Showing papers on "Saturable absorption published in 1995"
TL;DR: In this article, the authors showed that the nonlinear optical response due to instantaneous two-photon absorption can be used to yield effective values of the relevant parameters of optical nonlinearity due to reverse saturable absorption.
Abstract: The optical limiting action of C60 in toluene solution is mainly due to reverse saturable absorption (RSA). It is shown that the formalism describing nonlinear optical response due to instantaneous two-photon absorption can be used in the case of sequential two-photon absorption, yielding effective values of the relevant parameters of optical nonlinearity due to RSA. The effective two-photon absorption parameter beta eff and the effective nonlinear refractive index parameter gamma eff', which are related respectively to the imaginary and real parts of the effective third-order susceptibility chi eff(3) were measured by the z-scan technique as a function of fullerene concentration and of incident laser intensity and wavelength over the 420-640 nm region. The concentration dependence of these parameters indicates that the solution is optically thin as far as the ground state of C60 is concerned, whereas the wavelength dependence confirms the applicability of the formalism used in the sequential two-photon absorption model. Comparisons are made with other z-scan results on C60.
282 citations
TL;DR: It is shown that a soliton of the nonlinear Schrödinger equation perturbed by filter losses and/or the finite gain bandwidth of amplifiers can be kept stable by saturable absorbers with a relaxation time much longer than the width of the soliton.
Abstract: We show that a soliton of the nonlinear Schrodinger equation perturbed by filter losses and/or the finite gain bandwidth of amplifiers can be kept stable by saturable absorbers with a relaxation time much longer than the width of the soliton. This provides for ultrashort pulse generation with a slow saturable absorber only and may have possible applications in the stabilization of soliton storage rings.
255 citations
TL;DR: Stable single-frequency and polarization operation of a traveling-wave, Er(3+)-doped fiber loop laser is demonstrated by incorporating an unpumped Er(+3)- doped fiber section butted against a narrow-band feedback reflector with saturable absorber that acts as a narrow bandpass filter that automatically tracks the lasing wavelength.
Abstract: We demonstrate stable single-frequency and polarization operation of a travelling-wave Er3+:Yb3+-doped fiber loop laser by incorporating an unpumped Er3+-doped fiber section butted against a narrowband feedback reflector. The saturable absorber acts as a narrow bandpass filter which automatically tracks the lasing wavelength, thus ensuring single-frequency operation. Output powers up to 6.2 mW at 1535 nm were obtained for launched pump powers of 175 mW at 1064 nm. At this output, the RIN was less than -112 dB/Hz at frequencies above 200 kHz and the laser linewidth less than 0.95 kHz whilst the lasing frequency was observed to drift slowly (~ 170 MHz/hr) due to environmental effects.
241 citations
TL;DR: In this paper, the Fabry-Perot saturable absorber has been used to predict the dynamic behavior of a solid state laser in the important regimes of Q-switching, mode-locked Qswitching and continuous-wave mode locking.
Abstract: We have successfully demonstrated that an appropriately designed semiconductor saturable absorber device, the antiresonant Fabry-Perot saturable absorber, can reliably start and sustain stable mode locking of solid state lasers such as Nd:YAG, Nd:YLF, Nd:Glass, Cr:LiSAF, and Ti:sapphire lasers. Especially for solid state lasers with long upper-state lifetimes, previous attempts to produce self-starting passive mode locking with saturable absorbers was always accompanied by self-Q-switching. We derive criteria that characterize the dynamic behavior of solid state lasers in the important regimes of Q-switching, mode-locked Q-switching, and continuous-wave mode locking in the picosecond and femtosecond range for the pulsewidth. We demonstrate that semiconductor absorbers can be designed to predetermine the dynamic behavior of a laser for a given solid state laser material and present an experimental verification. This allows for the development and design of robust, compact pico- and femtosecond solid state laser sources for scientific and industrial applications.
197 citations
TL;DR: A passively mode-locked femtosecond Yb:YAG laser is demonstrated using different semiconductor saturable absorber devices, a high-finesse and a low- finesse antiresonant Fabry–Perot saturative absorber and mode locked the laser at either 1.03 or 1.05 μm.
