Showing papers on "Saturable absorption published in 1999"
TL;DR: In this paper, the transition between the regimes of cw mode locking and Q-switched mode locking was investigated, and an extended theory that took into account nonlinear soliton-shaping effects and gain filtering was developed.
Abstract: The use of a saturable absorber as a passive mode locker in a solid-state laser can introduce a tendency for Q-switched mode-locked operation. We have investigated the transition between the regimes of cw mode locking and Q-switched mode locking. Experimental data from Nd:YLF lasers in the picosecond domain and soliton mode-locked Nd:glass lasers in the femtosecond domain, both passively mode locked with semiconductor saturable absorber mirrors, were compared with predictions from an analytical model. The observed stability limits for the picosecond lasers agree well with a previously described model, while for soliton mode-locked femtosecond lasers we have developed an extended theory that takes into account nonlinear soliton-shaping effects and gain filtering. © 1999 Optical Society of America [S0740-3224(99)01001-2] OCIS codes: 140.3580, 140.4050, 140.3540, 140.7090.
809 citations
TL;DR: In this article, the possibilities of liquid phase epitaxy (LPE) as a versatile technique for the development of new miniature optical components in single crystal dielectric media were reviewed.
134 citations
TL;DR: It is shown that a laser with a saturable absorber, described by the Yamada model, displays excitability just below threshold: below threshold the laser produces pulse trains with minimal jitter for a particular optimal noise level.
Abstract: We show that a laser with a saturable absorber, described by the Yamada model, displays excitability just below threshold. A small perturbation, for example, a small input pulse, can trigger a single high output pulse, after which the system relaxes back to the off state. In order to study possible applications, such as pulse reshaping and clock recovery, approximate expressions are given for the excitability threshold and the delay between input and output pulses. Under the influence of optical noise, the system displays coherence resonance: below threshold the laser produces pulse trains with minimal jitter for a particular optimal noise level. This all-optical coherence resonance allows direct experimental verification.
125 citations
TL;DR: In this paper, the nonlinear reflectivity of semiconductor saturable absorber mirrors has been investigated as a function of incident energy fluence, and the presence of two-photon absorption in commonly used structures was confirmed via time-resolved differential reflectivity measurements.
Abstract: The nonlinear reflectivity of semiconductor saturable absorber mirrors has been investigated as a function of incident energy fluence. The presence of two-photon absorption in commonly used structures was confirmed via time-resolved differential reflectivity measurements. Theoretical calculations predict that two-photon absorption will expand the continuous-wave mode-locking stability regime against Q-switched mode-locking, yet may simultaneously induce multiple pulses in a laser cavity.
113 citations
TL;DR: In this paper, the Yamada model for self-pulsations in (semiconductor) lasers with saturable absorber is considered and a complete picture of all possible dynamics is presented in terms of two-dimensional bifurcation diagrams, in which they find a Bogdanov-takens bifurycation as an organizing center.
94 citations
TL;DR: Passive Q switching of Er:glass lasers has been demonstrated with Cr( 2+):ZnSe and Co(2+): ZnSe saturable absorbers and theoretical modeling exhibits satisfactory agreement with experimental data.
Abstract: Passive Q switching of Er:glass lasers has been demonstrated with Cr2+:ZnSe and Co2+:ZnSe saturable absorbers. A pulse duration of ?50 ns and an output pulse energy of 5 mJ were obtained with both Co:ZnSe and Cr:ZnSe passive shutters. A Q-switched conversion efficiency of as much as 26% was obtained for Cr:ZnSe. Theoretical modeling exhibits satisfactory agreement with experimental data.
93 citations
TL;DR: The ground state absorption cross sections of the Co2+:MgAl2O4 crystal were estimated to be (2.8 ± 0.4) × 10-19 cm2 at 1.34 and 1.54 µm, respectively.
