Showing papers on "Laser linewidth published in 1987"
TL;DR: The fundamental relationship between radiative lifetime and spectral linewidth of freeexcitons is demonstrated theoretically and experimentally for quasi 2D excitons in GaAs/AlGaAs quantum wells.
Abstract: The fundamental relationship between radiative lifetime and spectral linewidth of free excitons is demonstrated theoretically and experimentally for quasi 2D excitons in GaAs/AlGaAs quantum wells.
820 citations
TL;DR: In this article, the authors present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility.
Abstract: The objective of this paper is to present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility. After introducing the definition of α and discussing its dependence on carrier concentration, photon energy, and temperature, we give a short historical summary on how the concept of α evolved over the past two decades. This is followed by a discussion of α dependence on device structure in gain-guided and subdimensional lasers (quantum wells and quantum wires). The bulk of the paper is devoted to a detailed review of laser properties influenced by α and of associated methods of estimating the value of α. Results of measurements reported to date are collected and the most reliable methods are indicated.
646 citations
TL;DR: In this paper, the center frequency and linewidth of the barium atoms placed near the center of a concentric optical resonator are studied as functions of cavity tuning, and shifts in the transition center frequency, due to radiative level shifts, and changes in linwidth due to enhanced and suppressed spontaneous emission, are observed.
Abstract: The center frequency and linewidth of the $^{1}S_{0}\ensuremath{-}^{1}P_{1}$ resonance line of barium atoms placed near the center of a concentric optical resonator are studied as functions of cavity tuning. Shifts in the transition center frequency, due to radiative level shifts, and changes in linewidth, due to enhanced and suppressed spontaneous emission, are observed. A QED calculation which explicitly includes the resonator mode density gives good agreement with the data.
143 citations
TL;DR: In this article, the effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed.
Abstract: The effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed. The analysis applies to any type of laser cavity formed by a corrugated waveguide limited by partially reflecting facets. It is shown that the sensitivity to optical feedback on a facet is closely related to the power emitted through this facet. Numerical results on wavelength selectivity and on sensitivity to optical feedback are given for conventional DFB lasers having an AR-coated facet and for quarter-wave-shifted (QWS) DFB lasers with AR-coatings on both facets. Both laser types are found to be more sensitive to optical feedback on their AR-coated facet than Fabry-Perot lasers for low kL . On the other hand, QWS-DFB lasers are found to be relatively insensitive to optical feedback for large kL .
112 citations
TL;DR: In this paper, the diamagnetic field shifts for models consisting of a spherical shell of water and a hexagonally packed array of spherical air bubbles in water were constructed and calculated to explain the internal inhomogeneous broadening in lung tissue.
111 citations
TL;DR: In this paper, the mean atomic polarization depends on the relative phases of the squeezed vacuum and the coherent driving field, and the fluorescent spectrum is calculated and shows several modifications over the spectrum for normal resonance fluorescence.
Abstract: Fluorescence from a coherently driven two-level atom that is damped by a squeezed vacuum is studied. We show that the mean atomic polarization depends on the relative phases of the squeezed vacuum and the coherent driving field. The fluorescent spectrum is calculated and shows several modifications over the spectrum for normal resonance fluorescence. In particular, the central peak of the Mollow triplet has a linewidth that depends on the phase of the driving field. For strong squeezing this peak can either be much narrower or much broader than the natural linewidth of the atom.
107 citations
TL;DR: In this article, an InGaAsP double-channel-planar-buried-heterostructure laser diode with a 4 percent reflectivity antireflection-coated facet inside an external cavity consisting of a 060 numerical aperture lens and a 1200 line/mm diffraction grating was used.
