Polarized Emission Spectra Research Articles

Impact of Fe-impurity centers on phonon subsystem of wurtzite-type ZnO

The paper addresses the question of the structural and vibrational properties of Fe-doped ZnO in the wurtzite structure with a lattice without an inversion center. The ZnO crystals containing Fe impurities in different charged states are studied by means of density functional theory (DFT) and potential-based methods. A first-principles simulation is performed to determine the local atomic configurations near the considered defects. The DFT results are compared with those obtained using the shell model. Both approaches give a similar pattern of lattice distortion around the Fe-impurity centers occupying cation sites in the isoelectronic charge state Fe2＋ and single-positive-charge state Fe3＋. The phonon local symmetrized densities of states projected onto the displacement of ions surrounding the defects are calculated by a well-established recursion method. The frequencies of defect vibrations of various symmetry types induced by Fe impurities are determined. The calculations made it possible to interpret the structure of the phonon sideband accompanying the zero-phonon line in polarized emission spectra attributed to the Fe3＋ intracenter transitions, as well as to estimate the role of Fe ions in the formation of observed peaks.

Enhanced 2.8 μm emission of Ho,Pr:CaYAlO4 crystal

Ho,Pr:CaYAlO4 (Ho,Pr:CYA) crystal doped with 1 at.% Ho3+ and 0.1 at.% Pr3+ was successfully grown using the Czochralski method. Polarized absorption spectra, emission spectra, and fluorescence lifetime measurements were performed. The impact of Pr3+ co-doping on the ∼3 μm emission of Ho3+ ions was analyzed. The energy transfer efficiency from Ho3+:5I7 to Pr3+:3F2 energy level was calculated to be 60.66 %, indicating that Pr3+ effectively mitigated the self-termination effect in Ho,Pr:CYA crystals. The absorption cross-section at 645 nm was found to be 1.53 × 10−20 cm2 for σ polarization and 2.62 × 10−20 cm2 for π polarization. The emission cross-section at 2842 nm was calculated to be 0.86 × 10−20 cm2 for σ polarization and 1.33 × 10−20 cm2 for π polarization at 2908 nm, with a full width at half maximum (FWHM) of 139 nm and 88 nm, respectively. The fluorescence lifetimes of the 5I6 and 5I7 levels were measured to be 0.17 ms and 2.01 ms, respectively. These results collectively suggest that Ho,Pr:CYA crystals hold great potential as a candidate for 2.8 μm laser applications.

Spectroscopy and Kerr-lens mode-locked operation of Yb:GdScO3 crystal

A Kerr-lens mode-locked laser based on a Yb3+-doped disordered gadolinium scandate (Yb:GdScO3) crystal is reported for the first time, to the best of our knowledge. The crystal with the perovskite structure was grown using the Czochralski method, and its room temperature (RT) and low temperature (LT) spectra were also investigated. Due to the crystal's multisite structure (Gd3+/Sc3+ site), Yb:GdScO3 offers broad and intense polarized emission spectra in the near-infrared range (975–1075 nm). The stimulated emission cross section σSE is 0.46 × 10−20 cm2 at 1000 nm with an emission band width of 75.7 nm for E // b polarization. The continuous wave (CW) laser was operated pumped by a 976 nm fiber-coupled LD laser, resulting in a maximum output power of 8.74 W with a slope efficiency of 76.1% was obtained. Additionally, a pulses as short as 74 fs are generated at ∼1061.7 nm via Kerr-lens mode-locking. The average output power amounts to 32 mW at a pulse repetition rate of 101.4 MHz. All results indicate Yb:GdScO3 a promising candidate for 1 µm ultrashort laser.

Growth, polarized spectroscopy and high-performance laser operation of a novel mixed Tm:CaY0.9Lu0.1AlO4 crystal

Tm3+-doped CaY0.9Lu0.1AlO4 single crystal was successfully grown by the Czochralski method. The crystal structure, polarized absorption spectra and polarized emission spectra of Tm:CaY0.9Lu0.1AlO4 crystals were investigated. By using the Judd–Ofelt approach, the intensity parameters Ω2,4,6, spontaneous transition rate, branching ratios and radiative lifetimes were calculated. Diode-end-pumped continuous-wave Tm:CaY0.9Lu0.1AlO4 lasers have also been investigated by establishing a simple and compact plane-concave cavity with four differently coated output couplers. Four different lasing wavelengths at about 2029 nm, 2000 nm, 1966 nm and 1888 nm have been achieved with maximum output power and slope efficiency of (1.98 W, 15.1%), (5.89 W, 46.2%), (6.92 W, 54.9%) and (5.54 W, 44.7%), respectively. The results in regard to the broad emission spectra and good laser performance show that the Tm:CaY0.9Lu0.1AlO4 mixed crystal could be very promising for broadband tunable and/or femtosecond ultrafast laser generation in the important 2-μm spectral region.