Abstract: Saturable-absorber Q switching of a neodymium-doped
YAlO3 laser at 1.34 µm and an erbium-doped glass
laser at 1.54 µm with a
Co2+:MgAl2O4 crystal was
demonstrated. Q-switched 1.34-µm pulses of
19-mJ energy and 60-ns duration and Q-switched
1.54-µm pulses of 2.7-mJ energy and 75-ns width were
obtained. The ground-state absorption cross sections of the
Co2+:MgAl2O4 crystal were estimated
to be (2.8 ± 0.4) × 10-19 and (3.5 ±
0.6) × 10-19 cm2 at 1.34 and 1.54
µm, respectively. The
4T1(4F) → 4A2 relaxation time of the
Co2+ ion in the MgAl2O4 crystal was
measured to be ∼350 ns.
93 citations
TL;DR: In this article, the ground and excited state absorption cross sections of Cr/sup 4+/-doped yttrium aluminum garnet are reported, and their ratio is shown to weakly determine the energy output of a passively Q-switched Nd:glass laser using this material as the saturable absorber.
Abstract: Z-scan measurements of the ground and excited state absorption cross sections of Cr/sup 4+/-doped yttrium aluminum garnet are reported. These quantities are found to depend on crystal preparation but are independent of temperature from -60/spl deg/C to 98/spl deg/C. Their ratio is shown to weakly determine the energy output of a passively Q-switched Nd:glass laser using this material as the saturable absorber.
71 citations
Patent•
04 Jun 1999
TL;DR: In this article, the active medium (providing gain or saturable absorption) is shaped as a ring, situated in a region of the fiber' cross-section where the intensity of the signal light is substantially reduced compared to its peak value.
Abstract: Single- or few-moded waveguiding cladding-pumped lasers, superfluorescent sources, and amplifiers, as well as lasers, including those for high-energy pulses, are disclosed, in which the interaction between the waveguided light and a gain medium is substantially reduced. This leads to decreased losses of guided desired light as well as to decreased losses through emission of undesired light, compared to devices of the prior art. Furthermore, cross-talk and inter-symbol interference in semiconductor amplifiers can be reduced. We also disclose devices with a predetermined saturation power. As a preferred embodiment of the invention, we disclose a single (transverse) mode optical fiber laser or amplifier in which the active medium (providing gain or saturable absorption) is shaped as a ring, situated in a region of the fiber' cross-section where the intensity of the signal light is substantially reduced compared to its peak value. The fiber can be cladding-pumped.
68 citations
TL;DR: In this article, a passive Q-switched erbium-doped fiber laser can be constructed by inserting a segment of samariumdoped fibre into the ring cavity as saturable absorber.
59 citations
TL;DR: In this paper, the authors study stability and bifurcations of 1D localized structures in a laser with a saturable absorber and provide evidence for the existence of 3D "laser bullets".
Abstract: We study stability and bifurcations of 1D localized structures in a laser with a saturable absorber. Instability leading to oscillating localized structure is described. Our numerical study of light propagation in a dispersive medium with saturable gain and absorption provides evidence for the existence of 3D 'laser bullets'.
TL;DR: In this paper, the authors characterized and modeled the relaxation oscillations that are present in the output of a high-power free-running diode-pumped Tm-doped silica fiber laser.
Abstract: The relaxation oscillations that are present in the output of a high-power free-running diode-pumped Tm-doped silica fiber laser are characterized and modeled. The laser operates on the 3H4→3H6 quasi-three-level transition and operates efficiently from ∼1.9 to ∼2.0 µm. From the measurements of the 3F4→3H4 fluorescence after 1.98-µm pumping of a separate, heavily Tm-doped silica fiber, it is established that the 3H4, 3H4→3H6, 3F4 upconversion process is significant in heavily Tm-doped silica fibers. This process causes the saturable absorption that is indicated by the presence of the relaxation oscillations. A detailed theoretical model that describes the ion-pair dynamics relevant to the Tm-doped silica system is presented. Equations for the steady-state intracavity photon density and for the steady-state population densities of the isolated and paired ions are derived. A linear stability analysis and numerical analysis are also carried out. It is established that, for large emission-to-absorption cross-section ratios that are relevant to Tm-doped silica and for pump rates for which stable output is predicted, the oscillations are weakly damped before the steady state is reached. Best agreement between the experimental and model results is achieved when all the Tm3+ ions within the present fiber are considered paired.