Abstract: Bistability has been observed in the tuning characteristic and power versus current relation of a 13 μm grating-tuned external-cavity semiconductor laser Tuning-direction reversal, current variations, and feedback interruption can change the output power and threshold current at a given wavelength These effects are shown theoretically to be due to the coupling of the semiconductor gain and index of refraction From measurements of the semiconductor chip facet reflectivity, solitary laser diode mode spectrum, and tuning curve in the presence of external feedback, the analysis yields values for the external feedback strength, semiconductor modal loss, and linewidth enhancement factor Using an InGaAsP double-channel-planar-buried-heterostructure laser diode with a 4 percent reflectivity antireflection-coated facet inside an external cavity consisting of a 060 numerical aperture lens and a 1200 line/mm diffraction grating, we found 22 percent external feedback, 60 cm-1modal loss, and a linewidth enhancement factor \alpha = -71
75 citations
TL;DR: In this paper, the authors review the recent theories of the homogeneous linewidth of chromophores in glasses, using the Redfield relaxation theory as a starting point, and examine the role of fractons and other models for the width.
73 citations
TL;DR: The recent impetus of the semiconductor industry toward sub-micrometer feature sizes on integrated circuits has generated an immediate need for measurement tools and standards suitable for these features as discussed by the authors.
Abstract: The recent impetus of the semiconductor industry toward submicrometer feature sizes on integrated circuits has generated an immediate need for measurement tools and standards suitable for these features. Optical techniques have the advantages of being nondestructive and of having high throughput, but the disadvantage of using wavelengths comparable to feature size which results in complex scattered fields and image structures that are difficult to interpret. Although submicrometer opticallinewidth measurement is possible for 0.3 /-Lm feature sizes, current instrumentation and linewidth standards, particularly for wafers, wiII have to radicaIly improve May-June 1987
70 citations
TL;DR: Using laser frequency-modulation spectroscopy, statistical fine structure (SFS) is observed in the inhomogeneously broadened optical absorption of pentacene in p-terphenyl at liquid helium temperatures.
Abstract: : Using laser frequency-modulation spectroscopy; we have observed statistical fine structure (SFS) in the inhomogeneously broadened optical absorption of pentacene in p-terphenyl at liquid helium temperatures. SFS is the actual frequency-dependent, time-independent structure of the inhomogeneous line caused by the randomly varying number of centers in each frequency interval. The size of the SFS varies as the square root of the number of centers, and the autocorrelation of the SFS yields and estimate of the homogeneous linewidth without requiring spectral hole-burning or coherent transients. Keywords: Spectroscopy of defects in solids; Molecular spectroscopy; Statistical effects.
62 citations
TL;DR: In this paper, a correction factor for the spontaneous emission rate, which is introduced by the longitudinal field distribution within the laser cavity, was proposed. But this correction factor was not considered for index-guided semiconductor laser diodes.
Abstract: To calculate the linewidth for an index-guided semiconductor laser, one usually neglects a correction factor for the spontaneous emission rate, which is introduced by the longitudinal field distribution within the laser cavity. For FabryPerot lasers with cleaved facets the correction factor is small. However, for DFB lasers this correction factor may become quite significant, yielding a linewidth enhancement for DFB laser diodes.
Patent•
21 Sep 1987
TL;DR: A heterodyne laser spectroscopy system utilizes laser homodyne techniques for the purposes of laser isotope separation, vapor diagnostics, processing of precise laser frequency offsets from a reference frequency, and spectral analysis of a laser beam as discussed by the authors.
Abstract: A heterodyne laser spectroscopy system utilizes laser heterodyne techniques for purposes of laser isotope separation spectroscopy, vapor diagnostics, processing of precise laser frequency offsets from a reference frequency and the like, and provides spectral analysis of a laser beam.
TL;DR: In this article, the performance of a semiconductor laser pumped rubidium (87Rb) atomic clock was evaluated using two kinds of Rb gas cells and their performances were compared.
Abstract: Experiments were carried out to evaluate the performances of a semiconductor laser pumped rubidium (87Rb) atomic clock. Two kinds of Rb gas cells were used and their performances were compared [gas cell A (natural rubidium (87Rb/85Rb = \frac{3}{7} ) and buffer gases) and gas cell B (87Rb and buffer gases)]. The highest microwave frequency stabilities were estimated as 3.4 \times 10^{-12} \tau^{-1/2} and 2.7 \times 10^{-12} \tau^{-1/2} at the optimal gas cell temperatures of 60°C and 48°C for the gas cells A and B , respectively (τ: integration time). The light shift, i.e., microwave frequency shift induced by laser light, was measured as -0.50 Hz/MHz and -0.11 Hz/MHz for the gas cells A and B at their optimal operating conditions given above. As an improved experiment by utilizing high temporal coherence of the laser, a novel double resonance spectral line shape with a drastically narrower linewidth was demonstrated. A technique, similar to FM laser spectroscopy, was employed for this purpose by utilizing laser FM sidebands which are induced by microwave frequency modulation and nonlinear susceptibility of three-level87Rb atoms. The minimum linewidth obtained was 20 Hz, which can be used as a sensitive frequency discriminator for an improved87Rb atomic clock.
