DOCSLIB.ORG

Laser Driven Nuclear Reaction Studies

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Laser Driven Nuclear Reaction Studies Laser driven nuclear reaction studies: recent successes and new unique opportunities for future research Klaus M Spohr SUPA collaboration University of the West of Scotland & University of Strathclyde Overview • Laser driven Nuclear Physics: Introductory remarks – Development of high power laser systems – History and milestone achievements in laser-nuclear research • Laser induced nuclear photo-proton reaction studies – Motivation for measuring sint(γ,p) of Mg-,Ti-, Zn- and Mo-isotopes – Methodology and setup of IOQ Jena multi TW laser system – Results for sint(γ,p) in Mg-,Ti-, Zn- and Mo-isotopes – Conclusions, opportunities and future challenges • Photonuclear reaction studies using laser induced Compton backscattering (LICB): proposed studies & vision – The principle of ‘Laser Induced Compton Backscattering’ – Motivation – LICB experiment on resonant photoabsorption of Mößbauer nuclei – Some final thoughts: induced nuclear emission (lasing) – Summary Introductory remarks Development of high power laser systems HiPER NIF Development of high power laser systems • Chirped Pulse Amplification (CPA) by Strickland and Mourou allowed intensities I > 1015 Wcm-2 – CPA (Strickland D and Mourou G, Opt. Comm. 56 (3) 219 (1985)) • Ultrashort laserpulse up to the petawatt level with the laser pulse being stretched out temporally and spectrally prior to amplification – CPA is the current state-of-the-art technique for all of the highest power lasers >100 TW • Currently strongest civilian systems – NIF @ LLNL, I > 1022 Wcm-2 – 2009 ASTRA/GEMINI @ CLF RAL I ~1022 Wcm-2 – Vulcan @ CLF RAL, I > 1021 Wcm-2 • HiPER project I ~ 5 ×1024 Wcm-2 (2020) ‘game-changers’ NYT, March 2009 Chirped Pulse Amplification • Concept of Chirped Pulse Amplification (CPA) History and milestone achievements in laser-nuclear research • 1996 Femtosecond quasi-monoenergetic keV-pulses (atomic physics) – Schoenlein R et al., Science 274 236 (1996) • 2000 Laser-induced nuclear fission of 238U – Ledingham K et al.,PRL 84 899 (2000), Cowan T et al.,PRL 84 903 (2000) • 2003 Laser-induced fusion evaporation reactions – McKenna P et al., PRL 91 (7) 075006 (2003) • 2006 GeV electron beams from a centimetre-scale 40 TW laser accelerator – Leemans W et al., Nature Physics 2 (10) 696 (2006) • 2007/08 Proton acceleration to 60 MeV and proton focussing – Robson L et al., Nature Physics 3 (1) 58 (2007), Schollmeier M et al., PRL 101 055004 (2008) • 2007 High order harmonic keV radiation (HOHG) of high brightness – Dromey B et al., PRL 99 085001 (2007) • 2009 Highest density of antimatter in solids (e+) (20 MeV) via Bethe- Heitler process n(e+)=1016cm-3 – Chen H et al., PRL 102 105001 (2009) Laser induced nuclear photo-proton reaction studies The measurement of integral photonuclear cross-sections such as sint(γ, p) using nuclear activation is ideally suited for modern high power multi-TW laser systems • Table-top Laser systems as competitive tool for nuclear studies – High intensity and hot bremsstrahlung spectra kT>2 MeV – Bremsstrahlung spectra spans over GDR regime ~8 - 35 MeV – Multi-TW Ti:Sapphire Laser system at the IOQ Jena, Germany Motivation for measuring sint(γ,p) of Mg-,Ti-, Zn- and Mo-isotopes • Nuclear Theory: cross-sections for p-emission and capture in plasma conditions, need to extend astrophysical