Showing papers on "Laser linewidth published in 1989"
TL;DR: The microchip lasers demonstrate ways to reduce greatly the cost and complexity offabricating small lasers and electro-optic devices.
Abstract: Optically pumped, single-frequency, Nd-doped, solid-state lasers have been constructed using flat-flat cavities, which were diced from large dielectrically coated wafers of various crystals. For example, a Nd:YAG laser with a cavity length of 730 microm has operated at room temperature in a single longitudinal mode from a threshold of less than 1 mW to greater than 40 times the threshold. Theslope efficiency was greater than 30%. Heterodyne measurements showed an instrument-limited linewidth of 5 kHz. The microchip lasers demonstrate ways to reduce greatly the cost and complexity offabricating small lasers and electro-optic devices.
358 citations
TL;DR: Observations of the spectral response of the composite system to weak external modulation reveal a coupling-induced normal-mode splitting in the radiative processes for a collection of N two-state atoms strongly coupled to the field of a high-finesse optical cavity.
Abstract: An investigation of the radiative processes for a collection of N two-state atoms strongly coupled to the field of a high-finesse optical cavity is presented. Observations of the spectral response of the composite system to weak external modulation reveal a coupling-induced normal-mode splitting. Linewidth averaging leads to linewidths below the free-space atomic width.
335 citations
TL;DR: In this paper, a detailed theoretical analysis of the static and dynamic frequency noise power spectrum of the coupled cavity laser field is presented, and a detailed analysis of two optically self-locked diode lasers shows a nonLorentzian RF power spectrum.
Abstract: Recent progress on frequency stabilization of a diode laser emitting near 850 nm is discussed. A confocal Fabry-Perot cavity is used to feed back the beam from the diode laser and provide resonant optical stabilization of the semiconductor laser. A detailed theoretical analysis of the static and dynamic frequency noise power spectrum of the coupled cavity laser field is presented. Static-frequency noise reduction of 50-60 dB and reduction of the laser linewidth from 20 MHz to less than 4 kHz are obtained. Finally, a detailed analysis of the beat-note spectra of two optically self-locked diode lasers shows a nonLorentzian RF power spectrum. >
229 citations
TL;DR: Ground-state hyperfine splitting was measured with a linewidth of 2 Hz for laser-cooled sodium atoms pushed up on a vertical trajectory by radiation pressure to turn around due to gravity.
Abstract: Laser-cooled sodium atoms pushed up on a vertical trajectory by radiation pressure are observed to turn around due to gravity. The reatively long time the atoms spent freely falling in this ``atomic fountain'' allowed the ground-state hyperfine splitting to be measured with a linewidth of 2 Hz. After a 1000-s integration time, the center of the line was resolved to \ifmmode\pm\else\textpm\fi{}10 mHz. The absolute splitting was measured to be 1 771 626 129(2) Hz.
205 citations
TL;DR: In this paper, the authors proposed a site-selection spectroscopy technique to narrow the spectral line of a solids at low temperature using a narrow-band laser and a high resolution monochromator and/or a Fabry-Perot interferometer.
Abstract: The study of optical relaxation processes in solids at low temperature has progressed tremendously in the last 20 years due to the development of coherent optical techniques. The latter would not have been possible without the advent of narrow-band tunable lasers, on the one hand, and lasers with very short pulses (picoseconds, femtosecoods) on the other hand. Such coherent techniques are necessary because spectral line shapes of solids doped with guest molecules are seldom determined by dynamical interactions but principally by strain or structural disorder. This gives rise to inhomogeneous broadening, rlOh, which in crystalline hosts at low temperature varies between '" 0.1 and 10 cm -I, whereas in glasses it may amount to � 100-500 em-I. One of the techniques to achieve narrowing of spectral lines is site selection spectroscopy (1-3). A sub-ensemble of molecules within thc inhomogeneously broadened absorption band is selectively excited by mcans of a narrow-band laser, and the fluorescence or phosphoresccnce signal is detected with a high-resolution monochromator and/or a Fabry Perot interferometer. Fluorescence line-narrowing ( I) is a special case of this technique (for a review see 3). The intrinsic or homogeneous spectral linewidth, r hom, which yields information on the relaxation processes of the excited state, is given by the effective optical dephasing time, T2:
201 citations
TL;DR: In this paper, the advantages and drawbacks of diversity receivers, and recent experimental and theoretical research results are discussed, as well as a survey of phase-and polarization-diversity coherent optical techniques.