Temperature dependence of Cr:CYA effective emission cross-section

A high-quality Cr:CYA (Cr:CaYAlO4) single crystal fiber was grown by μ-PD (Micro-Pulling-Down) method. The E//a and E//c polarized excitation spectra of Cr:CYA at room temperature was measured. The crystal field parameters were calculated and the energy level structure of Cr:CYA was analyzed. We also measured the polarization emission spectra and lifetimes at different temperatures and calculated the effective emission cross-section. Based on the above data and Boltzmann law, the thermal distribution between the excited energy levels 2E and 4A2 at different temperatures was analyzed. The present work may be useful for guiding laser research on Cr:CYA and other Cr3+-doped laser crystals above room temperature.

Efficient continuous wave and broad tunable lasers with the Tm:GdScO3 crystal.

The spectroscopic properties and tunable laser performances of the orthorhombic perovskite Tm:GdScO3 crystal grown by the Czochralski method are comparatively studied for polarization along different crystallographic axes. The polarized emission spectrum of Tm:GdScO3 along the b-axis exhibits, to the best of our knowledge, the broadest bandwidth among all the single Tm3+-doped bulk gain media, indicating the strong inhomogeneous line broadening of Tm3+ ions in GdScO3 and thus leads to a broad and smooth gain spectrum. Tunable laser operation with a tuning range as broad as 321 nm from 1824 nm to 2145 nm is achieved, which indicates its potential for few-optical-cycle pulse generation in the 2-µm spectral range.

Spectroscopic properties of YPO4 crystals activated with Ho3+, Er3+, Tm3+

This paper presents a systematic investigation on the spectroscopic properties of YPO4 crystals activated with Ho3+, Er3+ or Tm3+, carried out in order to obtain preliminary information on the device potentialities of these materials. Relevant information about the radiative properties have been obtained by means of the Judd-Ofelt analysis of the polarized absorption spectra, measured at room temperature in the UV–vis–NIR region. The polarized emission spectra have been measured at 77 and 300 K in the visible and in the NIR upon laser excitation, and the transitions of major interest for application have been identified and characterized. The decay profiles of the main emission manifolds have been measured at room temperature in order to obtain information about the non-radiative processes active in the investigated crystals The stimulated emission cross sections have been estimated for the laser transitions in the NIR, indicating that these compounds can be considered suitable active media for laser operation.

Novel laser crystal Nd3+: Ca(Y, Gd)AlO4: A promising candidate for laser operation beyond 1.37 µm

A novel laser crystal Nd: CaGd0.1Y0.9AlO4 (Nd3+: Ca(Y, Gd)AlO4) crystal has been successfully grown by Czochralski (CZ) method. With the introduction of Gd3+ ions, this crystal has a more disorder structure than that of the Nd: CaYAlO4 (Nd: CYA). The full width at half-maximum (FWHM) of the π polarization emission spectra at around 1365 nm for the Nd3+: Ca(Y, Gd)AlO4 crystal was 53 nm, which is larger than that of Nd: CYA (35 nm) crystals, provided clear evidence for the more disorder structure. Moreover, its wide absorption spectral was maintained compared to the Nd: CYA crystal. At the same time, the effective dual-wavelength continuous-wave laser operation at 1358.4 nm and 1374 nm was realized of the as-grown crystal for the first time. These results suggest that the Nd3+: Ca(Y, Gd)AlO4 crystal is a promising disordered laser host for solid laser operation at the wavelength longer than 1370 nm in the range of 1.3–1.4 µm.

