Showing papers on "Laser linewidth published in 1997"
TL;DR: In this paper, a single mode operation of distributed feedback quantum cascade (QC) lasers is reported above room temperature at both 5.4 and 8 μm wavelengths. But the linewidth is limited by thermal drift during the pulse with a typical value of 0.3 cm−1 for a 10 ns long pulse at 300 K.
Abstract: Pulsed single mode operation of distributed feedback quantum cascade lasers is reported above room temperature at both 5.4 and 8 μm wavelengths. Peak optical powers up to 60 mW at 300 K are obtained with a tuning range of ∼60 nm from 100 to ∼320 K. The linewidth is limited by thermal drift during the pulse with a typical value of 0.3 cm−1 for a 10 ns long pulse at 300 K.
399 citations
Abstract: New reflection and transmission optical filters based on guided-mode resonances in multilayer waveguide gratings are characterized and compared with homogeneous thin-film filters. These guided-mode resonance filters are implemented by integration of diffraction gratings into classical thin-film multilayers to produce high-efficiency filter response and arbitrarily low sidebands extended over a large spectral range. Compared with homogeneous thin-film reflection filters, guided-mode resonance reflection filters require significantly fewer layers for a narrow linewidth and a high peak response to be obtained. The single-grating transmission filters presented have a narrower linewidth than Fabry–Perot filters with an equal number of layers and similar materials while maintaining high peak transmittance and low sidebands.
299 citations
TL;DR: The realization and demonstration of novel semiconductor waveguide-coupled microcavity ring and disk resonators to show the feasibility of such devices are reported.
Abstract: We report the realization and demonstration of novel semiconductor waveguide-coupled microcavity ring and disk resonators. For a 10.5-microm-diameter disk resonator, we measure a finesse of 120, a resonant linewidth of 0.18 nm, and a free-spectral range of 21.6 nm in the 1.55-mum-wavelength region. We present the nanofabrication methods and the experimental results for 10.5- and 20.5-mum-diameter ring and disk resonators to show the feasibility of such devices.
249 citations
TL;DR: In this article, the influence of power and pressure broadening and systematic shifts of the resonance frequency was studied for coherent dark resonances in a cesium vapor cell with phase-locked laser beams.
Abstract: When neon is introduced as a buffer gas the interaction time of cesium atoms in a vapor cell with resonant laser beams is drastically increased. Using a pair of phase-locked lasers we have observed linewidths as narrow as $42 $Hz for coherent dark resonances in a cesium vapor cell. We study the influence of power and pressure broadening and systematic shifts of the resonance frequency. Our experiments demonstrate that coherent dark resonances could rival direct radio-frequency precision measurements, which have a wide range of applications in physics.
185 citations
TL;DR: In this paper, a wavelength-swept fiber laser (WSFL) incorporating frequency shifted feedback and an intracavity passband filter is considered, in which the wavelength of the modeless output is linearly, continuously and repeatedly tuned (in time) by modulation of the filter peak wavelength and filter strength.
Abstract: This paper concerns a wavelength-swept fiber laser (WSFL) incorporating frequency shifted feedback and an intracavity passband filter, in which the wavelength of the modeless output is linearly, continuously and repeatedly tuned (in time) over a given range by modulation of the filter peak wavelength and filter strength. We show both numerically and experimentally that amplifier noise plays a key role in determining the operation of frequency-shifted fiber laser systems and that a "noisy" amplifier can be used to suppress the natural tendency of such lasers to pulse, allowing for continuous wave, modeless operation. Furthermore, we show that significant narrowing of a WSFL instantaneous swept linewidth can be obtained if the filter peak transmission wavelength is resonantly swept so as to follow the wavelength shift per pass due to the acoustooptic frequency shift. Using these ideas we go on to demonstrate and characterize a high-power diode-driven Er/sup 3+//Yb/sup 3+/ WSFL incorporating a bulk-optic acoustooptic tunable filter (AOTF). Linewidths as narrow as 9 GHz, sweep ranges up to 38 nm and output powers as high as 100 mW are obtained. Furthermore, we demonstrate the generation of user definable average spectral output by synchronous modulation of the filter strength and multiwavelength pulsed output at higher sweep rates. Excellent agreement between the experimental results and those of the numerical modeling is obtained. Our simulations show that reduced linewidth (<0.02 nm) and improved scan linearity should be readily achievable with realistic system improvements. We believe such sources to be of considerable physical and practical interest, with applications ranging from sensor array monitoring and device characterization through to low-coherence interferometry.
