Showing papers on "Laser linewidth published in 1991"

Analysis of semiconductor microcavity lasers using rate equations

Abstract: The rate equations for a microcavity semiconductor laser are solved and the steady-state behavior of the laser and some of its dynamic characteristics are investigated. It is shown that by manipulating the mode density and the spontaneous decay rates of the cavity modes, the threshold gain can be decreased and the modulation speed can be improved. However, in order to fully exploit the possibilities which the modification of the spontaneous decay opens up, the active material volume in the cavity must be smaller than a certain value. Threshold current using different definitions, population inversion factor, L-I curves, linewidth, and modulation response are discussed. >

External-cavity diode laser using a grazing-incidence diffraction grating

Abstract: An external cavity has been developed for use with commercial diode lasers. It uses a diffraction grating at grazing incidence for wavelength selection and output coupling. This configuration allows a GaAlAs diode laser to be tuned conveniently anywhere in a range greater than 20 nm. Also, the linewidth is reduced by a factor of more than 1000 from 40 MHz to less than 10 kHz. The new laser system should be useful for high-resolution spectroscopy, laser cooling of atoms, time standards, and coherent optical communications.

Narrow-linewidth stimulated Brillouin fiber laser and applications

Abstract: A stimulated Brillouin fiber ring laser with a spectral width of 2 kHz and an intrinsic linewidth of less than 30 Hz has been demonstrated. Applications of such a laser include laser linewidth narrowing, microwave frequency generation, high-rate amplitude modulation, and optical inertial rotation sensing.

Detection and spectroscopy of single pentacene molecules in a p‐terphenyl crystal by means of fluorescence excitation

Abstract: Recent advances in fluorescence excitation spectroscopy with high efficiency have produced greatly improved optical spectra for the first electronic transition of individual single molecules of pentacene in p‐terphenyl crystals at low temperatures (1.5 to 10 K). Two classes of single molecule behavior are observed: class I molecules have time‐independent resonance frequencies, and class II molecules show a diffusive motion among several resonant frequencies with time which we term ‘‘spectral diffusion’’ by analogy with a similar effect which is common in amorphous materials. The temperature dependence of the linewidth and the power dependence of the fluorescence emission rate and of the linewidth are reported and analyzed. Various forms of the surprising class II behavior are described, including jumping among several discrete frequencies, creeping toward the center of the inhomogeneous line in many small steps, and a wandering among many possible resonance frequencies. The occurrence of class II behavior is restricted to the wings of the inhomogeneous line suggesting that the effect is correlated with some form of local disorder. The spectral diffusion rate increases with increasing temperature, suggesting that the effect may be due to phonon‐assisted transitions of local degrees of freedom around the pentacene defect whose source remains to be identified conclusively.

High-performance 1.5 mu m wavelength InGaAs-InGaAsP strained quantum well lasers and amplifiers

Abstract: Improved performance of 1.5- mu m wavelength lasers and laser amplifiers using strained In/sub x/Ga/sub 1-x/As-InGaAsP quantum well devices is reported. The device structures fabricated to study the effects of strained quantum wells on their performance are described. These devices showed TM mode gain, demonstrating the strain-induced heavy-hole-light hole reversal in the valence band. Lasers using these tensile strained quantum wells show higher and narrower gain spectra and laser amplifiers have a higher differential gain compared to compressively strained quantum well devices. Consequently, the tensile strained quantum well lasers show the smallest linewidth enhancement factor alpha =1.5 (compression alpha =2.5) and the lowest K-factor of 0.22 ns (compression K=0.58 ns), resulting in an estimated intrinsic 3 dB modulation bandwidth of 40 GHz (compression 15 GHz). >

1/f frequency noise effects on self-heterodyne linewidth measurements

Abstract: The effects of a 1/f frequency noise on self-heterodyne detection are described, and the results are applied to the problem of laser diode linewidth measurement. The self-heterodyne autocorrelation function and power spectrum are evaluated for both the white and the 1/f components of the frequency noise. From numerical analysis, the power spectrum resulting from the 1/f frequency noise is shown to be approximately Gaussian, and an empirical expression is given for its linewidth. These results are applied to the problem of self-heterodyne linewidth measurements for coherent optical communications, and the amount of broadening due to 1/f frequency noise is predicted. >

