Doubly Passively Self-Q-Switched Cr4+:Nd3+:YAG Laser With a GaAs Output Coupler in a Short Cavity

By using a GaAs as both an output coupler and a saturable absorber, we present a doubly passively self-Q-switched Cr⁴⁺:Nd³⁺:YAG laser in a short cavity for the first time to our knowledge. This laser can generate more symmetric pulse shape and shorter pulsewidth in comparison with the solely self-Q-switched Cr⁴⁺:Nd³⁺:YAG laser. The output pulse energy and peak powers are higher than those in our previous doubly passively Q-switched lasers. By considering the Gaussian spatial distribution of the intra-cavity photon density and the free carrier absorption (FCA) in GaAs wafer, a set of modified rate equations have been introduced to describe the performances of the doubly Q-switched Cr ⁴⁺:Nd³⁺:YAG laser with GaAs coupler. The numerical solutions of the equations and the experimental results are found to agree with each other very well. The effect of FCA process in GaAs wafer has been discussed and proved to play an important role in the pulse compression and symmetry     

LiCaAlF6:Cr3+: a promising new solid-statelaser material

LiCaAlF₆:Cr³⁺ (Cr³⁺:LiCAF) exhibits an intrinsic (extrapolated maximum) slope efficiency of 67%. For comparison, the intrinsic slope efficiencies of BeAl₂O ₄:Cr³⁺ (alexandrite), Na₃Ga₂Li₃F₁₂:Cr³⁺ and ScBO₃:Cr³⁺ were found to be 65, 28, and 26%, respectively. The tuning range of LiCaAlF₆:Cr³⁺ was determined to be at least 720-840 nm. The conventional spectroscopic properties, such as the absorption, emission, and emission lifetimes as a function of temperature, are reported as well     

8B9--Laser emission at 1.06 µ from Nd3+-Yb3+glass

Laser emission at 1.015 μm occurs in glass singly doped and when sensitized with Nd³⁺. For double doping in a Li Mg Al Si glass, emission at 1.015 μm from Yb³⁺and 1.06 μm from Nd³⁺was reported. By monitoring the 1.35 μm fluorescent line of Nd³⁺, it can be shown that both Nd³⁺and Yb³⁺lase at 1.06 μm at room temperature in a silicate glass with 5 weight percent Nd2O3and 5 weight percent Yb2O3. Energy transfer from Nd³⁺to Yb³⁺is a linear function of the Yb³⁺concentration. The transfer increases with Nd³⁺concentration by about a factor of three in going from 1 weight percent Nd2O3to 6 weight percent Nd2O3and thereafter remains approximately constant. This indicates that the transfer from Nd³⁺to Yb³⁺is assisted by intermediate transfer steps between Nd³⁺ions. Additional transfer above 6 weight percent Nd2O3is prevented by concentration quenching.     

Spectroscopic and laser properties of Nd3+ in BIGaZLuTMnfluoride glass

The optical properties of Nd³⁺-doped fluoride BIGaZLuTMn glass have been investigated by using steady-state and time-resolved laser spectroscopy. Laser action has been obtained for the first time in this glass by flashlamp pumping. The influence of site-dependent effects on fluorescence lifetime and time-resolved stimulated emission has been proved     

Flashlamp-pumped Cr3+:GSAG laser

Flashlamp-pumped vibronic lasing has been demonstrated at room temperature with the garnet Cr³⁺: GSAG. Continuous wavelength tuning was observed from 765 to 801 nm in preliminary experiments. An energy output of 110 mJ/pulse was obtained at 784 nm with a slope efficiency of 0.12 percent. Wavelength dependent gain and loss data are presented and are discussed with reference to Cr³⁺: GSGG measurements.     

Self-Q-switched Nd3+: YAG and ruby lasers

Self-Q-switched operation of Nd³⁺: YAG lasers at 77°K and ruby lasers at 300 and 77°K pumped by the 5145-Å output of a pulsed argon ion laser is described. Self-Q-switched operation was obtained 1) by static mirror misalignment and 2) by static misalignment of the filament of the pumped laser material with respect to the mirror resonator axis. An output that consisted of a single giant pulse could be obtained for ruby by either method; for Nd³⁺: YAG, the output always consisted of one or more giant pulses and characteristic relaxation oscillations.     

