Showing papers in "IEEE Journal of Quantum Electronics in 1987"
TL;DR: In this article, a numerical Kramers-Kronig analysis is used to predict the refractive index perturbations produced in crystalline silicon by applied electric fields or by charge carriers.
Abstract: A numerical Kramers-Kronig analysis is used to predict the refractive-index perturbations produced in crystalline silicon by applied electric fields or by charge carriers. Results are obtained over the 1.0-2.0 \mu m optical wavelength range. The analysis makes use of experimental electroabsorption spectra and impurity-doping spectra taken from the literature. For electrorefraction at the indirect gap, we find \Delta n = 1.3 \times 10^{5} at \lambda = 1.07 \mu m when E = 10^{5} V/cm, while the Kerr effect gives \Delta n = 10^{-6} at that field strength. The charge-carrier effects are larger, and a depletion or injection of 1018carriers/cm3produces an index change of \pm1.5 \times 10^{-3} at \lambda = 1.3 \mu m.
2,502 citations
TL;DR: In this article, the authors derived the nonlinear wave equation for an envelope of an electromagnetic wave in a monomode dielectric waveguide and derived the coefficients of the Schrodinger equation with higher-order dispersion and dissipation (both linear and nonlinear) in terms of properties of the eigenfunction of the guided wave as well as of the material nonlinearity and dispersion.
Abstract: We derive the nonlinear wave equation for an envelope of an electromagnetic wave in a monomode dielectric waveguide. Concrete examples are given for a single-mode optical fiber where the coefficients of resultant nonlinear Schrodinger equation with higher-order dispersion and dissipation (both linear and nonlinear) are given in terms of properties of the eigenfunction of the guided wave as well as of the material nonlinearity and dispersion. Using a newly-developed perturbation method, we show that the higher-order dispersions (linear and nonlinear) perserve the profile of a single soliton but to split up a bound N soliton ( N \geq 2 ) into individual solitons with different heights which propagate at different velocities. We also show that the higher-order nonlinear dissipation due to the induced Raman effect downshifts the carrier frequency of a single soliton in proportion to the distance of propagation and to the fourth power of the soliton amplitude.
782 citations
TL;DR: In this article, the authors present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility.
Abstract: The objective of this paper is to present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility. After introducing the definition of α and discussing its dependence on carrier concentration, photon energy, and temperature, we give a short historical summary on how the concept of α evolved over the past two decades. This is followed by a discussion of α dependence on device structure in gain-guided and subdimensional lasers (quantum wells and quantum wires). The bulk of the paper is devoted to a detailed review of laser properties influenced by α and of associated methods of estimating the value of α. Results of measurements reported to date are collected and the most reliable methods are indicated.
646 citations
TL;DR: In this article, a telescope is placed between two grating compressors in order to modify the phase shift for different wavelengths of different wavelengths, and the telescope simultaneously provides high magnification to compensate more than 90 km of standard monomode fibers in the 1.6 μm region, yielding compression factors as high as 3000.
Abstract: A compressor is designed that presents an opposite sign of the dispersion to that of standard two grating compressors. This is achieved by placing a telescope between gratings in order to modify in an adequate manner the phase shift for different wavelengths. The telescope simultaneously provides a high magnification in order to compensate more than 90 km of standard monomode fibers in the 1.6 μm region, yielding compression factors as high as 3000. Analytical expressions for Gaussian beams are found and limitations due to lateral spectral walkoff and telescope pupils are discussed.
646 citations
TL;DR: It is concluded that "laser biostimulation" is of aPhotobiological nature, and low-power laser effects can be related to well-known photobiological phenomena.
Abstract: Quantitative studies of the action of low-power visible monochromatic light on various cells (E. coli, yeasts, HeLa) were performed to find irradiation conditions (wavelength, dose, intensity) conducive to vital activity stimulation. The action spectra of visible light on DNA and RNA synthesis in HeLa cells have maxima near 404, 620, 680, 760, and 830 nm. Growth simulation of E. coli is at a maximum when irradiated at 404, 454, 570, 620, and 750 nm, and biomass accumulation stimulation in yeasts has a maxima at 404, 570, 620, 680, and 760 nm. Absorption of quanta is only a trigger for the rearrangement of cellular metabolism, with photosignal transduction being effected by standard cellular means such as changes in the cAMP level. Respiratory chain components are discussed as primary photoacceptors. It is concluded that "laser biostimulation" is of a photobiological nature, and low-power laser effects can be related to well-known photobiological phenomena.