Journal Article•
TL;DR: Poly(indenofluorene) shows a strong degenerate four-wave mixing (DFWM) response when it is excited with 100-fs pulses at 800 nm, which is interpreted as being due to absorption saturation phenomena.
TL;DR: In this paper, a pump-probe technique with picosecond resolution was used to record and derive the differential and excited-state absorption (ESA) spectra of a Co2+:LaMgAl11O19 (LMA) single crystal in the visible and near-infrared spectral regions.
Abstract: A pump–probe technique with picosecond resolution was used to record and derive the differential and excited-state absorption (ESA) spectra of a Co2+:LaMgAl11O19 (LMA) single crystal in the visible and near-infrared spectral regions. Time resolution allowed us to observe ESA bands that can be assigned to a 4T2(4F)→4T1(4P) optical transition and to transitions from the thermally populated 2E(2G) excited state to doublet levels that arise from the 2F free-ion level of the tetrahedrally coordinated Co2+ ion. Intensity-dependent transmission measurements were also carried out at 1.34 and 1.54 µm. Passive Q switching of Nd3+:YAlO3 (1.34-µm) and of Er3+:glass (1.54-µm) lasers by use of the Co2+:LMA crystal as a saturable absorber was demonstrated. The pulse durations (energies) of the Q-switched Nd3+:YAlO3 and Er3+:glass lasers were found to be 75 ns (3.8 mJ) and 50 ns (4.5 mJ), respectively.
TL;DR: An erbium fiber laser is described that is passively mode locked by a novel, precision antireflection-coated semiconductor saturable-absorber mirror that incorporates an additional two-photon absorber.
Abstract: We describe an erbium fiber laser that is passively mode locked by a novel, precision antireflection-coated semiconductor saturable-absorber mirror that incorporates an additional two-photon absorber. It is shown that passive mode locking evolves from a Q?switching instability. The results are achieved by use of saturable absorbers that provide a large (15%) nonlinear (saturable) loss. Exploiting two-photon absorption can substantially reduce the peak power of the Q?switched pulses, which results in improved reliability of the laser. Moreover, two-photon absorption can be used to produce an optimal stability range for saturable-absorber mode locking.
TL;DR: In this article, the authors distinguish between two-photon absorption (TPA) and excited state absorption (ESA) using the Z-scan technique with 532 nm laser pulses of dual widths in the picosecond regime.
TL;DR: In this paper, a study of soliton generation by a passively mode-locked laser using a slow saturable absorber was performed, and it was shown theoretically that multisoliton regimes of generation are possible.
Abstract: We perform a study of soliton generation by a passively mode-locked laser using a slow saturable absorber. We show theoretically that multisoliton regimes of generation are possible. The values of the parameters are found where one-, two-, or three-soliton solutions exist.
TL;DR: In this paper, a simple frequency control method of a single-frequency fiber laser is proposed and demonstrated, where the mechanism of the frequency control arises from cooperatively induced spatial-hole burning (SHB) in a saturable absorber in the laser cavity.
Abstract: A simple frequency control method of a single-frequency fiber laser is proposed and demonstrated. The mechanism of the frequency control arises from cooperatively induced spatial-hole burning (SHB) in a saturable absorber in the laser cavity. The SHB is formed by an external frequency-stabilized light source and the lasing light. Consequently, the lasing frequency can be tuned to the external light frequency. Moreover, narrow-linewidth operation is possible even when an external-source with a broad-linewidth is employed.
TL;DR: In this paper, a theoretical steady-state rate-equation analysis is presented for investigating the critical conditions for the conversion from reverse saturable absorption (RSA) to saturated absorption (SSA).