173 citations
TL;DR: In this paper, a fast scan submillimeter spectroscopic technique (FASSST) was developed which uses a voltage tunable backward wave oscillator (BWO) as a primary source of radiation, but which uses optical calibration methods rather than the more traditional phase or frequency lock techniques.
Abstract: A new fast scan submillimeter spectroscopic technique (FASSST) has been developed which uses a voltage tunable backward wave oscillator (BWO) as a primary source of radiation, but which uses fast scan (∼105 Doppler limited resolution elements/s) and optical calibration methods rather than the more traditional phase or frequency lock techniques. Among its attributes are (1) absolute frequency calibration to ∼1/10 of a Doppler limited gaseous absorption linewidth (<0.1 MHz, 0.000 003 cm−1), (2) high sensitivity, and (3) the ability to measure many thousands of lines/s. Key elements which make this system possible include the excellent short term spectral purity of the broadly (∼100 GHz) tunable BWO; a very low noise, rapidly scannable high voltage power supply; fast data acquisition; and software capable of automated calibration and spectral line measurement. In addition to the unique spectroscopic power of the FASSST system, its implementation is simple enough that it has the prospect of impacting a wide range of scientific problems.
155 citations
117 citations
TL;DR: In this article, an efficient continuous-wave (CW) thulium-doped fiber laser emitting at wavelength, /spl lambda/=2.31 /spl mu/m is reported.
Abstract: Operation of an efficient continuous-wave (CW) thulium-doped fiber laser emitting at wavelength, /spl lambda/=2.31 /spl mu/m is reported. The fiber laser parameters are optimized with a view to ultimately producing a compact and efficient laser source for optical absorption based gas sensing. A number of fiber laser configurations are investigated to assess their suitability for narrow linewidth, tunable fiber laser operation emitting around /spl lambda/=2.3 /spl mu/m, which is a wavelength region of significant importance for hydrocarbon gas monitoring. Tuning ranges of 140 nm and linewidths of less than 210 MHz have been demonstrated with lasers with bulk external tuning grating. Preliminary hydrocarbon gas sensing investigation confirm the potential of this source for detection of ppb gas concentrations.
116 citations
TL;DR: In this article, stacked layers of self-assembled InP quantum dots embedded in Ga0.52In0.48P have been prepared by solid source molecular beam epitaxy and the distance between the dot layers has been varied from 2 to 16 nm.
Abstract: Stacked layers of self-assembled InP quantum dots embedded in Ga0.52In0.48P have been prepared by solid source molecular beam epitaxy. Thereby the distance between the dot layers has been varied from 2 to 16 nm. Cross sectional transmission electron microscopy shows that the InP dots are aligned in the growth direction [100]. As the distance between the dot layers is reduced, each dot of the first dot layer is reproduced in the upper layers, and this leads to an improvement of the dot size homogeneity of the stacked InP dot system. This is confirmed by photoluminescence (PL) measurements, which demonstrate a very narrow linewidth of 26 meV for a triple layer with 2 nm separation between the dot layers in comparison with a linewidth of 41 meV for a single layer sample. At the same time, the PL peak of the dots is shifted by 72 meV to lower energies which is ascribed to a reduced strain and strong electrical coupling between the densely stacked InP dots.
114 citations
TL;DR: In this article, the authors have observed granular structures with a diameter of 20-30 nm in resist films, and have determined that these structures cause the linewidth fluctuations.
Abstract: Linewidth fluctuation in resist patterns is a serious problem in electron beam nanolithography. We have observed granular structures with a diameter of 20–30 nm in resist films, and have determined that these structures cause the linewidth fluctuations. The granules are made up of polymer aggregates. We discuss the origin of the aggregates from the result that their size depends on the polymer molecular weight. We also show that the linewidth fluctuation is reduced, though the developing rate is slow, when the pattern size is less than the aggregate size. The linewidth dependence of the fluctuation and of the developing rate can be explained by the influence of the resist polymer aggregate on the development behavior.