518 citations
TL;DR: In this paper, the physical meaning and technical implications of nonlinear pulse propagation in birefringent, single-mode fibers are discussed in detail, and the modulational instability is studied.
Abstract: Equations describing nonlinear pulse propagation in birefringent, single-mode fibers are derived. The physical meaning and technical implications of these equations are then discussed in detail. Finally, the modulational instability is studied.
482 citations
TL;DR: In this article, a model for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium was developed for transitions to the manifolds4I 9/2 in Nd3+,4I 15/2 and 3H 6 in Tm3+.
Abstract: A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds4I 9/2 in Nd3+,4I 15/2 in Er3+,5I 8 in Ho3+and3H 6 in Tm3+. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the4F 3/2 -4I 9/2 transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.
399 citations
TL;DR: In this paper, the phase mismatch in the four-wave mixing process is clarified experimentally in a single-mode fiber transmission line at 825 nm wavelength, and the generated power of approximately 20 pW is measured successfully for input signal powers below 1 mW by the technique utilizing a heterodyne receiver and lock-in detector.
Abstract: The generation wave efficiency with respect to phase mismatch in the four-wave mixing process is clarified experimentally in a single-mode fiber transmission line at 825 nm wavelength. The generated power of approximately 20 pW is measured successfully for input signal powers below 1 mW by the technique utilizing a heterodyne receiver and lock-in detector. The calculated efficiency as a function of the equivalent frequency separation can well explain and reflect the results obtained experimentally. Furthermore, the efficiency at zero chromatic dispersion wavelengths of 1.3 and 1.55 μm is also discussed considering chromatic dispersion slope against wavelength.
393 citations
TL;DR: In this article, the authors calculate the electric field dependence of the linear and the third-order nonlinear intersubband optical absorption coefficients of a semiconductor quantum well in the infrared regime.
Abstract: Analytic forms of the linear and the third-order nonlinear optical intersubband absorption coefficients are obtained for general asymmetric quantum well systems using the density matrix formalism, taking into account the intrasubband relaxation. Based on this model, we calculate the electric field dependence of the linear and the third-order nonlinear intersubband optical absorption coefficients of a semiconductor quantum well. The energy of the peak optical intersubband absorption is around 100 meV (wavelength is 12.4 μm). Thus, electrooptical modulators and photodetectors in the infrared regime can be built based on the physical mechanisms discussed here. The contributors to the nonlinear absorption coefficient due to the electric field include 1) the matrix element variation and 2) the energy shifts. Numerical results are illustrated.
384 citations
TL;DR: In this paper, degenerate four-wave mixing measurements of the nonlinear coefficient of rutile and a number of optical glasses at 1.06 μm were reported and a figure of merit was defined to measure the suitability of a material for nonlinear waveguide switches.
Abstract: In this paper we report degenerate four-wave-mixing measurements of the nonlinear coefficient of rutile and a number of optical glasses at 1.06 μm. We define a figure of merit which measures the suitability of a material for nonlinear waveguide switches and show that the best glasses have figures of merit substantially higher than any other material. We include a brief discussion of the types of switching elements that could be made with these materials.
380 citations
TL;DR: The fluorescence spectra have been measured from native chromophores in malignant and normal human breast and lung tissues and the spectra profiles were found to be different in both species.
Abstract: The fluorescence spectra have been measured from native chromophores in malignant and normal human breast and lung tissues. The spectra profiles were found to be different in both species. In addition, one normal breast tissue exhibited Raman spectra.
TL;DR: In this paper, a single longitudinal mode (SLM) operating condition for phase-adjusted (PA) DFB lasers has been made clear both experimentally and theoretically, and a theory for the two-mode operation with the TE0 mode and the TE + 1 mode was developed.
