Tunable room-temperature laser action of Cr4+-doped Y3ScxAl5−xO12

A new class of tunable room-temperature Cr⁴⁺ lasers is presented: Cr⁴+-doped Y₃Sc_xAl_5–xO₁₂ garnets. With increasing scandium content the emission shifts to longer wavelengths due to the weakening of the crystal field. Free running laser wavelengths are 1440, 1498, 1548 and 1584 nm for x = 0, 0.5, 1.0 and 1.5, respectively. Continuous tunability is obtained from 1309 to 1628 nm.     

Pulsed laser action of Pr:GdLiF4 at room temperature

We realized, to our knowledge for the first time, laser emission in Pr:GdLiF₄ at seven wavelengths: 522 nm, 545 nm, 604.5 nm, 607 nm, 639 nm, 697 nm, and 720 nm. The crystal was pumped with an excimer laser pumped dye laser at 468 nm. All laser experiments were carried out at room temperature. We also achieved pulsed room temperature laser oscillation of Pr:KYF₄ at 642.5 nm pumped at 465 nm wavelength.     

Flashlamp-pumped Ti:Sapphire laser: Influence of the rod figure of merit and Ti3+ concentration

A flashlamp-pumped Ti:Sapphire laser is tested with rods of various Figures of Merit (FOM from 100 to 800) and Ti³⁺ concentrations (0.1 and 0.15% by weight) and we measured the laser energy dependence as a function of these parameters. Output energies above 2 J are obtained without dye converter, leading to a 1.8% overall efficiency and a 2.2% slope efficiency. The effects of pump pulse duration by variation of the discharge capacitance are also monitored.     

Efficient Continuous Wave-laser emission of Pr3+-doped fluorides at room temperature

We report, to our knowledge for the first time, Continuous Wave (CW) laser emission at room temperature of Pr:LiYF₄ (Pr.YLF) at six wavelengths: 522, 545, 607, 639.5, 720 and 907.4 nm. The pump source was an argon-ion laser tuned to a wavelength of = 457.9 nm. The maximum output powers at 522 nm (³P_i ³H₅) and 639.5 nm (³P₀ ³F₂) were 144 and 266 mW, respectively. We also observed CW laser action of Pr:GdLiF₄ (Pr: GLF) at = 639 nm and of Pr:KYF₄ (Pr: KYF) at = 642.5 nm.     

Polarized and time-resolved measurements of excited-state absorption and stimulated emission in Ti:YAlO3 and Ti:Al2O3

Pump-induced excited-state absorption (ESA) in the whole range of pump wavelengths prevents effective laser action of Ti:YAlO₃. The time-resolved measurement of this absorption allows the separation of excited-state absorption and losses due to transient colour centres. The influence of polarization on the ESA of Ti:YAlO₃ is only weak, as it is expected for a charge-transfer transition. No significant stimulated emission (SE) could be measured in the whole fluorescence region. In comparison, Ti:Al₂O₃ shows a broad SE spectrum corresponding to the tuning range of this laser material. The strongest SE was measured for Ec, which is the preferred polarization for laser action of Ti:Al₂O₃. Below 350 nm the long-wavelength edge of an ESA band was found.     

Infrared excited-state absorption and stimulated-emission cross sections of Er3+-doped crystals

Detailed spectra of the excited-state absorption and the stimulated-emission cross-sections of Er³⁺ -doped Y₃Al₅O₁₂, YAlO₃, LiYF₄, and KYF₄ crystals are analyzed in the infrared wavelength regions from 700 to 2100 nm. The spectra were measured with a pump and probe technique employing a double modulation scheme. For Er (2%): Y₃Al₅O₁₂ also the stimulated emission at 3 µm and the reabsorption due to excited-state absorption from the lower laser level are investigated.     

Blue emission in Ti-sapphire laser crystals

The time resolved emission spectrum of the blue band of Ti:sapphire laser crystal has been investigated as a function of temperature (range 10–290 K) and UV (266 nm) laser excitation intensity. Two blue emission bands, centred at 420 nm and 460 nm, have been detected. The 420 nm band is attributed to Ti⁴⁺ centres whereas the 460 nm one is proposed to be due to Ti³⁺ ions. The evolution of the emission spectrum vs the UV excitation intensity has shown that the concentration of Ti⁴⁺ centres is increased under UV irradiation at the cost of the centres responsible for the 460 nm band.     

