The spectroscopic and energy transfer characteristics of the rare earth ions used for silicate glass fibre lasers operating in the shortwave infrared

The continuing growth in the research and development of high power diode‐pumped fibre lasers relates to the exceptional thermal management provided by the extended geometry of the fibre and the small quantum defect associated with the 1 μm emitting Yb³⁺ ion. Lengthening the emission wavelength of diode‐pumped fibre lasers further into the infrared is important for many applications ranging from medicine to defence; however, extending the emission wavelength remains a challenge. This review will examine in detail the spectroscopy and the energy transfer processes that impact Tm³⁺‐doped and Ho³⁺‐doped silicate glasses that are used for fibre lasers in the 1.9 μm to 2.1 μm region of the shortwave infrared spectrum. We will explore a number of important applications that function in the shortwave infrared region that will benefit from using these light sources and I will suggest the reasons for choosing silicate glass over other glasses as the host material for this wavelength range.     

Flashlamp-excited dye lasers in the near infrared

The laser emission of flashlamp-excited polymethine dyes is investigated. The spectral shift towards longer wavelengths due to relatively slow pumping is discussed in terms of transient triplet-triplet absorption. First results concerning mode locking and tuning on the 785–805 nm and 872–880 nm ranges of two tricarbocyanine dyes are presented.     

The optical properties of trivalent rare earth ions (Er3+) doped borotellurite glass

Erbium doped borotellurite glass has been fabricated by using conventional melting method. The density and molar volume have been calculated and analyzed while their optical properties were studied by measuring the optical absorption and luminescence spectra at room temperature. From the XRD results, since the patterns do not exhibit any diffraction line thus it confirms their amorphous nature. It is found that the density of the glass samples increased and the molar volume decreased with respect to Er ions content. Meanwhile, the upconversion emissions centered at 487, 523, 558, 642, 695 and 782 nm have been observed under the 650 nm excitation in the ⁴ F _9/2 level. Some other results will be analysed and discussed in details.     

Intersubband electro-optic modulators for near and mid infrared applications

Optical transitions between conduction subbands of asymmetrical quantum-well structures can produce large second-order optical nonlinearities. In particular, it is possible to engineer asymmetrical quantum-well structures to have very large electro-optic (EO) coefficients. In this paper we study three alternative approaches to design and fabricate intersubband EO modulators, i.e. the Stark modulator, the quantum-interference (QI) modulator, and the carrier-density (CD) modulator. We show that near a given resonance the Stark modulator has the largest EO coefficient. However, the linear intersubband absorption limits the usability of this modulator to a very short device length. Far from resonance we found that the CD and the QI modulators are more efficient. Furthermore, we found that these modulators can be utilized for near-infrared modulation in the 1.3–1.5 μm spectral range. These modulators are almost unaffected by the linear intersubband absorption so that their efficiency can be very high. We present preliminary experimental results that demonstrate the operation of the QI modulator.     

Xanes study of trivalent and homogeneous mixed valent rare earth systems

We report for the first time a systematic study of X-ray absorption structures 20–30eV above the L_III edge (XANES) of homogeneous mixed valent (SmB₆, YbAl₂, CePd₃...) and trivalent reference Rare-Earth compounds (e.g. GdB₆, LaAl₂, NdPd₃). The XANES of integral valent compounds in simple structures (NaCl, AuCu₃...), which is due to multiple scattering of the photoelectron on the neighbouring atomic shells, is characterized by a single peak. On the contrary the XANES of mixed-valent materials presents a splitted structure which replicates the edge structures. We interpret this splitting as a direct evidence for the existence of two threshold energies and corresponding presumably to two different Rare-Earth metal distances in agreement with 4f fluctuations. Finally, we shall propose a consistent picture for core hole spectroscopies (L_III edge, XANES, EXAFS and XPS) in mixed-valent materials.     

Luminescent materials based on thin metal oxide films doped with rare earth ions

Luminescent films of TiO₂: Sm were prepared by the sol-gel method using the spray pyrolysis technique. Various techniques (including IR absorption, Raman, AFM, XPS, photoluminescence) were used to characterize the samples. After a thermal treatment up to 750°C, intense Sm³⁺ luminescence with a well-resolved fine structure was observed under optical excitation within the fundamental absorption band of the TiO₂ host. After further thermal treatments up to 950°C, the luminescence was quenched, although no anataseto-rutile phase transformation was observed. This behavior is attributed to nanocrystallinity and segregation of Sm ions in the surface layer. The text was submitted by the authors in English.     

Two-stage Raman converter covering the whole infrared spectrum with tunable solid-state lasers

A two-stage Raman-conversion system pumped with a Q-switched alexandrite laser is proposed for the generation of broadly tunable infrared radiation. The first stage is a high-pressure Raman cell which accepts a pump beam in long-focusing or parallel-beam geometry, while the successive second one is made of a multi-pass Raman cell with repeated focusing. Using a selected combination of vibrational or rotational Raman shifting by H₂, a spectrum ranging from 0.75 m to 15 m can be covered by this system.     