Investigation of the laser properties of Cr3+:LiSrGaF6

A boule of Cr:LiSGAF (Cr³⁺:LiSrGaF₆), the Ga analog of Cr:LiSAF, was grown, a laser sample was fabricated, and its efficiency was measured using a laser-pumped laser configuration. The laser performance near 820 nm and related properties of Cr:LiSGAF are reported. The use of Sr instead of Ca results in a red shift of the absorption and emission band (along with an increase in the emission cross section). Insight into the effect of a change in the identity of the substitutional site on the properties of the laser is provided     

Tunable Cr4+:YSO Q-switched Cr:LiCAF laser

Tunable passive Q-switching (781 nm to 806 nm at 300 K) of a flash-lamp pumped Cr³⁺:LiCaAlF₆ (Cr:LiCAF) laser with a Cr⁴⁺:Y₂SiO₅ (Cr⁴⁺:YSO) broad-band solid-state saturable absorber has been realized. Typical pulse widths of the Q-switched laser output ranged from 40 ns to 80 ns, depending on the lasing wavelength. Spectral narrowing and reduced beam diameter with the use of the saturable absorber were observed. The ground state and the excited state absorption cross sections of the Cr⁴⁺:YSO absorber were found by bleaching experiments to be (7.0±1.4)×10^-19 cm² and (2.3±0.5)×10^-19 cm² at 694 nm, respectively. Numerical simulation was utilized to simulate the Cr:LiCAF passive Q-switching with Cr⁴⁺ :YSO solid-state saturable absorber     

Efficient integrated Nd3+ fiber laser

An efficient, integrated, low-threshold, tunable, laser-diode pumped Nd³⁺ fiber laser has been fabricated. The integrated fiber laser incorporated two highly reflecting intracore Bragg reflectors, which were formed holographically by transversely exposing the core to a UV two-beam interference pattern. When the fiber laser was diode pumped, a maximum output of 2.3 mW was observed at 1.088 μm, and a slope efficiency of 41% was measured     

Temperature effects on the fluorescence characteristics of RbMnF3:Nd3+

The absorption, excitation, and fluorescence spectra and lifetimes of Mn²⁺and Nd³⁺in RbMnF3were investigated in the 5 to 300°K region. The fluorescence of Mn²⁺in these systems was found to originate from two metastable levels centered at 5820 and 6300 Å. The Nd³⁺emission appears as two groups of sharp lines centered atsim10 600and ∼8900 Å. Energy transfer from manganese to neodymium is observed even at room temperature where the Mn²⁺fluorescence is completely quenched and the energy transfer mechanism was found to be of nonradiative type. Detailed information was obtained on the temperature dependence of the fluorescence intensities and decay times of the manganese and neodymium emissions. The results give information on the kinetics of these fluorescent systems.     

Single-mode Nd3+-doped graded-index polymer waveguideamplifier

The first graded index (GRIN) polymer waveguide amplifier working at 1.06 μm wavelength has been realized, using a Nd³⁺: photolime gel material combination. Throughput intensity of 3.8 mW at 1.06 μm, corresponding to 8.5 dB gain, was observed when employing a 40 mW pumping laser beam operating at 790 nm. The gain medium is a 2.2 cm waveguide active region with Nd³⁺ concentration of 1.03×10²⁰/cm³. The GRIN characteristic of the photolime gel thin film provides a universal means for implementing polymer-based photonic integrated circuits (PICs) on any substrate of interest     

Fluorescence dynamics of Er3+ and Ho3+ ionsand energy transfer in some fluoride glasses

A detailed study at room temperature of the fluorescence dynamics of Er³⁺ and Ho³⁺ ions and energy transfer processes Er³⁺→Ho³⁺ in the ABLA, BATY, and BIZYT fluoride glasses is reported. Numerous concentrations and different selective laser excitations in the visible and infrared spectral ranges are used. The best concentrations and the more suitable glasses for laser applications at 2 μm are determined     

Tuning of a Tm3+:Ho3+: silica fiber laser at2 μm

Thermal tuning of a Tm³⁺:Ho³⁺:SiO₂ glass fiber laser was investigated. As a function of fiber length and temperature, the emission wavelength can be varied between 1960 and 2032 nm. The bandwidth of the laser emission is about 2 mm. Besides the wavelength also the change of threshold and slope efficiency with temperature and fiber length and the fiber absorption were measured     

