J. Herrmann

ETH Zurich

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Improving Reliability Calculation with Augmented Binary Decision Diagrams

J. Herrmann

The Augmented Ordered Binary Decision Diagram (OBDD-A) has been shown to be extremely efficient for reliability calculations, especially when combined with the Boundary Set method of partition representation. The existing OBDD-A follows the Boundary Set method closely, requiring the calculation of partition numbers large enough to exceed the capacity of native storage types in languages such as C++. By omitting the use of partition numbers the execution speed of the algorithm is increased, while the low memory usage of an OBDD-A is maintained. We compare the new OBDD-A to the existing version on a number of networks, showing that processing time for large networks increases significantly.

Binary decision diagram

Representation

10.1109/aina.2010.148

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Citations (14)

Probing Electron Wave-packet Interference

J. Herrmann Matteo Lucchini Arne Ludwig Mazyar Sabbar Reto Locher

We use attosecond transient absorption spectroscopy to investigate electron dynamics around the first ionization threshold of helium. Our results expose that electron wave-packet interference effects are insufficient to explain all the observed phenomena.

Attosecond

10.1364/cleo_qels.2013.qf2c.2

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A memory efficient algorithm for network reliability

J. Herrmann Sieteng Soh

We combine the augmented ordered binary decision diagram (OBDD-A) with the use of boundary sets to create a method for computing the exact K-terminal or all-terminal reliability of an undirected network with failed edges and perfect vertices. We present the results of implementing this algorithm and show that the execution time is comparable with the state of the art and the space requirement is greatly reduced. Indeed the space remains constant when networks increase in size but maintain their structure and maximum boundary set size; with the same amount of memory used for computing a 3 × 12 and a 3 × 1000 grid network.

Binary decision diagram

Constant (computer programming)

10.1109/apcc.2009.5375505

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Citations (9)

Coherent Quantum-Well Absorber Mode Locking for Excitation Dependent Dephasing

V. P. Kalosha Michael Müller J. Herrmann

Dephasing

Mode (computer interface)

Mode-Locking

10.1109/cleoe.1998.719049

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Mode locking of solid-state lasers by use of a slow saturable quantum-well absorber

Conference on Lasers and Electro-Optics Europe (1996)

J. Herrmann Michael Müller

Recent experiments succeeded in sub-100fs pulse generation from solid-state lasers by use of a saturable single-quantum-well absorber (SQW) yielding self-starting 34fs pulses in a ti.sapphire laser [1] as well as 90fs pulses in a diode pumped Cr:LiSAF laser [2]. These experimental findings can hardly be explained by the common theoretical understanding of passive mode locking in solid-state lasers which requires a fast saturable loss for stable pulse generation. The relaxation of the absorption bleaching in a GaAs quantum well at room temperature exhibits a bitemporal behavior where the fast component of about 200fs owing to thermal ionization of the exzitons is remarkably slower than the meanwhile achieved pulse width in the experiments. Recently we have proposed a novel mechanism for mode locking a solid state laser by use of a slow off-resonant saturable two-level absorber [3]. Here we analyze the operating conditions for this new mode locking scheme by use of a slow saturable SQW-absorber and calculate the dependence of the pulse parameters on the characteristical laser and absorber parameters. The underlying principle of mode locking of this mechanism is that in a first order expansion beyond the rate equation approximation a slow saturable absorber with an arbitrary large response time T 1 produces an additional intensity dependent loss Δ α = − γ d Δ n d ω I , where Δ n is the linear refractive index change owing to the near-resonant transition, γ is an absorber parameter and I is the pulse intensity. The physical origin of the intensity dependent loss Δ α is that due to the finite phase relaxation time τ a the coherent medium polarization encounters a group velocity change which leads owing to the slow saturation under off-resonance with d Δ n d ω | ω L > 0 to a negative fast saturable loss term Δ α < 0. To study this mechanism for a SQW absorber we consider a simple 2D free carrier band filling model [4]. Using these simplifications we derive the spectrum of the complex SQW-susceptibiliy χ ( ω ) in dependence on the optically induced carrier density N. Expanding the time-domain round trip operators with respect to small parameters we deduce a stationary mode locking equation which governs the steady-state pulse parameters of the mode locked laser. The calculated pulse parameters in dependence on the SQW and laser parameters shows that in a reasonably extended operating region a near-resonant slow saturable SQW-absorber always yields an additional fast saturable loss which is sufficient to provide and maintain stable passive mode locking in broad band solid state lasers. Thus, off-resonant slow passive mode locking (OPSM) [3] with a slow saturable SQW-absorber represents a reliable novel method for fs-pulse generation in solid-state lasers and can explain the main findings in recent experiments [1,2].

Saturable absorption

Q-switching

Mode-Locking

10.1364/cleo_europe.1996.cff4

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All-optical bistable switching in a metal-dielectric multilayer structure due to intensity-dependent sign of the effective dielectric constant

2007 Conference on Lasers and Electro-Optics (CLEO) (2007)

A. Husakou J. Herrmann

We numerically study light propagation through a nonlinear metal-dielectric multilayer structure, and predict all-optical bistable switching due to change of the effective dielectric constant from negative (low-transmission state) to positive (high-transmission state) values.

Bistability

Optical Bistability

Intensity

10.1109/cleo.2007.4453671

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Thermal management in high-power vertical-external-cavity surface-emitting lasers

Conference on Lasers and Electro-Optics (2012)

A. Chernikov J. Herrmann Maik Scheller Martín Koch Bernardette Kunert

Thermal properties of vertical-external-cavity surface-emitting lasers are studied in the high-power regime. The influence of pump profiles is investigated by spacially resolved temperature measurements. Optimized cooling provides 72 W output power.

10.1364/cleo_at.2012.jw2a.97

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Citations (2)

Power scaling and heat management in high-power VECSELs

Sangam Chatterjee Alexey Chernikov J. Herrmann Maik Scheller Martín Koch

Many applications of vertical-external-cavity surface-emitting lasers (VECSELs) [1], such as intra-cavity frequency mixing rely on the high-power characteristics of the devices. Generally, overheating limits any lasers performance and, thus, efficient cooling concepts are crucial for the high-power output [2]. Here, we experimentally investigate the thermal properties of a high-power device, focusing on the generation, distribution and removal of excess heat under extreme pumping conditions. Different heat-spreading and heat-transfer approaches are analyzed. The performance of the device is optimized yielding a maximum emitted power beyond 70W from a single spot. Finally, the potential for power-scaling in VECSELs and its restrictions are examined. Details on the chip and the experimental setup are given in [3].

Overheating (electricity)

10.1109/cleoe.2011.5942637

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Citations (2)

Hidden Mechanism for Mode Locking Solid-State Lasers by Use of a Slow Off-Resonant Saturable Absorber

Springer eBooks (1996)

J. Herrmann Michael Müller

Saturable absorption

Ti:sapphire laser

Mode-Locking

10.1007/978-1-4615-5897-2_14

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Citations (0)

Optical response of electron wave-packet interference revisited

Matteo Lucchini J. Herrmann Arne Ludwig Mazyar Sabbar Reto Locher

This work reports on the use of a pump-probe scheme, but change the time duration of the APT ranging from a pulse train envelope of - 25 fs down to a SAP of - 300 as.

Ranging

Envelope (radar)

Pulse duration

10.1109/cleoe-iqec.2013.6801161

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Citations (1)