John D. Myers

Upconversion effect on fluorescence quantum efficiency and heat generation in Nd 3+ -doped materials

The thermal lens technique was carried out to experimentally determine the influence of the energy transfer upconversion (ETU) processes on fluorescence quantum efficiency (eta) in Nd3+-doped materials. The samples with high Nd3+ concentration present a considerable reduction in eta?with the increasing excitation power due to the efficient ETU processes. Besides, the energy migration was identified as the mechanism responsible for the upconversion losses. In addition, it was verified that the critical inversion density is not concentration independent, as previously stated, but it decreases with the Nd concentration. Our results point out the approach based on TL technique as a valuable alternative because of its sensitivity allowing the measurements to be performed in a pump power regime that avoids damages in the investigated material.

Laser and thermal performance of a new erbium-doped phosphate laser glass

New erbium doped glass base compositions and sensitizer ion concentrations have been investigated. Laser, spectral, and thermo-mechanical properties have been tested. This study has resulted in a new erbium doped phosphate laser glass that exhibits improved thermal shock resistance and superior laser performance.

Ytterbium-doped phosphate laser glasses

Physical, spectral and laser properties of anew Yb3+ doped phosphate laser glass, QX/Yb, has been developed. This glass exhibits a low thermal expansion coefficient and a negative temperature coefficient of refractive index, resulting in an acceptable athermal behavior and an excellent thermal loading capability. The peak absorption and emission cross sections of Yb3+ were measured to be 1.06 X 10-20 cm2 and 0.903 X 10-20 cm2, respectively. The concentration quenching and the influence of the OH- content on fluorescence lifetimes were examined. Excellent laser performance with a slope efficient of 49 percent and a maximum output power of 400 mW was demonstrated.

Fluorescence lifetime and 980nm pump energy transfer dynamics in erbium and ytterbium co-doped phosphate laser glasses

Phosphate glasses are attractive laser oscillator/amplifier materials because unlike fluoride, silicate, and other laser glass materials it combines attractive properties such as good chemical durability, ion-exchangeability, high gain, low concentration quenching, and low upconversion losses. Phosphate glasses also exhibit very high solubility for rare earth ions. This feature permits the introduction of large concentrations of active ions into relatively small volumes resulting in smaller laser devices with high-energy storage capabilities. These high dopant concentrations also result in very rapid and efficient energy transfer between rare earth ions. This allows for the effective use of Yb3+ as a sensitizer for the Er3+ laser ion. Effective Er:Yb:Glass pumping, energy storage, and energy extraction involves the population of the 2F5/2 level of Yb3+ (~2ms fluorescence lifetime) and transferring energy to the 4I11/2 level of Er3+ (~500μsec transfer time); and a very rapid (< 1μsec) nonradiative decay of the Er3+ from the 4I11/2 state (with an 8ms fluorescence lifetime). In this study we measured the fluorescence lifetime for the 4I13/2 level of Er+3 on different glass samples with various concentrations of erbium. The data indicates that for doping levels up to 7% (wt.%) Er2O3 the lifetime remains above 7.0ms. Theoretically, this highly doped glass may produce greater than 20dB gain in 1cm path length. In additional fluorescence lifetime testing, ytterbium doped and erbium/ytterbium co-doped glasses samples were evaluated for concentration quenching and energy transfer rate as function of the Er3+ concentration rates. The effect on teh energy transfer efficiency and laser efficiency was analyzed.

Phosphate glasses for high average power lasers

This paper summaries our effort to develop new Nd3+, Er3+ and Yb3+ doped phosphate laser glasses, which exhibit high strength and low thermal expansion coefficient as well as acceptable optical athermal behavior. Ion-exchange chemical strengthening processes and laser performances of these glasses are presented.

Chemically stregthened Er3+, Nd3+ doped phosphate laser glasses

Significant enhancement of the thermal loading capability has been achieved with both Er3+ and Nd3+ doped inherently strong glasses by an ion-exchange chemical strengthening process. A free running laser with an average output power of 6.5 W and a Q-switched single mode laser with an energy of 5 mJ at a repetition rate of 15 Hz have been demonstrated at the 1.54 micrometers eye safe wavelength with strengthened QX/Er glass. An average output power of 110 W at 1.05 micrometers has been obtained employing a strengthened QX/Nd glass rod.

High repetition rate Q-switched erbium glass lasers

Many applications exist for eye safe laser operating at high repetition rates. This paper will discuss the operation of Q-switched Er:glass lasers at high repetition rates with peak powers in the megawatt range.

New Generation High Power Rare-Earth-Doped Phosphate Glass Fiber and Fiber Laser

High power, high brightness fiber lasers have numerous potential commercial and military applications. Fiber lasers with cladding pump designs represent a new generation of diode pumped configurations that are extremely efficient, have single mode output and may be operated with or without active cooling. Kigre has invented a new family of Er/Yb/Nd phosphate laser glass materials (designated QX) that promise to facilitate a quantum leap in fiber laser technology of this field. The new phosphate glass Rare-Earth doped fiber exhibit many advantages than Silica or Fluoride base fiber, see table.1. Instead of 30 to 50 meters of fused silica with a 50 mm bend radii; Kigres phosphate glass fiber amplifiers may be designed to be less than 4 meters long .Laser performance and various design parameters, such as the fiber core diameter, NA, inner cladding shape and doping concentration are evaluated. Laser performances was demonstrated for an experimental QX/Er doubled clading fiber commissioned by MIT having 8 micron core, a 240 X 300 micron rectangle shaped inner cladding with 0.4 NA and 500 micron outer clading.. Kigre obtained approximately 2 dB/cm gain from 15cm long fiber under 940nm pumping The same fiber was evaluated by researcher at MIT. They used 975nm pump source. Maximum 270mW output was demonstrated by 30 cm long fiber with Fresnel reflection resonator mirrors. The slope efficiency of absorbed pump power s 47%.

Practical internal combustion engine laser spark plug development

Fundamental studies on laser ignition have been performed by the US Department of Energy under ARES (Advanced Reciprocating Engines Systems) and by the California Energy Commission under ARICE (Advanced Reciprocating Internal Combustion Engine). These and other works have reported considerable increases in fuel efficiencies along with substantial reductions in green-house gas emissions when employing laser spark ignition. Practical commercial applications of this technology require low cost high peak power lasers. The lasers must be small, rugged and able to provide stable laser beam output operation under adverse mechanical and environmental conditions. New DPSS (Diode Pumped Solid State) lasers appear to meet these requirements. In this work we provide an evaluation of HESP (High Efficiency Side Pumped) DPSS laser design and performance with regard to its application as a practical laser spark plug for use in internal combustion engines.

Co2+:MgAl2O4 crystal passive Q-switch performance at 1.34, 1.44, and 1.54 μm

Passive Q-Switch characteristics of Co2+:MgAl2O3 sample were evaluated in a diode pumped QX/Er Erbium glass laser at 1535 nm, a flashlamp pumped Nd:YAG laser at 1.44 micrometers and Nd3+:KGd(WO4)2 laser at 1.34 micrometers .