Abstract: Progress in phase- and polarization-diversity coherent optical techniques has led to impressive receivers able to tolerate wide laser linewidth and large polarization fluctuations. The advantages and the drawbacks of diversity receivers, and recent experimental and theoretical research results are discussed. >
199 citations
TL;DR: The phase relaxation of two-dimensional (2D) heavy-hole excitons in a 12-nm GaAs single quantum well subjected to collisions with either free carriers or incoherent heavy- holes is investigated by time-resolved degenerate four-wave mixing.
Abstract: The phase relaxation of two-dimensional (2D) heavy-hole excitons in a 12-nm GaAs single quantum well subjected to collisions with either free carriers or incoherent heavy-hole excitons is investigated by time-resolved degenerate four-wave mixing. The homogeneous linewidth corresponding to the phase coherence time reveals a collisional broadening due to exciton-exciton scattering and an 8 times stronger exciton-free carrier scattering. Both scattering processes are enhanced for 2D excitons as compared to 3D excitons.
184 citations
TL;DR: In this paper, a 5-MHz residual linewidth is observed in the high-power limit of 1.3 mu m DFB (distributed feedback) semiconductor lasers.
Abstract: The FM-noise spectrum and the linewidth of 1.3 mu m DFB (distributed feedback) semiconductor lasers measured in the high-power state up to 20 mW are discussed. A 5-MHz residual linewidth is observed in the high-power limit. The FM-noise spectrum consists of white noise and 1/f noise. The spectral density of the white noise is reduced by the increase in the output power, whereas that of the 1/f noise is unchanged, which means that the linewidth residual in the high-power limit is caused by the 1/f noise rather than the white noise. The impact of the 1/f-type FM noise on coherent optical communication systems is also discussed. >
175 citations
TL;DR: The results indicate that the internal strains and fluctuations in CFP are the dominant contributions to linewidth, and the mosaic effect is negligible.
Abstract: The linewidth in the EPR spectra of ${\mathrm{Cr}}^{3+}$ ions in yttrium aluminum garnet single crystals is investigated at room temperature, and an anisotropic line broadening is observed. The characteristics of broadening resulting from the mosaic effect, internal strains, and fluctuations in the crystalline field parameter CFP are analyzed. A reasonable fit to experimental data is obtained using the hybrid model wherein the mosaic effect, internal strains, and fluctuations in CFP were considered, and the results indicate that the internal strains and fluctuations in CFP are the dominant contributions to linewidth, and the mosaic effect is negligible. The effect of the internal strains caused by impurities in the crystal on linewidth is discussed.
170 citations
TL;DR: The spontaneous-emission spectrum and the spectrum of weakly driven fluorescence for a two-level atom coupled to a resonant-cavity mode are calculated and it is shown that squeezing-induced narrowing can be observed using coupled-field and collective-polarization oscillators excited in a cavity containing N two- level atoms.
Abstract: We calculate the spontaneous-emission spectrum and the spectrum of weakly driven fluorescence for a two-level atom coupled to a resonant-cavity mode. For strong atom-cavity coupling the spectra split into two peaks that can have subnatural linewidths. If the cavity linewidth is negligible, the spontaneous-emission spectrum has half the radiative linewidth of the atom; the spectrum of weakly driven fluorescence shows an additional 36% squeezing-induced narrowing. These effects can be observed using coupled-field and collective-polarization oscillators excited in a cavity containing N two-level atoms.
153 citations
TL;DR: In this article, a detailed nonlinear model of the performance of single-frequency laser structures operating both below and above threshold is discussed, taking longitudinal-mode spatial hole burning into account.
Abstract: A detailed nonlinear model of the performance of single-frequency laser structures operating both below and above threshold is discussed. Arbitrary series combinations of uniform pitch grating, linearly-chirped pitch grating and plane guide sections can be analyzed-taking longitudinal-mode spatial hole burning into account. The material properties of each section of a device structure can be specified. The output power from each end of the laser and the emission wavelength, and the longitudinal intensity, carrier density, and relative permittivity profiles are predicted as a function of drive current above threshold for each lasing mode. The linewidth is also estimated while allowing for the nonuniform longitudinal distribution of spontaneous emission into the mode in a physical manner. The model was used to provide the data with which to trade off the numerous interacting performance parameters of a lambda /4 phase-shifted DFB (distributed-feedback) laser. The design options are then summarized. >
TL;DR: In this article, offset phase-locking of two Nd:YAG nonplanar ring laser by electronic feedback was reported, and the difference frequency was continuously tunable in three bands from 6 to 34 GHz and exhibits a hold-in range and linewidth of 82 MHz and < 1 mHz, respectively.