data sets for low-Z isotopes: 25Mg,48,49Ti, 68Zn and 97,98Mo (feasible with method) – Hauser-Feshbach code • Applied: GDR-regime of interest for technological R&D work – nuclear power, shielding, radiation transport, radiotherapy, reactor development (transmutation studies) & medical applications – IAEA: encourages experiments esp. to retrieve reaction data in the region of the Giant Dipole Resonance (GDR) esp. for ~40 isotopes • Limitations and ‘old’ age of measurements – Values of sint(g, p) for only 40 different stable isotopes are published – Ratios: sint(g, n)/sint(g, p) for Z=12-42 needed! – Accuracy of old measurements • Probing and enhancement of nuclear models and reaction codes – EMPIRE, GNASH Methodology and setup of IOQ Jena multi-TW laser system • Harvest the bremsstrahlung radiation of high-intensity laser generated relativistic electrons to induce reaction – Quasi-Maxwellian distribution: Tγ Te , McCall G,J Phys D 15 823 (1982) – Energy distribution of γ-radiation for temperatures achievable with multi- TW lasers extends over the full GDR-region • Measure the activity of the decay of the radioactive daughter nucleus • Characteristic g-rays of decay: intensity of photopeaks allows yield determination of original daughter products, hence sint(g, p) – Efficient Ge-detector system – Adjustments for: branching, detection efficiency (system, geometry), self- absorption, abundances; irradiation-, handling- and decay-time; contaminating reaction channels, target impurities and electro- disintegration • Introduced for laser nuclear physics by Stoyer et al. – Stoyer M et al., Rev Sci Inst 72 767 (2001) Schematic setup of IOQ Jena multi-TW laser system laser pulse E0 ~ 600 mJ Activation tlaser pulse ~ 80 fs Activation targets: MgF2,Ti,Zn,Mo λ = 800 nm thicknesses~2-4 mm P ~ 7.5 TW 9 ne per pulse ~ 2 - 5 ×10 p~ 80 bar (Elaser / Ee) ~ 0.6 - 1.5% ~5m Liesfeld B et al., J Phys D 79 1047 (2004) Schwörer H et al., PRL 86 2317 (2001) Setup of target chamber Target chamber f/2-mirror Target & radiator holder He gas-jet nozzle Laser-room university-scale system! Relativistic electrons from 10TW Laser-Gas Interaction Simulated e- density Simulated e- momentum distribution for different depths PIC simulations, Pukov A and Meyer-ter-Veen, PRL 76 (21) 3975 (1996) - Spatial confinement of e- Energy of e (measured) (measured, E=18 MeV) 2×106 1×106 250 mrad 0 from Guiletti A et al., PRL 101 105002 (2008) Simulated γ-distribution after Ta-radiator and Mo-target (GEANT4) Experimental considerations & limitations • Extraction & detection limit: 5 min ≲ t1/2 ≲ 200 days • kT measurement necessary with activation method • Bulk targets with natural abundances • Analysis: – Uncertainty from kT & Ge-efficiency – Activity is weighted with photon distribution and needs to be referenced to well known (g, n) channel in probe – To extract sint(g, p) the three parameters determining the GDR have to res be assumed based on models: s , res(i), Eres(I) kT measurement via Ta-activation fitted kT=2.73(22)MeV Activation spectra: MgF2-, Ti- and Zn-probes ~only 8 min of laser activation, 5000 pulses with 3-5 x1019 Wcm-2 Observed photo-proton channels Measured and simulated photo-reaction channels in 25Mg Experimental data & EMPIRE calculations sint (g, p) deduced from EMPIRE calculation is fully reproducing measured sint (g, p) Results for sint(γ,p) in Mg-,Ti-, Zn- and Mo-isotopes Agreement with TRK sum-rule 35 NZ • TRK Dipole