Abstract: A single longitudinal mode (SLM) operating condition for phase-adjusted (PA) DFB lasers has been made clear both experimentally and theoretically. As expected, we got a high SLM operation yield of 80 percent in a moderate coupled case up to a light output power of 10 mW. However, in the strongly coupled cases, the two-mode operation with the TE0 mode and the TE + 1 mode occurred frequently. To explain the two-mode operation and to optimize the PA-DFB laser structure, we have developed a theory. Taking the spatial hole burning along the laser axis into account, we succeeded in explaining the longitudinal mode behavior. From our theory, moderate coupling ( kL = 1.25 ) was found to be optimum to maintain the large threshold gain difference above threshold.
TL;DR: In this paper, the frequency response of a group of 1.3 μm InGaAsP vapor-phase-regrown buried heterostructure lasers of various cavity lengths is analyzed by fitting the measured response curves.
Abstract: The frequency response of a group of 1.3 μm InGaAsP vapor-phase-regrown buried heterostructure lasers of various cavity lengths is analyzed by fitting the measured response curves. The dependence of resonant frequency f 0 and damping rate \Gamma on bias power is determined. The differential gain coefficient for InGaAsP is determined as 3.5 \times 10^{-16} cm2. The damping rate is found to be proportional to the square of the resonant frequency with a proportionality factor which is independent of device geometry and facet reflectivity. The existence of such a universal relationship between \Gamma and f 0 and the observed magnitude of the damping rate is explained by the interband relaxation model of nonlinear gain.
TL;DR: In this article, the authors investigated the propagation of ultrashort (0.83 ps), intense dye laser pulses through a single-mode optical fiber and found that the parameters of this pulse closely correspond to those of the fundamental soliton solution of the nonlinear Schroedinger equation.
Abstract: The propagation of ultrashort (0.83 ps), intense dye laser pulses through a single-mode optical fiber is investigated. The input wavelength is tuned in the vicinity of the zero dispersion wavelength of the fiber. Although the input power is sufficient to generate solitons of up to the tenth order we do not observe the formation of high-order solitons. Instead, the input pulse breaks up temporally and spectrally after an initial stage of narrowing, and an ultrashort Stokes pulse is formed which shifts continuously to lower frequencies with increasing fiber length. The parameters of this pulse closely correspond to those of the fundamental soliton solution of the nonlinear Schroedinger equation. Using fiber lengths from a few meters up to 1 km the resulting pulse durations lie between 55 and 410 fs and the corresponding wavelengths between 1.36 and 1.54 μm. Numerical simulations solving a modified nonlinear Schroedinger equation including higher order dispersion and the Raman effect are in good agreement with the experimental results. It is shown that the principal soliton pulse shaping mechanisms are pulse narrowing and the soliton self-frequency shift.
TL;DR: In this article, an analytic expression for the nonlinear gain in multimode semiconductor lasers using the density-matrix formalism was obtained, and the agreement between the theoretical and experimental values supported the hypothesis that spectral hole burning is the dominant mechanism for the gain nonlinearities in semiconductor laser.
Abstract: The gain spectrum in semiconductor lasers is affected by the intensity-dependent nonlinear effects taking place due to a finite intraband relaxation time of charge carriers. We obtain an analytic expression for the nonlinear gain in multimode semiconductor lasers using the density-matrix formalism. In general, the nonlinear gain is found to consist of the symmetric and asymmetric components. The asymmetry does not have its origin in the carrier-induced index change, but is related to details of the gain spectrum. The general expression for the nonlinear gain is used to discuss the range of single-longitudinal-mode operation of distributed feedback lasers. It is also used to obtain an analytic expression for the self-saturation coefficient and to compare the predicted value to the experimental value for both GaAs and InGaAsP lasers. The agreement between the theoretical and the experimental values supports the hypothesis that spectral hole burning is the dominant mechanism for the gain nonlinearities in semiconductor lasers.
TL;DR: In this paper, the authors present a theory of adiabatic chirp reduction and narrowing of the Lorentzian laser line that occurs when a laser is coupled to an external passive resonator.
Abstract: We present a theory of adiabatic chirp reduction and narrowing of the Lorentzian laser line that occurs when a laser is coupled to an external passive resonator. Chirp reduction and line narrowing are simply related. We show that the reduction in the Lorentzian line width is equal to the square of the reduction in adiabatic chirp. Both are strongly enhanced near resonances of the external cavity.