Finite-element analysis of single-frequency silica-based Er3+-Yb3+ co-doped waveguide lasers

Continuous wave laser operations of silica-based Er³⁺-Yb³⁺ co-doped waveguides have been numerically analyzed by means of a finite-element method. The theoretical model, based on propagation-rate equations, describes uniform upconversion by a dipole-dipole interaction between Er³⁺ ions, and includes a pair-induced energy transfer process from Yb ³⁺-Er³⁺ Numerical results show that single-frequency operation with slope efficiency higher than 50% and threshold pump powers of few mW can be achieved in short and heavily doped waveguides equipped with input dielectric mirrors and output distributed Bragg reflectors     

Measurement of the stimulated emission cross section for the 4F3/2-4I13/2transition of Nd3+ in YAlO3 crystal

A method for the simultaneous measurement of the stimulated emission cross section and fluorescence lifetime by studying the relation between laser parameters and the laser relaxation oscillation frequency is discussed. The stimulated emission cross section for the ⁴F_3/2-⁴I_13/2 transition of Nd³⁺ ion in YAP crystal was measured to be (22±1)×10^-20 cm²     

Cr2+-doped zinc chalcogenides as efficient, widelytunable mid-infrared lasers

Transition-metal-doped zinc chalcogenide crystals have recently been investigated as potential mid-infrared lasers. Tetrahedrally coordinated Cr²⁺ ions are especially attractive as lasants on account of high luminescence quantum yields for emission in the 2000-3000-nm range. Radiative lifetimes and emission cross sections of the upper ⁵E state are respectively ~10 μs and ~10^-18 cm². The associated absorption band peaked at ~1800 mm enables laser-diode pumping of the Cr²⁺ systems. Laser demonstrations with ZnS:Cr and ZnSe:Cr (using a MgF₂:Co²⁺ laser pump source) gave slope efficiencies up to 30%. Excited-state-absorption losses appear small, and passive losses dominate at present. Tuning experiments with a diffraction grating produce a tuning range covering at least 2150-2800 nm. Laser crystals can be produced by Bridgman growth, seeded physical vapor transport, or diffusion doping. Zinc chalcogenide thermomechanical properties of interest for medium-to-high-power operation compare favorably with those of other host materials, except for the larger refractive-index derivative dn/dT     

Carrier-frequency-controlled gigabit pulse generation with a Nd3+: YAG laser

Optical pulses up to 1.25 Gbit/s were obtained with a Nd³⁺:YAG laser by multiple mode locking. The carrier frequency of mode-locked pulses was tuned through several tens of gigahertz by tilting an intracavity tuning etalon. Some detuning effects in forced mode locking will be also presented.     

Stimulated emission investigations of effects of electron-phonon interaction in crystals activated with Nd3+ions

Stimulated emission spectroscopic methods were applied to investigate the electron-phonon interaction in Y3Al5O12and LaF3crystals activated with Nd³⁺ions. Temperature broadening and shifting of laser lines as well as the variation in the rate of nonradiative decay of the⁴I_{11/2}state were studied. For the Y3Al5O12-Nd³⁺crystal, the analysis of the results on temperature broadening and line shifting reveal an effective Debye temperature of ∼600 K for the spectrum of impurity-active phonons. This value of TDvery nearly corresponds to the energy of effective phonons (∼400 cm^-1) which are responsible for the nonradiative decay of the⁴I_{11/2}state. For LaF3-Nd³⁺the effective TDvalues obtained by two different methods are 400 and 430 K, respectively. The temperature dependence of the threshold pumping energy for both laser crystals was computed theoretically. The physical factors governing this dependence are identified.     

Pump-power-dependent efficiency in a YAG: Nd3+laser

The efficiency of a YAG: Nd³⁺-laser and the influence of pump-power level and of spectral filtering the pump light was studied. The laser was pulsed high above threshold. Without filtering the pump light, the maximum laser emission was reached 30 μs before the maximum pump power. With filtered pump light, the efficiency is doubled and the laser emission roughly follows the pump power. Dynamic input-output characteristics show an efficiency minimum at the pump-power maximum.