Showing papers on "Laser linewidth published in 2001"
TL;DR: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated and self-organized, <0001> oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process.
Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 03 nanometer The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis
8,592 citations
TL;DR: In this article, a detailed review of the performance of quantum cascade (QC) laser can be found, where the inter-subband transition is characterized through ultrafast carrier dynamics and the absence of the linewidth enhancement factor, with both features expected to have significant impact on laser performance.
Abstract: Quantum cascade (`QC') lasers are reviewed. These are semiconductor injection lasers based on intersubband transitions in a multiple-quantum-well (QW) heterostructure, designed by means of band-structure engineering and grown by molecular beam epitaxy. The intersubband nature of the optical transition has several key advantages. First, the emission wavelength is primarily a function of the QW thickness. This characteristic allows choosing well-understood and reliable semiconductors for the generation of light in a wavelength range unrelated to the material's energy bandgap. Second, a cascade process in which multiple - often several tens of - photons are generated per electron becomes feasible, as the electron remains inside the conduction band throughout its traversal of the active region. This cascading process is behind the intrinsic high-power capabilities of the lasers. Finally, intersubband transitions are characterized through an ultrafast carrier dynamics and the absence of the linewidth enhancement factor, with both features being expected to have significant impact on laser performance. The first experimental demonstration by Faist et al in 1994 described a QC-laser emitting at 4.3 µm wavelength at cryogenic temperatures only. Since then, the lasers' performance has greatly improved, including operation spanning the mid- to far-infrared wavelength range from 3.5 to 24 µm, peak power levels in the Watt range and above-room-temperature (RT) pulsed operation for wavelengths from 4.5 to 16 µm. Three distinct designs of the active region, the so-called `vertical' and `diagonal' transition as well as the `superlattice' active regions, respectively, have emerged, and are used either with conventional dielectric or surface-plasmon waveguides. Fabricated as distributed feedback lasers they provide continuously tunable single-mode emission in the mid-infrared wavelength range. This feature together with the high optical peak power and RT operation makes QC-lasers a prime choice for narrow-band light sources in mid-infrared trace gas sensing applications. Finally, a manifestation of the high-speed capabilities can be seen in actively and passively mode-locked QC-lasers, where pulses as short as a few picoseconds with a repetition rate around 10 GHz have been measured.
637 citations
TL;DR: In this paper, the self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process, and they formed natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers.
Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated. The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process. These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers. Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 0.3 nanometer. The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources. These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis.
632 citations
TL;DR: In this article, two-dimensional Fourier transform electronic spectra of the cyanine dye IR144 in methanol are used to explore new aspects of optical 2D spectroscopy on a femtosecond timescale.
Abstract: Two-dimensional Fourier transform electronic spectra of the cyanine dye IR144 in methanol are used to explore new aspects of optical 2D spectroscopy on a femtosecond timescale The experiments reported here are pulse sequence and coherence pathway analogs of the two-dimensional magnetic resonance techniques known as COSY (correlated spectroscopy) and NOESY (nuclear Overhauser effect spectroscopy) Noncollinear three pulse scattering allows selection of electronic coherence pathways by choice of phase matching geometry, temporal pulse order, and Fourier transform variables Signal fields and delays between excitation pulses are measured by spectral interferometry Separate real (absorptive) and imaginary (dispersive) 2D spectra are generated by measuring the signal field at the sample exit, performing a 2D scan that equally weights rephasing and nonrephasing coherence pathways, and phasing the 2D spectra against spectrally resolved pump–probe signals A 3D signal propagation function is used to correct the 2D spectra for excitation pulse propagation and signal pulse generation inside the sample At relaxation times greater than all solvent and vibrational relaxation timescales, the experimental 2D electronic spectra can be predicted from linear spectroscopic measurements without any adjustable parameters The 2D correlation spectra verify recent computational predictions of a negative region above the diagonal, a displacement of the 2D peak off the diagonal, and a narrowing of the 2D cross-width below the vibrational linewidth The negative region arises from 4-level four-wave mixing processes with negative transition dipole products, the displacement off the diagonal arises from a dynamic Stokes shift during signal radiation, and the narrow 2D cross-width indicates femtosecond freezing of vibrational motion
342 citations
TL;DR: These results demonstrate that a transfer of electron angular momentum between the magnetic layers leads to additional relaxation torques.
