Gain Cross Section Research Articles

Gain properties of the transition emissions near the second telecommunication window in Ho 3+-doped multicomponent heavy-metal gallate glasses

Efficient infrared emissions near the second telecommunication window in Ho 3+-doped multicomponent heavy-metal gallate (MHG) glasses have been observed. The maximum stimulated emission cross-sections are calculated to be 2.94×10 −21 and 2.08×10 −21 cm 2 for 1200 and 1390 nm emissions, respectively. Excitation spectra reveal that the 642 and 538 nm wavelengths are practical pumping conditions for 1.2 and 1.39 μm emissions, respectively. Gain cross-sections are evaluated and positive gain bands have been anticipated. The theoretical gain results indicate that the appealing infrared emissions near the second telecommunication window from Ho 3 + -doped MHG glasses with low maximum phonon energy of ∼660 cm −1 make them attractive in developing ∼1.2 μm and E-band (1360–1460 nm) optical amplifiers.

Polarized spectral properties of Tm 3+:K 5Bi(MoO 4) 4 crystal

Trivalent thulium-doped K 5Bi(MoO 4) 4 single crystals were grown by the Czochralski method. Its polarized absorption and fluorescence spectra and fluorescence decay curves were recorded at room temperature. On the basis of the Judd–Ofelt theory, the spectral parameters of the Tm 3+:K 5Bi(MoO 4) 4 crystal were calculated. The cross relaxations between Tm 3+ ions were analyzed. The emission cross sections of the 3F 4 → 3H 6 transition were obtained by the Fuchtbauer–Ladenburg formula and then the gain cross sections around 1.9 μm were calculated. The peak emission cross section and width of emission band around 1.9 μm are comparable to those for Tm 3+:YAG and the tunable range is about 280 nm for the potential ∼1.9 μm laser operation via the 3F 4 → 3H 6 transition.

Structural and spectroscopic characterization of Yb3+ doped Lu2O3 transparent ceramics

Yb3+ doped Lu2O3 transparent ceramics were fabricated by the solid-state reaction method and sintered in H2 atmosphere. Structural and spectroscopic properties of Yb:Lu2O3 ceramics were studied. The Yb:Lu2O3 ceramic structure, and the lattice parameter are refined with the Rietveld method. Yb:Lu2O3 has broad absorption and emission bands with a long fluorescence lifetime (1.31ms). The energy level diagram is calculated based on the absorption and emission spectra, Yb3+ in Lu2O3 ceramics exhibits a big splitting energy of the 2F7/2 ground state (1023cm−1). Furthermore, the gain cross-section (σg) is estimated with different β values.

Spectroscopic investigation of Er 3+-doped (Gd 0.7Y 0.3) 2SiO 5 single crystal for potential application in 1.5 μm laser

The Er 3+:(Gd 0.7Y 0.3) 2SiO 5 (hereafter abbreviated as Er 3+:G 0.7Y 0.3SO) single crystals were grown by the Czochralski technique. The unpolarized absorption spectrum and photoluminescence (PL) spectra were measured at room temperature. The Judd–Ofelt phenomenological method was used to estimate the intensity parameters, radiative lifetimes and branching ratios of luminescence. The stimulated emission cross-section of the 4I 13/2 → 4I 15/2 transition of special interest of ∼1.5 μm laser was calculated by the Fuchtbauer–Ladenburg equation, and the relevant gain cross-sections were also estimated for several inverse-population parameters to evaluate a potential laser activity of the Er 3+:G 0.7Y 0.3SO system. Also, the potential range of the optical pumping was assessed based on the absorption cross-section at room temperature. Finally the excited state dynamics of the Er 3+:G 0.7Y 0.3SO system was investigated and experimental lifetimes of 4I 13/2 and 4I 11/2 levels were measured. Taking into account the satisfactory absorption near 971 and 1529 nm, and the high gain cross-section in the range of 1530–1620 nm, the Er 3+:G 0.7Y 0.3SO crystal can be considered as a promising active material for laser operation near 1.5 μm.

Optical characterization, 1.5 μm emission and IR-to-visible energy upconversion in Er 3+-doped fluorotellurite glasses

The optical properties of Er 3+ ions in a novel glass based on TeO 2–PbF 2–AlF 3 oxyfluoride tellurites have been investigated using steady-state and time-resolved spectroscopies as a function of the rare-earth doping concentration. Basic optical characterizations have been performed measuring and calculating the absorption and emission spectra and the cross-sections, the Judd–Ofelt intensity parameters, the radiative probabilities and the fluorescence decays and lifetimes. Special attention has been devoted to the broad 4I 13/2→ 4I 15/2 emission transition at around 1.53 μm since, with a wide broadening of around 70 nm and a relative long lifetime of around 3 ms compared to others glass hosts, it shows potential applications in the design of erbium-doped fiber amplifiers. The absorption, the stimulated emission and the gain cross-sections of this transition have been obtained and compared with that obtained in different hosts. Finally, infrared-to-visible upconversion processes exciting at around 800 nm have been analyzed and different mechanisms involved in the energy conversion have been proposed.