Explanation for TEM00 operation of heavily doped YAlO3:Er3+

Although pump energy is mainly absorbed at the border of a heavily doped YAlO₃:Er³⁺ rod, fundamental mode laser operation is achieved. The absorption of pumplight in the laser rod, energy transfer mechanisms and the population of the laser levels are discussed. A possible explanation of the inversion maximum in the center of the rod is given.     

Excited state absorption and stimulated emission of Nd3+ in crystals. Part I: Y3Al5O12, YAlO3, and Y2O3

4 F_3/2 excited state of the Nd³⁺ ion in Y₃Al₅O₁₂, YAlO₃, and Y₂O₃ were measured in a continuous wave pump- and probe experiment in a wide spectral range from 850 nm (780 nm for Y₃Al₅O₁₂) to 1500 nm. The cross sections were determined from a comparison with the emission spectra and the simultaneously measured ground state absorption bleaching. The strongest excited state absorption transitions were found in the 1220–1400 nm spectral region due to transitions to the ²G_9/2 and ⁴G_7/2 levels. The spectral positions of the measured transitions are in good agreement with the theoretically expected transitions calculated from the known Stark-level splittings. Received: 4 December 1997/Revised version: 8 May 1998     

High-power simultaneous dual-wavelength emission of an end-pumped Nd:YAG laser using the quasi-three-level and the four-level transition

An efficient continuous-wave (CW) simultaneous dual-wavelength lasing (SDWL) of an LD end-pumped Nd:YAG laser utilizing a quasi-three-level transition at 946 nm and a four-level transition at 1064 nm is reported. A theoretical model has been introduced to determine the threshold conditions for SDWL. The temperature distributions of a Nd:YAG crystal under different pump powers have been analyzed. In the experiments, a CW SDWL output power of 5.12 W at a temperature of 273 K has been achieved with a pump power of 17 W, giving a slope efficiency of 16.36%.     

Crystalline structure and optical spectroscopy of Er3+-doped KGd(WO4)2 single crystals

4 )₂ single crystals doped with Er³⁺ have been grown by the flux top-seeded-solution growth method. The crystallographic structure of the lattice has been refined, being the lattice constants a=10.652(4), b=10.374(6), c=7.582(2) Å, β=130.80(2)°. The refractive index dispersion of the host has been measured in the 350–1500 nm range. The optical absorption and photoluminescence properties of Er³⁺ have been characterised in the 5–300 K temperature range. At 5 K, the absorption and emission bands show the (2J+1)/2 multiplet splittings expected for the C₂ symmetry site of Er in the Gd site. The energy positions and halfwidths of the 72 sublevels observed have been tabulated as well as the cross sections of the different multiplets. Six emission band sets have been observed under excitation of the ⁴F_7/2 multiplet. The Judd–Ofelt (JO) parameters of Er³⁺ in KGW have been calculated: Ω₂=8.90×10^-20 cm², Ω₄=0.96×10^-20 cm², Ω₆=0.82×10^-20 cm². Lifetimes of the ⁴S_3/2, ⁴F_9/2, and ⁴I_11/2 multiplets have been measured in the 5–300 K range of temperature and compared with those calculated from the JO theory. A reduction of the ⁴S_3/2 and ⁴I_11/2 measured lifetimes with increasing erbium concentration has been observed, moreover the presence of multiphonon non-radiative processes is inferred from the temperature dependence of the lifetimes. Received: 15 December 1997/Revised version: 10 July 1998     

Slope efficiency of up to 73% for Yb:Ca4YO(BO3)3 crystal laser pumped by a laser diode

Yb:Ca₄YO(BO₃)₃ (Yb:YCOB) crystal with good quality and large size has been grown by the Czochralski method. The polarization absorption and fluorescence spectra have been measured. The laser action of the Yb:YCOB crystal has been demonstrated when it is pumped by a fiber-coupled laser diode (LD) at the wavelength of 976.4 nm. The pumping threshold is 55 mW, the light-light conversion efficiency is 58.7%, and a slope efficiency of up to 73% is thus calculated. Received: 16 December 1998 / Revised version: 4 February 1999 / Published online: 7 April 1999     

