Showing papers in "IEEE Journal of Quantum Electronics in 1970"
TL;DR: In this article, a complex Gaussian pulse is followed through one pass around the laser cavity to keep the pulse Gaussian, and the analysis is further extended to include effects of detuning of the modulator, in which case analytical expressions are obtained for the phase shift of the pulse within the modulation cycle, the shift of pulse spectrum off line center, the change in pulse length, and change in power output.
Abstract: A new general analysis for mode-locked operation of a homogeneously broadened laser with either internal phase (FM) or amplitude (AM) modulation is presented in this paper. In this analysis, a complex Gaussian pulse is followed through one pass around the laser cavity. Approximations are made to the line shape and modulation characteristics to keep the pulse Gaussian. After one round trip, a self-consistent solution is required. This yields simple analytic expressions for the pulse length, frequency chirp, and bandwidth of the mode-locked pulses. The analysis is further extended to include effects of detuning of the modulator, in which case analytical expressions are obtained for the phase shift of the pulse within the modulation cycle, the shift of the pulse spectrum off line center, the change in pulse length, and the change in power output. Numerical results for a typical Nd:YAG laser are given. In the case of the FM mode-locked laser it is found that there is a frequency chirp on the pulse and that this causes pulse compression and stretching when the modulator is detuned. Etalon effects and dispersion effects are also considered.
600 citations
TL;DR: In this article, an analysis of optical second-harmonic generation internal to the laser cavity is presented, and it is shown that the maximum secondharmonic power generated in this way is equal to the maximum fundamental power available from the laser.
Abstract: An analysis of optical second-harmonic generation internal to the laser cavity is presented. It is shown that the maximum second-harmonic power generated in this way is equal to the maximum fundamental power available from the laser. Further, it is found that there exists a value of nonlinearity that optimally couples the harmonic out for all power levels of the laser. The magnitude of the nonlinearity required for optimum coupling is shown to be proportional to the linear losses at the fundamental and inversely proportional to the saturation parameter for the laser transition. For the YAlG:Nd laser at 1.06 μ using Ba 2 NaNb 5 O 15 as the nonlinear material, the required crystal length for optimum coupling is given by l\min{c}\max{2}(cm)\simeq 2.7 \times 10^{2}L/f where L is the linear round-trip loss and f is the ratio of the fundamental power density in the nonlinear crystal to that in the laser medium. For low-loss cavities, optimum coupling can thus be achieved for crystal lengths of 1 cm or less. The use of a mirror or mirrors within the cavity, reflecting at the harmonic, is considered as a means to couple out the total harmonic in one direction. Considerations of temperature stability and the finite oscillating linewidth of the laser are shown to favor a configuration with a single harmonic mirror located on the same surface as the fundamental mirror.
247 citations
TL;DR: In this paper, the theory of the interaction of a linearly polarized wave with a continuously pumped YAG : Nd crystal has been refined, and experimental evidence illustrates the angular independence of the birefringence, describes the radial dependence, and explains the laser power losses involved.
Abstract: The thermally induced stress birefringence has been known to severely affect the performance of a solid-state laser system when the beam is linearly polarized. This paper refines the theory of the interaction of a linearly polarized wave with a continuously pumped YAG : Nd crystal; in conjunction with experimental evidence this paper illustrates the angular independence of the birefringence, describes the radial dependence, and explains the laser power losses involved.
203 citations
TL;DR: In this paper, the relationship between the acoustooptic figure of merit and acoustic loss is explored, and it is concluded that a high figure and low loss are compatible material properties for applications below approximately 0.5 GHz.
Abstract: Guide lines are presented for the selection of promising new acoustooptic materials for device applications. Previously, the selection of materials was based primarily on availability and intuition. Now it is possible to estimate an approximate acousto-optic figure of merit for a material knowing only its chemical composition and density. One of the first applications of these guide lines led to a detailed evaluation of lead molybdate, PbMoO 4 , a material known to have certain desirable physical properties. The results verified that PbMoO 4 has a high figure of merit, considerably greater than LiNbO 3 though somewhat less than α-HIO 3 . In addition to a high figure of merit, a material must also have a low acoustic loss if it is to be useful for device applications. The relationship between the acoustooptic figure of merit and acoustic loss is explored. Although only limited loss data are presently available, it is concluded that a high figure of merit and low loss are compatible material properties for applications below approximately 0.5 GHz. However, as future applications call for higher frequency operation, it appears that a tradeoff between low acoustic loss and high figure of merit will be required.