Abstract: Unique features of the Gilbert damping in magnetic multilayers were investigated by ferromagnetic resonance (FMR) using magnetic single and double layer structures prepared by molecular beam epitaxy. The FMR linewidth for the Fe films in the double layer structures was larger than the FMR linewidth in the single Fe films having the same thickness. The additional FMR linewidth scaled inversely with the film thickness, and increased linearly with increasing microwave frequency. These results demonstrate that a transfer of electron angular momentum between the magnetic layers leads to additional relaxation torques.
327 citations
TL;DR: In this article, the out-of-plane angular dependence of ferromagnetic resonance (FMR) was measured for NM/80NiFe(Py)/NM (NM=Cu, Ta, Pd and Pt) films with various Py, Cu and Ta thicknesses fabricated by magnetron sputtering.
Abstract: The out-of-plane angular dependence of ferromagnetic resonance (FMR) was measured for NM/80NiFe(Py)/NM (NM=Cu, Ta, Pd and Pt) films with various Py, Cu and Ta thicknesses fabricated by magnetron sputtering. The out-of-plane angular dependences of FMR resonance field and linewidth were analyzed using Landau-Lifshitz-Gilbert equation taking account of broadening of linewidth due to magnetic inhomogeneities in a film. Magnetic inhomogeneities were assumed to be the fluctuation of magnitude and direction of the effective demagnetization field which contains both demagnetization and perpendicular anisotropy field for a film. The calculations of the angular variations of linewidth agreed with the experimental ones quantitatively. The fluctuations of magnitude and direction of the effective demagnetization field, which are represented as Δ(4πMeff.) and ΔθH, respectively, increased with decreasing Py thickness for all NM/Py/NM films. ΔθH increased as the thicknesses of the buffer layers increased for Cu/Py(40 A)/Cu films and was almost constant with increasing buffer layer thickness for Ta/Py(40 A)/Ta films. Only in the case of NM=Pd and Pt films, the Gilbert damping parameter, which is the speed of decay of magnetization precession, was enhanced significantly as compared with that for the bulk sample and was dependent on Py thickness.
301 citations
TL;DR: In this paper, an enhanced Littrow configuration extended cavity diode laser (ECDL) can be tuned without changing the direction of the output beam using a plane mirror fixed parallel to the tuning diffraction grating.
Abstract: We have developed an enhanced Littrow configuration extended cavity diode laser (ECDL) that can be tuned without changing the direction of the output beam. The output of a conventional Littrow ECDL is reflected from a plane mirror fixed parallel to the tuning diffraction grating. Using a free-space Michelson wavemeter to measure the laser wavelength, we can tune the laser over a range greater than 10 nm without any alteration of alignment.
246 citations
TL;DR: Time-resolved luminescence measurements show a lifetime of the dot ground state of 800 ps, demonstrating the presence of pure dephasing at finite temperature, and the homogeneous width is lifetime limited only at temperatures approaching 0 K.
Abstract: We report measurements of ultralong coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of $3.5\ensuremath{\mu}\mathrm{eV}$, which is significantly smaller than the linewidth observed in single-dot luminescence. Time-resolved luminescence measurements show a lifetime of the dot ground state of 800 ps, demonstrating the presence of pure dephasing at finite temperature. The homogeneous width is lifetime limited only at temperatures approaching 0 K.
212 citations
Patent•
16 May 2001
TL;DR: In this article, focus offset coefficients are used to change the focus at points within a slot to compensate for the linewidth control parameter variations introduced by the factors contributing to such variations.
Abstract: Particular types of distortion within a lithographic system may be characterized by linewidth control parameters. Linewidth control parameters of any given line or feature within a printed pattern vary as a result of optical capabilities of the lithography apparatus used, particular characteristics of the reticle, focus setting, light dose fluctuations, etc. The instant invention uses focus offset coefficients to change the focus at points within a slot to compensate for the linewidth control parameter variations introduced by the factors contributing to such variations. Additionally, different focuses can be set dynamically along the scan for a particular slot point. A set, or sets, of focus offset coefficients is generated for a particular lithography apparatus, depending on the number of line width control parameters for which correction is desired.
198 citations
TL;DR: In this paper, a 750-Hz linewidth singlemode erbium-doped fiber (EDF) ring laser with wide tunability using a widely tunable fiber Bragg grating was demonstrated.
