Showing papers on "Amplified spontaneous emission published in 2001"

Exponential gain and saturation of a self-amplified spontaneous emission free-electron laser.

Abstract: Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.

Inhibition and enhancement of the spontaneous emission of quantum dots in structured microresonators.

Abstract: Spontaneous emission of quantum dot systems in laterally structured microcavities that exhibit photon confinement in all three directions has been studied by time-resolved photoluminescence spectroscopy. For on-resonance conditions, we find that the dot emission rate is increased substantially over that of the unstructured planar cavity. For off-resonance conditions, we are able to suppress the emission rate by an order of magnitude by using cavities with metal coatings, which we attribute to the suppression of leaky optical modes in these structures.

Optical gain in Si/SiO2 lattice: Experimental evidence with nanosecond pulses

Abstract: Experimental evidence of population inversion and amplified spontaneous emission was found for Si nanocrystallites embedded in SiO2 surrounding under pumping with 5 ns light pulses at 380, 400, and 500 nm. As an important property, our experiments show a short lifetime of the population inversion allowing a generation of short (a few nanosecond) amplified light pulses in the Si/SiO2 lattice. The estimate for optical gain in the present samples is 6 cm−1 at 720 nm.

Characteristics of Q-switched cladding-pumped ytterbium-doped fiber lasers with different high-energy fiber designs

Abstract: We theoretically and experimentally analyze Q-switched cladding pumped ytterbium-doped fiber lasers designed for high pulse energies. We compare the extractable energy from two high-energy fiber designs: (1) single- or few-moded low-NA large mode area (LMA) fibers and (2) large-core multimode fibers, which may incorporate a fiber taper for brightness enhancement. Our results show that the pulse energy is proportional to the effective core area and, therefore, LMA fibers and multimode fibers of comparable core size give comparable results. However, the energy storage in multimode fibers is mostly limited by strong losses due to amplified spontaneous emission (ASE) or even spurious lasing between pulses. The ASE power increases with the number of modes in a fiber. Furthermore, spurious feedback is more difficult to suppress with a higher NA, and Rayleigh back-scattering increases with higher NA, too. These effects are smaller in low-NA LMA fibers, allowing for somewhat higher energy storage. For the LMA fibers, we found that facet damage was a more severe restriction than ASE losses or spurious lasing. With a modified laser cavity, we could avoid facet damage in the LMA fiber, and reached output pulse energies as high as 2.3 mJ, limited by ASE. Theoretical estimates suggest that output pulse energies around 10 mJ are feasible with a larger core fiber, while maintaining a good beam quality.

Gamma and proton radiation effects in erbium-doped fiber amplifiers: active and passive measurements

Abstract: Commercially available Er-doped fibers were irradiated with 5.6 and 28 MeV protons and /sup 60/Co gamma rays, up to levels of 50 krad. White-light transmission spectra under passive conditions (no pump or signal) were measured at several radiation levels for the six types of fibers that were tested. The spectra were used to evaluate the relative radiation sensitivity of the fibers and compare gamma versus proton-induced damage for two fiber types. The amount of radiation damage for the fibers was observed to scale inversely with the Ge concentration. Samples from three of the fiber types were configured as optical amplifiers using 980-nm and 1550-nm pump and input signals. In situ measurements of the gain, noise figure, and amplified spontaneous emission (ASE) were made as a function of pump power at several levels of radiation. A computer code, based on a conventional Er-doped fiber amplifier (EDFA) model, was written to simulate performance, using input data provided by the fiber vendor and anchored to measurements made prior to radiation. A comparison between the simulations and experimental data shows that, in certain fibers where the damage is significant, the radiation-induced loss determined from amplifier measurements can be substantially less than that determined from passive transmission spectra.

Measurement of linewidth enhancement factor of semiconductor lasers using an injection-locking technique

Abstract: A new method for measuring the linewidth enhancement factor is presented. This idea is based on the relation between the upper and lower bounds of the locked and unlocked regimes when the detuning of the pump and slave laser is plotted as a function of the injection power. Our results are confirmed with an independent measurement using amplified spontaneous emission (ASE) spectroscopy as well as our theory, which takes account of the realistic quantum-well (QW) band structure and many-body effects. This method provides a new approach to measure the linewidth enhancement factor above laser threshold.

Chirped-pulse amplification of ultraviolet femtosecond pulses by use of Ce(3+):LiCaAlF(6) as a broadband, solid-state gain medium.

Abstract: Chirped-pulse amplification in the ultraviolet region is demonstrated by use of a broadband Ce3+:LiCaAlF6 laser medium. A modified bow-tie-style four-pass amplifier pumped by 100-mJ, 266-nm pulses from a Q-switched Nd:YAG laser has a gain factor of 370 and delivers 6-mJ, 290-nm pulses. After dispersion compensation, the output pulses can be compressed to 115 fs.