172 citations
NEC1
TL;DR: In this article, a lens-like glass fiber guide with a parabolic variation of refractive index has been developed, which has the following characteristics: simultaneous transmission of laser beams modulated by wide-band signals through narrow space; optical image transmission; realization of a lens with tiny aperture or with extremely short focal length.
Abstract: A lenslike glass fiber guide with a parabolic variation of refractive index has been developed. This optical guide named SELFOC® has the following characteristics: simultaneous transmission of laser beams modulated by wide-band signals through narrow space; optical image transmission; realization of a lens with tiny aperture or with extremely short focal length; and the possibility of being bent with a small radius of curvature without spoiling transmission characteristics. In the case of a typical fiber guide with length 1 meter and diameter 0.3 mm, transmission loss is about 0.2 dB and depolarization is about 20 dB at wavelength 0.63μ. The mode pattern of a laser beam after passing through the fiber guide is scarcely deformed. The fiber guide can be used as a transmission line or lens, in optical communication, optical data processing, and optical instruments.
167 citations
TL;DR: In this paper, the authors present experimental results for the Nd:YAG laser with internal phase modulation, and a method to measure the single-pass phase retardation of the modulator accurately at 1.06 μ is described in detail.
Abstract: In Part I of this paper [1], a theoretical analysis of the mode-locked homogeneous laser was given. In this part we present experimental results for the Nd:YAG laser with internal phase modulation. LiNbO 3 was used as the modulator crystal, and a method to measure the single-pass phase retardation of the modulator accurately at 1.06 μ is described in detail. The pulsewidth and spectral width of the mode-locked laser were measured as a function of depth of modulation, and good agreement with theory was obtained. Etalon effects in the laser were observed, and the results agreed very well with the theory. Mode-locked spectral bandwidths of up to 16 GHz, implying mode-locked pulses as short as 40 ps, were obtained.
133 citations
TL;DR: In this paper, the authors studied the time and spectral structure of the Nd:glass laser radiation using two-photon fluorescence (TPF) patterns, and found that the TPF patterns were consistent with a model where the laser emission has the character of Gaussian noise (thermal light), i.e., a case where the modes are randomly phased.
Abstract: The Nd:glass laser has become one of the most useful sources of light pulses a few picoseconds in duration. In this paper, we review the results of an extensive study of the time and spectral structure of the Nd:glass laser radiation. The time structure was studied by means of two-photon fluorescence (TPF) patterns: these were scanned by a very thin (28-μ) cell containing the fluorescent dye, the fluorescence being monitored by a photomultiplier. When the Nd:glass laser is Q switched by a rotating mirror or when it is free running, we find TPF patterns fully consistent with a model where the laser emission has the character of Gaussian noise (thermal light), i.e., a model where the modes are randomly phased. When the laser was simultaneously Q switched and mode locked we made two observations : 1) the TPF patterns show that the ultra-short pulses observed previously have an overall duration of ∼8 ps, but also possess an internal substructure containing peaks 0.4-0.8 ps in duration; 2) the spectral width of these pulses is Q -switched train and expands to ∼80 cm-1in the middle of the train. This rapid spectral broadening during pulse buildup is attributed to self-phase modulation in the laser glass matrix due to a nonlinear index n 2 which we evaluate as n{2}= (2 \pm 1) \times 10^{-22} m2/V2(or 1.8 \times 10^{-13} esu). Gain limiting due to this effect and self-focusing become very important at power densities above 1 GW/cm2, presenting a serious limitation on the energy density (J/cm2), which one may hope to extract from Nd: glass laser systems.
122 citations
TL;DR: A flashlamp-excited organic liquid laser system capable of stimulated emission down to 340 nm in the ultraviolet has been developed in this article, which has a rise time of 50 ns and energy capacity of 20 joules or more.
