Palsdottir, Bera

Poulsen, Ove

Shi, Yuan

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 17, 2017A stable, high-power broadband Pr3+-doped fiber superfluorescence sourceShi, Yuan; Poulsen, Ove; Palsdottir, BeraPublished in:Proceedings of 5th European Quantum Electronics ConferencePublication date:1994Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Shi, Y., Poulsen, O., & Palsdottir, B. (1994). A stable, high-power broadband Pr3+-doped fibersuperfluorescence source. In Proceedings of 5th European Quantum Electronics Conference (pp. 23-24). IEEE.MONDAY AFTERNOON f EQEC‘94 f 23 mode (NF and FF are identical) is shown in Fig. 3a. For larger arrays, the required pulse duration for generating the pure HermiteGaussian modes was even longer. The Hermite-Gaussian mode (NF and FF) of an 11x11 laser array, excited by a current pulse -1 microsec. long, is shown in Fig. 3b. The nonlinear evolution of these array modes and the analysis of time scales re- quired for achieving coherency over large arrays as well as the dynamic control over modal pattem by pulse width mod- ulation are discussed. 1. M. Orenstein, E. Kapon, N. G. Stoffel, J. P. Harbison, L. T. Florez, J. L. Wullert, Appl. Phys. Lett. 58, 804 (1991). M. Orenstein, E. Kapon, J. P. Harbison, L. T. Florez, N. G. Stoffel, Appl. Phys. Lett. 60,1535 (1992). 2. QMCZ 1430 laser emission in AI.Ga,.,As with indirect band gap A. Womer, R. Westphalig, H. Kalt, K. Kohler,‘ Fachbereich Physik der Universitdt Kaiserslautern, Enuin-Schr~inger-Straj3e, D- 67663 Kaiserslautern, Germany As a promising possibility to realize vis- ible lasers compatible with GaAs we re- port for the first time laser emission up to 300 K from AI,Ga,-,As with indirect band gap close to the direct-to-indirect crossover. Although AI,Ga,-,As is a material with an indirect fundamental band gap at a composition of x, 2 0.43 for 5 K,‘ the transition probability for indirect recom- bination is strongly enhanced because of effective alloy-disorder-induced interval- ley scattering2 for small energy separa- tion of the X-and r-conduction band min- ima. The resulting emission wavelength lies in the red spectral range (635 nm at 300 K).3 We performed photoluminescence measurements using stripe-like nanosec- ond excitation of samples, which are cleaved into resonators of around 100 Fm width. The samples consist of 0.5-pn thick active layers of AIIGal.,As between Ab.,G&,As cladding layers. Laser activ- ity is proved unambiguously by both cri- teria: threshold-like behavior of the onset of stimulated emission and occurrence of resonator-mode structures in the emis- sion spectra. Very sharp laser modes are demon- strated in Fig. 1 for a sample with a com- position of x = 0.43 at relatively low lat- tice temperature (80 K). Figure 2 shows laser emission at 270 K for a sample with composition of x = 0.46. This composition is more suitable for indirect-gap laser emission because of the temperature shift of the direct-to-indirect crossover to I, - 0.45 at 300 K. The product of mode sep- aration and cavity length is a constant value, so the mode structure can be as- signed unambiguously to the resonator. In comparison to emission from un- cleaved samples, the threshold is lowered dependent on the resonator quality by a factor of 2 until 10. A further promising property of AISa,-,As with indirect band gap is the only weak increase of the threshold for ’1 300 250 L-: T, = 80 K ‘ !  = 2.032 2.034 2.036 2.038 2.040 Photon Energy (eV) QMG2 Fig. 1. Laser emission at different pump intensities for a 90-pm- wide cleaved sample of Ab&&,,As at 80 K. The resonator modes are sharp and well separated at this temperature. 1.945 1.950 1.955 Photon Energy (eV) QMGZ Fig. 2. Laser emission at different pump intensities for a cleaved sample Ab,G&.,As at 270 K still showing a clear modulation of the spectra. laser emission with rising temperature. A comparison between the experimental data and a heuristic exponential depend- ence (see Fig. 3)43 yields a constant To = 195 K for a composition of x = 0.48. This property results in high stability of the laser activity, a relatively small threshold at room temperature, and a constant emission wavelength. To investigate the microscopic origin of the stimulated emission we addition- ally performed gain measurements with the variable stripe-length method at low temperature (20 K) for uncleaved sam- ples. The weaker transition probabilities for samples with larger aluminum con- centration result in higher thresholds for 5 . 