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We propose and demonstrate a tunable fiber laser based on an optical circulator (OC) and two tunable fiber Bragg gratings (TFBGs). The OC acts as a pump power router to improve the pumping efficiency, and a 4% increase in overall conversion efficiency has been observed. The combined tuning spectra range of two TFBGs could cover the entire C-band spectrum from 1530 to 1560 nm. Stable laser output power above 10 dBm is obtained using 1.9 m of erbium-doped fiber and TFBGs with 50% reflectivity. With power equalization by using variable optical attenuators, the power variation is less than 0.1 dB in the whole C band with narrow linewidth of 0.05 nm. A signal-to-noise ratio of 60 dB and a continuous tuning resolution of 0.5 nm have been achieved. The TFBG-based tunable fiber laser can be a promising light source for WDM transmission and fiber sensor applications. OCIS codes: 140.3510, 140.3600, 060.2330, 060.1810.

We present a general formula fitted for computing the amplification and laser output power in a Yb-doped material under various quasi-end-pumping configurations. These configurations include single pass pumping, backreflection pumping in which the pump is reflected by a mirror set on the rear face of the amplifier medium, contrapropagation pumping where two pump beams are launched on both sides of the amplifier and, for every configuration, regenerative pumping in which the transmitted or reflected pump beam is recycled using the proper apparatus. We show that, with regenerative pumping, the efficiency is drastically improved and the optimum amplifier length leading to the maximum laser output power is shorter compared with the one obtained with conventional pumping. In this model, we do not take temperature effect into account. OCIS codes: 140.3480, 140.5560.

A study demonstrates that the concept of the optically-pumped passively mode-locked, vertical-external-cavity surface-emitting semi-conductor laser (VECSEL), is suitable for the realization of picosecond laser sources in the 100-mW power class at high repetition rates up to 50 GHz. Results indicate that the high-repetition-rate passive mode locking is achieved, with a low-saturation-fluence semiconductor saturable absorber mirror (SESAM), incorporating a single layer of quantum-dots.

The satellite pulse generation in diode-pumped passively Q-switched Nd: GdV[O.sub.4] lasers with C[r.sup.4+]: YAG saturable absorber is investigated experimentally and numerically. Results demonstrate that not only could a slow Q-switch cause multiple Q-switched pulses, but a slow ion relaxation from the lower laser level to the ground state can also generate the same effect.

The passively Q-switched laser oscillation from an unprocessed Nd:La[B.sub.3][O.sub.6] cleavage microchip with a [Cr.sup.4+]:YAG saturable absorber in an end-pumped plano-plano resonator is described. The polarization and spectral properties of the laser radiation are measured and the results have shown that the unprocessed Nd:LaBO cleavage microchip is a good gain medium for the passively Q-switched microchip lasers.

The analytic and numerical method for determining the desired gradient of dopant density in edge-pumped slabs, which also applies equally to end-pumped slabs, is presented. Both analytic and numerical calculations show that the method could be used to design composite slab and ceramic slab lasers that are both efficiently and uniformly pumped with either monochromatic or broad-band diode arrays.

Optical amplification at 1530 nm in 980-nm pumped Er(super 3+) - Yb(super 3+) -diffused Ti:LiNbO3 strip waveguides is numerically analysed. A novel design idea that Yb(super 3+) is only incorporated at the end of the waveguide is proposed.

An analytical approach is proposed to calculate the stead-state three-dimensional temperature distribution in multi-layered structures, particularly when containing periodic stacks. This model is applied to the case of vertical-cavity surface-emitting lasers (VCSELs) under optical pumping and agrees excellently with experimental results.

An optical parametric oscillator is tuned to the resonance wavelength of the etalon in an optical pumping injection cavity (OPIC) laser with a type-II 'W' active region, thereby minimizing the threshold pump intensity and maximizing the output slope efficiency. The energy conversion efficiency is found to decrease by over a factor of 100 when the pump wavelength is tuned from the resonance condition (1822 nm at 300 K) to only slightly off resonance.

Cascade lasing from molecular HBr near 4(mu)m is demonstrated when pumped with an injection locked, frequency stabilized Nd:YAG near 1.34 (mu)m. Seven laser lines were identified corresponding to four rotation-vibration transitions starting from the v=3 level and three rotation-vibration transitions starting from the v=2 level.