Resonantly diode-pumped Ho^3+:Y_2O_3 ceramic 21 µm laser

We report what is believed to be the first laser operation based on Ho3+-doped Y2O3. The Ho3+:Y2O3 ceramic was resonantly diode-pumped at ~1.93 µm to produce up to 2.5 W of continuous wave (CW) output power at ~2.12 µm. The laser had a slope efficiency of ~35% with respect to absorbed power and a beam propagation factor of M2 ~1.1. We have measured the absorption and stimulated emission cross sections of Ho3+:Y2O3 at 77 K and 300 K and present the calculated gain cross section spectrum at 77 K for different excited state inversion levels.

Polarized spectroscopic properties of Ho 3+ ions in NaLa(MoO 4) 2 crystal

A Ho 3+-doped NaLa(MoO 4) 2 single crystal was grown by the Czochralski method. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were measured at room temperature. The spontaneous emission probabilities, radiative lifetimes, and fluorescence branching ratios of the typical fluorescence multiplets of Ho 3+ ions were calculated. The polarized stimulated emission and gain cross-sections of the 5 I 7 → 5 I 8 transition were obtained. The results show that the Ho 3+:NaLa(MoO 4) 2 crystal is a promising gain medium for tunable and ultrashort pulse lasers operating around 2.0 μm.

Growth and Characteristics of Yb-doped ${\rm Y}_{3}{\rm Ga}_{5}{\rm O}_{12}$ Laser Crystal

Ytterbium (Yb) doped rare-earth garnet Y3Ga5O12 (YGG) single crystal was grown by the optical floating zone method for the first time, to our knowledge. Its structure and cell parameter were determined by X-ray powder diffraction. The thermal properties of Yb:YGG, including specific heat, thermal expansion coefficient, thermal diffusion coefficient, and thermal conductivity, were investigated. The optical properties of the crystal were also studied and the effective gain cross sections were calculated. With the crystal cut along the 〈111〉 direction, laser performance was also demonstrated by using a laser diode as the pump source. All the results show that Yb:YGG can be an excellent laser medium for applications to tunable and ultrafast pulsed lasers.

Intensity parameters of Tm3+ doped Sc2O3 transparent ceramic laser material

This work is focused on spectral investigations of Tm3+ doped Sc2O3 transparent ceramic as potential material for diode-pumped solid-state laser emitting around 2μm. In the context of the Judd–Ofelt (J–O) theory a series of spectroscopic parameters such as J–O intensity parameters, oscillator strengths, radiative transitions probabilities, and radiative lifetimes as well as branching ratios are evaluated. The gain cross-sections which lead to an estimation of the probable operating laser wavelength for the 3F4→3H6 Tm3+ laser transition were also calculated.

Highly efficient, high-power, broadly tunable, cryogenically cooled and diode-pumped Yb:CaF_2

We present a high-power diode-pumped Yb:CaF(2) laser operating at cryogenic temperature (77 K). A laser output power of 97 W at 1034 nm was extracted for a pump power of 245 W. The corresponding global extraction efficiency (versus absorbed pump power) is 65%. The laser small signal gain was found to be equal to 3.1. The laser wavelength could be tuned between 990 and 1052 nm with peaks that correspond well to the structure of the gain cross-section spectra registered at low temperature.

Spectroscopic characterisation of Er-doped LuVO4 single crystals

The LuVO4:Er single crystals were grown by the Czochralski technique. The crystal-field split energy levels of Er3+ ion were derived experimentally employing absorption and emission spectra measured at T=10 K. The Judd–Ofelt phenomenological method was used to estimate intensity parameters, radiative lifetimes and branching ratios of luminescence. The excited state dynamics of the LuVO4:Er systems was investigated and experimental lifetimes of emitting levels were measured. The emission cross section of the 4I13/2→4I15/2 transition in the infrared was calculated by the Fuchtbauer–Ladenburg method. The gain cross section, estimated for several inverse-population parameters, allowed us to evaluate a potential laser activity of the LuVO4:Er system at 1.6 μm. Also, the potential range of the optical pumping was assessed based on absorption spectra achieved at the room temperature. The optical losses related to the green up-converted emission, encountered under the 978 nm excitation between 300 and 670 K were indicated and discussed. Spectroscopic peculiarities of the Er3+-doped LuVO4 crystal were discussed in relation to optical properties of the YVO4:Er and GdVO4:Er crystals. Taking into account the high quantum efficiency of the 4I13/2 level, and satisfactory absorption and emission features, the LuVO4:Er crystal can be considered as a promising active material for laser operation near 1.6 μm.

