Tunable single-frequency CW Cr<Superscript>2+</Superscript>:CdSe laser

Continuous tuning of the lasing wavelength from 2350 to 3450 nm in the cw Cr²⁺:CdSe laser is demonstrated. It is shown that the laser efficiently operates at a wavelength of 3.28 μm, which is promising for the methane optical frequency standard. The single-frequency mode of the laser with a lasing linewidth not exceeding 60 MHz is implemented in this spectral range.     

Adiabatic elastic moduli in ZnSe : Mn<Superscript>2+</Superscript> and ZnSe : V<Superscript>2+</Superscript> crystals

The temperature dependences of the elastic moduli C ₄₄ (C ₁₁ ? C ₁₂)/2 and C _l = (C ₁₁ + C ₁₂ + 2C ₄₄)/2 of ZnSe : V²⁺ (impurity concentration, 6 × 10¹⁸ cm^?3) and ZnSe : Mn²⁺ (9.4 × 10²⁰ cm^?3) are measured in the temperature range 1.4–100.0 K at frequencies of 52 and 156 MHz. The temperature dependences of the adiabatic elastic moduli are derived. It is established that softening of the symmetry modules is observed only in the crystal with an impurity having orbitally degenerate states.     

Spectral kinetic properties and lasing characteristics of diode-pumped Cr<Superscript>2+</Superscript>:ZnSe single crystals

The temperature and concentration quenching of the luminescence of Cr²⁺ ions in Cr:ZnSe crystals is experimentally investigated and the radiative lifetime of the upper lasing level is determined. The values of the cross sections of absorption from the ground state of Cr²⁺ ions in Cr:ZnSe crystals are refined. It is shown that the absorption from the excited state of Cr²⁺ ions is negligible near 1.5 μm. Lasing in Cr:ZnSe single crystals is implemented with an efficiency of 31% and an output power of 186 mW using laser diode pumping at a wavelength of 1.77 μm.     

Intracavity laser spectroscopy of CH<Subscript>4</Subscript> and NH<Subscript>3</Subscript> gases by using a pulse-periodic Cr<Superscript>2+</Superscript>:ZnSe laser

The results of studying the characteristics of an intracavity laser spectrometer based on a polycrystalline Cr²⁺:ZnSe laser operating in a pulse-periodic regime with the pulse-repetition rate of 3 kHz and pulse duration of ∼50 ns are presented. Intracavity spectra of absorption of NH₃ and CH₄ gases in the vicinity of 2.35 μm are measured. The estimate of the spectrometer sensitivity is provided.     

Nonlinear optical properties of Cr<Superscript>3+</Superscript>-doped laser crystals

The nonlinear optical properties in six Cr³⁺-doped laser crystals LiCaAlF₆, LiSrGaAlF₆, Gd₃Ga₅O₁₂, Gd₃Sc₂Ga₃O₁₂, LaMgAl₁₁O₁₉ and Alexandrite are investigated with the help of the Z-Scan technique at λ = 532 nm in the CW regime. The data reported here include particularly the excited state absorption cross section and the third-order nonlinear susceptibilities. It is found that the three first systems only exhibit both refractive and absorptive nonlinear effects, whereas the three others have only absorptive effects. Gd₃Ga₅O₁₂ shows the best nonlinear potentialities. The excited state absorption cross section corresponding mainly to the ⁴T₂ →   ⁴T₁ transition is found to be ranging between 8.9 × 10⁻²² cm² in LiSGaF and 3.1 × 10⁻²⁰ cm² in LaMgAl₁₁O₁₉. The calculated ratio of the third order nonlinear susceptibility to the ground state absorption coefficient is found to be largest in GGG with a value of 146 × 10⁻⁶ esu.cm and smallest in Alexandrite (0.6 × 10⁻⁶ esu.cm).     

Self-starting five optical cycle pulse generation in Cr<Superscript>4+</Superscript>:YAG laser

We report stable self-starting near-transform-limited 26-fs pulses at 250-mW output power from a Kerr-lens mode-locked (KLM) Cr⁴⁺:YAG laser using chirped mirrors in combination with prisms. The highest output power achieved in KLM regime was 600 mW at 55-fs pulse duration. The experimental results agree well with the results of theoretical analysis with respect to KLM self-starting ability and stability against continuous-wave and multi-pulse operation. Parameter ranges for stable transform-limited KLM pulses as well as the shortest achievable pulse durations are established. Using an InGaAs-InP semiconductor saturable absorber mirror we could obtain self-starting 57-fs pulses at the average output power of 200 mW. Two-photon absorption was found to be the main mechanism favoring the multiple-pulse operation. Received: 2 May 2002 / Revised version: 16 July 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +43-1/58801-38799, E-mail: sorokina@tuwien.ac.at     

Low-temperature relaxation in the ZnSe : V<Superscript>2+</Superscript> crystal

Low-temperature anomalies in absorption of the fast transverse and longitudinal ultrasonic waves are revealed in a ZnSe crystal lightly doped (5.6 × 10¹⁸ cm^?3) with V²⁺ ions. These anomalies are interpreted as a manifestation of the Jahn-Teller effect. The temperature dependence of the relaxation time of the impurity 3d electrons is established.     