Abstract: We demonstrate a 750-Hz linewidth single-mode erbium-doped fiber (EDF) ring laser with wide tunability using a widely tunable fiber Bragg grating (FBG). The stable single-mode operation is realized by using the FBG as a narrow wavelength-selective element and 4 m of unpumped EDF as a saturable absorber in the cavity. The 40-nm continuous tuning range of 1522-1562 nm is achieved using a highly stretchable FBG that exhibits a filter tuning range of over 52 nm. The grating is prepared with chemically stripped deuterium-loaded fiber to eliminate degrading factors for the grating strength, thereby achieving the wide tunability. The tuning range represents a 3.5-fold increase in wavelength tuning over previous use of FBGs.
178 citations
TL;DR: In this paper, a procedure of InAs/InP quantum dots elaboration emitting at 1.55 μm by gas source molecular beam epitaxy is described, based on a modification of the capping layer growth which is deposited in two steps, separated by a growth interruption under phosphorus flux.
Abstract: A procedure of InAs/InP quantum dots elaboration emitting at 1.55 μm by gas source molecular beam epitaxy is described. It is based on a modification of the capping layer growth which is deposited in two steps, separated by a growth interruption under phosphorus flux. The main effect of this two step capping layer growth is to reduce the height of the biggest islands and thus to decrease the photoluminescence linewidth of the quantum dots emission line. Transmission electron microscopy and photoluminescence experiments show that quantum dots structure are still present after growth interruption under phosphorus flux and that the photoluminescence linewidth at 1.55 μm is reduced from 120 to 50 meV, thanks to this procedure.
TL;DR: In this paper, the out-of-plane angular dependence of ferromagnetic resonance linewidth of non-magnetic metal (NM)/80NiFe(Py)(20-100 A)/NM (NM=Cu, Ta, Pd and Pt) sputtered films were measured for the investigation of magnetic damping.
TL;DR: A new primary frequency standard, the atomic caesium fountain CSF1, has been put into operation at the Physikalisch-Technische Bundesanstalt (PTB) as mentioned in this paper.
Abstract: A new primary frequency standard, the atomic caesium fountain CSF1, has been put into operation at the Physikalisch-Technische Bundesanstalt (PTB). 133Cs atoms are cooled in a magneto-optical trap and in optical molasses. They are launched to a height of 39 cm above the microwave cavity centre. The resulting Ramsey resonance signal has a full-width half-maximum linewidth (FWHM) of 0.88 Hz. The first uncertainty evaluation yields a relative 1 σ frequency uncertainty of 1.4 × 10−15. The short-term relative frequency instability of the CSF1 for averaging time τ is typically 3.5 × 10−13 (τ/s)−1/2, dictated by the available quartz oscillator as the local frequency source.
TL;DR: In this paper, an injection-seeded nanosecond terahertz (THz) wave parametric generator was demonstrated using nonlinear crystals that were pumped by a single frequency Nd:yttrium-aluminum-garnet laser.
Abstract: An injection-seeded nanosecond terahertz (THz) wave parametric generator was demonstrated using nonlinear crystals that were pumped by a single frequency Nd:yttrium–aluminum–garnet laser. Spectrum narrowing to the Fourier transform limit (ν=1.58 THz, Δν 100 mW peak) approximately 300 times higher than that of a conventional THz-wave parametric generator, which has no injection seeder. This compact system operates at room temperature and promises to be a widely tunable THz-wave source that will compete with free-electron lasers and p-Ge lasers.
TL;DR: The energy and the linewidth dispersion of a plasmon in a dense two-dimensional electron system in a metallic surface-state band on a silicon surface is studied for the first time.
Abstract: We have studied, for the first time, the energy and the linewidth dispersion of a plasmon in a dense two-dimensional electron system in a metallic surface-state band on a silicon surface. As expected from the considerably high effective density and long Fermi wavelength of the system, the plasmon energy dispersion exhibited an excellent agreement with the nearly free-electron theory. However, in a small wave number region below the Landau edge, we have observed an anomalous linewidth dispersion which nearly free-electron theories do not predict.
TL;DR: Bandpass filters based on guided-mode resonance effects in waveguide-grating structures are obtained by use of a genetic algorithm search-and-optimization routine and calculations show that narrow linewidths, high peaks, and low sideband transmittances can be achieved in thin-film diffractive devices with few layers.
