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Applied Physics B: Lasers and Optics

Frequency stabilization and output power undulations of diode lasers with feedback by volume holographic gratings

Sun, 2008-11-16 13:31 ? Guest

Abstract  The mode-hop behavior and the power characteristics of a laser diode with wavelength-selective optical feedback are experimentally investigated. The feedback is provided by external volume holographic gratings, also called ‘Bragg mirrors’, at normal incidence. We demonstrate that a Bragg mirror forces a laser diode to operate only within a narrow wavelength range, and that the emission wavelength of the laser diode is stabilized against variations of the injection current. Moreover, we present periodic undulations of the power characteristics of the laser, depending on the driving current. They can be qualitatively explained with a simple model which takes into account that the threshold gain in the laser system strongly depends on the wavelength.
  • Content Type Journal Article
  • DOI 10.1007/s00340-008-3290-1
  • Authors
    • F. Kroeger, University of Bonn Institute of Physics Wegelerstr. 8 53115 Bonn Germany
    • I.
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Noise caused by a finite extinction ratio of the light modulator in CW cavity ring-down spectroscopy

Sun, 2008-11-16 13:31 ? Guest

Abstract  A model is presented for the effect of a finite extinction ratio of the light modulator used in continuous wave cavity ring-down spectroscopy (CW-CRDS) experiments. We present a simple analytical expression for the minimum isolation required to prevent a significant increase in the fluctuations of the cavity decay rate, which determine the sensitivity of the method. We also present systematic measurements of the signal to noise in CW-CRDS as a function of the effective isolation of the light modulator, and excellent agreement with the model is found.
  • Content Type Journal Article
  • DOI 10.1007/s00340-008-3293-y
  • Authors
    • H. Huang, University of Virginia Department of Chemistry Charlottesville VA 22904-4319 USA
    • K. K.
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Thermal effects in singly resonant continuous-wave optical parametric oscillators

Sun, 2008-11-16 13:31 ? Guest

Abstract  Stability and tuning characteristics of continuous-wave optical parametric oscillators (CW OPOs) are affected by various thermal effects arising from optical absorption in nonlinear crystals. In this paper, we present an experimental study of such effects in a singly resonant CW OPO. The OPO operates in the 3-μm mid-infrared region and it is based on a MgO-doped periodically poled lithium niobate crystal. We focus our study on two thermally induced phenomena that have been recently reported to exist in singly resonant CW OPOs: optical bi-stability and thermal self-locking. Thermal self-locking effect, which is known to alter the stability and tuning properties of doubly and triply resonant CW OPOs, is shown to be also of importance in singly resonant OPOs. We report the stability and tuning characteristics of a thermally loaded OPO and discuss a simple temperature-tuning method that can be used to scan the OPO idler frequency continuously over several THz.

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Diode-pumped laser with Yb:YAG single-crystal fiber grown by the micro-pulling down technique

Sun, 2008-11-16 13:31 ? Guest

Abstract  Laser emission obtained from an Yb:YAG single-crystal fiber directly grown by the micro-pulling down technique is demonstrated for the first time. We achieved 11.2 W of continuous wave (CW) output power at 1031 nm for 55 W of incident pump power at 940 nm. In the Q-switched regime, we obtained pulses as short as 17 ns, for an average power of 2.3 W at 2 kHz corresponding to an energy of 1.15  mJ. In both cases, the M 2 factor was 2.5. This single-crystal fiber showed performance similar to a standard rod elaborated by the Czochralski method. The potential of Yb3+-doped single-crystal fibers is presented for scalable high-average and high-peak-power laser systems.
  • Content Type Journal Article
  • DOI 10.1007/s00340-008-3288-8
  • Authors
    • D.

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3.5-μm high-resolution gas sensing employing a LiNbO3 QPM-DFG waveguide module

Sun, 2008-11-16 13:31 ? Guest

Abstract  Diode laser technology coupled with a wavelength-conversion unit to produce mid-infrared narrow bandwidth laser light applicable to trace-gas detection and with the potential for high-resolution spectroscopy is described. Quasi-phase-matched difference-frequency generation (QPM-DFG) in a compact and fibre-coupled periodically poled lithium niobate (PPLN) waveguide module mixing 1063 and 1525-nm radiations has been adopted for generating 34 μW of 3.5-μm wavelength laser light. Optical detection methods, including sensitive wavelength modulation spectroscopy and a rapid wavelength chirp technique, have been employed with a single-pass cell to investigate methane and formaldehyde absorption profiles around 2855 cm−1, as proof of principle experiments for high sensitivity and resolution spectroscopy on atmospherically important molecules.