Sum Rule: s ~60 (MeVmb) 0 A • TRK=Thomas Reiche Kuhn Sum rule 1925 – A standard benchmark for E1-strengths • Aligned with data from Wyckoff J et al., PR 137 576 (1965) ─ Values of sint up to 35 MeV relative to the classical dipole sum rule show a monotonic increase with atomic weight – Correction factor ~ 0.85 - 1.25 Agreement with TRK sum-rule 2500 σ(γ,sn) from Lit. + σ(γ,p) Exp. TRK (folded with Wyckoff) 2000 only s(g,n) only σint(g,n) known 1500 [MeVmb] 1000 int s 500 0 25Mg 48Ti 49Ti 68Zn 69Zn 98Mo Isotope Total σint values ~ σint (g,sn) + σint (g,p) show good to excellent agreement with the TRK-sum rule. For 97Mo no σint (g,n) known Agreement with known σint-values this work Aligned acc. to branching 250 Literature 200 No errors given in 150 Literature values [MeVmb] 100 int s 50 0 64Zn (g, 2n)62Cu 70Zn (g, n)69mZn Ivanchenko V et al., Carlos P et al., Goryachev A et al., P.ZHETF1 11 452 (1966) NP A258 3652 (1976) Yad.Fiz. 38 121 (1982) Reaction All three measured σint-values for different targets and particle channels that can be benchmarked with known data show good agreement Known σint(g,n)/ σint(g,p) ratios (IAEA) p) g, Experiment added 15% ( int towards all existing data! this work σ n)/ g, ( int σ Conclusions, opportunities and future challenges • We measured a total of 6 new sint (g,p) values and hence deduced six new sint (g,n)/sint (g,p) ratios for light nuclei – First time laser driven research adds new data to nuclear physics – almost 15% of previously published data – Spohr K et al., New J Phys 10 043037 (2008) & New J Phys Best of 2008 collection • Conclusively proven that nuclear reactions can be produced and cross-section can be measured using table-top Laser systems – data agrees with TRK-sum rule – data agrees with EMPIRE calculations – data agrees with three previously known data-sets • A good base for a more extensive research investigation Conclusions, opportunities and future challenges • Opportunity for extended campaign: – Determination of >110 new sint (g, p) measurable with university- scale multi-TW laser systems is possible • ~90 lifetimes 5 min < t1/2 < 300 days (feasible) • Challenge ~25 lifetimes t1/2 < 5 min • Challenges: – Use of isotopic enriched targets – Rapid transport mechanism (@ e.g. ELBE) – On-line measurement of prompt g-radiation – Deflection of electrons, separation with small Halbach magnets – Lowering the uncertainties of kT measurement – Multi-Ge-system in coincidence – Particle detectors in coincidence, radiation resistant detectors Conclusions, opportunities and future challenges • Conjoined ELBE/Laser @ FZ-Dresden Rossendorf – SUPA has allocated beam-time quota – Elinac (40MeV) and 150 TW laser system (mid-2009) • We could use both systems and compare • 150 TW laser ~ E(e-) = ~80-90 MeV endpoint – Proposal to study sint (g,p) reaction of stable p-nuclei: • p-nuclei are neutron deficient (except 176Lu) nuclei that are shielded by their isobaric neighbours from production via the r-process and can not be produced by the s-process either • p-nuclei of astrophysical interest: 96Ru, 120Te, 130Ba, 156Dy, 162Er, 168Yb and 176Lu are feasible to study, yield improvement with new system ~103 • Understand formation of p-nuclei and support Hauser-Feshbach calculations • Higher power will give laser competitive edge over Elinacs Using different kT for evaluation of s(E) Unfold cross-section by using different kT values, 1 MeV <kT <10 MeV Collaborators K.