TL;DR: In this paper, a collection of two-level atoms within a high-finesse cavity was used to generate squeezed states of light, where the weak-field coupling of atoms to the cavity mode produces a splitting in the normal mode structure of the atom-field system that is large compared with the atomic linewidth.
Abstract: Experiments to generate squeezed states of light are described for a collection of two-level atoms within a high-finesse cavity. The investigation is conducted in a regime for which the weak-field coupling of atoms to the cavity mode produces a splitting in the normal mode structure of the atom-field system that is large compared with the atomic linewidth. Reductions in photocurrent noise of 30% (-1.55 dB) below the noise level set by the vacuum state of the field are observed in a balanced homodyne detector. A degree of squeezing of approximately 50% is inferred for the field state in the absence of propagation and detection losses. The observed spectrum of squeezing extends over a very broad range of frequencies (~±75 MHz), with the frequency of best squeezing corresponding to an offset from the optical carrier given by the normal mode splitting.
TL;DR: The construction and operation of a 109-nm, photoionization-pumped, single-pass laser in Xe III is described, which is fully saturated and produces an output energy of 20 microJ in a beam with 10-mrad divergence.
Abstract: We describe the construction and operation of a 109-nm, photoionization-pumped, single-pass laser in Xe iii. The laser is pumped by soft x rays emitted from a laser-produced plasma in a traveling-wave geometry. Using a 3.5-J, 300-psec, 1064-nm laser pump pulse, we measure a small-signal gain coefficient of 4.4 cm−1 and a total small-signal gain of exp(40). The laser is fully saturated and produces an output energy of 20 μJ in a beam with 10-mrad divergence.
TL;DR: In this paper, the SBS gain depends on the ratio of the pump coherence length to the characteristic gain length of SBS as well as on the frequency separation between the two pump waves to SBS linewidth.
Abstract: Stimulated Brillouin scattering (SBS), excited by two pump waves in single-mode fibers, is investigated both theoretically and experimentally. Steady-state calculations, supported by experimental results, show that the SBS gain depends on the ratio of the pump coherence length to the characteristic gain length of the SBS as well as on the ratio of the frequency separation between the two pump waves to the SBS linewidth. These dependences are fully analyzed by following the evolution of the pressure wave that is generated by the SBS interaction. The competition between four-wave mixing and SBS is also considered.
TL;DR: In this paper, the authors measured the intensity modulation level and the optical spectrum of the output of a multiple quantum well modulator, and used these data to deduce the electro-optic coefficients.
Abstract: We simultaneously measure the intensity modulation level and the optical spectrum of the output of a multiple quantum well modulator, and use these data to deduce the electro‐optic coefficients. The effect is quadratic, with a measured ‖s33‖=4.6×10−13 cm2/V2 at a wavelength 12 meV below the band gap. This is approximately 800 times the coefficient measured further from the band gap. We are able to achieve a fractional change in the refractive index of 3.7%. Despite the size of this effect, when we operate the device as an intensity modulator, we observe a linewidth enhancement factor of α=1.0, which means the chirp induced in the device’s output will be small.
TL;DR: Hall measurements on GaxIn1−xAsyP1−y epilayers lattice matched into InP at 300 and 77 K yielded electron mobility values that agreed closely with theoretical values calculated by using the one-phon... as discussed by the authors.
