Umit Demirbas

Intracavity-pumped Cr2+:ZnSe laser with ultrabroad tuning range between 1880 and 3100 nm

We obtained, what is to our knowledge, record tuning from an intracavity-pumped gain-switched Cr2+:ZnSe laser. In the experiments, a polycrystalline Cr2+:ZnSe sample with an absorption of about 43% at 1570 nm was used to minimize reabsorption losses at the lasing wavelengths below 2000 nm. By placing the gain medium inside the cavity of a pulsed KTP optical parametric oscillator (OPO) operating at 1570 nm, smooth, continuous tuning was achieved in the 1880-3100 nm range with four different sets of cavity optics. As high as 145 mW of average laser output power was obtained at 2365 nm with 1.2 W of intracavity OPO power.

Accurate determination of saturation parameters for Cr 4+ -doped solid-state saturable absorbers

We describe a systematic, rigorous procedure for the determination of the optical absorption saturation parameters for Cr4+:YAG and Cr4+:forsterite crystals at 1064 nm. A rate-equation approach was used to analyze the cw and pulsed transmission data of several crystals by accounting for the transverse as well as longitudinal variation of the beam intensity, saturation effects, and excited-state absorption. Use of an iterative procedure whereby the cw and pulsed data were simultaneously analyzed led to a considerable reduction in the error for the determination of cross sections. The average value of the absorption cross section sigmaa and the normalized excited-state absorption cross section fp=sigmaesa/sigmaa were determined to be 6.13×10−19 cm2 and 0.45, respectively, for Cr4+:forsterite and 19.6×10−19 cm2 and 0.06, respectively, for Cr4+:YAG. Detailed comparison was also made with previous saturation measurements in the literature. Our results further show that lumped models based on the thin-length approximation should be used with caution in the determination of cross sections, especially when the pump beam is tightly focused inside the absorber.

Absorption saturation analysis of Cr 2+ :ZnSe and Fe 2+ :ZnSe

We propose several methods for the accurate determination of the cross sections of solid-state saturable absorbers and apply them to the analysis of polycrystalline Cr2+:ZnSe and Fe2+:ZnSe. In the case of Cr2+:ZnSe, both z-scan and power-dependent transmission measurements were made by using a continuous-wave fiber laser at 1800 nm and a pulsed optical parametric oscillator at 1570 nm. The average ground-state absorption cross sections at the wavelengths of 1800 and 1570 nm were determined to be 6.17×10−19cm2 and 2.24×10−19cm2, respectively. Furthermore, the ratio of the cross sections at these wavelengths (2.75) was close to the value of 2.55 obtained from absorption spectrum measurements. Excited-state absorption was found to be negligible at both wavelengths. In the case of Fe2+:ZnSe, a tunable, pulsed Cr2+:ZnSe laser was used to obtain saturation data (z-scan and power-dependent saturation) at the wavelengths of 2645 and 2730 nm. Average ground-state absorption cross sections at 2645 and 2730 nm were determined to be 1.73×10−19cm2 and 2.47×10−19cm2, respectively, again in very good agreement with those obtained from absorption spectrum measurements.

Direct Experimental Determination of the Optimum Chromium Concentration in Continuous-Wave Cr

We employed several experimental techniques to measure the concentration dependence of the important laser parameters, and directly determine the optimum ion concentration for continuous-wave (CW) operation in room temperature Cr2+:ZnSe lasers. By using diffusion doping, 40 polycrystalline Cr2+:ZnSe samples with ion concentrations in the range of 0.8 times 1018 to 66 times 1018 ions/cm3 were prepared and used in this paper. Based on the spectroscopic measurements, empirical formulae showing the concentration dependence of the passive laser losses, fluorescence lifetime, and the fluorescence efficiency were obtained. By using the fluorescence efficiency data, the optimum chromium concentration, which maximizes the 2400-nm fluorescence intensity at a fixed excitation power, was determined to be 6 times 1018 ions/cm3. The dependence of the optimum concentration on sample length was further discussed. The CW power performance of the samples was also evaluated. At an incident pump power of 2.1 W, the optimum concentration for lasing was determined to be 8.5 times 1018 ions/cm3 that was in good agreement with the fluorescence measurements. The predictions of the fluorescence analysis and laser power measurements were in good agreement at low chromium concentrations. The observed discrepancy at higher doping levels was attributed to thermal loading.

