Laser/Plasma-Pumped Rare Gas Laser Guy Parsey, John Verboncoeur, Andrew Christlieb Michigan State University

Extending from diode-pumped alkali vapor lasers Kinetic Global Modeling Optically-Pumped Argon Laser Models (DPAL), Han and Heaven have shown that rare gas metastable states, np5(n + 1)s[3/2] , can operate as 2 General species continuity and electron energy equa- Recreating the experimental results of Han and Heaven the base of a three-level laser with excition of the tion (solved for T ) with reaction rates K e i • Optical pumping: centered at 811.75nm, ∆ν = 30GHz, duration (n + 1)s → (n + 1)p transitions. Though both the R dnα X α Y Deff 10ns, and energy of 0.25mJ rare gas lasers (RGL) and DPALs can be excited = νi Ki nj − 2 dt i j Λ Gas cell: R = 2.5cm, L=60cm over a range of pressures with incoherent optical pumping, RGLs do not suf- • " # REI d 3 Peff X • RF power: 18kV separated by 2.5 cm for 10ns fer from the highly reactive behavior of alkali met- neTe = − ne niKi∆Eij als. Since metastable populations are maintained dt 2 V i • Observed optimized delay between discharge and laser pulses 5-25µs Integrated reaction rates (when cross section is via electric discharge, we propose using a tuned elec- known, e.g. [4]) with parameterized EEDFs tron energy distribution function (EEDF) to modify Z ∞ Ki(x, Te) = dε v(ε)σi(ε)fe(ε, x, Te) RGL efficiencies and drive the population inversion. 0 The EEDF is maintained by the discharge along with the introduction of electron sources. Otherwise fitted ana- Using our kinetic global modeling framework lytical forms or con- (KGMf) and two gas systems (helium buffered ar- stants from the litera- gon and pure argon), we first validate the intracavity ture, e.g. [5], are used intensity laser model and then generate gain and en- for reaction rates ergy efficiency baselines for each system. Parameter MW power deposition: assumed power absorption Equilibrated argon species scanning methods are then used to find optimized Optimum delay time between MW discharge instead of RF: or time-enveloped effective electric field convoled responding to MW discharge EEDFs and system parameters for metastable pro- discharge and optical pump: nominal non-zero background and with EEDF followed by optical pumping pulse. −3 duction, generation of a lasing population inversion, [Arg] = 4.e25m → 2.3 µs 10ns gaussian discharge and increasing RGL operation efficiencies. Finally, Laser Model: Pumping and Output we determine if an RGL can operate without optical Pure Plasma Laser Concept Argon with Helium Buffer pumping. Two-way averaged plane-wave model with assump- Plotting the Argon excitation cross sections reveals a Difficulty in exciting He yields a good buffer gas tions on spectral distribution [3]. core problem of operating without optical pumping • He species DPAL → RGL Scaled gain term g considered: j + DPAL, first published by Krupke et. al. [1], βji = lgσji(nj− ni) Heg and He gi demonstrating three-level laser oscillation between Stim. emission • Non-linear the 2S , 2P , and 2P excited levels of Rb and relationship 1/2 1/2 3/2 ˜ stim βji Ψ Cs. Kji = between lg hνji + Wide-band incoherent Pumping intensity derived indepenent of the ν He:Ar ratio pumping to drive distribution Not directly possible: and output - Vaporized alkali metal P (t) intensity P 2 • Overlap between 1s5 Ω(t) = tP (1 − exp [β31])(1 + tP RP exp [β31]) Optimum He:Ar ratios and pulse delay times can be - Quench gas CH3 leads to lg and 2p10 occurs at found for each background pressure. hydrides (“laser snow”) The output intensity is defined from the two-way in- ~40eV ⇒ ⇒ ⇒ Han and Heaven [2] showed transitions between the tracavity circulating intensity, with continuity equa- • EEDF with bulk at References 3 3 3 noble gas excitations P2, S1, and D3 have the tion ~40eV will excite higher 2 same spectral properties as DPAL with benefits: dΨ(t) Ψ σ21c hν21 (unwanted) 2p states = (tLR exp [2β21] − 1) + n2 [1] Kanz, Krupke, Beach and Payne. Opt.Lett., 28, 2336 • Inert reagents in system dt τ l rt g [2] J. Han and M.C. Heaven. Opt. Lett., 37, 2157 • Lower temperature Which is related to the output intensity as Future Work [3] Rudolph, Zameroski, Hagar, Hostutler. J. Opt. Sc. Am. • Neutral collision partners β t (1 − R) exp [β ] I (t) = ηΨ(t) 21 L 21 B, 28, 1088 Both systems are attractive due to the coherent na- Lase 2 • Tracking a discretized spectral distribution (exp [β21] − 1)(1 + tLR exp [β21]) [4] Biagi-v8.9, http://www.lxcat.laplace.univ-tlse.fr, 7.4.12 ture of the output Note: R is the power reflectivity and t are the pump • Indirect methods for plasma pumped laser ∗ [5] NIST, http://www.nist.gov/pml/data/asd.cfm, 7.13.12 and laser gain cell window transmission coefficients • Continuing He buffer study with Kr