Abstract: Bandpass filters based on guided-mode resonance effects in waveguide-grating structures are obtained by use of a genetic algorithm search-and-optimization routine. Calculated examples show that narrow linewidths, high peaks, and low sideband transmittances can be achieved in thin-film diffractive devices with few layers. A filter with a linewidth of 0.2 nm at a central wavelength of 0.55 microm is demonstrated in a two-layer-two-grating structure. At 10.6-microm wavelength, a filter consisting of a single binary grating is obtained that has a linewidth of 12.7 nm and extended, low sideband transmittance. A three-layer device with a surface relief Si grating and two underlying homogeneous layers of SiO(2) and Si yields a high-efficiency filter centered at 1.55 microm with a linewidth of 0.1 nm.
TL;DR: In this article, the photonic band gap lasing action from a non-degenerate monopole-mode, high-quality factor cavity was demonstrated and identified from its mode shape, spectrum, and polarization.
Abstract: We propose and demonstrate photonic band gap lasing action from a nondegenerate monopole-mode, high-quality factor cavity. By optical pumping at room temperature, the monopole-mode laser is realized and identified from its mode shape, spectrum, and polarization. The monopole-mode laser shows nondegeneracy and genuine two-dimensional oscillation with incident threshold pump power less than 0.3 mW. This laser mode has a small modal volume of ∼4.5(λ/2nslab)3 and shows a quality factor of larger than 1900, estimated from the spectral linewidth below threshold.
TL;DR: In this paper, the relative intensity (RIN) and optical frequency (νrms) noise of Er-doped fiber Bragg grating lasers are investigated theoretically and experimentally.
TL;DR: In this article, a generalization of the Dicke model was proposed to describe localized, physically separated, saturable excitations, such as excitons bound on impurities, coupled to a single long-lived mode of an optical cavity.
Abstract: We consider a generalization of the Dicke model. This model describes localized, physically separated, saturable excitations, such as excitons bound on impurities, coupled to a single long-lived mode of an optical cavity. We consider the thermal equilibrium of this model at a fixed total number of excitons and photons. We find a phase in which both the cavity field and the excitonic polarization are coherent. This phase corresponds to a Bose condensate of cavity polaritons, generalized to allow for the fermionic internal structure of the excitons. It is separated from the normal state by an unusual reentrant phase boundary. We calculate the excitation energies of the model, and hence the optical absorption spectra of the cavity. In the condensed phase the absorption spectrum is gapped. The presence of this gap distinguishes the polariton condensate from the normal state and from a conventional laser, even when the inhomogeneous linewidth of the excitons is so large that there is no observable polariton splitting in the normal state.
TL;DR: In this paper, a passive microring-resonator-coupled semiconductor laser structure is proposed to improve the side-mode suppression ratio, linewidth and the frequency chirp of a conventional Fabry-Perot laser.
Abstract: In this letter, a passive microring-resonator-coupled semiconductor laser structure is proposed. The weakly coupled high-Q microring resonator provides a strong mode-selection filter and could considerably extend the effective cavity length of a conventional Fabry–Perot laser. The side-mode suppression ratio, the linewidth and the frequency chirp of this laser are dramatically improved comparing to distributed feedback and distributed Bragg reflector lasers.
Patent•
07 May 2001
TL;DR: In this article, a notch at the bottom of the gate is added to reduce the effective linewidth of transistors in an over-etch step, which can be done at a layer interface, such as a silicon-germanium interface.
Abstract: Transistor gate linewidths can be made to be effectively smaller by etching a notch at the bottom of the gate to reduce the effective linewidth. This can be done by etching at a layer interface, such as a silicon-germanium interface. in an over-etch step.
01 Nov 2001
TL;DR: In this paper, the photonic band gap lasing action from a non-degenerate monopole-mode, high-quality factor cavity was demonstrated by optical pumping at room temperature.
Abstract: We propose and demonstrate photonic band gap lasing action from a nondegenerate monopole-mode, high-quality factor cavity. By optical pumping at room temperature, the monopole-mode laser is realized and identified from its mode shape, spectrum, and polarization. The monopole-mode laser shows nondegeneracy and genuine two-dimensional oscillation with incident threshold pump power less than 0.3 mW. This laser mode has a small modal volume of ;4.5(l/2nslab) 3 and shows a quality factor of larger than 1900, estimated from the spectral linewidth below threshold. © 2001 American Institute of Physics. @DOI: 10.1063/1.1416163#
TL;DR: In this article, photoacoustic (PA) spectroscopy measurements of carbon dioxide, methanol, and ammonia were performed using a single-mode quantum cascade distributedfeedback laser, which operated in pulsed mode at moderate duty cycle and slightly below room temperature.