Near‐unity quantum efficiency of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a doubly periodic grating coupler

Abstract: Quantum well infrared detectors based on a waveguide with a doubly periodic grating coupler are shown to provide quantum efficiencies of nearly unity with respect to unpolarized polarization. This is a factor of six larger than for a conventional 45° polished edge detector with the same quantum well characteristics. As a further advantage the detector response becomes nearly insensitive to the polarization direction of the incident radiation. Detectors have been fabricated and tested. Measurements lead to a maximum quantum efficiency of 92% with respect to unpolarized radiation, with a response linewidth =0.8 μm, thus confirming theory.

Standing-wave monomode erbium fiber laser

Abstract: An integrated standing-wave, single frequency, erbium fiber laser having a laser linewidth of less than 47 kHz is reported. The monolithic fiber laser incorporated two highly reflective intracore Bragg reflectors which provide both cavity feedback and adequate longitudinal mode discrimination. The narrow linewidth single-mode operation and monolithic construction may make this a valuable communications/sensor source. >

Coherent propagation and quantum beats of quadrupole polaritons in Cu2O.

Abstract: Coherent propagation of quadrupole polaritons in ${\mathrm{Cu}}_{2}$O is demonstrated by time-resolved spectroscopy. This manifests itself in a strong distortion of the temporal shape of a picosecond optical pulse which is in resonance with the 1S exciton polariton. Oscillations with time-dependent period in the transmitted light intensity are quantitatively explained as resulting from quantum beats between the two branches of the exciton polariton. The analysis yields the homogeneous linewidth and oscillator strength.

Theory of linewidth for multielectrode laser diodes with spatially distributed noise sources

Abstract: A general theory of linewidth for single-frequency semiconductor lasers is presented. The effects of spatially distributed noise sources together with spatially varying carrier and photon densities and injection current are analyzed in a rigorous manner by solution of the scalar wave equation. A new rate equation for the electric field is derived, in which the longitudinal effects are represented in the form of the weight functions C/sub N/(z) and C/sub S/(z). These functions express the sensitivity of the (output) field to local changes in carrier and photon density at the position z. For Fabry-Perot laser's the z dependence of the C factors is shown to be negligible, in agreement with the fact that spatial hole burning is not considered to be important for Fabry-Perot lasers. For distributed-feedback (DFB) lasers, however, the z dependence is shown to be very significant. >

Self-starting passive mode locking

Abstract: We investigate the evolution of continuous-wave laser oscillation from free-running to mode-locked operation assuming a nonlinear device with an intensity-dependent transmittivity or reflectivity to be the mode-locking element. An intensity threshold for self-starting passive mode locking is predicted and related to the linewidth of the first beat note of the power spectrum of the free-running laser output. Experimental results confirm the predictions of the theory.

Coherent processes at surfaces: Free-induction decay and photon echo of the Si-H stretching vibration for H/Si(111).

Abstract: Using short infrared pulses and sum-frequency up-conversion, the dephasing of the transient polarization of the Si-H adsorbate-substrate vibration is followed in real time. At 120 K, dephasing due to homogeneous linewidth or inhomogeneous broadening are separated.

Coherence, amplification, and quantum effects in semiconductor lasers

Abstract: Line Broadening of Semiconductor Lasers (C. Henry). Modulation and Noise Spectra of Complicated Laser Structures (O. Nilsson, et al.). Frequency Tunability, Frequency Modulation, and Spectral Linewidth of Complicated Structure Lasers (Y. Yoshikuni). Spectroscopy by Semiconductor Lasers (M. Ohtsu & K. Nakagawa). Coherent Detection Using Semiconductor Lasers: System Design Concepts and Experiments (T. Hodgkinson). Traveling--Wave Semiconductor Laser Amplifiers (T. Saitoh & T. Mukai). Semiconductor Laser Amplifiers in High--Bit--Rate and Wavelength--Division--Multiplexed Optical Communication Systems (R. Jopson & T. Darcie). Injection--Locked Semiconductor Laser Amplifiers (S. Kobayashi). Photon Statistics and Mode Partition Noise of Semiconductor Lasers (P. Liu). Squeezed--State Generation by Semiconductor Lasers (Y. Yamamoto, et al.). Generation of Photon--Number--Squeezed Light by Semiconductor Incoherent Light Sources (M. Teich, et al.). Controlled Spontaneous Emission in Microcavity Semiconductor Lasers (Y. Yamamoto, et al.). Index.