Load more

Recommended publications
  • An Application of the Theory of Laser to Nitrogen Laser Pumped Dye Laser
    SD9900039 AN APPLICATION OF THE THEORY OF LASER TO NITROGEN LASER PUMPED DYE LASER FATIMA AHMED OSMAN A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Physics. UNIVERSITY OF KHARTOUM FACULTY OF SCIENCE DEPARTMENT OF PHYSICS MARCH 1998 \ 3 0-44 In this thesis we gave a general discussion on lasers, reviewing some of are properties, types and applications. We also conducted an experiment where we obtained a dye laser pumped by nitrogen laser with a wave length of 337.1 nm and a power of 5 Mw. It was noticed that the produced radiation possesses ^ characteristic^ different from those of other types of laser. This' characteristics determine^ the tunability i.e. the possibility of choosing the appropriately required wave-length of radiation for various applications. DEDICATION TO MY BELOVED PARENTS AND MY SISTER NADI A ACKNOWLEDGEMENTS I would like to express my deep gratitude to my supervisor Dr. AH El Tahir Sharaf El-Din, for his continuous support and guidance. I am also grateful to Dr. Maui Hammed Shaded, for encouragement, and advice in using the computer. Thanks also go to Ustaz Akram Yousif Ibrahim for helping me while conducting the experimental part of the thesis, and to Ustaz Abaker Ali Abdalla, for advising me in several respects. I also thank my teachers in the Physics Department, of the Faculty of Science, University of Khartoum and my colleagues and co- workers at laser laboratory whose support and encouragement me created the right atmosphere of research for me. Finally I would like to thank my brother Salah Ahmed Osman, Mr.
    [Show full text]
  • Population Inversion X-Ray Laser Oscillator
    Population inversion X-ray laser oscillator Aliaksei Halavanaua, Andrei Benediktovitchb, Alberto A. Lutmanc , Daniel DePonted, Daniele Coccoe , Nina Rohringerb,f, Uwe Bergmanng , and Claudio Pellegrinia,1 aAccelerator Research Division, SLAC National Accelerator Laboratory, Menlo Park, CA 94025; bCenter for Free Electron Laser Science, Deutsches Elektronen-Synchrotron, Hamburg 22607, Germany; cLinac & FEL division, SLAC National Accelerator Laboratory, Menlo Park, CA 94025; dLinac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025; eLawrence Berkeley National Laboratory, Berkeley, CA 94720; fDepartment of Physics, Universitat¨ Hamburg, Hamburg 20355, Germany; and gStanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 Contributed by Claudio Pellegrini, May 13, 2020 (sent for review March 23, 2020; reviewed by Roger Falcone and Szymon Suckewer) Oscillators are at the heart of optical lasers, providing stable, X-ray free-electron lasers (XFELs), first proposed in 1992 transform-limited pulses. Until now, laser oscillators have been (8, 9) and developed from the late 1990s to today (10), are a rev- available only in the infrared to visible and near-ultraviolet (UV) olutionary tool to explore matter at the atomic length and time spectral region. In this paper, we present a study of an oscilla- scale, with high peak power, transverse coherence, femtosecond tor operating in the 5- to 12-keV photon-energy range. We show pulse duration, and nanometer to angstrom wavelength range, that, using the Kα1 line of transition metal compounds as the but with limited longitudinal coherence and a photon energy gain medium, an X-ray free-electron laser as a periodic pump, and spread of the order of 0.1% (11).
    [Show full text]
  • Rate Equations
    Ultrafast Optical Physics II (SoSe 2019) Lecture 4, May 3, 2019 (1) Laser rate equations (2) Laser CW operation: stability and relaxation oscillation (3) Q-switching: active and passive 1 Possible laser cavity configurations The laser (oscillator) concept explained using a circuit model. 2 Self-consistent in steady state V.A. Lopota and H. Weber, fundamentals of the semiclassical laser theory 3 Laser rate equations Interaction cross section: [Unit: cm2] !") ") Spontaneous = −*") = − !$ τ21 emission § Interaction cross section is the probability that an interaction will occur between EM !" field and the atomic system. # = −'" ( !$ # § Interaction cross section only depends Absorption on the dipole matrix element and the linewidth of the transition !" ) Stimulated = −'")( !$ emission 4 How to achieve population inversion? relaxation relaxation rate relaxation Induced transitions Pumping rate relaxation Pumping by rate absorption relaxation relaxation rate Four-level gain medium 5 Laser rate equations for three-level laser medium If the relaxation rate is much faster than and the number of possible stimulated emission events that can occur , we can set N1 = 0 and obtain only a rate equation for the upper laser level: This equation is identical to the equation for the inversion of the two-level system: upper level lifetime equilibrium upper due to radiative and level population w/o non-radiative photons present processes 6 More on laser rate equations Laser gain material V:= Aeff L Mode volume fL: laser frequency I: Intensity vg: group velocity