Abstract: We demonstrate a passively mode-locked femtosecond Yb:YAG laser using different semiconductor saturable absorber devices, a high-finesse and a low-finesse antiresonant Fabry–Perot saturable absorber. We achieved pulses as short as 540 fs with dispersion compensation and 1.7-ps pulses without dispersion compensation. We also mode locked the laser at either 1.03 or 1.05 μm by adjusting the band gap and antiresonance wavelength design of the antiresonant Fabry–Perot saturable absorber.
143 citations
TL;DR: In this article, the ground state and excited state absorption cross sections of the Cr/sup 4+/:YSO absorber were found by bleaching experiments to be (7.0/spl plusmn/1.4)/spl times/10/sup -19/ cm/sup 2/ and (2.3/spl+mn/0.5)/spl-times/ 10/sup-19 cm/Sup 2/ at 694 nm, respectively.
Abstract: Tunable passive Q-switching (781 nm to 806 nm at 300 K) of a flash-lamp pumped Cr/sup 3+/:LiCaAlF/sub 6/ (Cr:LiCAF) laser with a Cr/sup 4+/:Y/sub 2/SiO/sub 5/ (Cr/sup 4+/:YSO) broad-band solid-state saturable absorber has been realized. Typical pulse widths of the Q-switched laser output ranged from 40 ns to 80 ns, depending on the lasing wavelength. Spectral narrowing and reduced beam diameter with the use of the saturable absorber were observed. The ground state and the excited state absorption cross sections of the Cr/sup 4+/:YSO absorber were found by bleaching experiments to be (7.0/spl plusmn/1.4)/spl times/10/sup -19/ cm/sup 2/ and (2.3/spl plusmn/0.5)/spl times/10/sup -19/ cm/sup 2/ at 694 nm, respectively. Numerical simulation was utilized to simulate the Cr:LiCAF passive Q-switching with Cr/sup 4+/:YSO solid-state saturable absorber. >
139 citations
TL;DR: In this paper, a large signal dynamic computer model was used to compare the performance of CPM and self-colliding pulse mode-locking (SCPM) in semiconductor laser devices.
Abstract: Monolithic colliding pulse mode-locking (CPM) in semiconductor lasers is compared with self colliding pulse mode-locking (SCPM) through a large signal dynamic computer model which incorporates most of the significant features of semiconductor lasers. These include gain saturation, spontaneous emission, the gain-frequency relation, and the line-width enhancement factor. This new model replicates many of the published experimental results and also gives additional insight into the internal operation of the device. In particular, gain saturation combined with the standing waves created by colliding pulses within the saturable absorber produce a transient gain grating. This is found to have significant effects in locking either the even or the odd modes together in CPM. A performance comparison between CPM and SCPM is completed and some key design parameters of both configurations are explored. >
128 citations
Patent•
05 Sep 1995
TL;DR: In this paper, a technique for the generation of femtosecond and picosecond (psec) pulses from model-clocked double-clad fiber cladding pumped with broad area diode laser arrays is disclosed.
Abstract: A technique for the generation of picosecond (psec) and femtosecond (fsec) pulses from modelocked double-clad fiber lasers cladding pumped with broad area diode laser arrays is disclosed. Using an erbium/ytterbium fiber oscillator, 560 fsec pulses with pulse energies up to 40 pJ are generated at a wavelength of 1560 nm. In a dispersion-compensated cavity, pulses as short as 170 fsec with pulse energies up to 50 pJ are obtained. By adding a negatively chirped fiber Bragg grating for additional intracavity dispersion control, pulse widths of 3 psec with pulse energies up to 1 nJ are obtained. A saturable absorber is used for pulse start up, whereas nonlinear polarization evolution is exploited for steady-state pulse shaping. An environmentally stable design is ensured by employing birefringent fibers and a compensation scheme for linear and nonlinear polarization drifts in the cavity.
114 citations
TL;DR: Passive Q switching of Er:glass (1.53 microm) with a new, robust, solid-state saturable absorber, Co(2+):Y(3)Sc(2)Ga( 3)O(12), has been demonstrated.