Abstract: A flashlamp-excited organic liquid laser system capable of stimulated emission down to 340 nm in the ultraviolet has been developed. The flashlamp has a rise time of 50 ns and energy capacity of 20 joules or more. There are several efficient laser compounds that emit below 400 nm, and the most promising appears to be the p-terphenyl laser, which emits at 341 nm and is capable of running in the superradiant mode. There are several interesting facets still unexplained in ultraviolet lasers. The possibility of singlet to triplet intersystem crossings in substances generally accepted as having unity fluorescence quantum efficiency has been encountered.
103 citations
Abstract: Self-induced sustained pulsations have been observed in the light output from GaAs injection lasers with tandem double-section stripe geometry. The pulsing behavior of the laser is analyzed using a repetitively Q -switched model similar to that of Basov. Exact numerical solutions to the nonlinear rate equations have been obtained, which are to be compared with our experimental results and with the results in the earlier work of Basov et al. An approximate approach using a phase-plane analysis is described, which yields a simple way for the determination of the regions of excitation currents that leads to the sustained pulsing solution.
89 citations
TL;DR: An external cavity coupled to a conventional Fabry-Perot GaAs diode laser operating continuously has been found to cause modulation of the light output at a frequency within the range 05 to several GHz.
Abstract: An external cavity coupled to a conventional Fabry-Perot GaAs diode laser operating continuously has been found to cause modulation of the light output at a frequency within the range 05 to several GHz The modulation depth is close to 100 percent and the linewidth can be made as narrow as 180 kHz The modulation is thought to be stimulated by the intensity noise fluctuations, which peak at the well-known spiking frequency f r The oscillations are strongly enhanced by a frequency locking action of the external cavity, being efficient when the external cavity round-trip time 2L/c , or a multiple thereof, corresponds to the inverse of the spiking frequency Since the latter is dependent on both pump current and temperature, the system can simply be tuned by adjusting the pump current For a fixed resonator length, the narrow-band oscillations occur in a small current range, in which an increase in frequency with increasing current at a rate of 400 kHz/mA is observed A small-signal analysis based on simple rate equations shows the influence of the external cavity on the intrinsic resonance frequency f r It demonstrates that self-modulation can only occur for small values of the coupling coefficient e between the laser diode and the external cavity
83 citations
TL;DR: In this article, the orders of nonlinearity of the interaction between an intense focused beam of optical photons and matter in gaseous form at low pressure (10-3torr) brings into play some strongly nonlinear processes.
Abstract: The interaction between an intense focused beam of optical photons and matter in gaseous form at low pressure (10-3torr) brings into play some strongly nonlinear processes. These multiphoton processes occur through the simultaneous absoprtion of several quanta by an atom that may be thus either excited or ionized. The orders of nonlinearity of the interaction of a multimode Q -switched laser beam with rare gas atoms were measured with laser intensities up to 1013W ċcm-2at 1.06μ and up to 1012W ċcm-2at 0.53μ. The energy of the number of quanta corresponding to the order of nonlinearity is always close to the energy of an atomic level. The results seem to emphasize the particularly important role performed by bound states during the ionization process. Thus a two-stage ionization process seems far more probable than a single direct transition between the ground state and the continuum spectrum. Experimental values of multiphoton ionization probabilities are also given after having precisely determined the spatiotemporal intensity distribution function.
TL;DR: In this paper, the authors derived expressions for the field induced in a thin-film waveguide by plane waves incident upon an adjacent frustrated total reflecting interface, and deduced an expression for the coupling coefficient for a Gaussian TEM 00 beam into such a guide as a function of the guide and beam parameters.
Abstract: We have derived expressions for the field induced in a thin-film waveguide by plane waves incident upon an adjacent frustrated total reflecting interface. From these, we have deduced an expression for the coupling coefficient for a Gaussian TEM 00 beam into such a guide as a function of the guide and beam parameters.
TL;DR: In this paper, the frequency-sweeping mode of a Nd :YAG 1.06-μ laser with an intracavity LiNbO 3 phase modulator has been demonstrated in excellent agreement with the theoretical expression Δ = (δ/π) where δ = peak single-pass phase retardation in the modulator, δ= axial mode spacing, Δ=modulator detuning, and Δ=resulting FM index of the laser output.