Injection locking in distributed feedback semiconductor lasers

Abstract: Injection locking properties of distributed feedback semiconductor lasers are studied systematically. Due to the high side mode suppression, these devices show different locking properties when compared to lasers with Fabry-Perot structures. The main result is the identification of four regimes for different injection levels. In particular, a symmetrical locking band at low optical injection level is confirmed. The presence of this symmetrical band can be exploited in some applications. As examples, the measurement of the linewidth enhancement factor and the phase-shift-keying modulation capability are reported. >

Narrow line semiconductor laser using fibre grating

Abstract: A narrow linewidth, low chirp, wavelength selectable, packaged alternative to current DFB structures has been developed which employs a fibre reflection grating incorporated in the fibre pigtail. The wavelength of the packaged device can be determined by the appropriate choice of fibre grating coupled to the antireflection coated facet of a 1.55μm BH laser. Linewidths of less than 50 kHz, sidemode suppression of more than 30 dB and chirp when modulated at 1.2 Gbit/s of <0.5 MHz have been demonstrated.

Ferromagnetic resonance linewidth of Fe ultrathin films grown on a bcc Cu substrate

Abstract: The ferromagnetic resonance (FMR) linewidth ΔH is a parameter used to characterize ultrathin film quality. The frequency‐independent part, ΔH(0), reflects the contribution of magnetic inhomogeneities. The linear part is caused by the intrinsic Gilbert damping mechanism. Recently we have found that the lattice reconstructions of substrate templates strongly affects the FMR linewidth. bcc Fe(001) films (∼10 ML) were grown on unreconstructed fcc Ag(001), bcc Cu(001), and on surface reconstructed bcc Cu(001) templates. Fe layers grown on unreconstructed Cu templates exhibited an isotropic FMR linewidth. Fe layers grown on reconstructed Cu templates, on the contrary, showed an anisotropic behavior in both the zero‐frequency FMR linewidth and the intrinsic damping parameter. Other magnetic parameters such as uniaxial and 4‐fold anisotropies are also discussed.

Ultralong optical dephasing time in Eu(3+):Y(2)SiO(5).

Abstract: We report what is to our knowledge the first measurement of linear and nonlinear spectroscopic properties for the 7F0− 5D0 transition of Eu3+:Y2SiO5. Two clearly resolved lines at 579.879 and 580.049 nm, stemming from different sites, show dissimilar photoluminescence and hole spectra. In addition, these two sites have different inhomogeneous and homogeneous linewidths, which suggests that the local-field effect is smaller for one site. Specifically, the less affected site exhibits the longest dephasing time (822 μs) of any solid, which corresponds to a homogeneous linewidth of 387 Hz, and this linewidth is found to persist for hours without apparent spectral diffusion.

Electrically tunable and polarization insensitive Fabry–Perot étalon with a liquid‐crystal film

Abstract: A polarization insensitive, electrically tunable Fabry–Perot structure is demonstrated. The polarization insensitivity is realized by using a twisted structure of a nematic liquid crystal such that the molecules at one surface are orthogonal to those at the other surface. In the high‐field regime, this configuration can be thought of as a structure composed of two orthogonal, birefringent slabs with the electrically controllable thickness. At low voltages the device is polarization sensitive but becomes polarization insensitive at relatively higher voltages. In the polarization insensitive region, the linewidth of the transmission peak is of the order of 0.5 nm and the tuning range is about 15 nm.

