Search results for "laserit"

Phased laser diode array permits selective excitation of ultrasonic guided waves in coated bone-mimicking tubes

2017

This paper validates simulation predictions, which state that specific modes could be enhanced in quantitative ultrasonic bone testing. Tunable selection of ultrasonic guided wave excitation is useful in non-destructive testing since it permits the mediation of energy into diagnostically useful modes while reducing the energy mediated into disturbing contributions. For instance, it is often challenging to distinguish and extract the useful modes from ultrasound signals measured in bone covered by a soft tissue. We show that a laser diode array can selectively excite ultrasound in bone mimicking phantoms. A fiber-coupled diode array (4 elements) illuminated two solid tubes (2-3mm wall thickn…

Resonance laser ionization developments for IGISOL-4

2012

The work presented in this thesis concentrates on the development of the FURIOS laser ion source towards e cient and selective production of low energy radioactive ion beams. This includes design and development of the ion guide and hot cavity catcher systems for laser ion source use, and the development of in-source and in-jet laser spectroscopy techniques. The work has been carried out at the IGISOL facility in the Accelerator laboratory of the University of Jyväskylä. The FURIOS facility was upgraded and developed during the move to the IGISOL-4 facility. The laser transport was greatly improved in order to allow a large fraction of the initial laser intensity to be transported into the …

Molekyylien linjautuminen laserkentässä

2009

Laser developments and high resolution resonance ionization spectroscopy of actinide elements

2014

Quantum effects in one-dimensional optical flat-band lattices

2011

I numerically simulated one-dimensional lattice systems describable by the Hubbard-model and containing a flat-band. I studied the manner in which particles initially held in place by a parabolic confinement potential are dispersed across the lattice after the potential is removed. I also studied currents flowing within one-dimensional Hubbard-rings. In both of these cases I observed that the flat dispersion relation of the flat-band manifests itself as the immobility of the particles occupying it. Particles occupying flat-band states do not disperse even after the removal of any external confinement, neither do they contribute to a current within a ring.

Revealing lattice disorder, oxygen incorporation and pore formation in laser induced two-photon oxidized graphene

2019

Abstract Laser induced two-photon oxidation has proven to be a reliable method to pattern and control the level of oxidation of single layer graphene, which in turn allows the development of graphene-based electronic and optoelectronic devices with an all-optical method. Here we provide a full structural and chemical description of modifications of air-suspended graphene during the oxidation process. By using different laser irradiation doses, we were able to show via transmission electron microscopy, electron energy loss spectroscopy, electron diffraction and Raman spectroscopy how graphene develops from its pristine form up to a completely oxidized, porous and amorphous carbon layer. Furt…

Characterization of a pulsed injection-locked Ti:sapphire laser and its application to high resolution resonance ionization spectroscopy of copper

2017

A high repetition rate pulsed Ti:sapphire laser injection-locked to a continuous wave seed source is presented. A spectral linewidth of 20 MHz at an average output power of 4W is demonstrated. An enhanced tuning range from 710-920 nm with a single broadband mirror set is realized by the inclusion of a single thin birefringent quartz plate for suppression of unseeded emission. The spectral properties have been analyzed using both a scanning Fabry-P´erot interferometer as well as crossed beam resonance ionization spectroscopy of the hyperfine levels of natural copper. Delayed ionization of the long-lived excited state is demonstrated for increased resolution. For the excited state hyperfine c…

Ytterbium-doped fibers for high-power fiber lasers

2021

Ytterbium (Yb) doped optical fibers are widely used in high-power applications and ultrafast lasing since they show adequate power-handling capability and provide desirable beam quality. Yb-doped fibers with large core area can support high power but often act as a multimode fiber and compromise the output beam quality. Hence, it is important to attain a proper balance between the power-handling capability and the beam quality. Yb-doped fibers as a gain medium in pulsed fiber laser systems are prone to nonlinear optical effects due to the presence of high peak power in the ultrashort pulses. Nonlinearity such as self phase modulation (SPM) affects the width and the shape of the pulse, both …

Estimation of forest stand characteristics using individual tree detection, stochastic geometry and a sequential spatial point process model

2022

Airborne Laser Scanning (ALS) results in point-wise measurements of canopy height, which can further be used for Individual Tree Detection (ITD). However, ITD cannot find all trees because small trees can hide below larger tree crowns. Here we discuss methods where the plot totals and means of tree-level characteristics are estimated in such context. The starting point is a previously presented Horvitz–Thompson-like (HT-like) estimator, where the detectability is based on the larger tree crowns and a tuning parameter that models the detection condition. We propose a new method which is based on modeling the spatial pattern of hidden tree locations using a sequential spatial point process mo…

Towards in-jet resonance ionization spectroscopy : An injection-locked Titanium:Sapphire laser system for the PALIS-facility

2018

This article presents a pulsed narrowband injection-locked Titanium:Sapphire laser aimed for high-resolution in-jet resonance ionization spectroscopy at the SLOWRI/PALIS at RIKEN. The laser has been integrated into the PALIS laser laboratory enabling it to be utilized with the existing broadband Titanium:Sapphire and dye lasers. The seed efficiency has been evaluated to be close to unity over the master laser wavelength range ∼ 753 to 791 nm, and the slope efficiency, namely the ratio of the pump power to the output power, was determined to be ∼ 30 % at 780 nm. A two-step ionization scheme with 386.4016 nm first step and 286.731 nm second step into an autoionizing state was developed for re…