    [Show full text]
  • Terahertz Sources
    Terahertz sources Pavel Shumyatsky Robert R. Alfano Downloaded from SPIE Digital Library on 22 Mar 2011 to 128.59.62.83. Terms of Use: http://spiedl.org/terms Journal of Biomedical Optics 16(3), 033001 (March 2011) Terahertz sources Pavel Shumyatsky and Robert R. Alfano City College of New York, Institute for Ultrafast Spectroscopy and Lasers, Physics Department, MR419, 160 Convent Avenue, New York, New York 10031 Abstract. We present an overview and history of terahertz (THz) sources for readers of the biomedical and optical community for applications in physics, biology, chemistry, medicine, imaging, and spectroscopy. THz low-frequency vibrational modes are involved in many biological, chemical, and solid state physical processes. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3554742] Keywords: terahertz sources; time domain terahertz spectroscopy; pumps; probes. Paper 10449VRR received Aug. 10, 2010; revised manuscript received Jan. 19, 2011; accepted for publication Jan. 25, 2011; published online Mar. 22, 2011. 1 Introduction Yajima et al.4 first reported on tunable far-infrared radiation by One of the most exciting areas today to explore scientific and optical difference-frequency mixing in nonlinear crystals. These engineering phenomena lies in the terahertz (THz) spectral re- works have laid the foundation and were used for a decade and gion. THz radiation are electromagnetic waves situated between initiated the difference-frequency generation (DFG), parametric the infrared and microwave regions of the spectrum. The THz amplification, and optical rectification methods. frequency range is defined as the region from 0.1 to 30 THz. The The THz region became more attractive for investigation active investigations of the terahertz spectral region did not start owing to the appearance of new methods for generating T-rays until two decades ago with the advent of ultrafast femtosecond based on picosecond and femtosecond laser pulses.
    [Show full text]
  • A Fundamental Approach to Phase Noise Reduction in Hybrid Si/III-V Lasers
    A fundamental approach to phase noise reduction in hybrid Si/III-V lasers Thesis by Scott Tiedeman Steger In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 2014 (Defended May 14, 2014) ii © 2014 Scott Tiedeman Steger All Rights Reserved iii Contents Acknowledgements ix Abstract xi 1 Introduction1 1.1 Narrow-linewidth laser sources in coherent communication......1 1.2 Low phase noise Si/III-V lasers.....................4 2 Phase noise in laser fields7 2.1 Optical cavities..............................8 2.1.1 Loss................................8 2.1.2 Gain................................9 2.1.3 Quality factor........................... 10 2.1.4 Threshold condition....................... 11 2.2 Interaction of carriers with cavity modes................ 11 2.2.1 Spontaneous transitions into the lasing mode.......... 12 2.2.2 Spontaneous transitions into all modes............. 17 2.2.3 The spontaneous emission coupling factor........... 19 2.2.4 Stimulated transitions...................... 19 2.3 A phenomenological calculation of spontaneous emission into a lasing mode above threshold........................... 21 2.3.1 Number of carriers........................ 21 2.3.2 Total spontaneous emission rate................. 21 2.4 Phasor description of phase noise in a laser............... 23 iv 2.4.1 Spontaneous photon generation................. 25 2.4.2 Photon storage.......................... 27 2.4.3 Spectral linewidth of the optical field.............. 29 2.4.4 Phase noise power spectral density............... 30 2.4.5 Linewidth enhancement factor.................. 32 2.4.6 Total linewidth.......................... 34 3 Phase noise in hybrid Si/III-V lasers 35 3.1 The advantages of hybrid Si/III-V...................