Abstract: Passive Q switching of Er:glass (1.53 microm) with a new, robust, solid-state saturable absorber, Co(2+):Y(3)Sc(2)Ga(3)O(12), has been demonstrated. Q-switched pulses of 20 ns and 4 mJ of energy were obtained. An absorption cross section of 5 x 10(-20) cm(2) was measured. Preliminary results for a Co(2+):Y(3)Al(5)O(12) saturable absorber Q switch are also discussed.
101 citations
TL;DR: In this article, the authors demonstrate passively mode-locked diode-pumped Nd:glass lasers with different media such as silicate, phosphate, and fluorophosphate that are homogeneously or inhomogeneously broadened.
Abstract: We demonstrate passively mode-locked diode-pumped Nd:glass lasers with different media such as silicate, phosphate, and fluorophosphate that are homogeneously or inhomogeneously broadened. An antiresonant Fabry-Perot saturable absorber starts and stabilizes the soliton mode-locked Nd:glass lasers, producing pulses as short as 130 fs at an average output power of 100 mW. With a cw Ti:sapphire pump laser we obtain pulses as short as 90 fs.
98 citations
Patent•
08 Feb 1995TL;DR: In this article, an apparatus and method for a passively Q-switched microlaser for producing high-peak-power pulses of light of extremely short duration are disclosed, consisting of a gain medium (12) and saturable absorber (14) disposed within a laser cavity.
Abstract: An apparatus and method for a passively Q-switched microlaser (10) for producing high-peak-power pulses of light of extremely short duration are disclosed. The apparatus comprises a gain medium (12) and saturable absorber (14) disposed within a laser cavity (16, 18). When the cavity (16, 18) is pumped, the saturable absorber (14) prevents the onset of lasing until the inversion density within the cavity (16, 18) reaches a critical value. The length of the cavity (16, 18), the material parameters, and the reflectivities of the mirrors (16, 18) are selected such that pulses of duration less than about 1 ns and of peak power in excess of about 10 kW are obtained. The invention has application in high-precision optical radar, nonlinear optics, micromachining, microsurgery, robotic vision, and other technologies requiring high-peak-power laser pulses of extremely short duration.
TL;DR: Very efficient ultrastable millimetre-wave signal generation using hybrid modelocking of a monolithic distributed Bragg reflector semiconductor laser was demonstrated for the first time in this article.
Abstract: Very efficient ultrastable millimetre-wave signal generation using hybrid modelocking of a monolithic distributed Bragg reflector semiconductor laser is demonstrated for the first time. Unlike conventional hybrid modelocking methods, a low-power (-1 dBm) RF signal is applied to the saturable absorber section of the laser. The detected laser output gives a 34 GHz signal with phase noise >
TL;DR: In this paper, the authors reported the measurement of reverse saturable absorption in four cubanelike transition-metal clusters with nanosecond laser pulses and presented a five-level rate-equation model in which ionization and germinate recombination were included.
Abstract: We report the measurement of reverse saturable absorption in four cubanelike transition-metal clusters with nanosecond laser pulses. We also present a five-level rate-equation model in which ionization and germinate recombination are included. A comparison between the model and the measured data shows that the population of the triplet states is generated mainly through the ionization–recombination process, and triplet–triplet absorption is responsible for the measured reverse saturable absorption.
TL;DR: Using an erbium-doped fiber laser passively mode locked by a semiconductor saturable absorber, five-ps pulses of a 2.3-nJ/pulse are generated, which are more than three times higher in energy than for other reported EDFL's.
Abstract: Using an erbium-doped fiber laser (EDFL) passively mode locked by a semiconductor saturable absorber, we generate 55-ps pulses of a 23-nJ/pulse, which are more than three times higher in energy than for other reported EDFL's We show that, by introduction of a linear loss element within the cavity, multiple pulsing behavior at high pump powers can be suppressed We also determine the saturable-absorber characteristics-absorbance versus wavelength near band gap-that are necessary to produce short mode-locked pulses
TL;DR: It is demonstrated experimentally that solid-state lasers with strong solitonlike pulse shaping can be mode locked by a slow saturable absorber only, and an extrapolation would predict that an asymptotically equal to 100-fs recovery time of a semiconductor absorber could support pulses into the 10-fs regime.