Abstract: We report offset phase-locking of two Nd:YAG nonplanar ring lasers by electronic feedback. The difference frequency is continuously tunable in three bands from 6 to 34 GHz and exhibits a hold-in range and linewidth of 82 MHz and <1 mHz, respectively.
TL;DR: In this paper, a two-crystal, walkoff-compensated optical parametric oscillator design using β-BaB2O4 was presented, which significantly improved the performance of the device.
Abstract: We report a novel, two‐crystal, walkoff‐compensated optical parametric oscillator design using β‐BaB2O4, which significantly improves the performance of the device. The oscillator is pumped at 354.7 nm and is tunable throughout 0.42–2.3 μm with overall conversion efficiencies as high as 32%. We also report on demonstration of linewidth narrowing in the same β‐BaB2O4 oscillator, obtaining linewidths as narrow as 0.3 A.
TL;DR: In this article, the linewidth enhancement factor alpha of a strained In/sub 0.20/As/InP quantum-well (QW) laser with 1.9% biaxial compression is analyzed by the k-p perturbation method using the effective mass approximation.
Abstract: The linewidth enhancement factor alpha of strained quantum-well lasers is analyzed by the k-p perturbation method using the effective-mass approximation. It is found that the alpha factor in a strained In/sub 0.80/Ga/sub 0.20/As/InP quantum-well (QW) laser with 1.9% biaxial compression is less than 1.5. For a strained QW laser with p-type modulation doping (MD) of 5*10/sup 18/ cm/sup -3/, the alpha factor is as small as 0.8. It is also demonstrated that the spectral linewidth and wavelength chirping in the strained MD QW laser are significantly less than those in conventional bulk and QW lasers. >
TL;DR: In this paper, a high-resolution spectrometer incorporating a narrow linewidth tunable dye laser and two long pass absorption cells has been used to provide measurements of water vapor absorption line parameters in the 720-nm wavelength region.
TL;DR: In this article, the power spectrum of the photocurrent resulting from two uncorrelated optical beams mixing on a photodetector is derived and a general rigorous theory of optical heterodyne and homodyne measurements is presented.
Abstract: A general rigorous theory of optical heterodyne and homodyne measurements is presented. The power spectrum of the photocurrent resulting from two uncorrelated optical beams mixing on a photodetector is derived. In particular, a rigorous analysis is presented for the delayed self-homodyne method which is used to characterize laser source linewidth by a Mach-Zehnder interferometer with a delay exceeding the source coherence length. Existing treatments are generalized to address non-Lorentzian laser sources of arbitrary lineshape. The analysis is further generalized to cover the case of modulated nonstationary sources. An example of the application of this theory is given. It is shown how the theory may be used to interpret an experimental result obtained using the gated delayed self-homodyne technique for characterizing the frequency chirp of laser sources under modulation. >
TL;DR: In this article, a 1.5μm-range λ/4-shifted DFB laser with a l.2 mm-longcavity and three electrodes has been fabricated.
Abstract: A 1.5μm-range λ/4-shifted DFB laser with a l.2 mm-longcavity and three electrodes has been fabricated. The lasing wavelength can be tuned electrically over a 1.9 nm range, maintaining the linewidth below 900 kHz and a constant output power of 20 mW. The minimum linewidth of 500 kHz is achieved by nonuniform current injection.
TL;DR: In this article, the intensity dependence of the linewidth enhancement factor was shown to become intensity dependent when the intraband relaxation effects responsible for nonlinear gain and index changes are incorporated in the theory of semiconductor lasers.
Abstract: The linewidth enhancement factor is shown to become intensity dependent when the intraband relaxation effects responsible for nonlinear gain and index changes are incorporated in the theory of semiconductor lasers. The intensity dependence of the linewidth enhancement factor influences many laser characteristics such as the frequency chirp, the modulation response, the injection-locking range, and the phase noise. In particular, it leads to a power-independent contribution to the laser linewidth. Furthermore, for semiconductor lasers detuned to operate away from the gain peak, the nonlinear index changes can even lead to a rebroadening of the laser linewidth at high-output powers. >
TL;DR: In this article, a numerical analysis of the stability of external cavity laser diodes with short external cavities is presented, and it is shown that if the external cavity is shorter than about 5 mm (air equivalent), the laser remains stable for any feedback from that cavity without any coherence collapse.