Spectroscopic characteristics and Judd-Ofelt analysis of Pr:GdScO3 crystal

The polarization absorption spectra of Pr3+-doped GdScO3 have been measured. Polarized emission spectra and fluorescence decay from the 3P0 upper level have been investigated. The strongest absorption peaks are located at 448 nm for a, b and c polarization, the absorption cross sections are 1.29 × 10−20 cm2, 0.98 × 10−20 cm2 and 1.57 × 10−20 cm2, respectively. The maximum emission cross section is located at 662 nm, which is 18.55 × 10−20 cm2 (a polarization), 12.74 × 10−20 cm2 (b polarization) and 22.41 × 10−20 cm2 (c polarization), and the FWHM is 10.02 nm, 9.38 nm and 10.14 nm, respectively. The fluorescence lifetime of 3P0 level is 12.39 μs. Those results indicated that Pr3+-doped GdScO3 crystal grown by the Czochralski method is a potential laser medium for visible laser operation.

Effects of conduction electron excitation on x-ray magnetic circularly polarized emission in itinerant ferromagnets

This study provides a theoretical method to calculate x-ray magnetic circularly polarized emission spectra at the K${}_{\ensuremath{\alpha}}$ transitions in transition-metal ferromagnets. The method is applied to metallic iron. It reproduces the observed tail structures which originate from the electron excitations on the correlated $d$ bands. Cosinusoidal emission angle dependence of the spectral intensity enables one to elucidate the magnetization directions deep inside of bulk ferromagnets.

Thermal, and optical features study of Dy:YAlO3 and Dy/Tb:YAlO3 crystals for yellow laser applications

Optical features of Dy3+:YAP and Dy3+/Tb3+:YAP single crystals that were successfully fabricated by the Czochralski method were reported. The thermal behaviors and XRD rocking curves of the grown Dy3+:YAP crystal were carried out. The identified broad absorption bands of Dy3+:6H15/2 → 4I15/2 with FWHMs approximately to 11 nm and the moderate absorption cross-sections at 450 nm in both crystals, imply their high suitability to the blue LD pumping. Polarized emission spectra with yellow fluorescence peaks at 572 nm were acquired in both crystals by means of a 450 nm Xenon lamp excitation. As compared with Dy3+:YAP crystal, the larger emission cross-sections of 7.83 × 10−21, 9.08 × 10−21 and 9.01 × 10−21 cm2 for E//a, E//b and E//c polarizations respectively, were determined in Dy3+/Tb3+:YAP crystal. Moreover, a slightly reduced lifetime of the upper laser level 4F9/2 and a much shortened lifetime of the lower laser level 6H13/2 were obtained in Dy3+/Tb3+:YAP crystal, implying the existent energy migration between Dy3+ and Tb3+, as well as an effective deactivation of Tb3+ to Dy3+. The role of Tb3+ to reinforce Dy3+:4F9/2 → 6H13/2 emission in YAP host was established. On the basis of the derived results, both crystals could be recognized as competitive materials for polarized yellow lasers, especially the Dy3+/Tb3+:YAP crystal.

Bifunctional Nd:CaSrNb2O7 crystal: A potential self-frequency-doubling laser material candidate

One of the convenient methods to obtain green laser is by self-frequency-doubling (SFD) technique, the key is the SFD laser crystal. In this article, a bulk single crystal of 3.34 at.% Nd:CaSrNb2O7 was successfully grown by Czochralski method at about 1481 °C. Its spectral and thermal properties were investigated. There is a broad and strong absorption band at around 804 nm, which is very suitable for AlGaAs laser diode pumping. The polarized emission spectra show large emission cross-sections and full width at half maximum at around 1068 nm, and the fluorescence lifetime is 202 μs? Moreover, the fluorescence quantum efficiency reaches to 98.6%. The long lifetime, large emission cross-section, and high fluorescence quantum efficiency of Nd:CaSrNb2O7 crystal indicate that it is easy to achieve laser oscillation. The second harmonic generation intensity of 3.34 at.% Nd:CaSrNb2O7 crystal is about 3 times that of KH2PO4, and phase matching can be realized in this crystal. All these results show that Nd:CaSrNb2O7 is a good bifunctional crystal, which possesses laser and nonlinear optical functions simultaneously, and also demonstrate that it is a promising SFD material.

