Effect of nanosecond laser pulses on atmospheric pressure plasma jets

master's thesis

• Title: Utjecaj nanosekundnih laserskih pulseva na atmosferske plazmene mlazove
• Author: Nikola Šegedin
• Mentor: Slobodan Milošević (mentor)
• Mentor: Maja Planinić (mentor)
• Committee member: Maja Planinić (predsjednik povjerenstva)
• Committee member: Slobodan Milošević (član povjerenstva)
• Committee member: Mirko Planinić (član povjerenstva)
• Committee member: Davor Horvatić (član povjerenstva)
• Committee member: Emil Tafra (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2017-07-12, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U ovom radu je promatran spektar laserske plazme na atmosferskom zraku, u heliju i helijevom plazmenom mlazu (jetu) u svrhu određivanja interakcije između laserske plazme, plinske mete i helijevog jeta. Pritom smo laserske snopove fokusirali na navedene plinske mete te promatrali interakciju pomoću LIBS spektrometra i vremenski razlučive spektroskopije. Laserski snop energije pulsa od 63.2 mJ i frekvencije 5Hz je fokusiran na plinsku metu ispred optičkog vlakna spojenog na LIBS spektrometar i monokromator s rešetkom. LIBS spektrometar je korišten za analiziranje spektara laserske plazme u heliju i na atmosferi. Pritom su uspješno određeni i navedeni prijelazi unutar atoma i iona koji tvore lasersku plazmu. Posebno je laserski snop fokusiran na helijev jet, a dobivena svjetlost je analizirana preko fotomultiplikatora čiji signal je bilježen i promatran u vremenu na računalu. U daljnjim analizama smo odredili spektralni profil helijeve linije valne duljine 388.86 nm za različite pomake u vremenu integracije. Također je određena ekscitacijska temperatura elektrona za različita vremena od početka laserskog pulsa. Poznavanjem eksitacijske temperature i Starkovog širenja odredili smo koncentraciju elektrona u volumenu interakcije. Pokazano je da prisustvo jeta ne utječe značajno na ekscitacijsku temperaturu elektrona i njihovu koncentraciju unutar laserske plazme, ali utječe na helijev emisijski spektar u kojem je smanjen intenzitet helijeve 388.86 linije u prisustvu jeta.

Abstract (english)

In this paper, we were examining the spectrum of laser plasmas in atmospheric air, helium gas target and helium jet while our objective was to determine interactions between laser plasmas and named targets. To do this we were focusing laser pulses on mentioned targets and observing interactions using LIBS spectrometer and method of time - resolved spectroscopy. A laser pulse of energy 63.2 mJ and repetition rate of 5 Hz was focused on the gas target in front of optical fiber that was connected to LIBS spectrometer and monochromator with the optical grating. LIBS spectrometer was used to analyze laser plasmas spectrum in helium and atmospheric gases. We were successful in determining laser plasmas spectrum and identifying atoms and ions inside the plasma. Furthermore, we were focusing laser pulses on atmospheric pressure helium plasma jet, and monitoring interactions using photomultiplier whose signal was recorded in time on the computer. In addition to this, spectral line profile of helium line 388.86 nm was observed in different time delays. By determining the width of line it was possible to calculate excitation temperature of electrons within laser plasmas. By knowing excitation temperature of electrons and Stark width we successfully calculated concentrations of electrons within laser plasmas. In our results, we showed that the presence of the jet didn’t have a significant effect on excitation temperature of electrons or their concentration within laser plasma, however it does effect the helium emission spectrum by reducing the intensity of helium 388.86 nm line in the presence of helium jet.

• Keywords: nanosekundni laserski pulsevi; atmosferski plazmeni mlazovi
• Keywords (english): nanosecond laser pulses; atmosferic pressure plasma jets
• Language: croatian
• URN:NBN: urn:nbn:hr:217:111673
• Study programme: Title: Fizika; smjerovi: nastavnički; Study programme type: sveučilišni; Study level: integrirani preddiplomski i diplomski; Academic / professional title: magistar/magistra edukacije fizike (magistar/magistra edukacije fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-01 13:01:37