Abstract: We demonstrate experimentally that solid-state lasers with strong solitonlike pulse shaping can be mode locked by a slow saturable absorber only, ie, the response time is much slower than the width of the soliton A Ti:sapphire laser mode locked by a low-temperature-grown GaAs absorber with 10-ps recovery time generates pulses as short as 300 fs without the need for Kerr-lens mode locking and critical cavity alignment An extrapolation of this result would predict that an ≈100-fs recovery time of a semiconductor absorber could support pulses into the 10-fs regime
Patent•
20 Oct 1995
TL;DR: In this article, the authors used semiconductor saturable absorbers with life-times of the order of 10 nsec into fiber lasers with cavity round-trip times of 100 nsec, leading to the stable generation of pulses at integer multiples of the fundamental cavity frequency.
Abstract: The generation of ultrashort pulses with adjustable repetition rates from passively modelocked fiber lasers is demonstrated. By inserting semiconductor saturable absorbers with life-times of the order of 10 nsec into fiber lasers with cavity round-trip times of the order of 100 nsec, passive harmonic modelocking is obtained, leading to the stable generation of pulses at integer multiples of the fundamental cavity frequency. For polarization states that allow for optical limiting of the lasers, pulses are obtained in a frequency range between 20 and 500 MHz., where different repetition rates can be simply selected by changing the pump power level to the cavity. The pulse jitter within one cavity round-trip time is measured to be between 300 psec and 50 psec, where side bands in the frequency domain may be suppressed by up to 70 dB. The saturable absorber acts to both stabilize the cavity repetition rate and to initiate passive modelocking, where nonlinear-polarization evolution is used to sustain modelocking and to suppress amplitude fluctuations of the pulses by providing for optical limiting. Practical embodiments can be obtained by employing environmentally stable cavity designs in polarization preserving single-clad and double clad fibers, where the latter fiber designs allow the pumping of the fiber lasers with broad area-diode array lasers.
TL;DR: Using a 15 nm-thick antireflection-coated GaAs absorber layer on an AlGaAs/AlAs Bragg mirror as a nonlinear reflector, the authors achieved self-starting passive modelocking of a Ti-sapphire laser with 34fs pulses without Kerr lens modelocking.
Abstract: Using a 15 nm-thick antireflection-coated GaAs absorber layer on an AlGaAs/AlAs Bragg mirror as a nonlinear reflector, we achieved self-starting passive modelocking of a Ti-sapphire laser with 34fs pulses without Kerr lens modelocking.
TL;DR: Self-starting of passively mode-locked lasers with fast saturable absorption is studied, and the basic assumption is that the lasers will self-start when cw operation is unstable and mode-lock operation is stable.
Abstract: Self-starting of passively mode-locked lasers with fast saturable absorption is studied. Our basic assumption is that the lasers will self-start when cw operation is unstable and mode-locked operation is stable. We start with a standard model, closely related to the Ginzburg–Landau equation, that is valid when the change in the time variation of the laser light during one round trip through the laser is small, and we determine the parameter regime in which cw mode operation becomes unstable. Coupled with previous results on the stability of mode-locked operation, these results allow us to determine when a laser will self-start. We apply our theory to figure-eight lasers with external gain.
Patent•
NEC1
TL;DR: In this paper, a mode-locked semiconductor laser with two resonator cavities formed by two facets and a distributed feedback structure between these two facets is presented. But the frequency of the high-frequency modulation is equal to the round trip frequency within the longer resonator cavity.