Abstract: GaxIn1−xAsyP1−y epilayers closely lattice matched, Δa/a≲5×10−4, have been reproducibly grown over the whole range of composition (y=2.2x, 1>y>0) by chemical beam epitaxy. The relative sticking coefficient (or equivalently the incorporation efficiency into the solid) of arsenic to phosphorus, i.e., SAs/SP was between 1.5 and 3 depending on the material composition. Such values indicate a very efficient incorporation of phosphorous in this process. Very intense efficient luminescence peaks due to excitonic transitions with linewidths full width at half‐maximum as narrow as 3 meV were obtained. Such a linewidth corresponds closely to the intrinsic linewidth due to alloy broadening in GaInAsP alloys. Furthermore, the photoluminescence spectra revealed that the donor‐to‐acceptor pair recombination was nearly absent. Hall measurements on GaxIn1−xAsyP1−y epilayers lattice matched into InP at 300 and 77 K yielded electron mobility values that agreed closely with theoretical values calculated by using the one‐phon...
TL;DR: In this paper, the authors describe the characteristics of the exploding-foil amplifier coupled with various inversion schemes: Ne-like and Ni-like collisional excitation as well as H-like three-body recombination.
Abstract: We describe our optical-laser-pumped x-ray laser program. Our long-term goal is to develop and utilize a fully coherent, gigowatt-power-level sub-44-A laser. To this end we have been studying the characteristics of the exploding-foil amplifier coupled with various inversion schemes: Ne-like and Ni-like collisional excitation as well as H-like three-body recombination. Most of our experimental results to date are for the Ne-like schemes; we have observed ~15 laser transitions in Se, Y, and Mo having wavelengths from 26.3 to 10.6 nm. Output power to at least 1 MW has been observed for the Se J = 2 to 1 lines at 20.6 and 20.9 A along with geometrical divergence patterns for the beam. We have also observed time-dependent beam refraction from these amplifiers and have been able to demonstrate double-pass amplification by using a multilayer mirror operated at normal incidence. Future plans for improving beam coherence and producing lasing at wavelengths shorter than 44 A are discussed.
TL;DR: In this paper, the authors used infrared emission spectroscopy to study the vibrational mode of on-top CO on Pt(111), as a function of coverage and of temperature, in the range from 210 to 400 K.
TL;DR: In this article, a broadband source suitable for fiber-optic gyroscopes with an output power greater than 10 mW at 1060 nm and a linewidth of 17 nm was demonstrated in a singlemode Nd-doped fibre.
Abstract: A broadband source suitable for fibre-optic gyroscopes with an output power greater than 10 mW at 1060 nm and a linewidth of 17 nm (FWHM) has been demonstrated in a singlemode Nd-doped fibre.
TL;DR: In this article, the effect of laser linewidth on the performance of coherent optical fiber transmission systems has been analyzed for two classes of coherent systems: those making a differential phase measurement, and those not using phase information.
Abstract: Recent theoretical analysis of the effect of using lasers with significant linewidths in coherent optical fiber transmission systems has shown how the design of the optical receiver, particularly the IF stage, affects the sensitivity. This paper reviews this theory for two classes of coherent systems-those making a differential phase measurement, and those not using phase information-where the requirements on laser linewidth are not stringent. We discuss the factors that affect the performance of systems with significant laser phase noise. Wherever possible, we compare the theoretical results with published system experiments. We show that our theory fits the experimental data well and indicates why experimental results have fallen short of the theoretical limits.
TL;DR: In this article, the weak probe-field absorption spectrum of a two level atom driven by a coherent pump field in a squeezed vacuum was calculated, where the probe field can show a linewidth smaller than the linear linwidth in normal vacuum.
TL;DR: In this paper, the authors present a solution to the lock-in detection method which is valid for arbitrary values of the modulation frequency, and their solutions agree with the results of the quasistatic theory, in the limit of small modulation frequency compared to the resonance linewidth.
Abstract: We present a solution to the lock‐in detection method which is valid for arbitrary values of the modulation frequency. Our solutions agree with the results of the quasistatic theory, in the limit of small modulation frequency compared to the resonance linewidth.
TL;DR: In this paper, the rotational constants of the upper and lower vibrational states of the Ne⋅OCS complex were determined using a diode laser for the vibrational transition near 2062 cm−1 correlating with the monomer ν3 mode.
