[PDF]  https://doi.org/10.3952/physics.v61i4.4641

Open access article / Atviros prieigos straipsnis
Lith. J. Phys. 61, 222–232 (2021)
 

NUMERICAL MODEL OF END-PUMPED Yb:YAG DOUBLE-PASS LASER AMPLIFIER EXPERIMENTALLY VALIDATED AT 129 W OUTPUT POWER
Laurynas Veselisa, Raimundas Burokasb, and Andrejus Michailovasa,b
  a Center for Physical Sciences and Technology, Savanorių 231, 02300 Vilnius, Lithuania
b Ekspla Ltd, Savanorių 237, 02300 Vilnius, Lithuania
Email: lveselis@gmail.com

Received 8 June 2021; revised 12 July 2021; accepted 15 July 2021

In this work, a double-pass end-pumped Yb:YAG amplifier system was investigated experimentally and numerically. The amplifier was seeded by a fibre-CPA based seed laser FemtoLux 30 (Ekspla). The presented laser system produced 129 W average power and 129 μJ energy pulses at 1 MHz pulse repetition rate, with optical-to-optical efficiency of 32% at room temperature (T = 20°C). The resulting beam quality was M2 ∼ 2.1 and the measured depolarization losses were to 17.9%. After the compression, 441 fs pulse duration was achieved. During the work, comprehensive amplifier modelling was performed using the code written in Matlab. The modelling results matched well the experimental data, providing the tool to predict the performance of laser systems based on ytterbium-doped isotropic crystalline, ceramic and glass laser materials prior to designing and manufacturing.
Keywords: solid-state amplifier, thermal effects, depolarization

IŠ GALO KAUPINAMO Yb:IAG DVIGUBO LĖKIO LAZERINIO STIPRINTUVO SKAITMENINIO MODELIO EKSPERIMENTINIS PAGRINDIMAS VEIKIANT 129 W VIDUTINE GALIA
Laurynas Veselisa, Raimundas Burokasb, Andrejus Michailovasa,b

a Fizinių ir technologijos mokslų centras, Vilnius, Lietuva
b UAB „Ekspla“, Vilnius, Lietuva
Yb:IAG yra viena iš efektyviausių lazerinio stiprinimo terpių su Yb3+ jonų priemaišomis, kuri pasižymi santykinai dideliu šiluminiu laidumu. Vis dėlto norint pasiekti didelį optinio stiprinimo efektyvumą kambario temperatūroje, stiprinimo terpė neišvengiamai turi būti kaupinama didelio intensyvumo kaupinimo spinduliuote, kuri sukelia nepageidaujamus reiškinius, pavyzdžiui, stiprinamo pluošto kokybės degradaciją ar stiprinamos spinduliuotės galios nuostolius dėl depoliarizacijos reiškinio.
Darbe aprašytas ir eksperimentiškai pagrįstas skaitmeninis modelis, kuris leidžia įvertinti dvigubo lėkio iš galo kaupinamo Yb:IAG lazerinio stiprintuvo pagrindinius parametrus: išėjimo galią, depoliarizacinius nuostolius ir stiprinamos spinduliuotės pluošto kokybės degradaciją. Stiprintuvo aktyvioji terpė, aušinama palaikant T = 20 °C temperatūrą, buvo kaupinama 280 W nuolatinės veikos spinduliuote (940 nm), kuri leido pasiekti 129 W suminę išėjimo galią (1 030 nm) esant 1 MHz impulsų pasikartojimo dažniui, atitinkančią 32 % optinį stiprinimo efektyvumą. Parodyta, kad tokioje sistemoje depoliarizaciniai nuostoliai yra reikšmingi, jie siekė 17,9 %; pluošto kokybė pastebimai suprastėja dėl stiprinimo soties ir terminių aberacijų – pluošto kokybės parametras siekė M2 ∼ 2,1, o pats pluoštas tapo ryškiai astigmatinis. Šie rezultatai sutapo su modeliavimo rezultatais.
Eksperimentiškai parodyta, kad sustiprinti impulsai yra kokybiškai spūdūs bėgant laikui – impulsai buvo suspausti difrakcinės gardelės impulsų spaustuve iki beveik spektriškai ribotos impulsų trukmės, 441 fs. Tokie lazerinės sistemos parametrai galėtų būti patrauklūs daugeliui sričių, pavyzdžiui, apdirbant medžiagas femtosekundiniais lazerio impulsais, jeigu bus išspręstos dvi pagrindinės problemos – galios nuostoliai dėl depoliarizacijos ir pluošto kokybės prastėjimas dėl šiluminių reiškinių. Pristatytas modelis tinka šiam uždaviniui, o pats sistemos tobulinimas numatytas tolimesniuose darbuose.


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