Abstract: A semiconductor laser is provided which is capable of generating a train of ultrashort light pulses with an ultrahigh repetition frequency and which is useful in optical communications and optical information processing. The semiconductor laser is a mode-locked semiconductor laser which has two resonator cavities which are formed by two facets and a distributed feedback structure between these two facets. The length of the resonator cavity formed between one facet and the distributed feedback structure is 1/m (where m is an integer) of the length of the resonator cavity formed by the other facet and the distributed feedback structure. A saturable absorption region and a high-frequency modulation region are provided within the longer of the resonator cavities. By making the high-frequency modulation frequency be equal to the round trip frequency of the light within the longer resonator cavity, mode-locked operation is achieved. Because of the linking of the shorter resonator cavity, a train of light pulses having a repetition frequency of m times the mode-locked pulse train frequency is obtained.
TL;DR: In this article, the dynamic characteristics of surface emitting lasers with a saturable absorbing layer are modelled, and shown to exhibit self-sustained pulsations up to 10 GHz, using a set of coupled rate equations to investigate the regions of self-pulsations, and show that there is an optimum position for the absorbing layer within the cavity structure to produce the widest range of pulsation frequencies.
Abstract: The dynamic characteristics of surface emitting lasers with a saturable absorbing layer are modelled, and shown to exhibit self-sustained pulsations up to 10 GHz. A set of coupled rate equations is used to investigate the regions of self-pulsations, and show that there is an optimum position for the absorbing layer within the cavity structure to produce the widest range of pulsation frequencies.
TL;DR: In this paper, the performance of a Q-switched Nd:YAG laser using Cr 4+ :YAG as a passive Q -switched was reported, which contained two orders of magnitude more energy than the free running spike.
TL;DR: Solitary-pulse generation in a degenerate optical parametric oscillator subjected to continuous-wave pumping is investigated theoretically and pulse stability is ensured by the parametric gain itself and does not require any fast saturable absorber action.
Abstract: Solitary-pulse generation in a degenerate optical parametric oscillator subjected to continuous-wave pumping is investigated theoretically. As with solitary lasers, pulse shaping is a phase effect induced by the interplay between self-phase modulation and group-delay dispersion, but pulse stability is ensured by the parametric gain itself and does not require any fast saturable absorber action.
TL;DR: In this paper, an optical pulse storage ring, storing 1.76 kb of 20 Gb/s pulsed, on-off keyed, noise-generated data has been demonstrated.
Abstract: An optical pulse storage ring, storing 1.76 kb of 20 Gb/s pulsed, on-off keyed, noise-generated data has been demonstrated. Stable operation is achieved using amplitude modulation, filtering, and artificial fast saturable absorption. Patterns with widely varying densities of ONE's have been stored, including patterns with all ONE's (harmonic mode-locking). >
TL;DR: The scaling of the antiresonant Fabry-Perot saturable absorber toward a novel antiref lection-coated thin saturated absorber is demonstrated and discussed and soliton mode-locked self-starting 34-fs pulses over the full cavity stability regime are obtained.
Abstract: We demonstrate and discuss the scaling of the antiresonant Fabry–Perot saturable absorber toward a novel antireflection-coated thin saturable absorber. With a Ti:sapphire laser we obtained self-starting Kerr-lens mode-locked pulses as short as 19 fs. With the higher modulation depth of the thin saturable absorber we obtained soliton mode-locked self-starting 34-fs pulses over the full cavity stability regime with a significantly shorter mode-locking buildup time. The pulse duration was limited only by the semiconductor Bragg mirror.
TL;DR: A general ten-level density-matrix model and its simplified models for the three cases of excited-state nonlinear absorption behaviors are proposed and in good agreement with the experimental results.
Abstract: Three typical excited-state nonlinear absorption effects in molecular systems with weak ground-state absorption (at 532 nm) are experimentally demonstrated: (a) reverse saturable absorption (RSA) caused by strong triplet first-to-second excited-state absorption in a copper phthalocyanine solution with 15-ns laser pulses; (b) RSA caused by strong singlet first-to-second excited-state absorption in a ${\mathrm{C}}_{60}$ solution with 21-ps laser pulses; (c) the RSA-SA turnover caused by strong singlet first-to-second excited-state absorption and weak singlet second-to-third excited-state absorption in a metallo-porphyrin-like solution with 21-ps laser pulses. To simulate these excited-state nonlinear absorption behaviors we propose a general ten-level density-matrix model and its simplified models for the three cases. All simulations are in good agreement with the experimental results.