Spectroscopic characterization and laser performance of diode-laser-pumped Nd: GdVO4

We have carried out a detailed spectroscopic characterization of Nd: GdVO₄, a new laser crystal with high effective absorption and emission cross sections. The accidental degeneracy of the upper⁴ F _3/2 laser level decreases the number of emission lines and creates -together with the anisotropic crystal field - high emission cross sections (7.6 × 10^–19 cm² at 1.06 µm and 300 K). In addition, the lines are strongly homogeneously broadened (1.6 nm for the 808.4 nm diode-laser pump transition). The temperature dependences of lifetime, linewidths, and cross sections have been determined. Slope efficiencies up to 57% with respect to the absorbed diode-laser pump power and output powers up to 0.8 W have been achieved at 1.06 µm from a 2 mm long crystal. Intracavity second-harmonic generation, using a KTP crystal, is demonstrated.     

Temporal evolution of the emission spectra of color center lasers

The mode spectrum of a homogeneously broadened laser is mainly influenced by mode competition effects. In this paper the temporal evolution of the emission spectra of color center lasers caused by mode competition is investigated. The results are compared with a theoretical estimation.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

High-efficiency flashlamp-pumped Nd:KGW laser

The laser performance of a Nd:KGW rod has been studied in a single flashlamp cavity in the free running as well as in the Q-switched mode of operation at input energies ranging from 1–25J. The results of Nd:KGW have been compared with Nd:YAG operated under identical experimental conditions. The laser extraction efficiency of the Nd:KGW rod was observed to be 2.5 times higher at a much lower threshold than that of the Nd:YAG rod. The intrinsic slope efficiency was determined to be 2.25% and 8.840% for Nd:YAG and Nd:KGW rods, respectively.     

Continuous-wave tunable Cr2+:ZnS laser

We report the first continuous-wave tunable over ∼280 nm around 2.3 μm room-temperature operation of a chemical vapor transport-grown and diffusion-doped Cr²⁺:ZnS laser, pumped by a Co:MgF₂ laser at 1.67 μm and generating over 100 mW of output power at 16% slope efficiency. The self-consistent results of the laser and spectroscopic analysis demonstrate a large potential of this crystal as an active medium for diode-pumped tunable mid-infrared sources. Received: 7 January 2002 / Revised: 14 March 2002 / Published online: 2 May 2002     

Efficiency of diode-pumped 1.35µm laser from Nd:KGW

A set of quasi-Continuous-Wave (CW) diode lasers has been used to pump Nd:KGW and to generate 1.35µm laser radiation at room temperature. The optical-to-optical and slope efficiencies have been measured and compared with those of Nd:YAG at identical experimental conditions.     

Autocorrelation coefficient of the radiation output of a frequency-doubled Nd:YAG laser

The autocorrelation coefficient of a frequency-doubled Nd:YAG laser output has been extracted for various operating conditions from the pulse form measured by a streak camera and from the enhancement of the nonresonant CARS intensity for correlated as against uncorrelated pump beams. The measured values are compared with values in the normalized Gaussian model.     

Effect of Nd concentration on the Nd:KGW laser

The effect of Nd concentration on the laser performance at 1064 nm from Nd:KGW has been studied in a single flash-lamp cavity. The Nd concentrations used were 3, 5, and 6 at.% in 6 mm diameter and 80 mm long KGW rods. The 5 at % Nd-doped KGW rod was found to have the highest laser extraction efficiency as compared to the 3 at.% and 6 at.% rods.     

Vacuum ultraviolet gain measurements in optically pumped LiYF4:Nd3+

 We present measurements of the net-induced gain on the 5d–4f transition at 186 nm in LiYF₄ : Nd³⁺ optically pumped by radiation from a molecular fluorine laser. It is found that for LiYF₄ : Nd³⁺, one of a series of potential continuously tunable VUV lasers, relatively strong excited-state absorption results in net-induced loss. The prospects for VUV laser operation being realised in other rare-earth-doped fluorides is discussed. Received: 4 March 1996/Revised version: 10 July 1996