    [Show full text]
  • Arxiv:1410.6667V2 [Physics.Optics]
    Self-starting stable coherent mode-locking in a two-section laser R. M. Arkhipova, M. V. Arkhipovb, I. Babushkinc,d a ITMO University, Kronverkskiy prospekt, 49, 197101 St. Petersburg, Russia, b Faculty of Physics, St. Petersburg State University, Ulyanovskaya 1, Petrodvoretz, St. Petersburg 198504, Russia c Institute of Quantum Optics, Leibniz University Hannover, Welfengarten 1 30167, Hannover, Germany d Max Born Institute, Max Born Str. 2a, 12489 Berlin, Germany Coherent mode-locking (CML) uses self-induced transparency (SIT) soliton formation to achieve, in contrast to conventional schemes based on absorption saturation, the pulse durations below the limit allowed by the gain line width. Despite of the great promise it is difficult to realize it experimentally because a complicated setup is required. In all previous theoretical considerations CML is believed to be non-self-starting. In this article we show that if the cavity length is selected properly, a very stable (CML) regime can be realized in an elementary two-section ring-cavity geometry, and this regime is self-developing from the non-lasing state. The stability of the pulsed regime is the result of a dynamical stabilization mechanism arising due to finite-cavity-size effects. I. INTRODUCTION Development of ultrashort laser pulse sources with high repetition rates and peak power is an area of principal in- terest in optics. Such lasers have applications in a high- bit-rate optical communications, real time-monitoring of ultrafast processes in matter etc. A well-known method for generating high power ultrashort optical pulses is a passive mode-locking (PML) [1–6]. In order to achieve PML, a nonlinear saturable absorbing medium is placed into the laser cavity.
    [Show full text]
  • Chapter 6. Laser: Theory and Applications
    Chapter 6. Laser: Theory and Applications Reading: Sigman, Chapter 6, 7, and 26 Bransden & Joachain, Chapter 15 Laser Basics Light Amplification by Stimulated Emission of Radiation hν = E − E E1 1 0 Stimulated emission hν E0 Population inversion (N1 > N0) ⇒ laser, maser 2 2 4π ⎛ e ⎞ I(ω ) 2 Transition rate W = ⎜ ⎟ 01 M (ω ) ∝ I(ω ) for stimulated emission 01 2 ⎜ ⎟ 2 01 01 01 m c ⎝ 4πε0 ⎠ ω01 Incident light intensity Pumping (optical, electrical, etc.) for population inversion Gain medium High reflector Out coupler Optical cavity Longitudinal Modes in an Optical Cavity EM wave in a cavity Boundary condition: λ cτ πc L = m = m = m m = 1, 2, 3, … 2 2 ω 2L c π c ⇒ λ = ,ν = m, ω = m m 2L L 2L Round-trip time of flight: T = = mτ c Typical laser cavity: L = 1.5 m, λ = 0.75 µm 2L 3 m : T = = =10−8 sec =10 nsec : c 3×108 m / sec 1 ⇒ ν = =108 Hz =100 MHz R T 2L 3 m L m = = = 4×106 = 4 milion !! λ 0.75×10−6 m Single mode 2 2 I(t) = cosω0t = cost Spectrum Intensity 1 Frequency Intensity -100 -50 0 50 100 Time Cavity Quality Factors, Qc End mirror L Out coupler R ≈ 1 T = 1 ~ 5 % Energy loss by reflection, transmission, etc. ∞ −δct /T −iω0t E(ω) = E0e e dt ∫0 E e−δct /T e−iω0t 0 E = 0 i(ω −ω0 ) +δc /T t E(ω) 2 Lorentzian Emission spectrum 2 2 E δ c ω E(ω) = 0 ~ = 2 2 2 T Q (ω −ω ) +δ /T c 0 c ω ω0 Energy of circulating EM wave, Icirc(t) ⎡ t ⎤ 2L T = Icirc (t) = Icirc (0)×exp⎢−δ c ⎥, : round-trip time of flight ⎣ T ⎦ c Number of round trips in t ⎡ ω ⎤ ⇒ Icirc (t) = Icirc (0)×exp⎢− t⎥ ⎣ Qc ⎦ Q-factor of a RLC circuit ωT 4π L 1 ω ωL Q = = Q = = where
    [Show full text]
  • Step-Pulse Modulation of Gain-Switched Semiconductor Pulsed Laser
    applied sciences Article Step-Pulse Modulation of Gain-Switched Semiconductor Pulsed Laser Bin Li , Changyan Sun, Yun Ling *, Heng Zhou and Kun Qiu School of Information and Communication Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China; [email protected] (B.L.); [email protected] (C.S.); [email protected] (H.Z.); [email protected] (K.Q.) * Correspondence: [email protected] Received: 12 December 2018; Accepted: 8 February 2019; Published: 12 February 2019 Featured Application: The proposed novel approach presented in this paper offers a highly effective modulated method for a gain-switched semiconductor laser. As a result, we can acquire the output pulse with a higher peak power (the limit can be reached) and shorter width and can be incorporated as a practical and cost-effective approach for many fields which need high extinction ratio short pulse, such as the optical time domain