1 0 ’ 1  0 40 80 120 160 200 240 280 320 360 L.anicc Temperature (K)  QMGZ Fig. 3. Threshold for laser emission as a function of lattice temperature for three samples with two different aluminum concentrations. The dotted lines are fits with 1, * exp(T/T,) yielding the constant To, which describes the threshold behavior. stimulated emission and therefore in higher carrier densities, which broaden the gain spectrum and increase the re- normalization effect. The carrier densities and temperatures can be extracted from lineshape fits using a model that includes self-consistently the renormalization of three conduction bands. Absolute values of the maximum gain are 200-250 cm-’. Our results seem to be very promising because laser activity is achieved with a very simple kind of resonator. Improve- ments in the laser performance should be achievable in an easy way by high-reflec- tivity coating of the resonator and opti- mized index guiding of the optical wave. *Fraunhofer Institut IAF, Tullastraj3e 72, D- 79108 Freiburg, Germany 1. D. J. Wolford, W. Y. Hsu, J. D. Dow, B. G. Streetman, J. Lumin. 18/19, 863 (1978). H. Kalt, W. W. Riihle, K. Reimann, M. Rinker, E. Bauser, Phys. Rev. B 43, 12364 (1991). M. Rinker, H. Kalt, Y.-C. Lu, E. Bau- ser, l? Ganser, K. Kohler, Appl. Phys. Lett. 59, 1102 (1991). A. Haug, Appl. Phys. B 44,151 (1987). 2. 3. 4. QMG3 1445 A stable, high-power broadband PI”-doped fiber superfluorescence source Yuan Shi, Ove Poulsen, b r a  Pblsd6ttir,’ Mikroelektronik Centre!, Building 345 East, Technical University of Denmark, DK-2800 Lyngby, Denmark Broadband superfluorescence sources are required for high-grade fiber-optic gyroscopes, signal-processing fiber sys- tems, atomic physics, and fiber sensors. Nd”- and Er”-doped fiber superflu- orescence have been demon- strated. We report the results of a Pr3’- doped silica fiber superfluorescent source at 1049 nm. The mean-wave- length versus pump power and pump wavelength is investigated. By using both single-pass and double- pass experimental configurations? the doped fiber superfluorescent source is in- vestigated with a 592 nm dye laser pump. The output power and linewidth versus absorbed pump power for the double-pass configuration are shown in Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on July 07,2010 at 13:44:29 UTC from IEEE Xplore.  Restrictions apply. 24 1 EQEc'94 1 MONDAY AFTERNOON 0 D 50 100 150 2W Absorbed pump power (mW) QMCJ Fig. 1 .  The output power and linewidth of the double-pass configuration versus the absorbed pump power. The inset is one of the typical output spectra. 1065 I 1045 I 560 575 590 605 620 635 Pump wavelength (nm) QMCJ Fig. 2. The peak wavelength of the superfluorescence emission versus pump wavelength for the double-pass configuration. Fig. 1. With increasing of pump power, the linewidth narrows sharply from -35 nm to -21 nm reaching saturation re- gime. The output power has a straight l i e f i t  slope efficiency of 40%. One of the typical output spectra is shown as inset of Fig. 1. It has a smooth Gaussian-Like structure. A maximum output power of -61 mW is achieved. The peak superfluorescent wave- length versus pump wavelength at a same absorbed pump power is shown in Fig. 2. The large variation of the peak wavelength is caused by site-to-site var- iations in the ionic environment of the glass matrix, giving rise to different po- sitions of Pr-energy levels (inhomoge- neous broadening). Increasing the pump wavelength from 570 nm to 600 nm, the peak is shifted to shorter wavelength, in contrast to the normal behavior, where increasing pump wavelength results in an increasing in emission wavelength. This is attributed to the two different ma- trix sites of the doped fiber' broadening differently. So the large inhomogeneous broadening linewidth and the two host matrix sites in the Alco-doped silica fiber demonstrate the broad variation of peak superfluorescent wavelength. The intensity-weighted mean wave- length is one of the important parameters of the broadband source. The mean wavelength versus the absorbed pump power is shown in Fig. 3. It only has a small variation of 0.4 nm and a negative slope with inmasing of pump power. This advantageous property stems from < '"L 717 - ~ -100 Absorbed pump power ImWi Q M C 3  Fig. 3. The mtensity-weighted mean wavelength versus pump power. the weak unsymmetric fluorescence gain spectrum of the Pr"-doped fiber. For a doped fiber with a strong unsymmetric fluorescence spectrum, the gain at emis- sion peak and dominant emission side exceeds gain of the weak fluorescence side. With increasing of pump power, the mean wavelength will shift significantly to the stronger emission wavelength side. This impairs output spectral stability with rrspect to output power. For the P?'