Semiconductor laser stabilization by external optical feedback

Abstract: A report is presented on a general theory describing the effect of external optical feedback on the steady-state noise characteristics of single-mode semiconductor lasers. The theory is valid for arbitrarily strong feedback and arbitrary optical feedback configuration and spectrum. A generalized Langevin rate equation is derived. The equation is, in general, infinite order in d/dt constituting an infinite-order correction to the low-frequency weak-feedback analysis. The general formalism includes relaxation oscillations and permits analysis of the effect of feedback on the laser linewidth, frequency noise, relative intensity noise, and the relaxation oscillation sidebands in the field spectrum. The theory is applied to two important feedback configurations: the laser coupled to a single mirror and the laser coupled to a high-Q cavity. >

Sub‐100 nm lines produced by direct laser ablation in polyimide

Abstract: Periodic line structures with a period of 167 nm and linewidths varying from 35 to 100 nm have been produced on polyimide by direct ablation with a KrF laser using an interferometric technique. Since ablation is a nonlinear process, the resolution can exceed that expected from the wavelength and numerical aperture of the system and the linewidth can be controlled by varying the laser fluence. This externally generated period of 167 nm prevents the spontaneous growth of periodic surface structures due to radiation remnants.

Simple CD measurement of periodic structures on photomasks

Abstract: For critical dimension (CD) metrology of photomasks, a laser scatterometer linewidth measurement tool provides noncontact rapid, and nondestructive measurement of linewidth. Calculation of the linewidth is based on a rigorous theoretical model, thus eliminating the need for calibrations. A chrome-on-glass diffraction grating is illuminated with a laser. A photodetector mounted behind the photomask measures the scattered power in each diffracted order. This provides data for the rigorous theoretical model which provides a relationship between the linewidth of the photomask grating and the fraction of total power diffracted into the transmitted zero-order. This scatterometer linewidth measurement technique provides a simple, rapid, nondestructive, and noncontact method of linewidth determination which takes into account the effect of the glass substrate on which the grating is placed. This technique is insensitive to variations in angle of incidence, spot size, position of the spot on the grating, polarization and wavelength.

Corrugation-pitch modulated MQW-DFB lasers with narrow spectral linewidth

Abstract: Narrow spectral linewidth lasers are developed for optical coherent transmission systems. To obtain a narrow spectral linewidth, a CPM (corrugation-pitch modulated) structure is introduced into 1200- mu m-long MQW-DFB (multi-quantum well distributed feedback) lasers. The CPM structure effectively suppresses the axial spatial hole burning effect and stabilized single-mode spectrum at high output powers. A spectral linewidth of 170 kHz was achieved at an output power of 25 mW. Details of corrugation fabrication method that makes the CPM structure possible are described. >

Raman Spectroscopy of Cesium Atoms in a Laser Trap

Abstract: Cold cesium atoms in a magneto-optical trap are probed by an additional weak laser beam. Resonances having a subnatural linewidth are observed on the probe beam absorption when the probe frequency is scanned about the trapping beam frequency. These resonances are interpreted in terms of stimulated Raman processes. They provide information on the internal as well as external states of the atoms in the trap.

Measurement of carrier lifetime and linewidth enhancement factor for 1.5- mu m ridge-waveguide laser amplifier

Abstract: Semiconductor optical amplifiers are used for investigation of the effective carrier lifetime and the linewidth enhancement factor. Contrary to semiconductor lasers, semiconductor optical amplifiers allow measurement at high levels of injected carrier density. The carrier lifetime and the linewidth enhancement factor are measured with a simple dynamic self-heterodyne method. Carrier lifetimes of 750 ps at the threshold current for the SOA without antireflection coating and 200 ps at high injection have been found. The linewidth enhancement factor is measured to be between 4 and 17 which fits with a simple empirical expression. >

Narrowband lidar technique for sodium temperature and Doppler wind observations of the upper atmosphere

Abstract: A new two-frequency lidar for measuring mesospheric Na temperature profiles is described that uses a stabilized CW single-mode dye laser oscillator (rms frequency jitter less than 1 MHz) followed by a pulsed dye power amplifier (140 MHz FWHM linewidth) that is pumped by an injection-locked Nd:YAG laser. The laser oscillator is tuned to the two operating freqencies by observing the Doppler-free structure of the Na D2 fluorescence spectrum in a vapor cell. The lidar technique and initial observations of the temperature profile between 82 and 102 km at Ft. Collins, CO are described. Absolute temperature accuracies at the Na layer peak of better than + or - 3 K with a vertical resolution of 1 km and an integration period of approximately 5 min were achieved in this initial experiment. Finally, a multiple frequency technique for the simultaneous measurement of both temperature and Doppler wind profiles is discussed.