Spectroscopy of the Bi 4Si 3O 12:Er 3+ glass for optical amplification and laser application

Spectroscopic characterization for optical amplification and laser application of the Er 3+-doped Bi 4Si 3O 12 glass is performed through its absorption and luminescence spectra. The spontaneous radiative transition probabilities from the first seven excited states to the ending states are calculated to obtain the luminescence branching ratios and radiative lifetimes. Intense infrared to visible luminescence of the Er 3+ ion is observed with 4I 9/2 state excitation (800 nm) under a 200 mW laser excitation power. The value obtained for the ratio of the 4I 11/2 → 4F 7/2 excited-state absorption oscillator strength to the 4I 15/2 → 4I 11/2 ground state absorption oscillator strength is in accordance with those reported for Er 3+-doped materials pumped efficiently at 4I 11/2 level excitation wavelengths. Gain cross-section spectra as a function of the inverted population rate and the stimulated emission cross-section spectrum were determined for the 4I 13/2 → 4I 15/2 infrared (IR) laser transition. The large gain bandwidth of the 4I 13/2 → 4I 15/2 IR emission has resulted in being close to those reported for Er 3+-doped oxide glasses suitable for broadband amplifiers.

Optical gain of the1.54 μmemission in MBE-grown Si:Er nanolayers

We present investigations of the optical gain cross section of 1.54 μm Er-related emission at 4.2 K in Si/Si:Er molecular-beam-epitaxy-grown multinanolayers. This ultranarrow (full width at half maximum below 8 μeV) emission originating from the unique Er-related optical complex, Er-1 center, ensures the best condition to achieve stimulated emission. The experiments were carried out using a combination of the variable stripe length and shifting excitation spot techniques under pulsed and continuous-wave excitations. The comparison of results for both excitation regimes enables to estimate an optical gain within the strong optical losses due to the free carrier absorption. Based on these measurements, the upper limit of the optical gain cross section of 10−17 cm2 and the gain coefficient of 8.8 cm−1 are deduced.

Growth, optical parameters, and spectroscopic properties of crystals of disordered scheelite-like molybdates NaLa x Gd1 − x (MoO4)2 (x = 0–1) activated by Tm3+ ions

Polarized optical absorption spectra in the range of 450–2000 nm have been recorded for the Czochralski-grown concentration series of single crystals of mixed scheelite-like molybdates NaLa x Gd1 − x (MoO4)2(x = 0–1) activated by Tm3+ ions. The intensity parameters Ω t (t = 2, 4, 6) of the crystals grown were determined by the Judd-Ofelt method, and the values found were used to estimate the probabilities and emission branching ratios for a number of radiative transitions of Tm3+ ions. The main optical constants of an Na0.909La0.490Gd0.498Tm0.035Mo2.020O8.048 crystal were found and the temperature dependences of the refractive index for the ordinary and extraordinary waves were investigated in the temperature range of 293–373 K. The spectral dependences of the emission cross section for the expected 3 F 4 → 3 H 6 laser transition of Tm3+ ions in an Na0.908La0.301Gd0.676Tm0.048Mo2.019O8.043 crystal were measured in the spectral range of 1500–2000 nm. The gain cross section of the active medium on the 3 F 4 → 3 H 6 laser transition of Tm3+ ions in this crystal was calculated using the spectral dependences of the absorption and emission cross sections.

Violet and blue upconversion luminescence in Tm3+/Yb3+ codoped Y2O3 transparent ceramic

Tm 3 + / Yb 3 + codoped Y2O3 transparent ceramics were fabricated and characterized from the point of upconversion luminescence. All the samples exhibited high transparency not only in near-infrared band but also in visible region. Under 980 nm excitation, the ceramics gave upconversion luminescence with very intense blue (485 nm) and considerably intense violet (360 nm) emissions. It was worthy to point out that the upconversion luminescence contained six emission bands, which dispersed in the region from 294 to 809 nm. The strongest blue emission (485 nm) was obtained with (Tm0.002Yb0.03Y0.958Zr0.01)2O3 ceramic (Yb/Tm=15). The mechanism of all upconversion emission bands were investigated in detail. The absorption, emission, and gain cross-section of blue emission (485 nm) were calculated, which indicated that Tm3+/Yb3+ codoped Y2O3 transparent ceramic has tremendous potential in short wavelength laser.