Abstract: The FM-laser or frequency-sweeping mode of laser oscillation has been demonstrated in a Nd :YAG 1.06-μ laser with an intracavity LiNbO 3 phase modulator. The experimental results are in excellent agreement with the theoretical expression \Delta= (\Delta\Omega/\Delta
u) (\delta/\pi) where δ= peak single-pass phase retardation in the modulator, \Delta\Omega = axial mode spacing, \Delta
u =modulator detuning, and Δ=resulting FM index of the laser output. Modulation indices as large as \Delta \approx 230 rad have been obtained, in which case the instantaneous laser frequency is sweeping over a full spectral range of 2\Delta \cdot f_{m} \approx 120 GHz (≈ 4 cm-1) at a repetition frequency f_{m} \approx 260 MHz, with a time-bandwidth product per period \approx 2\Delta \approx 460 . The coherently mode-locked spectral bandwidth thus obtained in the FM-laser case is very much wider than can be achieved in the pulsed mode-locked case with the same Nd:YAG laser. Some possible ways of using this broad-band coherent FM spectrum are suggested.
TL;DR: In this article, the general considerations and principles involved with IR image up-conversion are presented and discussed, the factors that limit the resolution of the upconverted image are analyzed and the merits of three types of optical systems are discussed with regard to resolution and efficiency of upconversion.
Abstract: The general considerations and principles involved with IR image up-conversion are presented and discussed. The factors that limit the resolution of the up-converted image are analyzed and the merits of three types of optical systems are discussed with regard to resolution and efficiency of up-conversion. Several characteristics of six nonlinear crystals are calculated and compared.
TL;DR: In this paper, a series of diagnostic experiments was undertaken in order to gain some understanding of the physical processes occurring in the high-power directly excited CO laser, including the UV and visible sidelight for a directly excited and flow-type CO laser.
Abstract: A series of diagnostic experiments was undertaken in order to gain some understanding of the physical processes occurring in the high-power directly excited CO laser. These included studies of the UV and visible sidelight for a directly excited and flow-type CO laser; a comparison of various gas mixtures for laser operation at 77 and 195°K wall temperatures; a study of the laser spectral output as a function of cavity (wavelength-selective and free-running) operational mode (CW or Q-switched), gas pressure, and discharge current; and a measurement of the laser recovery time. Some of the more important conclusions of these experiments were that a CO-N 2 -O 2 -He mixture is superior to CO-N 2 -He or CO-O 2 -He mixture at 77 and 195°K; that freeze-out of O 3 and CO 2 is an important phenomenon at 77°K; and that both rotational and vibrational cross relaxation appear to be occurring in the CO during CW lasing. Also a discussion of three possible inversion mechanisms is included. An inversion based on the V-V cross-pumping theory of Treanor et al. [16] appears to be most consistent with our experimental results.
TL;DR: A review of papers published on laser interaction with solids, from the point of view of plasma production, can be found in this paper, where the material is divided into one section dealing with theoretical work and one dealing with experiments.
Abstract: This paper provides a review of papers published on laser interaction with solids, from the point of view of plasma production. The material is divided into one section dealing with theoretical work and one dealing with experiments. In addition, an extensive bibliography of papers published on the subject up to the end of 1968 is presented.
TL;DR: In this paper, the authors studied three-wave parametric interactions in media exhibiting group-velocity dispersion and found the existence of steady-state pulse solutions in the parametric system, which are analogues of pi and two-pi pulses.
Abstract: Three-wave parametric interactions are studied in media exhibiting group-velocity dispersion. Under certain conditions these interactions may be described by the same equations that govern pulse propagation in a two-level resonant system. This analogy suggests the existence of steady-state pulse solutions in the three-wave parametric system. Such solutions are found, and are analogues of pi and two-pi pulses. The variety of solutions in the parametric system is greater than in the resonant case.
TL;DR: In this article, the authors used a passively Q-switched ruby laser, operating in a single axial and transverse mode, to produce sparks produced in a number of gases at pressures ranging from 760 to 9000 mmHg.