Amplified spontaneous emission in active channel waveguides produced by electron-beam lithography in LiF crystals

Abstract: In this letter we report the observation of amplified spontaneous emission of the red light from LiF:F2 centers in active channel waveguides realized by electron-beam lithography in lithium fluoride crystals. Low pumping power densities have been used in quasi-continuous-wave regime at room temperature; the appreciable values of the gain coefficients, 4.67 cm−1 with an exciting power density of 0.31 W/cm2 at 458 nm, make this material a good candidate for the realization of active integrated optical devices.

Generation of high-energy femtosecond pulses in multimode-core Yb-fiber chirped-pulse amplification systems.

Abstract: 220-fs pulses with energies of ~100microJ have been generated by use of two different configurations of diode-pumped Yb-fiber chirped-pulse amplification systems. Energy scaling was demonstrated with 25-microm -core diameter fibers, in which stable diffraction-limited output (M(2)~1.1) was achieved. A two-stage fiber-amplifier system produced average powers of up to 5.5 W at ~1- MHz pulse-repetition rate. A double-pass configuration provided 53-dB gain in a single Yb-fiber amplifier stage, thus eliminating the necessity for multiple amplification stages as well as the need for using polarization-preserving fibers.

Continuous-wave and passively Q-switched cladding-pumped planar waveguide lasers

Abstract: Greater than 12 W of average output power has been generated from a diode-pumped Yb:YAG cladding-pumped planar waveguide laser. The laser radiation developed is linearly polarized and diffraction limited in the guiding dimension. A slope efficiency of 0.5 W/W with a peak optical–optical conversion efficiency of 0.31 W/W is achieved. In a related structure, greater than 8 W of Q-switched average output power has been generated from a Nd:YAG cladding-pumped planar waveguide laser by incorporation of a Cr4+:YAG passive Q switch monolithically into the waveguide structure. Pulse widths of 3 ns and pulse-repetition frequencies as high as 80 kHz have been demonstrated. A slope efficiency of 0.28 W/W with a peak optical–optical conversion efficiency of 0.21 W/W is achieved.

Excited-state quenching of a highly luminescent conjugated polymer

Abstract: The optical properties of a luminescent polymer, poly[1,4-phenylene-1,2-di(phenoxyphenyl) vinylene], have been investigated. Its photoluminescence yield increases unusually in the solid-state over solution, 52%–6% respectively. Investigations into the stimulated emission properties of this material were carried out but no amplified spontaneous emission was observed. To investigate the presence of excited-state absorption features, the photoinduced absorption spectrum was measured. An observed polaron absorption band, from 1.5 to 2.25 eV, overlaps the emission spectra and therefore quenches stimulated emission. This highlights the need to consider the effects of excited-state absorption on the emission when synthesizing new materials.

Optical gain in silicon nanocrystals

Abstract: Silicon nanocrystals, formed by ion implantation and subsequent thermal annealing, show positive optical gain under intense laser excitation. Gain has been measured by the variable strip length method where the amplified spontaneous emission intensity, which is emitted from the sample edge, is measured as a function of the excitation volume. Exponential increase, line narrowing and directionality of stimulated emission have been measured. In addition, by growing silicon nanocrystals in a quartz substrate, single pass gain in pump and probe transmission experiments has been measured. Material gain values as high as those typically found in III-V semiconductors quantum dots have been measured. We claim that population inversion is realized between the fundamental and the recently identified Si equals O interface state. This model explains the gain observations and could account for the lack of auger saturation, free carrier absorption and size dispersion. Critical issues to obtain sizable gain are (1) high oxide quality, (2) high areal density of silicon nanocrystals, and (3) nanocrystals placed in the core region of a waveguide.

Large spontaneous emission factor of 0.1 in a microdisk injection laser

Abstract: A large spontaneous emission factor of 0.1 was evaluated in a 1.56 /spl mu/m-GaInAsP microdisk injection laser operating under continuous-wave condition with a threshold current of 50 /spl mu/A. Some clear evidence of the large spontaneous emission factor, i.e., superlinear light-current characteristics and nonclamped carrier-current characteristics, were observed. It was confirmed that the matching of the lasing wavelength to the spontaneous emission allowed larger spontaneous emission factor.