Polarized spectroscopy and Judd-Ofelt analysis of Pr:LuYAP crystal

Pr 3+ ions doped Lu 0.7 Y 0 . 3 AlO 3 (LuYAP) crystal was successfully grown by the Czochralski method. Polarized absorption and polarized emission spectrum were recorded at room temperature. Using Judd-Ofelt theory, the intensity parameters Ω t, eff (t = 2, 4, 6) were calculated to be 3.52 × 10 −20 cm 2 , 1.43 × 10 −20 cm 2 , 15.88 × 10 −20 cm 2 , respectively. Based on F-L formula, the emission cross-sections peaking at 624 nm were calculated to be 1.67 × 10 −19 cm 2 , 8.71 × 10 −20 cm 2 and 8.00 × 10 −20 cm 2 for the a, b, and c polarization. The radiative lifetime and fluorescence lifetime was calculated to be 17.85 μs and 13.47 μs, respectively. All the results indicate that Pr:LuYAP is a potential material for visible laser operation. • Pr:LuYAP crystal was grown by Czochralski method. • Absorption and emission spectrum was recorded at room temperature. • Judd-Ofelt theory was used to analyze the spectroscopic properties of Pr:LuYAP. • Pr:LuYAP crystal is a potential laser material for visible laser output.

Yb: CaYAl3O7 crystal: a promising candidate for an ultrashort pulse laser with a disordered structure

We report on the crystal growth, structure, thermal, spectral properties, and laser performance of a novel disordered crystal, Yb3+-doped CaYAl3O7 (Yb: CYAM). The complete set of anisotropic thermal properties were systematically studied. Due to the random distributions of Y3+ and Ca2+ ions, the internal disordered structure determines a significant broadening of the absorption (FWHM=25 nm) and emission (FWHM=60 nm) bands. Polarized absorption, emission and gain cross-section spectra are determined. A maximum σem at 1011 nm for π polarization was calculated to be 0.57 × 10−20 cm2. CW laser operation at 1.06 µm with the c-cut sample has been demonstrated. A maximum power of 505 mW was achieved at 1026.5 nm, corresponding to the slope efficiency and optical conversion efficiency being 12.5% and 6.7%, respectively. Yb: CYAM crystal reveals its superiority and potentiality in the ultrashort pulse laser field.

Optical shaping of the polarization anisotropy in a laterally coupled quantum dot dimer

We find that the emission from laterally coupled quantum dots is strongly polarized along the coupled direction [1bar 10], and its polarization anisotropy can be shaped by changing the orientation of the polarized excitation. When the nonresonant excitation is linearly polarized perpendicular to the coupled direction [110], excitons (X1 and X2) and local biexcitons (X1X1 and X2X2) from the two separate quantum dots (QD1 and QD2) show emission anisotropy with a small degree of polarization (10%). On the other hand, when the excitation polarization is parallel to the coupled direction [1bar 10], the polarization anisotropy of excitons, local biexcitons, and coupled biexcitons (X1X2) is enhanced with a degree of polarization of 74%. We also observed a consistent anisotropy in the time-resolved photoluminescence. The decay rate of the polarized photoluminescence intensity along the coupled direction is relatively high, but the anisotropic decay rate can be modified by changing the orientation of the polarized excitation. An energy difference is also observed between the polarized emission spectra parallel and perpendicular to the coupled direction, and it increases by up to three times by changing the excitation polarization orientation from [110] to [1bar 10]. These results suggest that the dipole–dipole interaction across the two separate quantum dots is mediated and that the anisotropic wavefunctions of the excitons and biexcitons are shaped by the excitation polarization.

Emission properties of Tm3+-doped CaF2, KY3F10, LiYF4, LiLuF 4 and BaY2F8 crystals at 1.5 μm and 2.3 μm

Thulium ions (Tm3+) are known for their emissions in the near- and mid-infrared spectral ranges suitable for efficient laser operation. We systematically study the stimulated-emission cross-sections σSE for the 3H4 → 3F4 (at ~1.5 μm) and 3H4 → 3H5 (at ~2.3 μm) Tm3+ transitions in five low-phonon energy fluoride single-crystals, namely, cubic Tm:CaF2 and Tm:KY3F10, tetragonal Tm:LiYF4 and Tm:LiLuF4 and monoclinic Tm:BaY2F8. A promising material is Tm:BaY2F8 which offers broad and intense polarized emission spectra in the mid-infrared (2251–2452 nm); the maximum σSE is 0.39 × 10−20 cm2 at 2289 nm (for E ||Z) and the emission bandwidth is exceeding 100 nm (for E ||X). We also revise the transition probabilities for Tm3+ ions in LiLuF4 and BaY2F8 crystals using the Judd-Ofelt formalism and accounting for an intermediate configuration interaction (ICI).