A local oscillator for laser-pumped gas-cell rubidium frequency standards was described. The effects caused by noise in the microwave and laser sources were reduced to achieve a frequency stability of one order of magnitude better than other lamp-pumped devices. The short-term frequency stability was affected by the phase modulation noise in the microwave synthesizer, the photocurrent noise on the detector and the combined effect on laser frequency noise with light shift.

We demonstrate and analyze an upconversion blue fiber laser pumped by two wavelengths. Lasing at 0.48 [[micro]meter] with very low pump threshold power is obtained from a Tm-doped fluorozirconate fiber that is counterpropagating pumped by 1.21- and 0.649-[[micro]meter] light. We employed a rate-equation analysis using parameters obtained by fitting to the experimental data to predict the 0.48-[[micro]meter] output characteristics as a function of fiber length and output reflectivity.

Theoretical analysis of a tandem optical parametric oscillator (TOPO) reveals that the generation of principal OPO signal pumps a secondary OPO. The two OPOs are singly resonant and their output produces high efficiency over a large dynamic range in the pump intensity. The Nd:YAG-pumped monolithic TOPO generate three infrared wavelengths in high-transmission bands of atmospheric water vapor.

Gain measurements are carried out for different lengths of three types of erbium-doped silica fiber with different pump powers at 1480 nm. From these measurements a relation is established for each type of fiber between gain and the attenuation factor of the pump power. This relation is in complete agreement with the one predicted by an analytic model based on overlapping factors, which makes it possible to obtain methods for the experimental characterization of doped fibers.

The refractive index of erbium-doped fiber amplifiers measured by a Mach-Zehnder interferometer agree well with the theoretical values obtained by using the Kramers-Kronig equation. Higher germanium content of the fibers produces faster changes in the refractive index spectra leading to higher dispersion. Dispersion due to the pump-induced variation in refractive index is significant in short doped-fiber devices such as soliton lasers.

Laser-induced predissociative fluorescence is often used for diagnostics because its short-lived upper states are minimally disturbed by collisions. We discuss the effects of lower-state collisions with parameters relevant to our atmospheric [H.sub.2]-[O.sub.2] flame. A pulse of tunable KrF excimer-laser light induces the A [left arrow] X, [Q.sub.1](11), 3 [left arrow! 0 transition in OH. We measure the intensity and the polarization of the resulting A [right arrow] X, [Q.sub.1](11), 3 [right arrow] 2 fluorescence as a function of laser bightness. A simple model that uses no adjustable parameters produces a reasonable fit to the data. It predicts that, even at very modest laser energies, the fluorescence intensity is almost directly proportional to the rate constant for rotational energy transfer (RET) within the lower vibrational state. That rate constant can be a strong function of local conditions. Furthermore, under typical operating conditions the excimer will pump an amount of OH out of the lower state that is many times as large as that originally present. This occurs because RET within the X-state continuously replenishes the lower state during the laser pulse. Even when this occurs, the signal may still vary linearly with laser intensity, and the polarization may be nearly that expected for weak pumping. At the higher laser intensities, a significant fraction of the measured OH arises from two-photon photodissociation of the water from the flame reaction. Key words: Laser-induced fluorescence, laser diagnostics, OH, polarization, rotational energy transfer, photodissociation.

We have constructed an optical parametric oscillator to generate 75-ps near-transform-limited pulses with wavelengths tunable about 1.053 [[micro]meter] for use in pump-probe studies of self-focusing. The singly resonant oscillator uses a Brewster-cut Li[B.sub.3][O.sub.5] crystal that is oriented for type-II phase matching and synchronously pumped by the amplified and frequency-tripled pulse trains from a mode-locked and Q-switched Nd:YLF laser. An intracavity Pockels cell is used to switch out single 0.5-MW pulses at rates of I to 10 Hz. The design, construction, and performance of the oscillator are discussed. Measured performance is compared with design predictions and with detailed numerical simulations.

A simple theoretical modeling of the static properties of a fiber laser that includes distributed losses and inhomogeneous pumping is presented. Closed-form expressions for both the output and the backward (at the input mirror) intensities are obtained. The model is based on an extended formulation of the Rigrod's theory. It is shown that the laser responds differently depending on the length of the fiber. In particular, we show that for long (short) lasers optimal output power is achieved with low (high) output-coupler reflectivities. Experimental evidence of these results is obtained with Nd-doped fiber lasers with various lengths.