reflectometry. Abstract: To improve the peak power and extinction ratio and produce ultra-short pulses, a novel approach is presented in this paper offers a highly effective modulated method for a gain-switched semiconductor laser by using step-pulse signal modulation. For the purpose of single pulse output, then the effects on the output from the gain-switched semiconductor laser are studied by simulating single mode rate equation when changing the amplitude and width of the modulated signal. The results show that the proposed method can effectively accelerate the accumulation speed of the population inversion and we can acquire the output pulse with higher peak power and shorter width. Compared with the traditional rectangular wave modulation, this method is advantageous to obtain a high gain switching effect by increasing the second modulation current and reduce the pulse width to saturation at the best working point.
    [Show full text]
  • 23. Lasers II Four-Level Systems Are the Best for Lasers
    23. Lasers II Four-level systems are the best for lasers Steady-state conditions: - threshold - longitudinal modes Some laser examples “The teleforce ray will send concentrated beams of particles through the free air, of such tremendous energy that they will bring down a fleet of 10,000 enemy airplanes at a distance of 250 miles from the defending nation's border and will cause armies of millions to drop dead in their tracks.” - Nikolai Tesla, 1937 Two-, three-, and four-level systems Two-level Three-level Four-level system system system Fast decay Fast decay Pump Pump Laser Transition Laser Transition Transition Transition Laser Pump Transition Transition Fast decay At best, you get If you hit it hard, equal populations. Lasing is easy! you get lasing. No lasing. II/ sat always NN negative 1/ I Isat Gain must exceed loss Having a population inversion (N < 0) isn’t enough. Additional losses in intensity occur, due to absorption, scattering, and reflections. Also there is an output beam… L I1 I0 output I2 a laser medium with gain, I3 G = exp(gL) Mirror with Mirror with R < 100% R = 100% The laser will lase if the beam maintains Gain = Loss its intensity after one round trip, that is, if: This means: I3 = I0. Here, it means a condition on I3: II30 exp(gLR ) exp(gLI ) 0 In this expression, we are ignoring sources of loss other than the mirror reflectivity R. This is an approximation, because there are always other sources of loss. N < 0 is necessary, but not sufficient. Solving for g, we find: 1 gRln(1/ ) 2L There is a minimum value of the gain which is required in order to turn on a laser.
    [Show full text]
  • Amplified Spontaneous Emission at 5.23 Μm in Two-Photon Excited Rb Vapour
    Amplified spontaneous emission at 5.23 μm in two-photon excited Rb vapour A.M. Akulshin1, N. Rahaman1, S.A. Suslov2 and R.J. McLean1 1Centre for Quantum and Optical Science, Swinburne University of Technology, PO Box 218, Melbourne 3122, Australia 2Department of Mathematics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne 3122, Australia Abstract. Population inversion on the 5D5/2-6P3/2 transition in Rb atoms produced by cw laser excitation at different wavelengths has been analysed by comparing the generated mid-IR radiation at 5.23 μm originating from amplified spontaneous emission (ASE) and isotropic blue fluorescence at 420 nm. Using a novel method for detection of two photon excitation via ASE, we have observed directional co- and counter-propagating emission at 5.23 μm. Evidence of a threshold-like characteristic is found in the ASE dependences on laser detuning and Rb number density. We find that the power dependences of the backward- and forward- directed emission can be very similar and demonstrate a pronounced saturation characteristic, however their spectral dependences are not identical. The presented observations could be useful for enhancing efficiency of frequency mixing processes and new field generation in atomic media. 1. Introduction The interest in frequency conversion of resonant light and laser-like new field generation in atomic media specially prepared by resonant laser light is driven by a number of possible applications [1, 2, 3, 4]. The transfer of population to excited levels, particularly to create population inversion on strong transitions in the optical domain, is an essential part of the nonlinear process of frequency up- and down-conversion [5, 6, 7].