TL;DR: In this paper, a general theory of semiconductor lasers is presented in which the static and dynamic properties are expressed in terms of the effective left and right reflectivities at a given reference plane in the laser.
Abstract: A general theory of semiconductor lasers is presented in which the static and dynamic properties are expressed in terms of the effective left and right reflectivities at a given reference plane in the laser. The theory applies to Fabry-Perot and DFB solitary lasers and to laser configurations with strong optical feedback or strong light injection.
TL;DR: In this article, a harmonic generator with a set of thin plates with a large ratio of surface area to volume, and cooling the exposed surfaces with a flowing gas, is proposed.
Abstract: High average power frequency conversion using solid-state nonlinear materials is discussed. Recent laboratory experience and new developments in design concepts show that current technology, a few tens of watts, may be extended by several orders of magnitude. For example, using KD*P, efficient doubling (> 70 percent) of Nd:YAG at average powers approaching 100 KW is possible; for doubling to the blue or UV regions the average power may approach 1 MW. Configurations using segmented apertures permit essentially unlimited scaling of average power. High average power is achieved by configuring the nonlinear material as a set of thin plates with a large ratio of surface area to volume, and cooling the exposed surfaces with a flowing gas. The design and material fabrication of such a harmonic generator is well within current technology.
TL;DR: In this paper, a monocrystalline indium phosphide substrate of a predetermined conductivity type is used for a semiconductor laser, where a wide range of laser emission wavelengths can be obtained by varying the composition of monocrystaline alloys employed as semiconductor material.
Abstract: A semiconductor laser wherein a wide range of laser emission wavelengths can be obtained by varying the composition of monocrystalline alloys employed as semiconductor material. The semiconductor structure comprises on a monocrystalline indium phosphide substrate of a predetermined conductivity type successive epitaxial layers consisting of a first confinement layer of the same conductivity type, an active layer having the formula (Gax Al1-x)0.47 In0.53 As where x is within the range of 0 to 0.27, and a second confinement layer of opposite conductivity type. The confinement layers are composed of either InP or a ternary alloy Al0.47 In0.53 As or a quaternary alloy Gax' Al1-x' Asy' Sb1-y' where x' and y' are chosen so that the material should have a predetermined crystal lattice and an energy gap of greater width than the substrate material.
TL;DR: A three-dimensional model for estimating light distribution in laser irradiated tissue is presented in this article, where multiple scattering and absorption of the laser beam are modeled using seven fluxes One-, two-, and three dimensional solutions are discussed and light distributions computed from the seven flux model are compared to those computed with the diffusion approximation.
Abstract: A three-dimensional model for estimating light distribution in laser irradiated tissue is presented Multiple scattering and absorption of the laser beam are modeled using seven fluxes One-, two-, and three-dimensional solutions are discussed and light distributions computed from the seven flux model are compared to those computed with the diffusion approximation Methods for obtaining the phase function, absorption coefficient, and scattering coefficient for tissue are discussed and illustrated with measurements for human aortic vessel wall at the wavelength of 6328 nm Measured values are used in the seven flux model to estimate the rate of heat generation in the vessel wall
TL;DR: In this article, the authors presented a theoretical and experimental study in terms of small-signal gain, signal gain saturation, and noise characteristics of a 1.5 μm GaInAsP traveling-wave amplifier (TWA), realized through the application of SiO x film antireflection coatings.
Abstract: This paper presents a theoretical and experimental study in terms of small-signal gain, signal gain saturation, and noise characteristics of a 1.5 μm GaInAsP traveling-wave amplifier (TWA), realized through the application of SiO x film antireflection coatings. This TWA, having a residual facet reflectivity of 0.04 percent, exhibits a wide, flat signal gain spectrum and a saturation output power of +7 dBm at a 20 dB signal gain. The TWA also has a noise figure of 5.2 dB, which is the smallest value reported for semiconductor laser amplifiers. The experimental results are confirmed to be in good agreement with the theoretical predictions based on the multimode traveling-wave rate equations in conjunction with the photon statistic master equation analysis, which takes into account the amplifier material and device structural parameters. Signal gain undulation, saturation output power, and noise figure are also theoretically evaluated as functions of the facet reflectivity. The superior performance of the TWA demonstrates that the device is favorable for use in linear optical repeaters in fiber transmission systems.