Abstract: We present photoacoustic (PA) spectroscopy measurements of carbon dioxide, methanol, and ammonia. The light source for the excitation was a single-mode quantum cascade distributed-feedback laser, which was operated in pulsed mode at moderate duty cycle and slightly below room temperature. Temperature tuning resulted in a typical wavelength range of 3 cm-1 at a linewidth of 0.2 cm-1. The setup was based on a Herriott multipass arrangement around the PA cell; the cell was equipped with a radial 16-microphone array to increase sensitivity. Despite the relatively small average laser power, the ammonia detection limit was 300 parts in 109 by volume.
TL;DR: A tunable quantum-cascade (QC) laser has been flown on NASA's ER-2 high-altitude aircraft to produce the first atmospheric gas measurements with this newly invented device, an important milestone in the QC laser's future planetary, industrial, and commercial applications.
Abstract: A tunable quantum-cascade (QC) laser has been flown on NASA’s ER-2 high-altitude aircraft to produce the first atmospheric gas measurements with this newly invented device, an important milestone in the QC laser’s future planetary, industrial, and commercial applications. Using a cryogenically cooled QC laser during a series of 20 aircraft flights beginning in September 1999 and extending through March 2000, we took measurements of methane (CH4) and nitrous oxide (N2O) gas up to ∼20 km in the stratosphere over North America, Scandinavia, and Russia. The QC laser operating near an 8-µm wavelength was produced by the groups of Capasso and Cho of Bell Laboratories, Lucent Technologies, where QC lasers were invented in 1994. Compared with its companion lead salt diode lasers that were also flown on these flights, the single-mode QC laser cooled to 82 K and produced higher output power (10 mW), narrower laser linewidth (17 MHz), increased measurement precision (a factor of 3), and better spectral stability (∼0.1 cm-1 K). The sensitivity of the QC laser channel was estimated to correspond to a minimum-detectable mixing ratio for methane of approximately 2 parts per billion by volume.
TL;DR: In this article, the authors derive simple expressions to connect the linewidths of the waves interacting in the fiber, and show that the magnitude of the narrowing effect depends only on the acoustic damping rate and the cavity loss rate.
Abstract: In Brillouin fiber lasers, the phase fluctuations of the pump laser are transferred to the emitted Stokes field after being strongly reduced. The result is a linewidth narrowing that we study both experimentally and theoretically. We derive simple expressions to connect the linewidths of the waves interacting in the fiber, and we show that the magnitude of the narrowing effect depends only on the acoustic damping rate and the cavity loss rate. We successfully compare these theoretical predictions with experimental results obtained by recording the response of a Brillouin fiber ring laser to frequency modulation of the pump field.
TL;DR: In this article, a new method for measuring the linewidth enhancement factor is presented based on the relation between the upper and lower bounds of the locked and unlocked regimes when the detuning of the pump and slave laser is plotted as a function of the injection power.
Abstract: A new method for measuring the linewidth enhancement factor is presented. This idea is based on the relation between the upper and lower bounds of the locked and unlocked regimes when the detuning of the pump and slave laser is plotted as a function of the injection power. Our results are confirmed with an independent measurement using amplified spontaneous emission (ASE) spectroscopy as well as our theory, which takes account of the realistic quantum-well (QW) band structure and many-body effects. This method provides a new approach to measure the linewidth enhancement factor above laser threshold.
TL;DR: The airborne differential absorption lidar LEANDRE II, developed for profiling tropospheric water-vapor mixing ratios, is described.
Abstract: The airborne differential absorption lidar LEANDRE II, developed for profiling tropospheric water-vapor mixing ratios, is described. The emitter is a flash-lamp-pumped alexandrite laser, which operates in a double-pulse, dual-wavelength mode in the 727–736 nm spectral domain. Two 50-mJ successive on-line and off-line pulses with an output linewidth of 2.4 × 10-2 cm-1 and a spectral purity larger than 99.99% are emitted at a 50-µs time interval. The spectral positioning is controlled in real time by a wavemeter with an absolute accuracy of 5 × 10-3 cm-1. The receiver is a 30-cm aperture telescope with a 3.5-mrad field of view and a 1-nm filter bandwidth. These instrument characteristics are defined for measuring the water-vapor mixing ratio with an accuracy better than 0.5 g kg-1 in the first 5 km of the atmosphere with a range resolution of 300 m, integration on 100 shots, and an instrumental systematic error of less than 2%. The sensitivity study and first results are presented in part II [Appl. Opt.40, 3462–3475 (2001)].