TL;DR: Passive Q-switching of a diode-pumped Nd:YAG laser is demonstrated using a GaAs wafer as saturable absorber as well as output coupler in this article.
TL;DR: In this paper, external modulation on the Cr4+:YAG saturable absorber by a laser diode is proposed to alleviate the timing jitter problem, which reduces the jitter by a factor of 2.5.
Abstract: The timing jitter of passively Q-switched Nd:Y3Al5O12/Cr4+:Y3Al5O12 (Nd:YAG/Cr4+:YAG) laser is studied both numerically and experimentally. It is found that spontaneous noise in the microwatt range can significantly affect the repetition rate of high-power Q-switched lasers, and creates large pulse-to-pulse timing jitter. External modulation on the Cr4+:YAG saturable absorber by a laser diode is proposed to alleviate this jitter problem. Reduction in timing jitter by a factor of 2.5 is demonstrated.
TL;DR: In this paper, the ultrafast nonlinear dynamics of InGaAs/InP semiconductor saturable absorber mirrors are investigated using reflective pump-probe measurements using reflective reflectivity measurements.
Abstract: The ultrafast nonlinear dynamics of InGaAs/InP semiconductor saturable absorber mirrors are investigated using reflective pump–probe measurements. At high fluence, ultrafast induced absorption begins to dominate over absorption bleaching. Above the InGaAs quantum well band gap, the differential reflectivity shows a ∼1 ps transient due to nonequilibrium carrier dynamics. Below band gap, the signal is dominated by a strong two-photon absorption component followed by induced absorption that decays with a time constant of ∼5 ps; these components are attributed to nonlinear absorption and subsequent carrier diffusion in the InP layer.
TL;DR: In this paper, a red alexandrite laser with a potential tunability range between 700 and 818 nm and a frequency doubled Nd:YAG laser operating at 532 nm was reported.
TL;DR: In this paper, a passively mode-locked laser diode stabilized by subharmonic-frequency optical pulse injection was shown to reduce the timing jitter to less than that of the master laser pulses.
Abstract: Reduction of the timing jitter to less than that of the master laser pulses was achieved for a passively mode-locked laser diode stabilized by subharmonic-frequency optical pulse injection. Detailed investigation revealed that this phenomenon originates from the short-term stability of the mode locking frequency under passively mode-locking operation with suitable bias conditions of the saturable absorber and the gain sections.
TL;DR: In this paper, the reverse saturable absorption (RSA) of C60-doped porous sol-gel glasses was investigated by single and double-pulse pump-probe experiments.
Abstract: We investigate the nonlinear absorption of C60-doped porous sol-gel glasses by single- and double-pulse pump–probe experiments. We find that the reverse saturable absorption (RSA) of these samples can be explained in the frame of a five level system as it is commonly used for C60 solutions. We observe a strong saturation of the RSA at high fluences, especially if the molecules are prepared in the triplet state. In a double-pulse pump–probe experiment we measure the triplet quantum yield for C60 solutions (0.8) and doped glasses (0.25) and the singlet and triplet absorption cross sections. In the first excited singlet state (S1) lifetimes of 1 ns and 65 ps are determined in solutions and glasses, respectively. We find that the dynamics of both depopulation processes, direct S1–S0 relaxation, and intersystem crossing is faster in glasses than in the case where C60 is in solution in a liquid aromatic solvent. We tentatively explain these findings by the absence of a stabilizing solvent and a perturbation of ...
TL;DR: In this article, the transverse effects of a degenerate optical parametric oscillator with a saturable absorber were studied and the analysis of two-dimensional stationary and time-dependent localized patterns was performed.
Abstract: We study the transverse effects in a degenerate optical parametric oscillator with a saturable absorber. We focus on the analysis of two-dimensional stationary and time-dependent localized patterns. The homogeneous steady-state solution is destabilized by a Hopf bifurcation to periodic states with finite wave number and a Turing bifurcation. These bifurcations are close enough that they interact. This leads to localized structures consisting of a sharp peak emitting concentric rings of alternating high and low intensities.