113 citations
TL;DR: In this article, the effect of quantum interference between the two transition pathways from the excited doublet to the ground level of a driven V atom on the spectral features of the resonance fluorescence emission was investigated.
Abstract: We investigate the effect of quantum interference between the two transition pathways from the excited doublet to the ground level of a driven V atom on the spectral features of the resonance fluorescence emission. The ultranarrow spectral line at line center, which arises due to quantum interference, occurs over a wide range of parameters. The smaller the ratio of the excited doublet splitting to the effective Rabi frequency, the more pronounced the spectral line narrowing. However, the fluorescence emission is completely quenched when the atomic dipole moments are exactly parallel and the driving field is tuned to the average frequency of the atomic transitions. The narrow line is due to the slow decay rate of one dressed state, while the quenching arises from dressed-state trapping. A finite laser linewidth destroys the spectral narrowing features and the fluorescence quenching.
TL;DR: In this article, high crystalline quality epitaxial GaN films with thicknesses 0.5-1.5 μm have been successfully grown directly on Al2O3(0001) substrate by pulsed laser deposition (PLD).
Abstract: High crystalline quality epitaxial GaN films with thicknesses 0.5–1.5 μm have been successfully grown directly on Al2O3(0001) substrate by pulsed laser deposition (PLD). For films grown at 950 °C, we obtained an x-ray diffraction rocking curve linewidth of 7 arc min. The ion channeling minimum yield in the near-surface region (∼2000 A) for a 0.5 μm thick film was ∼3%–4% indicating a high degree of crystallinity. The optical absorption edge measured by UV-visible spectroscopy was sharp, and the band gap was found to be 3.4 eV. The crystalline properties of these PLD GaN films are comparable to those grown by metalorganic chemical vapor deposition and molecular beam epitaxy.
TL;DR: In this article, an optically pumped waveguide structure with methyl substituted conjugated ladder type poly(paraphenylene) as the active material was fabricated, and the choice of the device parameters allowed one to observe a high directionality, a small beam divergence, a complete linear polarization, and a linewidth with an upper limit of 1.7 nm at a considerable low threshold of 3 kW/cm2 at room temperature.
Abstract: An optically pumped waveguide structure has been fabricated with methyl substituted conjugated laddertype poly(paraphenylene) as the active material. The choice of the device parameters allows one to observe a high directionality, a small beam divergence, a complete linear polarization, and a linewidth with an upper limit of 1.7 nm at a considerable low threshold of 3 kW/cm2 at room temperature.
TL;DR: In this paper, a detailed experimental study of the dc, microwave, and noise properties of flux-flow oscillators (FFO's) was performed for integration with a SIS mixer for use in submillimeter wave receivers.
Abstract: Flux-flow oscillators (FFO's) are being developed for integration with a SIS mixer for use in submillimeter wave receivers. The present work contains a detailed experimental study of the dc, microwave, and noise properties of ${\mathrm{N}\mathrm{b}\ensuremath{-}\mathrm{A}\mathrm{l}\mathrm{O}}_{x}\ensuremath{-}\mathrm{Nb}$ FFO's. A model based on the Josephson self-pumping effect is proposed for an explanation of the experimental current-voltage characteristics. A reliable technique based on harmonic mixing is used to determine the spectral linewidth of the radiation emitted by the integrated FFO's up to 600 GHz. Comprehensive measurements of the dependence of the linewidth on the dynamic resistance and the applied magnetic field have been performed. In the resonant regime a linewidth as small as 200 kHz is obtained at 450 GHz. The experimental data are compared with recent theoretical predictions.
TL;DR: In this paper, a laser model based on feedback produced by scattering has been developed to explain the narrow linewidth emission and input-output behavior observed in scattering gain media, which includes the detailed spectral properties of the dye gain system.
Abstract: A laser model based on feedback produced by scattering has been developed to explain the narrow linewidth emission and input–output behavior observed in scattering gain media. The model is based on the transient two-level laser equations and includes the detailed spectral properties of the dye gain system. Monte Carlo methods were employed to calculate the threshold gain required for modeling the input–output and linewidth emission characteristics.
TL;DR: In this paper, the phase change on reflection of incident light is dependent on the wavelength, the angle of incidence, the type of metal, and the metal thickness, which can be exploited to improve the performance of planar metal mirror microcavities.