Patent•
25 Jan 1995TL;DR: In this article, a diode-pumped monolithic laser is fabricated from a self-dubling host material co-doped with two ionic species, where one ionic dopant converts pump radiation to continuous radiation at a fundamental frequency and the other dopant acts as a saturable absorber to Q-switch the fundamental radiation which is then frequency doubled to produce pulsed high-intensity green light, the green light being either outputted or further frequency-doubled, into pulsed coherent UV radiation, by means of a nonlinear crystal.
Abstract: A diode-pumped monolithic laser is fabricated from a self-doubling host material co-doped with two ionic species, where one ionic dopant converts pump radiation to continuous radiation at a fundamental frequency and the other dopant acts as a saturable absorber to Q-switch the fundamental radiation which is then frequency doubled to produce pulsed high-intensity green light, the green light being either outputted or further frequency-doubled, into pulsed coherent UV radiation, by means of a non-linear crystal.
TL;DR: In this paper, the authors present a numerical model of the absorption and carrier dynamics in these saturable absorbers, including high-field and space-charge effects, in addition to the spectral hole burning and carrier heating typically considered in semiconductor laser amplifiers.
Abstract: Pump-probe measurements in reverse-biased GaAs-GaAlAs waveguide saturable absorbers used in mode-locked diode lasers reveal an ultrafast transient in the absorption recovery dynamics, and a second slower signal before the final recovery. In this paper, we present a numerical model of the absorption and carrier dynamics in these saturable absorbers. The model includes high-field and space-charge effects, in addition to the spectral hole burning and carrier heating typically considered in semiconductor laser amplifiers. The results of the model indicate that field-induced carrier heating strongly influences the absorption dynamics in saturable absorbers. Screening of the electric field by drifting photogenerated charges affects the sweepout of carriers from the absorbing region, and thus, influences the absorption dynamics as well. >
NEC1
TL;DR: In this article, an asymmetric colliding-pulse mode-locking was successfully demonstrated in an InGaAsP laser, which had a single saturable absorber section located partway along the cavity length, and showed modelocking operation at harmonics of the cavity roundtrip frequency.
Abstract: Asymmetric colliding-pulse mode-locking was successfully demonstrated in an InGaAsP laser. This laser had a single saturable absorber section located partway along the cavity length, and showed mode-locking operation at harmonics of the cavity roundtrip frequency. The method verified that optical pulse repetition up to subterahertz rates can be generated with nearly 1-mm-long mode-locked InGaAsP lasers.
TL;DR: This work passively Q switched a monolithic Nd:YAG ring laser using an evanescent-wave coupled antiresonant Fabry–Perot saturable absorber to demonstrate the coupling strength between the crystal and the absorber.
Abstract: We passively Q switched a monolithic Nd:YAG ring laser [monolithic isolated single-mode end-pumped ring laser (MISER)] using an evanescent-wave coupled antiresonant Fabry–Perot saturable absorber. Single-frequency, 0.7-μJ pulses with a pulse width below 100 ns at an ≈1-MHz repetition rate are demonstrated. Pulse width and repetition rate can be varied by changing the distance and thus the coupling strength between the crystal and the absorber.
Patent•
05 May 1995
TL;DR: In this paper, a Q-switch crystal is formed of a host material having a concentration of Co 2+ ions therein, so as to be a saturable absorber of light of a wavelength of from about 0.95 to about 1.65 micrometers.
Abstract: A laser system includes a laser resonator cavity having a resonant axis and a lasing element within the laser resonator cavity. The lasing element emits, under stimulation, light at a wavelength of from about 0.95 to about 1.65 micrometers. There is a flash lamp which optically pumps the lasing element to emit light. A Q-switch crystal lies along the resonant axis within the laser resonator cavity. The Q-switch crystal is formed of a host material having a concentration of Co 2+ ions therein, so as to be a saturable absorber of light of a wavelength of from about 0.95 to about 1.65 micrometers. The Q-switch crystal is preferably Co 2+ -doped yttrium-scandium-gallium garnet or Co 2+ -doped yttrium-aluminum garnet.