TL;DR: In this article, a monolithic passively mode-locked laser diodes with bandgap-wavelength detuned saturable absorbers using selective growth was fabricated, and the pulsewidth shortened with increasing detuning of the absorber toward shorter wavelengths.
Abstract: We fabricated monolithic passively mode-locked laser diodes with bandgap-wavelength detuned saturable absorbers using selective growth. The pulsewidth shortened with increasing detuning of the absorber toward shorter wavelengths. For the detuned absorber, the pulsewidth was reduced to 1.2 ps, compared to 2.6 ps for the nondetuned absorber. This originated in broadened mode-locked spectra and reduced absorption recovery time under larger reverse bias voltages for detuned saturable absorbers.
TL;DR: In this paper, the authors measured intensity-dependent prism coupling of poly(p-phenylenevinylene) thin films with picosecond laser pulses in the range 750-1600 nm.
Abstract: We have measured intensity-dependent prism coupling of poly(p-phenylenevinylene) thin films with picosecond laser pulses in the range 750–1600 nm. We developed a refined evaluation method that yields the signs and absolute values of the nonlinear refractive index n2 and the nonlinear absorption coefficient α2. Strong two-photon absorption levels were found at 2.8 and 3.1 eV. We observed a resonance at 1.3 eV that behaves as saturable absorption, and several additional resonances and sign changes of n2 at even lower photon energies. We demonstrate reversible refractive-index changes Δn=+0.002 at 910–950 nm on a picosecond time scale. Even larger Δn appear feasible.
TL;DR: In this paper, a nonlinear loss term caused by the frequency doubler was introduced into the coupled rate equations describing the operation of saturable absorber passively Q-switched lasers, which can express the harmonic pulse characteristics such as peak power, pulse energy, pulsewidth, and a factor describing pulse symmetry.
Abstract: Passively Q-switched lasers can be optimized by the choice of two factors: (1) reflectivity of the output coupler and (2) transmission of an unsaturated absorber. When intracavity frequency doubling is adopted, the nonlinear crystal behaves as a nonlinear output coupler. In this paper, we generalize the optimization theory for intracavity frequency-doubled passively (Q)-switched lasers. By introducing a nonlinear loss term caused by the frequency doubler into the coupled rate equations describing the operation of saturable absorber passively Q-switched lasers, we can express the harmonic pulse characteristics such as peak power, pulse energy, pulsewidth, and a factor describing pulse symmetry. Using the Lagrange multiplier technique to maximize the peak power of the second harmonic for a given pump level, we obtain an additional constraint equation describing the relation of a frequency-doubling factor to a normalized intermediate variable, which can be solved quickly to determine the characteristics of the pulse. The frequency-doubling factor, which is a normalized key parameter, is found to depend not only on the commonly used coefficient of the nonlinear frequency doubler and the emission cross section of the laser medium, but also on the laser cavity optical length. We plot design curves indicating the key parameter and the pulse characteristics via two normalized variables, one representing the pump level, and the other representing the laser emission medium and the absorber medium. Using these curves and expressions, one can design an optimal passively Q-switched intracavity frequency-doubled miniature laser and predict the pulse characteristics without relying on computer calculation.
TL;DR: In this article, a wedge-shaped saturable absorber structure based on commercial semiconductor-doped glasses was used to start Kerr-lens mode locking, and transform-limited 52-fs pulses were generated.
Abstract: We report a novel wedge-shaped saturable absorber structure based on commercial semiconductor-doped glasses. By use of several different semiconductor-doped glasses, fast saturable absorber passive mode locking of a Ti:Al2O3 laser was demonstrated, which generated pulse durations as short as 2 ps in the 780–860-nm range. These saturable absorbers were also used to start Kerr-lens mode locking, and transform-limited 52-fs pulses were generated. Photodarkening effects in the semiconductor-doped glasses have been observed and characterized on a femtosecond time scale.