Abstract: Infrared absorption spectra for molecular beams of Ne⋅OCS have been observed with a diode laser for the vibrational transition near 2062 cm−1 correlating with the monomer ν3 mode. The linewidths were ∼150 MHz (FWHM), giving rotationally resolved spectra and allowing the upper and lower vibrational state A, B, and C rotational constants to be determined along with the frequency of the band origin. No broadening in excess of that expected from Doppler effects and laser linewidth was observed, setting a lower limit of 10−9 s on the lifetime of the upper state. Rotational transitions for the vibrational ground state were observed by microwave–infrared double resonance experiments. The ∼150 kHz linewidths in these experiments increased the precision of the rotational constants and permitted the quartic centrifugal distortion constants for the ground state to be determined. The effective structure of the Ne⋅OCS complex was calculated from the rotational constant data. The vibrational frequency and structural re...
TL;DR: In this article, the detuning effect on the spectral linewidth in the DFB laser has been investigated and it was shown that the lasing wavelength of DFB was set at the shorter side of the gain peak by 10 nm.
Abstract: The detuning effect on the spectral linewidth in the DFB laser has been investigated. When we set the lasing wavelength of the DFB laser at the shorter side of the gain peak by 10 nm, a reduction in spectral linewidth of 50% was obtained experimentally. This result agreed with the theoretical prediction.
NEC1
TL;DR: In this paper, a 1.5 μm frequency-tunable distributed Bragg reflector (DBR) laser was developed to achieve large frequency modulation (FM) efficiency of 1-3 GHz/mA and flat FM response up to a few hundred MHz.
Abstract: A 1.5 μm frequency-tunable distributed Bragg reflector (DBR) laser was developed. Frequency tuning was performed by injecting current into the DBR region where the refractive index was reduced to result in the Bragg frequency change. Threshold current and external quantum efficiency were 16 mA and 26 percent, respectively. The maximum continuous wavelength tuning range was 1.03 nm ( = 136 GHz). Spectral linewidth was maintained at an almost constant value when the wavelength was tuned. Large frequency modulation (FM) efficiency of 1-3 GHz/mA and flat FM response up to a few hundred MHz were obtained.
TL;DR: In this paper, a coupled phase-shift distributed-feedback structure is proposed to achieve narrow-linewidth laser emission, and the mode properties are analyzed and the narrowest linewidth is calculated taking into account the spatial hole burning effect.
Abstract: A coupled phase-shift distributed-feedback structure is proposed to achieve narrow-linewidth laser emission. Its mode properties are analysed and the narrowest linewidth is calculated taking into account the spatial hole burning effect. It is found that, by coupling two DFB laser units, the linewidth can be made as narrow as 0.1 MHz, which is an order of magnitude improvement over the value for the conventional distributed-feedback laser structure.
TL;DR: In this article, an electro-optically tunable, single-frequency extended cavity laser with a linewidth of less than 60 kHz was reported, which consists of a 1.5μm InGaAsP gain medium and a narrow-band Ti:LiNbO3 wavelength filter (Δλ≊12 A).
Abstract: We report an electro‐optically tunable, single‐frequency extended cavity laser with a linewidth of less than 60 kHz. The laser consists of a 1.5‐μm InGaAsP gain medium and an electro‐optically tunable, narrow‐band Ti:LiNbO3 wavelength filter (Δλ≊12 A). Electro‐optic tuning over at least 70 A and single‐frequency operation with output power of more than 1 mW have been demonstrated. The laser linewidth was measured by beating the laser against a 1.523‐μm HeNe laser.
TL;DR: Direct writing onto Si has been demonstrated by electron beam induced surface reaction using a XeF2 source and an enormously high etching yield of about 100 Si atoms per electron has been observed for electron stimulated etching using the Xe F2 source.
Abstract: Direct writing onto Si has been demonstrated by electron beam induced surface reaction using a XeF2 source. The electron beam stimulated etched depth for Si(100) is proportional to the electron dose. Etch depth by electron beam stimulated etching is 500 nm at 10 kV accelerating voltage, 4×10−3 C/cm2 dose, and 5 mTorr XeF2 gas pressure. An enormously high etching yield of about 100 Si atoms per electron has been observed for electron stimulated etching using the XeF2 source. A 0.5‐μm linewidth pattern has been fabricated at a 4×10−3 C/cm2 dose.