TL;DR: In this paper, the principles of a powerful multicolor imaging system for tissue fluorescence diagnostics are discussed, where four individually spectrally filtered images are formed on a matrix detector by means of a split-mirror arrangement.
Abstract: The principles of a powerful multicolor imaging system for tissue fluorescence diagnostics are discussed. Four individually spectrally filtered images are formed on a matrix detector by means of a split-mirror arrangement. The four images are processed in a computer, pixel by pixel, by means of mathematical operations, leading to an optimized contrast image, which enhances a selected feature. The system is being developed primarily for medical fluorescence imaging, but has wide applications in fluorescence, reflectance, and transmission monitoring related to a wide range of industrial and environmental problems. The system operation is described for the case of linear imaging on a diode array detector. Laser-induced fluorescence is used for cancer tumor and atherosclerotic plaque demarcation using the contrast enhancement capabilities of this imaging system. Further examples of applications include fluorescing minerals and flames.
TL;DR: In this paper, a system that expands and recompresses an ultrashort pulse by means of diffraction gratings is described, and the expansion can be large enough to broaden the pulse to several nanoseconds.
Abstract: A system that expands and recompresses an ultrashort pulse by means of diffraction gratings is described. The expansion can be large enough to broaden the pulse to several nanoseconds. In this manner, as the signal and pump pulses have similar lengths, high-efficiency amplifiers can be designed. The expansion avoids inefficient energy storage in high-gain amplifiers and nonlinear effects in the amplifier medium, and the amplified spontaneous emission is drastically reduced by working in a saturated amplifier regime.
TL;DR: In this paper, the authors measured the low-frequency electrooptic and piezoelectric coefficients in undoped BaTiO 3 and Sr x Ba 1-x Nb 2 O 6 (x = 0.61 ) crystals using interferometric techniques.
Abstract: We have measured the low-frequency ("unclamped") electrooptic and piezoelectric coefficients in undoped BaTiO 3 and Sr x Ba 1-x Nb 2 O 6 ( x = 0.61 ) crystals using interferometric techniques. The contribution of the piezoelectric effect to the Pockels measurements is discussed. For an applied ac electric field in the range 0.1-200 V/cm, the electrooptic and piezoelectric effects are linear in the magnitude of the applied field and independent of its frequency in the range 10 Hz-100 kHz. The unclamped electrooptic coefficients of poled BaTiO 3 single crystals are r_{13} = 19.5 \pm 1 pm/V and r_{33} = 97 \pm 7 pm/V, and for strontium barium niobate are r_{13} = 47 \pm 5 pm/V and r_{33} = 235 \pm 21 pm/V, all measured at a wavelength of 514.5 nm and at T = 23\deg C. For the barium titanate samples the measured Pockels coefficient r_{c} \equiv r_{33} - (n_{1}/n_{3})^{3} r_{13} = 79 \pm 6 pm/V is in good agreement with the value r_{c} = 76 \pm 7 pm/V computed from the above values of r 13 and r 33 , where n 1 and n 3 are the ordinary and extraordinary indexes of refraction, respectively. The measured piezoelectric ] coefficient is d_{23} = +28.7 \pm 2 pm/V for barium titanate, and is d_{23} = +24.6 \pm 2 pm/V for strontium barium niobate. We also measured the photorefractive coupling of two optical beams in the crystals, and we show that the dependence of the coupling strength on beam polarization is in fair agreement with the measured values of the Pockels coefficients.
TL;DR: In this article, the effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed.
Abstract: The effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed. The analysis applies to any type of laser cavity formed by a corrugated waveguide limited by partially reflecting facets. It is shown that the sensitivity to optical feedback on a facet is closely related to the power emitted through this facet. Numerical results on wavelength selectivity and on sensitivity to optical feedback are given for conventional DFB lasers having an AR-coated facet and for quarter-wave-shifted (QWS) DFB lasers with AR-coatings on both facets. Both laser types are found to be more sensitive to optical feedback on their AR-coated facet than Fabry-Perot lasers for low kL . On the other hand, QWS-DFB lasers are found to be relatively insensitive to optical feedback for large kL .