A theoretical model is used to study the actual noise process that contributes to the growth of Stokes pulses during stimulated Raman scattering of picosecond pump pulses in optical fibers. Coupled nonlinear equations are employed to establish the relations between the fibers' physical parameters, such as the pulse width and the gain and index spectra. Results show that the pulse narrowing of the Stokes pulse decreases when the pump pulse is lowered to 2.0 picoseconds, while a rise in the pump power increases Stokes-pulse amplification and reduces the minimum pulse width.

Spectroscopic measurements are carried out to evaluate the performance of a 1.064-micrometer band upconversion thulium-doped fluoride fiber amplifier and a laser operating at 1.47 micrometers. The devices are subjected to optical pumping prior to the measurement of their emission spectra. Results show that upconversion pumping forms a population inversion in the 3F4 and 3H4 states in the fluoride fiber of the amplifier and laser.

A laser-generated tungsten plasma serves as a pumping source for laser oscillations in Cd II on the 4d9 5s2 2D(sub 5/2)-4d10 5p 2p(sub 3/2) transition at 441.6 nm. Mach-Zehnder interferometer helps estimate the axial electron density.

An ensemble Monte Carlo method helps evaluate the photoexcited electron-hole pairs' dynamics in Ge and reveals the scattering of electrons from the optically coupled area through the Lambda and Xi valleys to the L valleys. This relaxation of electrons causes the holes to be predominant in the nonlinear absorption spectra. At 1.5 eV photoexcitation, distortion of the band-structure leads to enhanced contribution by the holes to the pump energy transient.

Theoretical analysis of the coherent optical pumping in semiconductor lasers reveals the non-feasibility of attaining a threshold gain value and a regime in which coherent effects are essential for photon absorption at lasing and pump frequencies, respectively. The analysis helps derive mathematical conditions that confer an electrical incoherence behavior to the optically pumped system.

Analysis of a quantum well-based far infrared laser that employs optical pumping to incorporate population inversion in the laser reveals that a high pumping power density is essential to induce population inversion in the valence band structure with high intersubband scattering rates while a moderate pumping power density is sufficient in the conduction band structure. A maximum population inversion of 2.1 times 10 to the power of 11 sq cm is seen for conduction band structure at 2 kW/sq cm of pumping power density.

Optical AlGaAsInP laser diode pumping in a dye laser with oxazine 750, rhodamine 700 or oxazine 1 dyes confers a low threshold laser operation in the 740-800 nm wavelength range. A DCM-based dye laser displays output power of 361 mW and optical conversion efficiency of 50%. Parametric changes in the 615-690 nm range help characterize the dye laser.

Optical pumping using laser diodes and transfer of all rubidium atoms to one of the M(F) = O sublevels using RF pi-pulses helps achieve an increase in the performance of Rubidium Frequency Standard (RFS). Sequential application of the two radio-frequency pi-pulses is done only after optical pumping of the rubidium vapor. The optical pumping and laser pulse application also enhance the signal-to-noise by more than a factor of 70 to 90.

Analysis of the type I phase matching in Nd:YAG-pumped beta-BaB2O4 optical parametric oscillator in noncollinear and collinear phase-matched configurations reveals that during collinear phase-matching the optical conversion efficiency rises from 10.7% to 40%. A theoretical noncollinear phase matching model helps determine the tuning response of each oscillator. The tuning range lies between 450 nm and 1.68 micrometer.

Use of a waveguide CO2 laser with 300 MHz tunability as optical pumping source, the IR optoacoustic absorption data of (13)CD(3)OH and Fourier transform spectrum of (13)CD(3)OH helps search for new far infrared laser lines. Out of the thirteen new laser lines detected, three correspond to the absorbing transitions associated with the weak asymmetric bending mode of (13)CD(3).

Experimental studies demonstrate two- and single-wavelength upconversion pumping in Er3+:YAlO3 lasers. The laser output power depends on the crystal temperature and reaches the maximum value at 34 degrees K while the pump wavelength determines the use of a particular pumping mechanism. The laser displays an optical conversion efficiency of 13%.

Theoretical analysis of the single-mode operation of a coaxially diode-pumped Nd:YAG laser reveals that pump beams with larger waist sizes improve the single frequency performance of the lasers. Appropriate use of crystal and cavity lengths also improve the single frequency performance. Lasers with a wide gain bandwidth display a distance of two or more cavity modes between the second longitudinal mode that is to begin lasing and the fundamental mode.

An analysis of two-wave mixing in Ce-SBN photorefractive crystals reveals pseudo-periodical differences in the mixing signal at various pump-to-signal ratios. Large modulations cause periodic variations in the signal. A modified theory for two-wave mixing involves large modulation effects and indicates that small pump-to-signal ratios reduce the periodic variations in the signal.