    [Show full text]
  • Study of the Population Inversion Mechanisms and Superradiance on Ion Transitions of Molecular Nitrogen in the Filament
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Electronic archive of Tomsk Polytechnic University Study of the population inversion mechanisms and superradiance on ion transitions of molecular nitrogen in the filament N.G. Ivanov1, V.F. Losev1,2, V.E. Prokop’ev1,3 1Institute of High Current Electronics SB RAS, Akademichesky Avenue 2/3, 634055, Tomsk, Russia, [email protected] 2National Research Tomsk Polytechnic University, Lenin Avenue 30, 634050, Tomsk, Russia 3National Research Tomsk State University, 36, Lenina Ave., 634050, Tomsk, Russia ABSTRACT 3 3 + The experimental results of the inversion population mechanisms study in the resonant electronic transition B Пg–A Σu of nitrogen ions by optically pumped of air and pure nitrogen by femtosecond laser pulse at a wavelength of 950 nm are + 2 + presented. It is shown that the inversion results from selective settling of N2 (B Σu , v' =0) excited state by multiphoton excitation of the autoionization states of the nitrogen molecule with energy of 18.7 eV. Seed photon for superradiance at transitions of molecular nitrogen ions are photons the axial supercontinuum occurring in the filament on the respective wavelengths. The mode of the superradiance at a wavelength λ = 358.4 nm referred to the transition of the CN molecules was realized. Keywords: inversion population, mechanisms, filament, femtosecond laser pulse, multiphoton ionization, molecular, nitrogen 1. INTRODUCTION For the first time lasing in nitrogen it was obtained in 1963 in a pulsed discharge plasma of low pressure in the 3 3 + 3 3 transitions of first (B Пg – A Σu , the wavelength λ = 1046.9) and second (С Пu - B Пg, λ =337.1 nm) positive systems of molecular nitrogen [1].
    [Show full text]
  • Introduction to Laser Physics
    Introduction to Laser Physics Laura Corner Cockcroft Institute for Accelerator Science Liverpool University, UK CERN Accelerator School High Gradient Wakefield Accelerators Sesimbra, Portugal, March 2019 1 Outline • What is a laser? • Basic laser physics • Different types of laser systems. • High power lasers Suggested reading: • ‘Lasers’, A.E. Siegman, University Science Books • ‘Principles of Lasers’, O. Svelto, Springer • ‘Laser Physics’, S. Hooker & C. Webb, Oxford University Press • ‘Optical Electronics in Modern Communications’, A. Yariv, Oxford University Press CERN High Gradient Accelerator School, Sesimbra Portugal, March 2019 2 LASER Light Amplification by Stimulated Emission of Radiation CERN High Gradient Accelerator School, Sesimbra Portugal, March 2019 3 What makes lasers special? • They produce a directional beam. •They have a narrow spectrum (or bandwidth). •They are coherent. Slide courtesy Prof. S. Hooker CERN High Gradient Accelerator School, Sesimbra Portugal, March 2019 4 Einstein model • Einstein identified 3 ways in which atoms exchange energy with a radiation field • Absorption • Spontaneous emission spontaneousstimulatedabsorption emission emission • Stimulated emission • Rate of absorption/stimulated emission dependent on no of photons & number of atoms in lower/upper state. ‣ photon needs to have correct energy Albert Einstein ‣ the number of photons can be amplified Slide courtesy Prof. S. Hooker CERN High Gradient Accelerator School, Sesimbra Portugal, March 2019 5 Lasers: the basic idea We want lots of this...
    [Show full text]