Abstract: Results of a numerical analysis of the stability of external cavity lasers with short external cavities are presented. If the external cavity is shorter than about 5 mm (air equivalent), the laser remains stable for any feedback from that cavity without any coherence collapse. The results can be considered also as guidelines for the design of laser diodes with integrated passive cavities. >
TL;DR: A frequency-stabilized diode-pumped Nd:YAG laser is described that is actively frequency stabilized relative to a reference Fabry-Perot cavity using the Pound-Drever technique and its ability to reduce the laser frequency noise close to the shotnoise limit.
Abstract: We describe a frequency-stabilized diode-pumped Nd:YAG laser that is actively frequency stabilized relative to a reference Fabry-Perot cavity using the Pound-Drever technique. We describe the servo loop and the measurement of its noise and gain performance and demonstrate its ability to reduce the laser frequency noise close to the shotnoise limit of 12.5 mHz/ radicalHz. This corresponds to a linewidth of approximately 1 mHz, well below the Schawlow-Townes limit of 0.13 Hz that applies for a free-running laser.
TL;DR: In this paper, a stable external cavity GaAlAs laser with fullwidth-at-half-maximum (FWHM) linewidth of less than 3 kHz is discussed.
Abstract: Stable external cavity GaAlAs lasers operated with full-width-at-half-maximum (FWHM) linewidths of less than 3 kHz are discussed. Offset frequency locking has been demonstrated over long periods to within the 10-Hz resolution bandwidth of the experiment. The spectral characteristics of these devices are presented graphically. >
TL;DR: In this article, a study of wavelength tuning characteristics when both phase control and DBR currents are varied is discussed, and the change of threshold current, output power, and linewidth under wavelength tuning is also investigated.
Abstract: A study of wavelength tuning characteristics when both phase control and DBR currents are varied is discussed. The change of threshold current, output power, and linewidth under wavelength tuning is also investigated. These characteristics are in good agreement with the theoretical analysis. Additional large-linewidth broadening under wavelength tuning which cannot be explained was observed. >
TL;DR: In this paper, a wideband, highly sensitive measurement has been achieved for a p-i-n photodiode and a Ge avalanche photodode from DC to 20 GHz using 1.3 mu m distributed-feedback laser diodes.
Abstract: Measurements have been carried out using 1.3- mu m distributed-feedback laser diodes (DFB-LDs). The frequency difference of the LDs is continuously varied with temperature changes of a few degrees and the spectral linewidth of one of the LDs is narrowed by optical feedback using a grating. Wideband, highly sensitive measurement has been achieved for a p-i-n photodiode and a Ge avalanche photodiode from DC to 20 GHz. The result is compared with that of the pulse spectrum analysis (PSA) method. Although the finite pulsewidth in the PSA method causes roll-off in the frequency response, the optical heterodyne method has the advantage for very wideband frequency response measurement. The S/N ratio in the optical heterodyne method can be made as high ( approximately 40 dB) as that of the PSA method by narrowing the spectral linewidth of DFB-LDs. >
TL;DR: In this paper, 100 parallel, modulation-doped GaAs/AlGaAs wires, each about 40 nm wide, have been fabricated and tested at 4.2 and 77 K. The wires were created by ion milling a shallow grating into the doped AlGaAs layer.
Abstract: Devices consisting of 100 parallel, modulation‐doped GaAs/AlGaAs wires, each about 40 nm wide, have been fabricated and tested at 4.2 and 77 K. The wires were created by ion milling a shallow grating into the doped AlGaAs layer. The mask for etching the grating was produced by x‐ray nanolithography, and lift‐off of Ti/Au. The grating period was 200 nm and the linewidth about 85 nm. Backgate bias or illumination was used to modulate the charge density in the wires. Conductance measurements at 4.2 K provide clear evidence of quasi‐one‐dimensional density of states. A corresponding modulation of the electron mobility, above and below values in the two‐dimensional system, was observed.
Patent•
10 Mar 1989TL;DR: A tunable dye laser has been found particularly suited to selective photothermolysis as discussed by the authors, which makes the system suitable for a wider range of applications by modifying the laser to generate a spatially noncoherent beam.
Abstract: A tunable dye laser has been found particularly suited to selective photothermolysis A longer pulse duration which makes the system suitable for a wider range of applications is obtained by modifying the laser to generate a spatially noncoherent beam The optical system at each end of the laser cell, which may include a lens or spherical mirror, refocuses the aperture of the dye cell near to itself so that substantially all light emanating from the dye cell is returned to the dye cell until the light passes through one of the optic systems as a noncoherent laser beam A tunable intracavity element tunes the laser across the gain curve of the dye solution The pulse duration of the laser beam can be selected from a range of durations up to about one millisecond
TL;DR: In this article, the authors show that a laser in which the active region consists of a strained-layer structure should have improved dynamics and noise characteristics, and that the relaxation oscillation frequency is enhanced and the linewidth enhancement factor is reduced by strain.
