Krste Pangovski

Control of Material Transport Through Pulse Shape Manipulation—A Development Toward Designer Pulses

The variety of laser systems available to industrial laser users is growing and the choice of the correct laser for a material target application is often based on an empirical assessment. Industrial master oscillator power amplifier systems with tuneable temporal pulse shapes have now entered the market, providing enormous pulse parameter flexibility in an already crowded parameter space. In this paper, an approach is developed to design interaction parameters based on observations of material responses. Energy and material transport mechanisms are studied using pulsed digital holography, post process analysis techniques and finite-difference modelling to understand the key response mechanisms for a variety of temporal pulse envelopes incident on a silicon 〈1|1|1〉 substrate. The temporal envelope is shown to be the primary control parameter of the source term that determines the subsequent material response and the resulting surface morphology. A double peak energy-bridged temporal pulse shape designed through direct application of holographic imaging data is shown to substantially improve surface quality.

Investigation of pulse shape characteristics on the laser ablation dynamics of TiN coatings in the ns regime

In this work, the ablation dynamics of TiN coating with a ns-pulsed fibre laser in a wide range of pulse durations were studied. Critical time instances within the pulse duration were assessed by reflected pulse analysis. Digital holography was employed to investigate the shock wave expansion dynamics within and beyond the pulse duration. The results depict that the absorption behaviour changes as a function of the pulse rise time. Moreover, planar expansion of the shock wave is observed, which is generally linked to higher machining quality and absence of excessive plasma. The results of the study are interpreted to depict the required characteristics of optimized pulse shapes in the ns-region for improved micromachining performance.

A holographic method for optimisation of laser-based production processes

Abstract A digital holographic system is used to image the plume dynamics of a train of picosecond laser pulses interacting with titanium, aluminium, copper and brass. The recorded process dynamics are used to propose two optimisation strategies: first, by observing the time at which the plume fully dissipates and, second, through calculation of the minimum beam displacement required to maximise energy delivery to the sample by avoiding the plume. The proposed approach could further be applied in real industrial process design, allowing laser users to formulate a processing strategy based on process dynamics rather than lengthy post-process evaluation of a sample.

Designer pulses for precise machining of silicon – A step towards photonic compositions

The past decade has seen the introduction of high performance short-pulse systems such as fiber and disk lasers with repetition rates in the several hundred-kHz range. These have provided the user with a wide range of interaction parameters to chose from. The availability of high speed optical imaging techniques has also provided the opportunity to explore high-speed laser matter interactions in greater detail. In this paper we demonstrate a single pulse study of a decaying tail in the pulse envelope using “unfilled” and “energy filled” pulses. We demonstrate a Pulsed digital holography (PDH) system used to study the shock wave dynamics, laser induced plasma and energy deposition efficiencies of single and multi-pulse interactions of 200 ns shaped laser pulses, with a temporal resolution of < 10 ns. Finally, we demonstrate novel designer pulses that show improved material response and increased penetration depth at a fraction of the energetic cost of conventional pulses.The past decade has seen the introduction of high performance short-pulse systems such as fiber and disk lasers with repetition rates in the several hundred-kHz range. These have provided the user with a wide range of interaction parameters to chose from. The availability of high speed optical imaging techniques has also provided the opportunity to explore high-speed laser matter interactions in greater detail. In this paper we demonstrate a single pulse study of a decaying tail in the pulse envelope using “unfilled” and “energy filled” pulses. We demonstrate a Pulsed digital holography (PDH) system used to study the shock wave dynamics, laser induced plasma and energy deposition efficiencies of single and multi-pulse interactions of 200 ns shaped laser pulses, with a temporal resolution of < 10 ns. Finally, we demonstrate novel designer pulses that show improved material response and increased penetration depth at a fraction of the energetic cost of conventional pulses.

Tunable Broadband Radiation Generated Via Ultrafast Laser Illumination of an Inductively Charged Superconducting Ring.

An electromagnetic transmitter typically consists of individual components such as a waveguide, antenna, power supply, and an oscillator. In this communication we circumvent complications associated with connecting these individual components and instead combine them into a non-traditional, photonic enabled, compact transmitter device for tunable, ultrawide band (UWB) radiation. This device is a centimeter scale, continuous, thin film superconducting ring supporting a persistent super-current. An ultrafast laser pulse (required) illuminates the ring (either at a point or uniformly around the ring) and perturbs the super-current by the de-pairing and recombination of Cooper pairs. This generates a microwave pulse where both ring and laser pulse geometry dictates the radiated spectrum’s shape. The transmitting device is self contained and completely isolated from conductive components that are observed to interfere with the generated signal. A rich spectrum is observed that extends beyond 30 GHz (equipment limited) and illustrates the complex super-current dynamics bridging optical, THz, and microwave wavelengths.

Investigation of low nanosecond light-matter interaction mechanisms

Laser ablation of solid Silicon targets using pulsed Yb fiber lasers of pulse duration 1.5-400 ns Yb fiber lasers is studied in this work. Material responses of a range of pulse envelopes are examined including front peak (FP) and double peak (DP) pulses. Theoretical models for the interactions are examined and qualitative explanations of material response experiments are presented.Laser ablation of solid Silicon targets using pulsed Yb fiber lasers of pulse duration 1.5-400 ns Yb fiber lasers is studied in this work. Material responses of a range of pulse envelopes are examined including front peak (FP) and double peak (DP) pulses. Theoretical models for the interactions are examined and qualitative explanations of material response experiments are presented.