Abstract: In thin metal films the phase change on reflection of incident light is dependent on the wavelength, the angle of incidence, the type of metal, and the metal thickness. These properties have been exploited to improve the performance of planar metal mirror microcavities. We model substantial alteration of peak emission wavelength and linewidth with mirror thickness. This allows the tuning of the cavity resonance wavelength by variation of metal mirror thickness. The dependence of the phase change on wavelength and angle of incidence can also be used to suppress the angular dependence of the cavity resonance wavelength. These effects are observed in silver-mirrored cavities containing the polymers poly(p-phenylene vinylene), (PPV), and a cyano-substituted derivative of PPV, MEH-CN-PPV.
TL;DR: In this article, a 1.5/spl mu/m vertical cavity laser with two fused AlGaAs-GaAs mirrors with a strain-compensated InGaAsP-InP MQW active region was used for current confinement.
Abstract: We report on 64/spl deg/C continuous-wave (CW) operation of a 1.5-/spl mu/m vertical-cavity laser. This laser consists of two fused AlGaAs-GaAs mirrors with a strain-compensated InGaAsP-InP MQW active region. Selective lateral oxidation is used for current confinement. Minimum room-temperature threshold current is as low as 0.8 mA, and maximum CW output power is as high as 1 mW at 15/spl deg/C. Pulsed operation is achieved up to 100/spl deg/C. Current spreading losses and device heating are analyzed in detail. Dynamic parameters such as maximum 3-dB parameters such as maximum, 3-dB bandwidth (4.7 GHz), alpha factor (4.0), and linewidth (39 MHz) are also investigated.
TL;DR: In this paper, temperature and intensity dependence of photoluminescence from self-organized InAs quantum dots grown by molecular-beam epitaxy on GaAs(100) was investigated.
Abstract: We report measurements of the temperature and intensity dependence of photoluminescence from self-organized InAs quantum dots grown by molecular-beam epitaxy on GaAs(100). At low temperatures we observed a reduction in the emission linewidth with increasing temperature that is followed by an increase in the linewidth at higher temperatures. We have also found that the photoluminescence spectra from our samples undergo an asymmetric temperature-dependent blueshift with increasing pump intensity. The dependence of the photoluminescence spectra on the temperature and degree of excitation are explained in terms of a competition between a saturable confined-electron to confined-hole transition and an excited-state transition involving the ground confined-electron state and the two-dimensional hole continuum associated with the wetting layer. At high excitation levels the photoluminescence spectra appear to be dominated by the wetting layer transition.
TL;DR: In this article, a discriminator-aided optical phase-locked loop (OPLL) with significantly enhanced frequency acquisition capability is presented, whose pull-in range is measured to be 300 MHz and can be easily extended further.
Abstract: A discriminator-aided optical phase-locked loop (OPLL) with significantly enhanced frequency acquisition capability is presented. Its pull-in range is measured to be 300 MHz and can be easily extended further. Two grating-tuned external-cavity semiconductor lasers (ECSLs) were realized with more than 30-dB side-mode suppression ratio. These two lasers were allowed to beat on a fast detector and were offset phase locked. The generated microwave signal was found to be a replica of the reference RF signal close to the carrier, The noise level was measured to be -70 dBc/Hz close to the carrier and less than -100 dBc/Hz at 4 MHz away and beyond from the carrier. The total phase variance is 0.11 rad/sup 2/ over a 500-MHz bandwidth. The linewidth full width at half maximum (FWHM) of the locked signal was directly measured to be of order 1 mHz.
TL;DR: In this article, the spectrum of the fluorescent radiation of a single trapped 24 Mg + -ion at low excitation intensity was investigated by heterodyning it with a sideband of the single mode laser radiation used to excite the ion, resulting in a linewidth of 6 Hz.
TL;DR: In this article, Singlemode UV-induced distributed feedback (DFB) fiber lasers with a linewidth of < 15 kHz and a sidemode suppression better than 61 dB are presented.
Abstract: Singlemode UV-induced distributed feedback (DFB) fibre lasers with a linewidth of < 15 kHz and a sidemode suppression better than 61 dB are presented. The stability of the lasers is verified by a 10 Gbit/s transmission experiment. Five DFB fibre lasers are cascaded and pumped by a single semiconductor laser, thereby forming a multiwavelength source for WDM systems.
