T. Töpfer

Diode-pumped erbium-ytterbium-glass laser passively Q-switched with a PbS semiconductor quantum-dot doped glass

Q-switched and cw operation of different diodepumped erbium-ytterbium doped glasses at 1.5 μm has been studied in a compact microlaser setup. For Q-switching we used a novel PbS semiconductor quantum-dot doped glass which offers low saturation intensity compared with typical absorbers used and a fast time response. The cw laser delivered output powers of 35 mW with slope efficiencies of 16%. In Q-switched operation pulse energies of 1 μJ at repetition rates of 1–2 kHz and pulse durations of about 30–50 ns, depending on absorber thickness were obtained. PACS: 42.55.Xi; 42.60.Gd; 42.70.Hj The eyesafe wavelength region of the optical spectrum (1.5–1.6 μm) is favoured for applications such as telemetry and ranging [1–4]. Erbium ions in glass hosts are the material of choice if a laser directly emitting in this spectral region without use of nonlinear frequency conversion is desired. Numerous studies in this field have been carried out on actively [2, 4] as well as on passively Q-switched lasers [5, 6]. For compactness, simplicity, and robustness in everyday use the research tends towards diode-pumped passively Q-switched setups [7], avoiding maintenance neccesary for flashlamp pumping and additional electronic equipment required for active switching. Saturable absorbers currently used are erbium [8], uranium [9] and cobalt [10] ions in different crystal hosts. All absorbers are used in resonator setups of a few centimeter length, setting a limit for compactness. All of these absorbers have a relatively high saturation intensity of about 40–200 MW/cm2. In a diodepumped setup these intensities are normally not accessible with single-emitter laser-diode pump-sources with pump powers of 1–2 W. The use of semiconductor quantum-dot doped glass is an interesting possibility to overcome this problem. With an saturation intensity of 0.18 MW/cm2 in PbS-doped glass [11] complete bleaching of the absorber is possible with the intensities achievable in a standard microlaser setup. Another way for Q-switching is the use of semiconductor saturable absorber mirrors [5, 7] which offer a similar saturation characteristic based on quantum wells with their one-dimensional confinement of electronic states in contrast to the three-dimensional confinement in quantumdots. Their production process is complicated because of the sophisticated MOCVD techniques necessary for production of these devices. Semiconductor quantum-dot doped glasses on the other hand can be produced by common melting techniques well known and elaborated in glass technology and can be easily tuned in their spectral properties by changing the quantum-dot size by different growth conditions. Details about the glass composition are to be found in [12].

Scaling laser-diode pumped solid-state amplifiers to the petawatt level

Summary form only given. Increased performance of high-power laser-diodes, decline in laser-diode-power cost, development of new lasing materials, progress on key optical components, and novel pulse-compression techniques enable the design of efficient petawatt-class amplifiers based on diode-pumped chirped-pulse amplification technology. New research in high-field plasma physics, laser-pumped X-ray sources, laser fusion, particle accelerators and generators, as well as astro-physics is envisioned. We have developed laser-diode bars for long pulse pumping that deliver more than 200 W peak-power at almost 50% electrical to optical efficiency. Progress in semiconductor technology, heat-sink design, and diode packaging ensures safe pulsed operation for the required lifetime at driving currents of more than 220 A.. The system design of POLARIS (Petawatt Optical Laser Amplifier for Radiation Intensive Experiments) and supporting data is presented, and the prospects and scaleability of diode-pumped high-power laser-technology discussed. The front-end consisting of a Ti:sapphire oscillator, a low-aberration stretcher, and a regenerative amplifier delivers 1 mJ in 2 ns pulses with 14 nm band width centered at 1035 nm.

Optical properties of CaF2 and Yb3+:CaF2 for laser applications

Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

Optical properties of CaF 2 and Yb 3+ :CaF 2 for laser applications

Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

Optical properties of CaF[sub]2[/sub] and Yb[sup]3+[/sup]:CaF[sub]2[/sub] for laser applications

Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

Nonlinear refractive index of fluoride phosphate laser glasses

Summary form only given. When matter is exposed to intense electric fields polarization is no longer proportional to the electric field and the change in polarizability has to be extended by terms proportional to the square of the electric field. It follows for the refractive index: n=n/sub 0/+n~/sub 2/ /sup 2/=n/sub 0/+n/sub 2/I. Various methods exist to predict the nonlinear refractive index. One approach employs the d-line refractive index and the Abbe-number /spl nu//sub d/, which is defined as the inverse ratio of relative dispersion. Nonlinear refractive indices in fluoride phosphate glasses were determined by degenerate four-wave mixing relative to a reference sample.