大口径谐振腔式固体激光中的动力学不稳定性研究

大口径谐振腔式固体激光定标到足够高功率后,由于非稳定腔内激光不对称振荡导致介质上激光强度横向不均匀,激光提取与介质产热耦合会引起激光输出功率和光束质量在时域上的不稳定性。针对三种激光器构型:Nd:YAG薄片、Yb:YAG薄片和浸入式液冷叠片激光器,通过理论分析与数值模拟揭示了其各自不同的光热耦合机制及其影响因素,给出了激光输出的瞬态演化规律。结果表明,前两种构型中基于激光动力学的光热耦合具有饱和效应,其动力学不稳定性只出现在特定参数区间,可以通过恰当的设计加以避免;第三种构型中动力学不稳定性表现出明显的阈值特征,在强光状态下只能通过减少冷却液吸收系数来抑制。     

纳米晶体中稀土离子的发光性质及其变化机理研究

近年来, 纳米晶体中稀土离子发光性质的研究越来越受到人们的广泛关注, 这是因为纳米稀土发光材料在发光、高清显示、光电子纳米器件、生物荧光标记、激光和闪烁体等众多领域有着重要的应用前景。本项目采用软化学合成方法如水热法、溶胶-凝胶法等, 通过合成工艺的调控, 设计并合成出一系列不同颗粒尺寸、分散均匀、形貌可控的稀土离子掺杂氧化物(氟化物)微/纳米晶体, 利用激发、发射、漫反射以及高分辨激光光谱等光谱分析手段对其发光性质进行研究, 弄清影响发光行为的本质原因。同时, 结合光谱实验数据, 利用密度泛函理论和复杂晶体化学键介电理论方法进行理论计算, 成功解释了光谱变化规律和不同稀土离子间能量传递机理, 为相关稀土光谱研究奠定了理论和实验基础。     

大口径谐振腔式固体激光中的动力学不稳定性研究

大口径谐振腔式固体激光定标到足够高功率后,由于非稳定腔内激光不对称振荡导致介质上激光强度横向不均匀,激光提取与介质产热耦合会引起激光输出功率和光束质量在时域上的不稳定性。针对三种激光器构型：Nd:YAG 薄片、Yb:YAG薄片和浸入式液冷叠片激光器,通过理论分析与数值模拟揭示了其各自不同的光热耦合机制及其影响因素,给出了激光输出的瞬态演化规律。结果表明,前两种构型中基于激光动力学的光热耦合具有饱和效应,其动力学不稳定性只出现在特定参数区间,可以通过恰当的设计加以避免;第三种构型中动力学不稳定性表现出明显的阈值特征,在强光状态下只能通过减少冷却液吸收系数来抑制。     

Tunable far-infrared solid-state lasers based on hot holes in germanium

The basic principles for achieving population inversion and stimulated emission in the far-infrared fromp-Ge are discussed. In the heavy-light hole lasing mode a broad gain region is found resulting in a broad multimode spectrum due to intracavity modes. By attaching external plates of germanium a single mode operation is realized. The obtained powers are in the W range with linewidths of 0.2 cm^–1. A single mode magnetically tunable coherent source is achieved with the light hole cyclotron resonance laser. With external mirrors a tuning range from 20 to 120cm^–1 with magnetic fields between 1 and 6 T is achieved. The intensity of the single mode is in the order of W, the linewidth below 0.2 cm^–1.     

Far infrared electronic transitions in rare earth doped barium fluoride

Single crystals of barium fluoride doped with different rare earth ions (Tb-Sm-Nd-Pr-Dy-Ho-Er) have been grown in a He atmosphere. The far infrared (FIR) spectra observed at 1.4 K show common features at 75.5-125-131 and 156 cm⁻¹. They are explained in terms of localised vibration of the compensation F⁻ ion in a cubic site (v̇_c = 131 cm⁻¹), a tetragonal one (v̇_L = 75.5 cm⁻¹ ; v̇_T = 156 cm⁻¹) and a trigonal one (v̇_L = 125 cm⁻¹). The different frequencie can be calculated in the assumption of a cubic harmonic oscillator (v̇_c = 131 cm⁻¹) with Coulomb perturbations due to the RE ion at different positions.Special features are observed at 41.2 cm⁻¹ for BaF₂: Dy⁺³; 37 cm⁻¹ and 50.4 cm⁻¹ for BaF₂: Ho³⁺; 69.2 and 70.3 cm⁻¹ for BaF₂: Er³⁺. They arise from electronic transitions. The Zeeman effect gives information on the Landé g factors of both ground and excited levels with magnetic fields smaller than 50 kG.     

Spin-lattice relaxation times of rare earth ions in binary nitrates

The Van Vleck method is used with the point-charge model to calculate the spin-lattice relaxation times of the Ce³⁺ ion in binary nitrates. Normal coordinates are found for the icosahedral XY₁₂ complex containing the paramagnetic ion and its nearest neighborhood. The theoretical transition probabilities for the purely ionic model turn out to be slightly above the experimental results, so covalent effects are important.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 31–37, August, 1969.The author thanks L. K. Aminov for supervision of and assistance in this study.     

The magnetic hyperfine fields of rare earth ions in metals

Data for the magnetic dipole hyperfine interaction of essentially single rare earth ions in metals, measured with different experimental methods, are collected and discussed. Depending on the host, the magnetic hyperfine field of these paramagnetic ions remains undisturbed by the environment, or it is enlarged, or weakened or can even become completely lost. If there are magnetic ions in the neighbourhood, the magnetic interaction can enlarge the hyperfine field of the single ion by a transferred hyperfine field. The reason of the demagnetization effect may be crystal field splitting and hybridization. The core polarization field of the free rare earth ions is redetermined from measurements of the hyperfine interaction in nonmagnetic metals at low magnetic ion concentration.