Patent•
08 Sep 1997TL;DR: In this paper, an electronic sweep waveform is used to frequency modulate the acoustic signal produced by the acousto-optic modulator, which provides a broader spectral width, on the order of 19 nm.
Abstract: A laser source comprises an optical fiber doped with a homogeneously broadened lasing medium, preferably with Erbium, pumped by a laser pump source and an intracavity acousto-optic modulator. When the acousto-optic modulator is driven by a variable frequency source, the Erbium fluorescence line emitted by the Erbium-doped optical fiber can be electronically tuned. In another embodiment, an electronic sweep waveform is used to frequency modulate the acoustic signal produced by the acousto-optic modulator. Without the low-rate frequency modulation, Erbium in a silica optical fiber is a mostly homogeneously broadened gain medium with a narrow laser linewidth. When measured on a long time scale, low-rate frequency modulation provides a broader spectral width, on the order of 19 nm, which makes such a source an ideal source for certain optical applications such as fiber optic gyroscopes.
TL;DR: In this paper, a cavity ring down (CRD) detection scheme was proposed to measure the rate of polarization rotation of gas-phase molecules in the presence of a pulsed light source.
Abstract: both techniques. The b 1 S g (v852) X 3 Sg (v950) transition of molecular oxygen around 628 nm is used to demonstrate the possibility to selectively measure either the polarization-dependent absorption or the resonant magneto-optical rotation of gas-phase molecules in the appropriate setup. Just as in CRD absorption spectroscopy, where the rate of absorption is measured, in the here presented polarization-dependent CRD ~PDCRD! detection scheme the rate of polarization rotation is measured, which enables the polarization rotation to be quantitatively determined. Apart from studying electro-optic and magneto-optic phenomena on gas-phase species, the PDCRD detection scheme is demonstrated to be applicable to the study of magneto-optical rotation in transparent solid samples as well. © 1997 American Institute of Physics.@S0021-9606~97!00836-2# In 1988 O’Keefe and Deacon demonstrated a new direct absorption spectroscopic technique that can be performed with a pulsed light source and that has a significantly higher sensitivity than obtainable in ‘‘conventional’’ absorption spectroscopy. This so-called cavity ring down ~CRD! technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined in a closed optical cavity with a highQ factor. 1 The advantage over normal absorption spectroscopy results from ~i! the intrinsic insensitivity of the CRD technique to light source intensity fluctuations, and ~ii! the extremely long effective path lengths ~many kilometers! that can be realized in stable optical cavities. Since the technique is based on a pulsed measurement, it can be used in combination with pulsed molecular beams 2‐4 and it can also be used to study dynamical processes via time-resolved absorption measurements. 5 As long as mirrors with a sufficiently high reflectivity, detectors with a sufficiently fast time response, and tunable ~pulsed! light sources are available there is no intrinsic limitation to the spectral region in which CRD can be applied. By now, successful application of CRD spectroscopy has been demonstrated from the uv part of the spectrum 6 to the ir spectral region. 7,8 The application of CRD is most straightforward if it can be assumed that the linewidth of the light source can be neglected relative to the width of the molecular absorption. It has been shown, however, that if this assumption is no longer valid, one can still extract the correct absorption coefficient from the measured transients, provided the spectral intensity distribution of the light source is known. 6,9 As a consequence, it has been experimentally demonstrated that one does not necessarily need a narrow-band pulsed laser to perform a CRD experiment. One might just as well use a polychromatic light source and extract the spectral information after spectrally dispersing the light exiting the cavity, either in a monochromator or by using a Fourier transform spectrometer. 8,10
TL;DR: A brief review of the recent emergence of semiconducting π -conjugated polymers as solid-state laser materials is given in this article, where gain narrowing is explained in terms of amplified spontaneous emission (ASE) in planar waveguides, which allows the distance traveled by emitted photons to exceed the short intrinsic gain lengths.
TL;DR: In this paper, the first oscillation of an all solid-state FSF laser was demonstrated, and it turned out experimentally that the oscillation spectrum consists of a continuously chirped comb of frequency components.