Two quasi-CW microlens-collimated diode bars used to pump a cavity-dumped, Q-switched, single-transverse-mode Nd:YLF laser generate 4.5-ns and 4-mJ pulses at 60 W. The pumping action is longitudinal to the diode bars and uses only one optical element. This pumping technique is applicable to any solid-state laser crystal with high-power diode-pump bars.

Repetitively Q-switched operation of an end-pumped Nd:YAG laser over the range of 200 Hz to 3 kHz using an intracavity chopper is demonstrated. Performance is shown to be comparable to that achieved with an acousto-optic Q switch under similar conditions. The advantages and limitations of the mechanical Q switch are described. Parametric variations of output coupling and pump power lead to an extended empirical description of repetitively Q-switched laser operation. The insertion loss as a function of aperture-edge penetration into the resonator is reported, and a definition of the mechanical Q-switch opening time is provided. Q-switched pulsewidths as short as 35 ns were obtained for the Nd:YAG laser, with a peak power-enhancement factor in excess of 300.

Raman-shifted F2 laser determines small signal transient absorption of a discharge-pumped F2 laser medium. The small-signal net gain is measured as the sum of transient absorption of 2.5% and stationary absorption of 0.5% per centimeter for 6-atmosphere laser media. The laser excitation state is at a rate of 26 million watts per cubic centimeter. The additional absorption in the laser reduces the energy extraction, although the laser exhibits large gain-to-loss ratio.

The gain characteristics of the holmium-doped yttrium lithium fluoride (YLF) amplifier at various energy levels are studied. An amplifier model is used to describe the fundamental laser emission parameters, such as the stimulated emission cross section, quantum efficiency and holmium ion concentrations. The amplifier gain measurements are then obtained using a flash-pumped laser rod. Results show that large amount of holmium dopants can improve the gain characteristics of the YLF amplifier.

The performance of a linear cavity Nd:LNA laser at continuous wave (CW), Q-switchedand mode-locked conditions is evaluated. CW, Q-switched and mode-locking experiments are performed on an Nd:LNA crystal pumped by a Ti:sapphire laser source operating at 200 milliwatts. The tests are conducted under varying frequency and drive power values. Results indicate that pulsed laser operation enhances the CW slope and relative efficiencies of the Nd:LNA device.

The laser properties of diode-laser-pumped neodymium-doped strontium fluorovanadate samples cut perpendicular to the x(a) and y axes have been investigated. A slope efficiency of 36% for the 1.065-[[micro]meter] laser line and a lasing threshold of 6.8 mW have been measured for the x(a)-axis-cut crystal. Data are also presented for the laser's performance as a function of crystal temperature and for the variation of the central peak wavelength with the incident pump power. Key words: Diode laser, pump, strontium fluerovanadate.

An injection-seeded optical parametric oscillator operating near 486.1 nm has been demonstrated. The optical parametric oscillator was pumped by the third harmonic of a Nd:YAG laser and was frequency controlled by injecting an idler wave near 1313 nm from a Nd:YLF laser. A line-narrowed signal output of 0.014 nm was demonstrated.

Byline: W. Precht, A. Czyzniewski, K Reszka The paper presents investigation results on the effect of the pumping rate and the manner of nitrogen injection on the stability and hysteresis in TiN coatings processes. It was found that the critical value of the pumping rate depends on the manner in which the nitrogen is injected into the reaction chamber. The effect of hysteresis on the nitrogen partial pressure characteristic decays when the pumping rate of the reactive gas exceeds the critical rate. It was shown that a slight effect of hysteresis is likely to appear on the pressure-and-flow characteristic as result of the manner in which the experiment is carried out.

The application of a new high power narrow line width external cavity diode laser for rubidium spin exchange optical pumping of [129 sup]Xe compounds is analyzed. The results demonstrate that the use of the optical pumping method can be extremely helpful in enhancing the observed nuclear polarization.

The cavity length characterization of a W optical pumping injection cavity (OPIC) laser with a room temperature emission wavelength of 3.2 [micro]m by using pump wavelength tuning to achieve resonant optical pumping is presented. The studies have shown that when compared to other optically pumped type-II W lasers and electrically injected interband cascade lasers, a less reduction is found in the differential gain with increasing temperature, which is consistent with the high temperature operation of these OPIC devices.