^{2 + }

Tm3+-doped glasses have two emission bands that peak around 1470 nm and 1800 nm in the near infrared, making them potentially important in the development of fiber-optic amplifiers and fiber lasers. The relative strength and the quantum efficiency of these bands depend on the glass composition as well as the active ion concentration. In this study, we have investigated the variation of the luminescence strengths as a function of glass composition and Tm3+ ion concentration in a new type of Tm3+-doped tellurite glass. In the experiments, two sets of samples with the host composition (1-x)TeO2-(x)PbF2 were prepared. In the first set, the active ion concentration was constant (1 mol. % Tm3+) and x=10, 15, 17, 20, 22 and 25 mol. %. The second set had samples with x=10 mol. % and the active ion concentration varied from 0.2 to 1 mol. %. In the experiments, absorption measurements were first made to determine the spontaneous emission probabilities of the 4f-4f transitions of the Tm3+ ions. The calculations were made by using the Judd-Ofelt theory. The samples were then excited with a 785-nm diode to measure the relative emission strengths of the 1470-nm and 1800-nm bands. Our results show that as the Tm3+ ion concentration increases from 0.2 mol. % to 1 mol. %, the ratio of the 1470-nm intensity decreases from 0.98 to 0.18 relative to that of the 1800-nm band.

:ZnSe Lasers

Diode-pumped femtosecond Cr:Colquiriite lasers are a versatile, low-cost complementary technology to Ti:Sapphire. Modelocked tuning of >100-nm, GHz repetition-rates and timing jitters of 156 attoseconds (10 kHz-10 MHz) are demonstrated from different Cr:Colquiriite laser implementations.

Spectroscopic properties of Tm 3+ :TeO 2 -PbF 2 glasses in the near infrared

We report on the generation of 9.9-nJ, 95-fs pulses at a repetition rate of 9.58 MHz from a multipass-cavity Cr3+:LiCAF laser pumped by single-mode diodes with a total absorbed pump power of only 540 mW.

Compact and Low-Cost Fs Diode-Pumped Cr:Colquiriite Laser Technology

67-fs pulses with an average power of 300 mW and pulse repetition rate of 120 MHz were obtained from a diode-pumped Cr3+:LiCAF laser. A semiconductor saturable absorber mirror enabled stable and self-starting mode-locked operation.

10-nJ Multipass-Cavity Femtosecond Cr 3+ :LiCAF Laser Pumped by Low-Power Single-Mode Diodes

By using a Cr2+:ZnSe sample with reduced reabsorption losses and by employing intracavity pumping inside a 1570-nm KTP optical parametric oscillator, we demonstrated ultrabroad tuning of a gain-switched Cr2+:ZnSe laser between 1880 and 3100 nm

High Average-Power Diode-Pumped Femtosecond Cr 3+ :LiCAF Laser

Power performance of a compact, broadly tunable, continuous-wave (cw) Cr2+:ZnSe laser pumped by a thulium fiber laser at 1800 nm was investigated. In the lasing experiments, a Cr2+:ZnSe sample with a small-signal differential absorption coefficient of 11 cm-1 and a fluorescence lifetime of 4.6 μs was used. An astigmatically compensated x-cavity with 15 % output coupler produced as high as 640 mW of output power at 2480 nm with 2.5 W of incident pump power. Resonator losses were investigated using three different methods, and an in-depth analysis of the results was performed. The stimulated emission cross section values determined from laser threshold data and fluorescence measurements were in good agreement with each other. Finally, broad, continuous tuning of the laser was demonstrated between 2240 and 2900 nm by using an intracavity Brewster-cut MgF2 prism and a single set of optics.