Abstract: A laser cavity closed via the first-order diffracted light of an acoustooptic modulator is referred to as a frequency-shifted feedback laser (FSF laser). This laser exhibits outstanding features in its oscillation spectrum. We previously demonstrated the first oscillation of an all solid-state FSF laser, and it turned out experimentally that the oscillation spectrum consists of a continuously chirped comb of frequency components. Furthermore, we have been investigating oscillation dynamics both experimentally and analytically for a better understanding of FSF laser. Here experimental results and analyses on the spectral characteristics of the laser are discussed.
TL;DR: In this article, a transfer-matrix method capable of simulating the effects of nonuniform gratings on the filtering, amplification, and bistability characteristics of distributed feedback (DFB) semiconductor laser amplifiers is presented.
Abstract: We present a transfer-matrix method capable of simulating the effects of nonuniform gratings on the filtering, amplification, and bistability characteristics of distributed feedback (DFB) semiconductor laser amplifiers. The linewidth enhancement factor is incorporated in a way that allows direct gain-tuning of the bistability hysteresis. As an example, we compare a /spl lambda//4 phase-shifted DFB amplifier with and without spatial chirp. For amplifiers driven to yield the same unsaturated peak amplifier gain, positive linear chirp widens the spectral range of low-threshold switching and increases the switching contrast.
TL;DR: In this paper, a pulsed injection-seeded optical parametric oscillator (OPO) has been studied and its suitability for applications requiring dual-wavelength operation has been demonstrated.
TL;DR: In this paper, the authors developed a compact, narrow-linewidth, tunable source of THz radiation for spectroscopy and other high-resolution applications using a DBR diode laser.
Abstract: A compact, narrow-linewidth, tunable source of THz radiation has been developed for spectroscopy and other high-resolution applications. Distributed-Bragg-reflector (DBR) diode lasers at 850 nm are used to pump a low-temperature-grown GaAs photomixer. Resonant optical feedback is employed to stabilize the center frequencies and narrow the linewidths of the DBR lasers. The heterodyne linewidth full-width at half-maximum of two optically locked DBR lasers is 50 kHz on the 20 ms time scale and 2 MHz over 10 s; free-running DBR lasers have linewidths of 40 and 90 MHz on such time scales. This instrument has been used to obtain rotational spectra of acetonitrile (CH3CN) at 313 GHz. Detection limits of 1 × 10^–4 Hz^1/2 (noise/total power) have been achieved, with the noise floor dominated by the detector's noise equivalent power.
TL;DR: In this paper, the authors used an acousto-optic modulator to stabilize a free-running continuous wave (CW) laser diode in the presence of strong reflections from a high finesse Fabry-Perot resonator.
Abstract: By using an acousto-optic modulator, we have stabilized a free-running continuous wave (CW) laser diode in the presence of strong reflections from a high finesse Fabry–Perot resonator. The laser diode linewidth can be stabilized from several MHz, for high resolution spectroscopy of species at low pressures, to several hundred MHz, for lower resolution spectroscopy of species at atmospheric pressures. We demonstrated CW cavity ring-down spectroscopy of water vapor at both 1 atm and 5 Torr. We achieved ring-down repetition rates of 10–50 kHz, and a noise level of 2×10−8 cm−1.
TL;DR: In this article, the three-dimensional localization of a single ion to the Lamb-Dicke limit in a radio-frequency trap has been combined with the technique of heterodyne detection to provide high-resolution spectroscopy of the fluorescent light of the ion.
Abstract: The three-dimensional localization of a single ion to the Lamb–Dicke limit in a radio-frequency trap has been combined with the technique of heterodyne detection to provide high-resolution spectroscopy of the fluorescent light of the ion. A coherent component with a linewidth of 0·7 Hz, corresponding to elastic scattering of the incident laser light, was observed in the heterodyne signal. The method may be extended to observe the narrow sidebands related to the secular motion in the trap, yielding information on the dynamics of the ion. Quantum properties of the fluorescent radiation can be detected by probing higher order field correlations. As an example we investigated the phenomenon of antibunching which appears as intensity anticorrelations of the emitted radiation. A measurement of intensity cross-correlations of the fluorescent light superimposed with a weak local oscillator is expected to permit the observation of squeezing in the resonance fluorescence of a single ion.