Random Population of Quantum Dots in InAs–GaAs Laser Structures

We have measured the spontaneous emission rates, absorption, and gain spectra of quantum dots between 20 K and 350 K using the segmented contact method, exploiting self assembled dots with a bimodal size distribution. At 20 K, we find a linear relationship between the radiative rates of the ground states of small and large sets of dots, and using absorption data we show the slope corresponds to random population of states at different energy with equal probability. The emission spectra indicate relaxation of carriers from excited to ground states in the same set of dots at 20 K. We have developed a rate equation model to describe the transition from thermal to random population, including relaxation between excited and ground states in the same dot. This produces a Fermi-Dirac occupation distribution of electrons in all states at 350 K with a global quasi Fermi level. At 20 K all ground states have the same occupation probability, irrespective of their energy. Using values for spontaneous lifetime and gain cross section from absorption data, these rate equations give a very good description of the experimental results for radiative threshold current density as a function of temperature, reproducing the minimum at 200 K, and thereby modeling the transition from the thermal regime at high temperature, to the random regime at low temperature.

High values of gain cross section and luminescence quantum efficiency in OH^−-free Ti^3+-doped low-silica calcium aluminosilicate glass

We recently reported that Ti(3+)-doped low-silica calcium aluminosilicate glass presents long luminescence lifetime (170 micros) and broad emission band (190 nm) shifted toward the visible region when compared with those from Ti(3+):sapphire single crystal and Ti(3+)-doped glasses [Phys. Rev. Lett.100, 027402 (2008)]. Here we demonstrate that this glass also shows high values of both gain cross section (approximately 4.7 x 10(-19) cm(2)) and luminescence quantum efficiency (approximately 70%). By comparing these values with those for Ti(3+):sapphire crystal, we can conclude that the studied Ti(3+)-doped glass is a promising system for tunable solid-state lasers.

Crystal growth and spectroscopic properties of erbium doped Lu 2SiO 5

A high optical quality erbium doped Lu 2SiO 5 single crystal has been grown by the Czochralski method. The distribution coefficient of Er 3+ was measured to be ∼0.926. The absorption and emission spectra as well as the fluorescence decay curve of the excited state 4I 13/2 were measured at room temperature. The spectroscopic parameters were calculated using the Judd–Ofelt theory, and the J–O parameters Ω 2 , Ω 4 and Ω 6 were found to be 4.451×10 -20, 1.614×10 -20 and 1.158×10 -20 cm 2, respectively. The room-temperature fluorescence lifetime of the Er 3+ 4I 13/2→ 4I 15/2 transition was measured to be 7.74 ms. The absorption and emission cross-section as well as the gain cross-section in the eye-safe regime of 1400–1700 nm were also determined and discussed.

Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer

Ho 3 + / Yb 3 + codoped lanthanum aluminum germanate glasses are prepared simply by melt-quenching method. The 2 μm emission characteristic and energy transfer from Yb3+ to Ho3+ upon excitation of a conventional 980 nm laser diode is investigated and the energy transfer efficiency is as high as 83%. The spectroscopic parameters are calculated based on Judd–Ofelt (J-O) theory, the intensity parameters Ω2, Ω4, and Ω6 are 4.44, 1.92, and 1.11×10−20 cm2, respectively. The transition probabilities and branching ratios are also estimated by using the J-O parameters. Beer–Lambert and Fuchtbauer–Ladenburg theories are applied to calculate the absorption, emission, and gain cross sections of I57→I58 transition.

Optical properties of Si/Si:Er multi-nanolayer structures grown by SMBE method

Among Er-doped crystalline Si materials, Si/Si:Er multi-nanolayer structures grown by sublimation molecular beam epitaxy (SMBE) technique present extraordinary optical properties, with a narrow linewidth of the Er-related emission at 1.5 μm. Based on spectral analysis, the splitting of the ground state of Er3+ ions and the presence of only a single type of Er-related optical center, labeled Er-1, have been conclusively established. In this contribution, we briefly summarize some of the unique optical properties of Si/Si:Er multi-nanolayer structures: preferential formation of the Er-1 center and its microscopic structure, level of optical activity of Er, and relations with a donor level as well as with oxygen co-doping. Then we report on the most recent results on optical gain in Si/Si:Er multi-nanolayers. From variable stripe-length (VSL) and shifted excitation spot (SES) experiments, we estimated maximum gain cross section of Er-1 in the multi-nanolayer structure at about σ~10−17 cm2. We also evaluate the magnitude of induced absorption by free carriers, and show that it precludes observation of the net optical gain.