Passive Q-switching of a laser-diode-pumped intracavity-frequency-doubling Nd:Nd<Superscript>3+</Superscript>:NaY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>/KTP laser with Cr<Superscript>4+</Superscript>:YAG saturable absorber

Nd³⁺:NaY(WO₄)₂, known as Nd:NYW, is a new type crystal. By using laser-diode as pump source, a passive Q-switching of intracavity-frequency-doubling Nd:NYW/KTP laser has been realized with Cr⁴⁺:YAG saturable absorber. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on incident pump power for different small-signal transmissions of Cr⁴⁺:YAG are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

Radiative transitions and spectral-hole burning in MgO: Cr<Superscript>3+</Superscript> nanocrystals

Luminescence spectra of Cr³⁺ ions in nanocrystalline MgO obtained by sol-gel technology were studied. The radiative lifetime of excited ²E states of cubic and tetragonal Cr³⁺ centers was found to be considerably longer than that of bulk single crystals. This effect is caused by a modified effective refractive index of the inhomogeneous medium. Burning of long-lived spectral holes in the ⁴A₂-²E transition profile of cubic centers was observed, which sets nanocrystalline samples strongly apart from bulk crystals, where no hole burning was found.     

Single diode-pumped, 1.7 ns microchip laser by Nd:YAG/Cr<Superscript>4+</Superscript>:YAG composite crystal

A single diode-pumped passively Q-switched composite Nd:YAG/Cr⁴⁺:YAG laser, which cavity mirrors were deposited directly onto the crystal, was demonstrated in this paper. At the incident power of 2.75 W, the maximum average output power of 365 mW and the shortest pulse width of 1.7 ns were obtained, corresponding the repetition rate of 14.6 kHz. The single-pulse energy and the peak power were estimated to be 25 μJ and 14 kW, respectively. The corresponding optical-optical conversion efficiency was 13.3%.     

Absorption saturation properties and laser Q-switch performance of Cr<Superscript>5+</Superscript>-doped YVO<Subscript>4</Subscript> crystal

The ground-state and excited-state absorption cross sections of a Cr⁵⁺:YVO₄ single crystal were determined by the intensity-dependant transmission measurements to be(2.0±0.4)×10^-18 cm² and less than 0.1×10^-18 cm² at 1.08 μm, respectively. The bleaching relaxation time of the Cr⁵⁺:YVO₄ crystal was estimated to be 3.5±1.5 ns. Passive Q-switching of a diode-pumped Yb³⁺:YVO₄ laser with the Cr⁵⁺:YVO₄ saturable absorber was realized. PACS 42.55.Xi; 42.60.Gd; 42.70.Hj     

High-frequency EPR of Cr<Superscript>2+</Superscript> ions in CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript>

High-frequency broad-band (65–240 GHz) EPR is used to study impurity centers of bivalent chromium in a CdGa₂S₄ crystal. It is found that the EPR spectra correspond to tetragonal symmetry. The spin Hamiltonian H = βB · g · S + B ₂ ⁰ O ₂ ⁰ + B ₄ ⁰ O ₄ ⁰ + B ₄ ⁴ O ₄ ⁴ with the parameters B ₂ ⁰ =23659±2 MHz, B ₄ ⁰ =1.9±1 MHz, |B ₄ ⁴ |=54.2±2 MHz, g_‖=1.93±0.02, and g_⊥=1.99±0.02 is used to describe the observed spectra. It is concluded that chromium ions occupy one of the tetrahedrally coordinated cation positions.     

Timing-jitter reduced high-repetition-rate Q-switched Nd:YVO<Subscript>4</Subscript>/Cr<Superscript>4+</Superscript>:YAG micro laser with low pump power

We report a high repetition rate Q-switched Nd:YVO₄/Cr⁴⁺:YAG micro laser with small pump power. Unwanted defects in pulse train, which are inherently large in passively Q-switched laser, was simply minimized by controlling temperature of Nd:YVO₄/Cr⁴⁺:YAG medium. When T ₀ = 90% Cr⁴⁺:YAG and R _OC = 90% output coupler were used, Q-switched Nd:YVO₄/Cr⁴⁺:YAG micro laser showed the optimum output; maximum output power of 58 mW, optical-to-optical efficiency of 9.1%, repetition rate of 1.1 MHz, and pulse width of 57 ns were achieved with 640 mW pumping. MHz-order repetition rate in Nd:YVO₄/Cr⁴⁺:YAG Q-switched laser with low pumping (<1 W) is the highest value to the best of our knowledge.     