- doped silica fiber, the mean wavelength shifts to shorter wavelength because the increasing of pump power is as small as 0.4 nm. This wavelength shift should be reduced in the saturation regime. A stable, single-mode-broadband Pr"-doped fiber superfluorescence source is demonstrated with a high out- put power of 61 mW and linewidth of 20 nm. Good output spectral stability is achieved. *Lycom A/S, NKT All6 75, DK-2605 Brmdby, Denmark 1. M. J. F. DigoMet, K. Liu, "Analysis of a 1060-nm Nd : SiO, superfluores- cent fiber laser" J. of Lightwave Technology 7, 1009-1015 (1989). 2. K. Iwatsuki, "Er-doped superflu- orescence fiber laser pumped by 1.48 Fm laser diode" IEEE Photon. Tech. Lett., 2,237-238 (1990). 3. Yuan Shi, 0. Poulsen, "Tunable Pr3'- doped silica-based fiber lasers" in CLEO '93 Tech. Digest (OSA, 1993) paper CThS13. QMG4 1500 The short pulse duration limit for KrF laser systems I. N. Ross, P. Simon,* S. Szatmari," P. Matousek, K. Osvay," M. J. Shaw, Central Laser Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OXON 0 x 1 1  OQX, U.K. The short pulse duration limit in high- power laser systems employing chirped pulse amplification is set by the limita- tions on width and shape and relative phase across the output spectrum. It is possible to improve the criteria for as- sessing the spectrum by looking at the re- lationship between a spectral distribution and its Fourier transform. This shows that the pulse duration at FWHM is more closely related to the spectral width in the wings of the spectrum, at perhaps the 5% level, than to the FWHM. Conversely, the shape of the spectrum is reflected more in the wings of the pulse and is important in the assessment of pulse contrast ratio. The pulse duration achievable with any laser system is determined by a num- ber of factors including the input spec- trum, the amplifier gain spectral profile, any spectrally sensitive components, and the gain and saturation levels. Methods of optimizing the system include spectral filtering' and spatial dispersion.' The ad- dition of passive spectral filtering can only lead to a modest reduction in pulse duration of perhaps 30%. However, it can also control the pulse shape and give, for example, pulses with a shorter rise time, and this may be useful for some applications. In a heavily saturated amplifier such as KrF, the shortest pulses should be achievable using spatial dispersion in the amplifier. However, this may not be a practical solution for many large systems. KrF lasers have been shown to dem- onstrate an apparent absorption feature close to the center of the spectral gain line.' This anomaly can increase the min- imum pulse duration achievable with a KrF laser to more than 250 f s 4  An exper- imental study has been carried out to leam more about this anomaly so as to assess the fundamental pulse duration limit and to enable proper optimization of the system to achieve this limit. Pulses as short as 70 fs have been obtained where additional benefit has been de- rived from the saturation of a chirped pulse to maintain the maximum spectral width. *Laser Laboratorium, Gottingen, Germany *'JATE University, Szeged, Hungary 1. M. D. Perry, F. G. Patterson, J. Wes- ton, Opt Lett 15, 381 (1990). 2. S. Szatmari, P. Simon, H. Gerhardt, Opt Comm 79, 64 (1990). 3. H. lava, et al . ,  Appl Phys B 42, 11 _ _  . (1987). I. N. Ross, et al., submitted to Opt 4. Comm QMG5 1515 Generation of ultrashort x-ray pulses with high-contrast ultrahigh-intensity fs-lasers G. Korn, J. C. Kieffer,' Z. Jiang,* G. Mourou, Center for UltraJast optical Science, University of Michigan, 2200 Bonisteef Blvd., Ann Arbor, MI, 48109-2099, USA We review terawatt solid-state lasers based on chirped pulse amplification and their important parameters for high- intensity laser plasma interaction experi- ments. Interaction experiments have been performed with our 400 fs multiterawatt Nd : glass laser. High-efficiency second harmonic generation of pulses with in- tensities up to 500 GW/cmZ enabled us to enerate intensities up to 4 x 10" W/ cm'at A = 527 nm. These pulses were fo- cused on low and high z-material targets. Time resolved keV spectroscopy shows that short, several ps long x-ray bursts are generated when high-contrast fs-laser radiation is used to heat the plasma. Elec- tron densities up to 3 X lo" cm-' are pro- duced. Conversion efficiencies in the 4 A-8 show that fs-laser-generated pi- cosecond x-ray pulses give enough flux for future applications. Directions are dis- Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on July 07,2010 at 13:44:29 UTC from IEEE Xplore.  Restrictions apply. 

A stable, high-power broadband Pr3+-doped fiber superfluorescence source

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A stable, high-power broadband Pr3+-doped fiber superfluorescence source

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