Abstract: Using a passively Q -switched ruby laser, operating in a single axial and transverse mode, sparks produced in a number of gases at pressures ranging from 760 to 9000 mmHg have been studied. Breakdown threshold measurements for both single and multimode laser radiation have been made and in addition, the characteristics of the sparks produced with single-mode radiation have been investigated. Photography at 90° of the scattered laser light showed the existence of scattering regions with transverse dimensions not exceeding the 5-μ resolution of the optical system. Furthermore, a large amount of laser light is scattered in the forward direction. The intensity, angular distribution, and spectral characteristics of this scattered radiation have been determined. Various possible mechanisms that could account for these phenomena are discussed, and it is concluded that self-focusing of the laser beam after the initiation of the breakdown process may be occurring.
TL;DR: In this article, a steady state analysis of doubly and singly resonant optical parametric oscillators is presented, where the pump wave is reflected back upon itself after passing through the nonlinear medium.
Abstract: Several important characteristics of optical parametric oscillators can be substantially improved by nonresonantly reflecting the pump wave back upon itself after it has passed through the nonlinear medium. Benefits are reduced thresholds, decreased buildup times, and improved efficiencies. Steady-state analyses of doubly and singly resonant oscillators are presented.
TL;DR: In this article, an analysis of the saturable absorption of SF 6 at 10.59 μ was presented, where a model for the absorber was developed and experiments were performed to determine the value of the saturation parameter.
Abstract: An analysis of the saturable absorption of SF 6 at 10.59 μ is presented. A model for the absorber is developed and experiments have been performed to determine the value of the saturation parameter. It is shown that at pressures above 0.1 torr, the saturation parameter varies linearly with the pressure and is governed by the relaxation time of the lowest level ν 6 . Effects of temperature on the absorption are discussed.
TL;DR: In this article, a simple analysis of the mode-locking behavior of a homogeneous laser with an intracavity FM modulator is presented, showing that the mode locking behavior changes rapidly and asymmetrically when the modulation frequency is detuned by small amounts from its optimum value.
Abstract: The mode-locking behavior of a homogeneous laser with an intracavity FM modulator changes rapidly and asymmetrically when the modulation frequency is detuned by small amounts from its optimum value. We develop here a simple analysis of these detuning effects. The analysis gives explicit expressions for all aspects of the mode-locking behavior as functions of detuning. A physical interpretation of the analysis also makes clear which physical mechanisms are responsible for the detuning behavior.
TL;DR: In this article, the properties of the rhodamine 6G flashlamp-pumped circulating dye laser with cyclooctatetraene and cycloheptatriene as triplet-state quenchers are described.
Abstract: The properties of the rhodamine 6G flashlamp-pumped circulating dye laser with cyclooctatetraene and cycloheptatriene as triplet-state quenchers are described. Particular attention is given to such observables as pulse duration, frequency sweep, and early termination of the laser pulse. From the experimental results and the theory of dye lasers, it is concluded that the thermal effects may not play a dominant role in such lasers.
TL;DR: In this paper, a method for stabilizing the frequency of a single-J -value CO 2 laser to the center of its output power versus frequency curve based upon the variation of the impedance of the plasma tube with the optical power extracted is described.
Abstract: A method for stabilizing the frequency of a single- J - value CO 2 laser to the center of its output power versus frequency curve based upon the variation of the impedance of the plasma tube with the optical power extracted is described. Frequency modulation of the laser produces an ac component of voltage drop across the plasma tube, which is synchronously detected to generate a frequency-error signal.
TL;DR: In this paper, a simple frequency stabilization scheme based on birefringent etalons is described, which does not require laser modulation and major problems associated with stable single-frequency operation of solid-state lasers are discussed.
Abstract: It is shown how intracavity etalons can be optimally designed for axial mode selection and frequency stabilization of gas and crystal lasers. Relevant laser parameters, required etalon properties, and expected losses are determined. A simple frequency stabilization scheme based on birefringent etalons is described, which does not require laser modulation. Major problems associated with stable single-frequency operation of solid-state lasers are discussed. Using an optimally designed crystal quartz etalon, a Nd:YAG laser could be stabilized to 10-7in frequency and 2 percent in amplitude. The linearly polarized single frequency TEM 00 output was 150 mW, which compares to an unpolarized 12-mode output of 400 mW for the bare laser.