Spectral and generation properties of a new laser crystal (Cr<Superscript>3+</Superscript>,Li): Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript>

Based on the results of a comparative analysis of luminescence spectroscopy and EPR spectroscopy data, it was found for the first time that the wide-band luminescence of Cr³⁺ ions in a forsterite crystal is due to the Cr³⁺-V_Mg center or, in a crystal additionally doped with lithium, to a Cr³⁺-Li⁺ center. For the first time, tunable laser action was obtained with Cr³⁺-Li⁺ centers responsible for the wide-band luminescence.     

Structural Properties of Cr<Superscript>3+</Superscript>-Doped Cadmium Oxide Nanopowders

The Cr³⁺-doped cadmium oxide nanopowder is prepared at room temperature by a mild and simple solution method. The prepared powder is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical, electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) techniques. The XRD powder pattern reveals the lattice structure and cell parameters are evaluated. The SEM image shows the stone-like morphology of the nanopowder. The optical absorption spectrum indicates the distorted octahedral site symmetry of Cr³⁺ ions. The crystal field Dq and interelectronic repulsion parameters B and C are evaluated. The EPR spectrum gives a resonance signal at g = 1.973 for Cr³⁺ ions. The FT-IR spectrum reveals the characteristic vibrations of cadmium oxide.     

Passively Q-switched intracavity frequency-doubled Nd:LuVO<Subscript>4</Subscript>/LBO green laser with a Cr<Superscript>4+</Superscript>:YAG saturable absorber

This work presents experimental results concerning a passively Q-switched intracavity frequencydoubled Nd:LuVO₄/LBO green laser with a Cr⁴⁺:YAG saturable absorber operated at the wavelength of 0.53 μm. A maximal output power of 1.28 W was obtained at a pump power of 16.34 W, and peak power, pulse width as well as repetition frequency were 1.48 kW, 41 ns and 21 kHz, respectively.     

Interaction of <Superscript>3</Superscript>He<Superscript>2+</Superscript> and Ar<Superscript>6+</Superscript> ions with acetylene,ethylene, and ethane molecules

Time-of-flight mass spectroscopy methods are employed for studying processes occurring during capture of electrons by ³He²⁺ and Ar⁶⁺ multiply charged ions with energy 6z keV (z is the ion charge) from C₂H _n molecules (n = 2, 4, 6) with different multiplicities of C-C bonds. Fragmentation schemes of the molecular ions formed in such processes are established from analysis of correlations of recording times for all fragment ions. The absolute values of the cross sections of capture of an electron and capture with ionization are measured, as well as the cross sections of formation of fragment ions in these processes. The absolute values of total capture cross sections for several electrons are determined.     

基于简单MOPA结构实现3.08 kW全光纤窄线宽线偏振激光输出

基于简单的主振荡功率放大结构,演示了一种高功率窄线宽线性偏振全光纤激光器,其最大输出功率为3.08 kW,3 dB线宽为0.2 nm。在整个功率缩放过程中,偏振消光比约为94%,光束质量M ²约为1.4。这是国内外首次实现3 kW全保偏光纤激光输出,与基于相位调制的窄线宽激光器相比,该激光器可实现近似的线宽,同时具有受激布里渊散射阈值高、系统结构简单、成本低等特点。     

Low-threshold supercontinuum generation from an extruded SF6 PCF using a compact Cr<Superscript>4+</Superscript>:YAG laser

The modal properties of an extruded SF6 photonic crystal fiber (PCF) have been analyzed on the basis of a full-vector model. The favorable dispersion properties (the zero-dispersion wavelength for a PCF with 4.5-m core size lies at approximately 1.5 m) and the large nonlinearity figure of up to 280 W^-1km^-1 may provide more than an octave of spectral broadening with launched pulse energies below 200 pJ. In agreement with simulations, experiments have demonstrated the low-energy spectral broadening under excitation by -–60 70fs pulses from a compact mode-locked Cr⁴⁺:YAG laser operating at a 100-MHz repetition rate. Besides the spectral broadening due to the soliton-fission mechanism, the rich mode structure of the fiber allows third-order harmonic generation and four-wave mixing, which extend the supercontinuum spectrum down to the visible-wavelength range. PACS 42.65.Tg; 42.81.Dp     

All-fiber ultra-narrow linewidth 50 pm Tm<Superscript>3+</Superscript>-doped double-clad fiber laser at 1948 nm

A high stability all-fiber LD-clad-pumped Tm³⁺-doped fiber laser was reported. The fiber laser had the ultra-narrow linewidth 50 pm at 1.948 μm with the maximal output power of 12.8 W. The slope efficiency was 28.9%, and threshold was 5.7 W. The double-clad Tm³⁺-doped fiber core was multi-mode, which had a demission of 25/250 μm with the core NA of 0.1 and inner-clad NA of 0.46. The high reflectivity coupler FBG was directly written into the single-mode passive photosensitive optical fiber core, which had a core diameter of 15 μm and NA of 0.1. The cavity was build-up by the high reflectivity FBG and the output fiber end Fresnel reflectivity.