TL;DR: In this paper, the effect of the XeCl laser optical pulse duration (7-300 ns) on the threshold fluence for ablation of arterial wall and on the quality of the cut in human postmortem artery was examined.
Abstract: The results of recent work directed towards the application of excimer lasers to angioplasty are presented. Several laser-tissue interactions are examined, including the effect of the XeCl laser optical pulse duration (7-300 ns) on the threshold fluence for ablation of arterial wall and on the quality of the cut in human postmortem artery, the potential for altering the ablation threshold fluence of arterial plaque in swine by treatment with hematoporphyrin derivative, and the healing response of swine arterial wall to surgical irradiation with an argon laser and a pulsed XeCl laser. The dependence of damage thresholds and transmission properties of selected commercial fused silica fibers on the laser pulsewidth and wavelength are determined.
TL;DR: In this paper, the authors proposed a non-Markovian relaxation process to estimate the spontaneous emission spectrum of a GaAlAs laser, which is in fair agreement with the observed one.
Abstract: Homogeneous broadenings and gain spectra in semiconductor lasers have been theoretically estimated, involving non-Markovian relaxation processes. The estimated spontaneous emission spectrum is in fair agreement with the observed one for a GaAlAs laser. The advantages of the present model, compared to conventional Lorentzian and delta-function models, are discussed.
TL;DR: In this paper, the authors explored the possibility of using a relativistic plasma density wave as a wiggler for producing free-electron laser radiation, and showed that the effect of such a wave on FEL gain can be very large.
Abstract: We explore the possibility of using a relativistic plasma density wave as a wiggler for producing free-electron laser radiation. Such a wiggler is a purely electric wiggler with frequency ω p (plasma frequency) and wavenumber k p . If an electron beam is injected parallel to the plasma wave wavefront, it is wiggled transversely with an apparent wiggler wavelength \lambda_{w} = 2\pi c/\omega_{p} . Using plasma densities in the 1017(cm-3) range, λ w of order 100 μm may be obtained, thereby permitting generation of short wavelength radiation with modest energy beams. The effective wiggler strength a_{w} = eA/mc^{2} \sim 0.5 can be extremely large. We discuss the excitation methods for such wigglers and examine the constraints imposed by the plasma medium on FEL gain in this scheme.
TL;DR: If this technique can be adapted to the endoscopic visualization of arteries in vivo (angios, Copy), it could become an important tool for the diagnosis of atherosclerosis and for the monitoring of atheroma ablation during laser angioplasty.
Abstract: A new medical imaging technique for arterial walls based on laser-induced autoflnorescence spectroscopy is reported. The internal surface of isolated arteries with or without atherosclerosis is irradiated with an argon ion laser (458 nm) and the peak intensity of the excited autofluorescence spectrum is related to the composition of the arterial wall. The higher autofluorescence intensity in the range between approximately 480 and 630 nm for grossly calcified tissue compared to normal or noncalcified atherosclerotic tissue is used to produce maps of the arterial wall. These images delineate the calcified areas of the sample with good spatial resolution. If this technique can be adapted to the endoscopic visualization of arteries in vivo (angios, Copy), it could become an important tool for the diagnosis of atherosclerosis and for the monitoring of atheroma ablation during laser angioplasty.
TL;DR: In this paper, the first study of laser-tissue interaction in the femtosecond time regime was performed in chinchilla grey rabbits, where exposure to single laser pulses of 80 fs duration at 625 nm was performed.
Abstract: We report the first study of laser-tissue interaction in the femtosecond time regime. Retinal damage thresholds and mechanisms produced by exposure to high-intensity femtosecond laser pulses were investigated in chinchilla grey rabbits. Exposures were performed using single laser pulses of 80 fs duration at 625 nm. ED 50 injury thresholds of 0.75 and 4.5 μJ were measured using fluorescein angiographic and ophthalmoscopic visibility criteria evaluating 204 laser exposures. Ultrastructural studies including light and electron microscopy were performed on selected lesions. Results suggest that the primary energy deposition in the retina occurs in melanin, However, in contrast to laser injuries produced by longer pulses, exposures of more than 100 × threshold in the 50-100 \mu J range did not produce significantly more severe lesions or hemorrhage. This suggests the presence of a nonlinear damage limiting mechanics in tissue exposed to femtosecond laser pulses.