Dr. Joachim Hein Profile

Dr. Joachim Hein

Senior Scientist at Friedrich-Schiller-Univ Jena

SPIE Involvement:

Conference Chair | Conference Program Committee | Editor | Author

Publications (27)

SPIE Conference Volume | July 31, 2017

High-Power, High-Energy, and High-Intensity Laser Technology III

PROCEEDINGS ARTICLE | June 9, 2017

Pump-induced phase aberrations in Yb3+-doped materials (Conference Presentation)

Proc. SPIE. 10238, High-Power, High-Energy, and High-Intensity Laser Technology III

KEYWORDS: Modulation, High power lasers, Laser applications, Phase shift keying, Semiconductor lasers, Diodes, Optical pumping, Laser optics, Optical damage, Laser systems engineering

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Optical pumping of laser materials is an effective way to create a population inversion necessary for laser operation. However, a fraction of the pump energy is always transfered as heat into the laser material, which is mainly caused by the quantum defect. For Yb3+-doped materials, the small energy difference between the pump level and the laser level and the pumping with narrowband high-power laser diodes result in a quantum defect of approx. 9%, which is significantly lower compared to other dopants e.g. Ti3+ (33%) or Nd3+ (24%). Due to the low heat introduction, high optical-to-optical efficiency and high repetition rate laser systems based on diode-pumping are well-suited for a number of applications. Here, however, laser beam quality is of crucial importance. Phase distortions and beam profile modulations can lead to optical damages as well as a significant reduction of the focal spot intensity. Pump-induced phase aberrations are the main cause for phase distortions of the amplified laser beam. The heat transferred to the material causes a change of the refractive index (dn/dT), thermal expansion and stress within the laser material, eventually leading to spatial phase aberrations (also called ‘thermal lens’). However, the spatially dependent distribution of the population inversion itself also leads to spatial phase aberrations. Since electron excitation directly leads to a change in the charge distribution of the laser active ions, the dynamic response of the material to external fields changes. These electronic phase aberrations (also called ‘population lens’) are described by a change in the polarizability of the material. Due to the low quantum defect of Yb3+-doped materials, this effect becomes more important. We show the first comprehensive spatio-temporal characterization of the pump-induced phase aberration including both effects. A high-resolution interference measurement was carried out with time steps of 50µs for times during the pump period and the cooling period between subsequent pump pulses. We found that both phase effects significantly contribute to the overall phase distortions. Since the temporal characteristic of the electronic phase depends on the fluorescence lifetime and the thermal phase on the thermal diffusivity, both phase effects could be distinguished by their different lifetimes. The measurements were carried out for Yb:YAG, Yb:CaF2 and Yb:glass, and are in excellent agreement to our detailed, COMSOL-based, spatio-temporal phase simulations. Since Yb:CaF2 and Yb:glass provide a negative dn/dT, the electronic phase change becomes even more important and, in case of Yb:CaF2, almost completely compensates the thermal phase imprint of a pump pulse during the time frame of laser pulse amplification.

PROCEEDINGS ARTICLE | May 11, 2017

Temperature dependent spectroscopic characterization of Tm:YAG crystals as potential laser medium for pulsed high energy laser amplifiers

Proc. SPIE. 10238, High-Power, High-Energy, and High-Intensity Laser Technology III

KEYWORDS: Spectroscopy, High power lasers, Luminescence, Crystals, Quantum efficiency, Semiconductor lasers, Diodes, Laser crystals, Signal detection, Pulsed laser operation, Cryogenics, Temperature metrology, Absorption

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PROCEEDINGS ARTICLE | February 22, 2017

Progress in joule-class diode laser bars and high brightness modules for application in long-pulse pumping of solid state amplifiers

Proc. SPIE. 10086, High-Power Diode Laser Technology XV

KEYWORDS: Packaging, Optical amplifiers, Polarization, High power lasers, Laser crystals

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SPIE Conference Volume | June 4, 2015

High-Power, High-Energy, and High-Intensity Laser Technology II

PROCEEDINGS ARTICLE | May 12, 2015

Investigation of Yb3+-doped alumino-silicate glasses for high energy class diode pumped solid state lasers

Proc. SPIE. 9513, High-Power, High-Energy, and High-Intensity Laser Technology II

KEYWORDS: Oscillators, Glasses, Laser induced damage, Luminescence, Quantum efficiency, Doping, Semiconductor lasers, Diodes, Laser damage threshold, Absorption

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PROCEEDINGS ARTICLE | March 13, 2015

Progress in high-energy-class diode laser pump sources

Proc. SPIE. 9348, High-Power Diode Laser Technology and Applications XIII

KEYWORDS: Packaging, Resonators, Waveguides, Copper, Resistance, Solid state lasers, Semiconductor lasers, Collimation, Aluminum, Laser systems engineering

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PROCEEDINGS ARTICLE | October 31, 2014

Influence of polishing and coating techniques on laser induced damage on AR-coated ceramic Yb:YAG

Proc. SPIE. 9237, Laser-Induced Damage in Optical Materials: 2014

KEYWORDS: Polishing, Laser induced damage, Ceramics, Ions, Coating, Inspection, Ion beams, YAG lasers, Magnetorheological finishing, Laser systems engineering

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SPIE Conference Volume | May 22, 2013

High-Power, High-Energy, and High-Intensity Laser Technology; and Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers

PROCEEDINGS ARTICLE | May 7, 2013

Diode-pumped, cryogenically cooled, femtosecond burst mode laser

Proc. SPIE. 8780, High-Power, High-Energy, and High-Intensity Laser Technology; and Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers

KEYWORDS: Energy efficiency, Mirrors, Optical amplifiers, Femtosecond phenomena, Semiconductor lasers, Relays, Diodes, Picosecond phenomena, Pulsed laser operation, Laser systems engineering

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PROCEEDINGS ARTICLE | May 7, 2013

Spectroscopic characterization of various Yb3+ doped laser materials at cryogenic temperatures for the development of high energy class diode pumped solid state lasers

Proc. SPIE. 8780, High-Power, High-Energy, and High-Intensity Laser Technology; and Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers

KEYWORDS: Spectroscopy, Luminescence, Laser applications, Semiconductor lasers, Ytterbium, Phonons, Cryogenics, Temperature metrology, Diode pumped solid state lasers, Absorption

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PROCEEDINGS ARTICLE | May 7, 2013

Multipass amplifiers of POLARIS

Proc. SPIE. 8780, High-Power, High-Energy, and High-Intensity Laser Technology; and Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers

KEYWORDS: Mirrors, Optical amplifiers, Homogenization, Glasses, Laser applications, Laser development, Wavefronts, Amplifiers, Pulsed laser operation, Laser systems engineering

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PROCEEDINGS ARTICLE | February 18, 2013

HiLASE cryogenically-cooled diode-pumped laser prototype for inertial fusion energy

Proc. SPIE. 8602, High Power Lasers for Fusion Research II

KEYWORDS: Optical amplifiers, Spatial filters, Doping, Semiconductor lasers, Head, Ytterbium, Helium, Cryogenics, Laser systems engineering, Fusion energy

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