TL;DR: In this article, the relative energy per laser pulse was measured for nine new and 19 previously reported dye solutions in equilibrium with partial pressures of oxygen ranging from 0 to 1 atmosphere, and it was shown that dissolved oxygen can dramatically influence the intensity of flashlamp-pumped organic-dye lasers.
Abstract: Dissolved oxygen was found to dramatically influence the intensity of flashlamp-pumped organic-dye lasers. The relative energy per laser pulse was measured for nine new and 19 previously reported dye solutions in equilibrium with partial pressures of oxygen ranging from 0 to 1 atmosphere.
TL;DR: In this article, self-induced intensity pulsations of continuously operating GaAs injection lasers have been frequency stabilized and narrowed by applying to the laser microwave feedback signals derived from the electrical and optical outputs of the laser itself.
Abstract: Self-induced intensity pulsations of continuously operating GaAs injection lasers have been frequency stabilized and narrowed by applying to the laser microwave feedback signals derived from the electrical and optical outputs of the laser itself. The width of the optical pulses has been reduced to less than 180 ps at a pulse rate whose spectral width was simultaneously reduced to less than 30 kHz. Significant differences between electrical and optical methods of feedback are demonstrated and discussed.
TL;DR: In this paper, a 50kV laser-triggered spark gap operated at repetition rates to 50 pps was described, and the dependence of delay and jitter was investigated as a function of gas mixture, pressure, laser power and electrode material.
Abstract: A 50-kV laser-triggered spark gap operated at repetition rates to 50 pps is described. Jitter of delay time as low as ± 0.1 ns was demonstrated. Dependence of delay and jitter was investigated as a function of gas mixture, pressure, laser power, and electrode material. Subnanosecond jitter was obtained with as little as 0.17 mJ in a 6-ns giant pulse from a Nd+3in a YAG laser. The dielectric gases used included a high proportion of Ar mixed with N 2 or SF 6 .
TL;DR: In this paper, it has been shown that the laser threshold currents and efficiency with increasing Al content is very close to the theoretically predicted variation based on the change of the internal quantum efficiency, assuming a direct-to-indirect bandgap energy transition at 1.92 eV.
Abstract: The detailed properties of "close-confinement" LPE (AlGa)As junction lasers have been studied in the Al composition range where the alloy has a direct bandgap transition. It has been shown that the laser efficiency is essentially independent of wavelength at 300°K between 9000 and 8000 A. This is important in applications where photocathodes are used to detect the laser radiation or where optical pumping of Nd:YAG laser is desired. Continuously operating red-emitting lasers at 77°K (6635 A) have also been fabricated. At room temperature, the lowest threshold current density, 8300 A/cm2for low Al content, ( x \leq 0.1 ) is only slightly higher than in GaAs, which is indicative of the excellent metallurgical properties possible in this alloy system. An external differential quantum efficiency of 43 percent at 300°K ( x \leq 0.1 ) nearly equals the best GaAs laser value. Furthermore, the relatively low series resistance in these devices makes possible power conversion efficiencies of ∼10 percent at 300°K and ∼50 percent at 77°K. The variation of the laser threshold currents and efficiency with increasing Al content is very close to the theoretically predicted variation based on the change of the internal quantum efficiency, assuming a direct-to-indirect bandgap energy transition at 1.92 eV. This suggests that the best devices perform very nearly at their theoretically predicted maximum in relation to present similarly constructed GaAs lasers.
Abstract: The spectral distribution of the output of a pulsed HF laser shows evidence of cascading from the \upsilon = 2 level to the ground state. Both calculations and experimental results indicate gain coefficients of 1 cm-1at HF pressure of 1 torr.
TL;DR: In this paper, a slotted hollow-cathode laser tube is presented, which operates at low voltage in a transverse discharge configuration and provides uniform axial distribution of laser media, especially metal vapors.
Abstract: Design features of a slotted hollow-cathode laser tube are presented. The tube operates at low voltage in a transverse-discharge configuration and provides uniform axial distribution of laser media, especially metal vapors. The design lends itself readily to all-metal construction.