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Laser-induced point-defect reaction in proton-irradiated SiC

Sun, 2008-11-16 13:31 ? Guest

Abstract  The defects produced in 4H-SiC epitaxial layers by irradiation with 200-keV H+ were characterized by low-temperature photoluminescence. These defects induce sharp luminescent lines, the so-called alphabet lines. Their intensity shows an evolution under UV-laser irradiation not previously observed. By monitoring the change in the resulting photoluminescence spectra versus time, we distinguish two original ‘families’ of peaks called PB1 and PB2. They display a different, and opposite, behaviour with laser irradiation but they are strongly correlated. In particular, the recovering rate of the PB1 family and the growth rate of the PB2 family are the same, indicating a structural rearrangement of defects.
  • Content Type Journal Article
  • Category Rapid communication
  • DOI 10.1007/s00340-008-3302-1
  • Authors
    • M. Zimbone, Catania University Physics Department Via S.

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Thermal lens effects in an Er3+:YAG laser with crystalline fiber geometry

Sun, 2008-11-16 13:31 ? Guest

Abstract  A resonantly diode-pumped high-power continuous-wave Er3+:YAG laser with a crystalline fiber geometry based on total-internal-reflection pump guiding is reported. Up to 9.4 W of output power could be generated and a slope efficiency of 46.8% was achieved. Intrinsic efficiencies reached up to 48.8% and an optimum outcoupling of ∼20% was found. A strong thermal lens was observed and cavity stability and hysteresis effects were studied.
  • Content Type Journal Article
  • DOI 10.1007/s00340-008-3292-z
  • Authors
    • M.

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Laser desorption studies using laser-induced fluorescence of large aromatic molecules

Sun, 2008-11-16 13:31 ? Guest

Abstract  Pulsed laser desorption of non-volatile organic dye molecules paraterphenyl and tetra-t-butyl-p-quinquephenyl (QUI) was studied using gas phase ultraviolet laser induced fluorescence, following heating of a steel substrate by a pulsed 1.06-µm Nd:YAG laser. The fluorescence signal intensity is linear in concentration up to at least 30 monolayers and shows infrared power threshold behavior, as expected for evaporation, at ∼0.2 J/cm2. Similar signal levels were also observed in air, with 532-nm heating, and using other metallic or dark black surfaces.
  • Content Type Journal Article
  • DOI 10.1007/s00340-008-3295-9
  • Authors
    • G. P. Smith, SRI International Molecular Physics Laboratory Menlo Park CA 94025 USA
    • B. Krancevic, SRI International Molecular Physics Laboratory Menlo Park CA 94025 USA
    • D. L. Huestis, SRI International Molecular Physics Laboratory Menlo Park CA 94025 USA
    • H.
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Aging effect on blue luminescent silicon nanocrystals prepared by pulsed laser ablation of silicon wafer in de-ionized water

Sun, 2008-11-16 13:31 ? Guest

Abstract  Blue luminescent colloidal silicon nanocrystals (Si-ncs) were synthesized at room temperature by nanosecond pulsed laser ablation of a single-crystal silicon target in de-ionized water. Irregular Si-nc fragments obtained by laser ablation are stabilized into regularly shaped, spherical, and well-separated aggregates during the aging process in water. Aging in de-ionized water for several weeks improved the photoluminescence (PL) intensity. At least two weeks of aging are necessary for observation of broad blue room temperature PL with a maximum centered at 420 nm. Detailed structural analysis revealed that agglomerates after aging for several months contain Si-ncs with irregular shape smaller than the quantum confinement limit (<5 nm). These blue luminescent Si-ncs dispersed in de-ionized water exhibited a PL decay time of 6 ns, which is much faster than that of Si-ncs prepared in traditional ways (usually on the order of microseconds).

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Continuous-wave cavity-ringdown detection of stimulated Raman gain spectra

Sun, 2008-11-16 13:31 ? Guest

Abstract  Cavity ringdown (CRD) spectroscopy, with its high sensitivity, provides a novel way to perform continuous-wave (cw) stimulated Raman gain (SRG) spectroscopy, rather than by conventional optically detected coherent Raman techniques. Tunable cw laser light at ∼1544 nm is used to probe ringdown decay from a rapidly-swept, high-finesse optical cavity containing a gas-phase sample of interest and itself located inside the cavity of a cw single-longitudinal-mode Nd:YAG ring laser operating at ∼1064.4 nm. This approach is used to measure cw SRG spectra of the ν 1 fundamental rovibrational Raman band of methane gas at ∼2916.5 cm−1. The resulting SRG-CRD resonances have ringdown times longer than in the off-resonance case, in contrast to the usual shorter ringdown times arising from absorption and other loss processes. Previously reported noise-equivalent sensitivities have been substantially improved, by using a second ringdown cavity to facilitate subtraction of infrared-absorption background signals.

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