 488nm (1896-2384 nm) when the temperature of active medium was increasing. Pulsed laser operation from Cr:ZnSe active medium longitudinally pumped by an Er:YLF laser at 1735nm was investigated. The temperature dependence of Cr:ZnSe laser output energy and oscillation spectrum were studied. The highest output energy was 3.84mJ at 78K which together with the FWHM pulse duration of μ200 s corresponds to the power of 19mW. The laser radiation emission was observed at three wavelength bands which intensity was changing during the increase of crystal temperature. However, the oscillation band around wavelength of ~2360nm occurred for all measured temperatures. As a result, by cooling the system, the wavelength of maximum absorption is being shifted to the longer wavelengths as well as the wavelength of maximum fluorescence spectrum intensity.
Room temperature lasing of a set of Cd1-xMnxTe solid-solution crystals doped with Fe2+ ions was obtained under optical pumping by 4.1 μm liquid nitrogen cooled Fe2+:ZnSe laser. Oscillation wavelength maxima were found to increase linearly with Mn content x increase at a rate of about 60 nm per each 10 % of Mn content in the sample. The central oscillation wavelength as high as 5940 nm was obtained for sample with the highest Mn content (x = 0.76). The output energy was found to decrease for samples with higher Mn content due to very strong nonradiative fluorescence quenching.
Chromium ions Cr2+ are known to have good fluorescence properties in the mid-infrared spectral region around the
wavelength of 2.5 μm. The aim of this study was the investigation of new laser crystal materials – Zn0.95Mn0.05Se,
Zn0.70Mn 0.30Se, and Zn0.75Mg0.25Se doped by Cr2+ ions and comparison of their spectral and laser characteristics.
The spectroscopic parameters as absorption and fluorescence spectra as well as lifetimes were measured. As optical
pumping the laser diode generating radiation at the wavelength of 1.69 μm (pulse repetition rate 10 Hz, pulse width
2 ms) was used. The longitudinal-pumped resonator was hemispherical with an output coupler radius of curvature
150 mm. The laser emission spectra were investigated and the highest intensity of emitted radiation was achieved at
wavelengths 2451 nm, 2469 nm, and 2470 nm from the Cr:Zn0.95Mn0.05Se, Cr:Zn0.70Mn0.30Se, and Cr:Zn0.75Mg0.25Se laser
systems, respectively. The input-output characteristics of laser systems were measured; the maximum output peak power
177 mW was obtained for Cr:Zn0.95Mn0.05Se laser system with slope efficiency of 6.3 % with respect to absorbed peak
power. The output peak power as well as output beam spatial structure were stable during measurements. For the
selection of the lasing wavelength, the single 1.5 mm thick quartz plate was placed at the Brewster angle inside
the optical resonator between the output coupler and laser active medium. This element provided the tuning in
the wavelength range 2290–2578 nm, 2353–2543 nm, and 2420–2551 nm for Cr:Zn0.95Mn0.05Se, Cr:Zn0.70Mn0.30Se, and
Cr:Zn0.75Mg0.25Se, respectively. The obtained spectral FWHM linewidth of the individual output radiation was ~ 10 nm.
A comparison with previously measured Cr:ZnSe laser system was added in the end
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