Crystal growth and spectroscopic characterization of Sm:LaMgAl11O19 crystal

LaMgAl11O19 (LMA) crystal with nominal Sm3+ concentrations of 8 at.% was grown by the Czochralski method. Polarized absorption spectra, polarized emission spectra and fluorescence decay curve of Sm:LMA crystal were recorded at room temperature. The absorption cross-sections at 404 nm were calculated to be 2.33 × 10−20 cm2 and 0.86 × 10−20 cm2 for σ and π polarization, respectively. The spontaneous transition rates, branching ratios and the radiative lifetime of the 4G5/2 multiplet, were calculated. The Judd-Ofelt theory has been applied to evaluate the Ωt (t = 2, 4, 6) intensity parameters. The highest stimulated emission cross-sections for the 4G5/2 → 6H7/2 transition around 594 nm were calculated to be 1.67 × 10−21 cm2 for σ polarization and 1.15 × 10−21 cm2 for π polarization, with full width at half maximum (FWHM) of 7.68 nm and 7.27 nm, respectively. The fluorescence lifetime of the 4G5/2 manifold was 1.84 ms. All the results show that Sm:LMA crystal would be a promising orange-red solid state laser material.

Yb Sensitized Near-Stoichiometric Er:LiNbO3 Single Crystal: A Matrix for Optical Communication and Upconversion Emission

Ytterbium and erbium codoped crystals have attracted considerable interest in the application of eye-safe laser, upconversion laser, and low-loss optical communication. Despite the lithium niobate (LiNbO3, LN) single crystal has been accepted as an ideal crystal matrix for Yb3+ and Er3+ ions possessing significant application potential in self-upconversion laser, the Yb and Er codoped near-stoichiometric LN (NSLN) crystal has rarely been studied. This is due to the difficulty of the NSLN crystal growth compared with that of the congruent LN (CLN). In this paper, an Yb, Er codoped near-stoichiometric LN (Yb, Er:NSLN) crystal was grown by the Czochrolski method for the first time. Spectra studies showed the constrained peak splitting at 378, 526, and 650 nm of the Yb, Er:NSLN crystal compared with Yb, Er:CLN crystal. It was attributed to the low concentration of intrinsic defects which constrained the Stark-split of the three energy levels of 4G11/2, 2H11/2, and 4F9/2 energy states. Some spectral changes are verified induced by the stoichiometric composition in the polarized emission spectra. The Yb, Er:NSLN crystal has high potential in upconversion laser application.

Efficient 1620 nm continuous-wave laser operation of Czochralski grown Er:Yb:Lu2Si2O7 crystal.

Efficient continuous-wave diode-pumped laser operation of Czochralski grown Er:Yb:Lu2Si2O7 crystal is reported. Polarized absorption and emission spectra, fluorescence lifetimes, and energy transfer efficiency from Yb3+ to Er3+ were determined. A maximal output power of 522 mW was achieved at 1620 nm with slope efficiency of 15.8% and absorbed pump threshold of 470 mW. Among the Er3+ and Yb3+ co-doped materials with long fluorescence lifetimes of the upper level 4I13/2, which are candidates for gain media of pulsed laser around 1.55 μm with high energy, comprehensive performance of the Er:Yb:Lu2Si2O7 crystal is the best till now.

Parallel Three-Dimensional Tracking of Quantum Rods Using Polarization-Sensitive Spectroscopic Photon Localization Microscopy

Semiconductor nanocrystals and their variants are widely used in biological research as fluorescent probes. Their unique characteristics, such as intense brightness, tunable emission properties, and resistance to photobleaching, make them ideal candidates for single-molecule imaging and tracking with localization precision far beyond the diffraction limit. Their fluorescence polarization states and emission spectra can be further utilized to probe changes in their mechanical properties and residing nanoenvironments. We developed a three-dimensional (3D), polarization-sensitive, spectroscopic photon localization microscopy (3D-Polar-SPLM) that enables parallel 3D tracking of individual quantum rods (QRs) while simultaneously capturing their fluorescence spectra and polarization states. Using 3D-Polar-SPLM, we spatially localized individual QRs with a lateral localization precision of 8 nm and an axial localization precision of 35 nm. In addition, we achieved a spectral resolution of 2 nm and a polarization...