Abstract: We show that a laser in which the active region consists of a strained-layer structure should have improved dynamics and noise characteristics. We find that the relaxation oscillation frequency is enhanced and the linewidth enhancement factor is reduced by strain.
TL;DR: In this article, an improved model for multi-quantum-well laser operation is presented, which includes the effects of band nonparabolicity, revised band offsets at the heterojunction interface, nonradiative processes in the barrier and waveguide regions, and the energy-dependent spectral linewidth.
Abstract: Existing theoretical models for multi-quantum-well laser operation are not always accurate in evaluating band-filling characteristics. This, as a result of the partial omission of some significant physical processes or simplified modeling, sometimes leads to excessively optimistic prediction of threshold-current reduction in these types of lasers. An improved model which includes the effects of band nonparabolicity, revised band offsets at the heterojunction interface, nonradiative processes in the barrier and waveguide regions, and the energy-dependent spectral linewidth has been developed. It is tested satisfactorily by comparing its numerical prediction to the experimental results on cavity-length dependence of threshold current for lasers with a different number of quantum wells. >
TL;DR: In the present work an external cavity is used to maintain a spectral linewidth of less than 1 MHz in a diode running at 2.5% of its rated power of 30 mW, resulting in a modulation depth enhancement by a factor of 30 over the high-power limit.
Abstract: Feedback phenomena in lasers induce modulation signals that can be used for ranging and velocimetry. The modulation depth of a backscatter-modulated semiconductor laser diode is considerably enhanced by operating the diode near the lasing threshold. In the present work an external cavity is used to maintain a spectral linewidth of less than 1 MHz in a diode running at 2.5% of its rated power of 30 mW, resulting in a modulation depth enhancement by a factor of 30 over the high-power limit. Coherent velocimetry has been performed for targets at a distance of 50 m, or 20 times farther than the previously published operational range for backscatter-modulated laser diodes. Light power of less than 10 pW at the collection aperture produces useful modulation signals.
TL;DR: An approximate steady-state solution of the Q representation for the laser field, which consists of two identical peaks of elliptical type, is found and the phase variance is calculated and, for any given mean photon number, the minimum variance in the phase quadrature is obtained as a function of the initial atomic variables.
Abstract: We develop a nonlinear theory of a two-photon correlated-spontaneous-emission laser (CEL) by using an effective interaction Hamiltonian for a two-level system coupled by a two-photon transition. Assuming that the active atoms are prepared initially in a coherent superposition of two atomic levels involved in the two-photon transition, we derive a master equation for the field-density operator by using our quantum theory for coherently pumped lasers. The steady-state properties of the two-photon CEL are studied by converting the field master equation into a Fokker-Planck equation for the antinormal-ordering Q representation of the field-density operator. Because of the injected atomic coherence, the drift and diffusion coefficients become phase sensitive. This leads to laser phase locking and an extra two-photon CEL gain. The laser field can build up from a vacuum in the no-population-inversion region, in contrast to an ordinary two-photon laser for which triggering is needed. We find an approximate steady-state solution of the Q representation for the laser field, which consists of two identical peaks of elliptical type. We calculate the phase variance and, for any given mean photon number, obtain the minimum variance in the phase quadrature as a function of the initial atomic variables. Squeezing of the quantum noise in the phase quadrature is found and it exhibits the following features: (1) it is possible only when the laser intensity is smaller than a certain value; (2) it becomes most significant for small mean photon number, which is achievable in the no-population-inversion region; and (3) a maximum of 50% squeezing can be asymptotically approached in the small laser intensity limit. As a by-product we also study the ordinary two-photon laser and find, e.g., photon-number variance and laser linewidth.
TL;DR: In this article, continuous-wave lasing was obtained at 2.714μm in a fluorozirconate single-mode fiber when pumping at 476.5, 501.7 or 647.1 nm.
Abstract: Continuous-wave lasing has been obtained at 2.714μm in a fluorozirconate single-mode fibre when pumping at 476.5, 501.7 or 647.1 nm. A threshold pump power of 7mW, an output laser power of 250μW and a linewidth less than 2 nm were measured