Gas performance control system for gas discharge lasers

Abstract: An excimer or molecular fluorine laser system includes a discharge chamber containing a gas mixture, multiple electrodes connected to a power supply circuit for energizing the gas mixture, a resonator for generating a laser beam, a processor, and means for monitoring an amplified spontaneous emission (ASE) signal of the laser, such as preferably an ASE detector. The processor receives a signal from the preferred ASE detector indicative of the ASE signal of the laser. Based on the signal from the ASE detector, the processor determines whether to initiate a responsive action for adjusting a parameter of the laser system.

Gain enhanced L-band Er/sup 3+/-doped fiber amplifier utilizing unwanted backward ASE

Abstract: A novel method of enhancing gain in the long wavelength band erbium-doped fiber amplifier is described using the unwanted amplified spontaneous emission (ASE) self-pumping technique. A dual-stage amplifier is deployed, where the unwanted backward ASE from the first stage is fully utilized to pump the second stage amplifier. Gain improvement is observed that enables support for higher channel capacities in wavelength-division-multiplexed systems with negligible noise figure penalties. Flat-gain values in excess of 24 dB and noise figures <5 dB are obtained from the proposed amplifier with a higher channel counts compared to the conventional amplifier.

Broadband amplified spontaneous emission light source

Abstract: A broadband ASE light source is provided which comprises an amplifying optical fiber doped with rare earth; a pumping light source and an output port both which are connected to one end of the amplifying optical fiber via a multiplexer ; and a reflecting or circulating member which is connected to the other end of the amplifying optical fiber, whereby the amplifying optical fiber emits ASE light containing a first and second wavelength bands through the port. Particularly, a second pumping light source may be connected to the other end of the amplifying optical fiber via another multiplexer to widen the wavelength hand to longer wavelength side. Further, using the amplifying Er-doped optical fiber with the pumping light sources having wavelength of a 980 nm band, the ASE light source can be emit a flattened broadband of 1530 to 1610 nm, combining the two wavelength bands of 1530 to 1570 nm and 1570 to 1610 nm. The input power supplied for the amplifying fiber from the second pumping light source may be less than 20% of the input power supplied for the amplifying fiber from the first pumping light source.

Novel 1500 nm-band EDFA with discrete Raman amplifier

Abstract: We first demonstrate amplification in EDFA at wavelengths of 1489-1519 nm using a multi-stage configuration of silica-based EDF (erbium doped fiber) and ASE (amplified spontaneous emission) suppressing filters. The Raman/EDFA hybrid amplifier realizes a useful S-band optical amplifier with dispersion compensation and low non-linearity.

Transfer standard for the spectral density of relative intensity noise of optical fiber sources near 1550 nm

Abstract: We have developed a transfer standard for the spectral density of relative intensity noise (RIN) of optical fiber sources near 1550 nm. Amplified spontaneous emission (ASE) from an erbium-doped fiber amplifier (EDFA), when it is optically filtered over a narrow band (<5 nm), yields a stable RIN spectrum that is practically constant to several tens of gigahertz. The RIN is calculated from the power spectral density as measured with a calibrated optical spectrum analyzer. For a typical device it is -110 dB/Hz, with uncertainty ⩽0.12 dB/Hz. The invariance of the RIN under attenuation yields a considerable dynamic range with respect to rf noise levels. Results are compared with those from a second method that uses a distributed-feedback laser (DFB) that has a Poisson-limited RIN. Application of each method to the same RIN measurement system yields frequency-dependent calibration functions that, when they are averaged, differ by ⩽0.2 dB.

Amplified spontaneous emission in neat films of arylene-vinylene polymers

Abstract: Amplified spontaneous emission (travelling-wave lasing) was achieved for a set of 18 poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) related arylene-vinylene copolymers, a part of which substituted with additional phenyl groups at the vinyl double bond. Wave-guiding neat thin films on glass substrates were used. The samples were transversally pumped with single second harmonic pulses of a mode-locked ruby laser (wavelength 347.15 nm). Travelling-wave emission occurred in the wavelength region between 485 and 650 nm. Repeat unit based absorption cross-section spectra, normalized fluorescence quantum distributions, and amplified spontaneous emission spectra are presented. Ground-state absorption cross-sections at the wavelengths of peak amplified emission are extracted from effective gain length measurements. Effective stimulated emission cross-sections are derived from pump pulse energy densities necessary for optical narrowing.