TL;DR: In this article, the effects of interface roughness and phonon scattering on inter-band absorption linewidth in a modulation-doped GaAs/AlAs quantum well were investigated.
Abstract: We experimentally and theoretically study the effects of interface roughness and phonon scattering on intersubband absorption linewidth in a modulation-doped GaAs/AlAs quantum well. Quantitative comparisons between experimental results and theoretical calculations make it clear that interface roughness scattering is the dominant scattering mechanism for absorption linewidth in the temperature range below 300 K. Even at room temperature, phonon scattering processes contribute little to linewidth, while polar-optical phonon scattering limits electron mobility.
TL;DR: In this article, the authors analyzed the effect of coherent scattering inside an optical cavity in terms of the modified emission spectrum and showed that the cooling efficiency and volume can be significantly enhanced in resonators with transverse-mode degeneracy.
Abstract: Laser cooling by coherent scattering inside an optical cavity, a method proposed for cooling the motion of arbitrary particles that scatter light, is analyzed in terms of the modified emission spectrum. In contrast to conventional Doppler cooling, this method invokes the two-photon Doppler effect along the direction of the momentum transferred in the scattering process. Three-dimensional cooling can therefore be achieved with a single optical cavity. Both in the free-particle regime ~cavity Doppler cooling! and in the strong-confiment regime ~cavity sideband cooling! the minimum temperature is determined by the resonator linewidth and independent of the atomic level structure. The cooling efficiency and volume are significantly enhanced in resonators with transverse-mode degeneracy, such as the confocal resonator.
TL;DR: The 1S-2P transition in atomic hydrogen has been observed for the first time with almost natural linewidth and shows that laser cooling and detection with continuous Lyman- alpha radiation has excellent prospects for future experiments with antihydrogen.
Abstract: The search for physics beyond the standard model is a strong inspiration to test the CPT symmetry to ultrahigh precision. Properties such as inertial mass, magnetic moment, or chargemass ratios [1] have been compared between elementary particles and their antimatter equivalent. Low energy atomic antimatter would open a new field of testing CPT by comparing properties of internal atomic structure [2,3]. It would possibly even make the experimental observation of the effect of gravity on antimatter feasible [4,5]. The recent trapping and cooling of both antiprotons and positrons at CERN’s new antiprotondecelerator (AD) [6] and the progress in producing atoms from ions and electrons [7] indicate that creation of cold antihydrogen could be imminent. Besides magnetic confinement, optical means of measurement and manipulation of the antiatoms will play a pivotal role as any contact with matter results in rapid annihilation. The 1S-2P transition is the first and strongest transition suitable for fluorescence detection and laser cooling of magnetically confined antihydrogen in the ground state. However, producing radiation at the required wavelength of 121.56 nm (Lyman-a) in the vacuum ultraviolet (VUV) is still a challenge. In this Letter, we report on the first near-natural linewidth atomic hydrogen excitation of the 1S-2P transition. The results obtained with hydrogen are a direct measure of what can be achieved with antihydrogen as the internal energy structure is expected to be the same to high precision. To induce the 1S-2P transition we use a significantly improved continuous coherent Lyman-a source. Laser cooling and spectroscopy with pulsed Lyman-a has been demonstrated for magnetically trapped hydrogen [8] before. However, the use of a continuous source of Lyman-a is strongly preferred as it allows for more efficient laser cooling without saturation and has a more favorable duty cycle of 100%. The bandwidth is far superior to pulsed sources, which allows for a higher selectivity of sublevels in a magnetic trap. This should enable low-loss laser cooling to the Doppler limit of 2.4 mK. Our source of Lyman-a radiation (see Fig. 1) is based on continuous four-wave mixing (FWM) in natural mercury vapor which produces the sum frequency of three incident laser beams [9]. We employ fundamental beams at wavelengths of 257 and 399 nm for an exact two-photon resonance with the 7s 1 S0 state of mercury (mass 202 isotope,