1.55 mu m gain-coupled quantum-well distributed feedback lasers with high single-mode yield and narrow linewidth

Abstract: The fabrication and characteristics of gain-coupled 1.55- mu m GaInAlAs quantum-well metal-clad ridge-waveguide distributed-feedback lasers are discussed. The gain-coupling mechanism was provided by a thin ternary loss grating layer with an estimated gain-coupling strength of about 30/cm. For as-cleaved devices, the single-mode yield was as high as 70 and 95% for 600- and 800- mu m-long devices, respectively. Typical threshold currents were 40 and 55 mA, respectively. Both the high single-mode yield and the pronounced asymmetric spectra were calculated theoretically and give a strong indication that a significant amount of gain coupling was realized in the laser structure. For a 600- mu m-long device, a continuous-wave (CW) output power of 10 mW and a minimum linewidth of 1.6 MHz were measured. >

Dependence of polarization, gain, linewidth enhancement factor, and K factor on the sign of the strain of InGaAs/InP strained‐layer multiquantum well lasers

Abstract: The sign of the strain in a multiquantum well (MQW) active layer of an InGaAs/InP laser determines whether lasing occurs from the electron–heavy hole transition or from the electron‐light hole transition. Lasing from the electron‐light hole transition is reported to provide a much better performance than predicted by theory. It is concluded that this gives the best device performance, providing a higher differential gain, a lower threshold current, a record low linewidth enhancement factor of 1.5, and a K factor of 0.22 ns, potentially allowing a 3 dB modulation bandwidth of 40 GHz.

Acoustically tuned erbium-doped fiber ring laser.

Abstract: We report what is to our knowledge the first narrow-linewidth, continuously tunable laser that uses an acousto-optic filter to achieve a broad tuning range. The unidirectional ring-laser configuration incorporates an erbium-doped fiber amplifier as the gain medium and an integrated, frequency-shift-compensated acousto-optic filter as the tuning element. Using a 980-nm optical pump with 60 mW of launched power, we obtained nearly 2 mW of laser output with 10% output coupling. A tuning range of 40 nm was achieved, centered about 1545 nm. Single-longitudinal-mode operation with a 10-kHz linewidth was demonstrated, although the laser wavelength hopped between nearby longitudinal modes because of path-length fluctuations. Wavelength switching at rates up to 100 kHz was examined.

Radiation-matter oscillations and spectral line narrowing in field-correlated four-wave mixing. I. Theory.

Abstract: New radiation-matter phenomena in four-wave mixing spectroscopies, given a theoretical basis in the preceding paper [Dugan and Albrecht, Phys. Rev. A 43, 3877 (1991)], are examined experimentally here. A new class of Rabi detuning oscillations is recorded in interferometric coherent Stokes Raman scattering (CSRS). Two identical nanosecond incoherent light fields are mutually delayed, while simultaneously mixing in a nonlinear medium with a narrow-band field of a different color. Spectral filtering of the CSRS signal is essential. From such signals the frequencies and the dephasing rate constants can be a measure of the Raman-active vibrations in both the electronic ground state and the electronic excited state of the scattering chromophore. In principle, analogous probing of vibronic transitions is possible. Detuning oscillations for multimode systems are presented. It is shown how they are transformed into quantum beats, exactly those seen with femtosecond CSRS, when the narrow-band field is made broad and/or the detection is ``white.'' Finally, an example of the sub-Raman linewidth spectral feature, predicted in the preceding paper, is presented. It determines a Raman frequency, but does not carry its linewidth.

Temperature-dependent plasmon frequency and linewidth in a semimetal.

Abstract: High-resolution electron-energy-loss spectroscopy of the surface of graphite reveals a discrete loss feature attributed to the excitation of a π-band plasmon polarized with E∥c. The frequency of the plasmon is found to be strongly temperature dependent. This arises from the contribution of thermally generated carriers to the plasma frequency, as confirmed by explicit calculations using the graphite band structure