Performance control system and method for gas discharge lasers

Abstract: A method is provided for determining the status of a gas mixture of a laser system including a gas discharge laser which generates an output beam and has a discharge chamber containing a gas mixture within which energy is supplied to the gas mixture by a power supply via application of a driving voltage to a discharge circuit. A master data set of an output parameter such as any of output beam energy, bandwidth, spectrum width, long axial beam profile, short axial beam profile, beam divergence, energy stability, energy efficiency, width of the discharge, temporal beam coherence, spatial beam coherence, spatial pulse width, amplified spontaneous emission and temporal pulse width versus an input parameter such as driving voltage is generated corresponding to an optimal gas mixture status, preferably after a new fill and typically at the factory, and alternatively following a new fill at the fab. Preferably several master data sets are measured and stored following new fills corresponding to various ages and other conditions of the laser system. The master data set is stored into a memory of the control system. Several more calibration data sets are also preferably generated corresponding to other gas mixture or laser operating conditions. At another time, during a check sub-routine preferably during a subsequent start-up procedure or during each subsequent start-up procedure, a current status data set of the output and input parameters is generated corresponding to the current status of the gas mixture. The current status data set is then compared with the master data set and deviations of the current status and master data sets are noted. A follow-up procedure may be performed, preferably automatically as initiated by the processor, based on the comparison.

Properties of Tm 3+ -doped tellurite glasses for 1.4-μm amplifier

Abstract: Recent studies on optical properties of Tm3+-doped tellurite glasses are presented as candidate materials of 1.4 micrometers amplifier. Usually, non-oxide fiber hosts with lower phonon energy are required, because the initial 3H4 level is easily quenched in high-phonon-energy environment. However, the restriction is not so server as that of the Pr3+:1G4 for 1.3(Mu) M amplifiers due to the moderate energy gap. The Judd-Ofelt analysis showed 96 percent quantum efficiency in a tellurite host. To overcome the problem of intensity amplified spontaneous emission of competitive 0.80micrometers transition from the initial 3H4 level, an Nd-doped cladding was proposed utilizing a strong absorption band. Improved emission was obtained as a result of radiative energy transfers between Tm3+ and Nd3+ ion. Also, the effect of codopants, such as Eu3+, Tb3+, Ho3+, on the lifetime of the Tm3+-levels was investigated for efficient population inversion between the 3H4 and 3F4. The Ho3+ showed the best selectivity in quenching effect. Owing to its quantum efficiency and better fiberizability than fluorides, the Tm-doped tellurite glass can be a potential candidate of the amplifier at the S+-band in the WDM telecommunication.

Non-white photodetection noise at the output of an optical amplifier: theory and experiment

Abstract: Based on the statistical properties of amplified spontaneous emission, the photodetection noise spectrum at the output of an optical amplifier is calculated. The results revealed that the signal-spontaneous emission beat noise spectrum is a transposition of the spontaneous-emission spectrum to the low-frequency domain, and the spontaneous emission-spontaneous emission beat noise spectrum is the auto-correlation function of the spontaneous-emission spectrum. These theoretical results are verified experimentally on an erbium-doped fiber amplifier, filtered by a Mach-Zehnder interferometer.

Gain and noise in ytterbium-sensitized erbium-doped fiber amplifiers: measurements and simulations

Abstract: The fiber gain and noise figure in erbium (Er)-ytterbium (Yb) codoped fiber amplifiers are experimentally studied and theoretically modeled. The different fiber parameters for the model are found in separate characterization measurements. The comparison between the measured and calculated data show excellent agreement. In addition, we demonstrate the design process for a specific cladding-pumped fiber to find the optimum fiber length.

Broadband Raman gain characterisation in various optical fibres

Abstract: The Raman gain coefficient of several different types of optical fibres has been quantified using a sensitive technique based upon the measurement of backward amplified spontaneous emission. Spectral measurement of the effect of the variation of germanium doping in the fibre is also reported.

Efficient high-gain laser amplification from a low-gain amplifier by use of self-imaging multipass geometry

Abstract: We characterize a self-imaging multipass amplifier scheme that provides both high extraction efficiency and overall gain. A diode-pumped slab amplifier with a single-pass small-signal gain of 2.5 is used in a 16-pass mode to amplify an input pulse from 50 µJ to 50 mJ, extracting approximately 22% of the stored energy. A stimulated Brillouin-scattering phase-conjugate mirror provides isolation from amplified spontaneous emission, prevents gain depletion, and also ensures good beam quality. The system can be operated from 10 Hz to in excess of 450 Hz, with modest changes in the beam quality and energy. The scheme has the potential to be scaled to higher-energy and higher-power systems.

Amplified spontaneous emission from a soluble thiophene-based oligomer

Abstract: Optical gain is demonstrated, through pump-probe measurement, in a spin-coated film of a quinquethiophene-S,S-dioxide. The temporal evolution of the gain as a function of the pump intensity shows a progressive shortening of the lifetime as the pump intensity increases. The photoluminescence spectra show line narrowing for excitation intensity higher than 960 μJ cm−2. From these measurements, we conclude that oligothiophene-S,S-dioxides are valuable candidates for thin-film organic light amplifier and lasers.