CW atomic oxygen laser at 4.56 µ

CW laser oscillation at 4.56 μ was observed in atomic oxygen produced in a magnetic induction discharge located at the upstream end of a fast flow system. The laser transition has been identified and an inversion scheme is proposed.     

CW laser oscillation at 6127 Å in singly ionized iodine

CW laser action has been obtained on the 6127-Å transition ofI(II) in a He-CdI2discharge. Relative output power has been measured as a function of discharge current, helium pressure, and CdI2temperature.     

LNA: A new CW Nd laser tunable around 1.05 and 1.08 µm

We have investigated the CW laser properties of the lanthamide hexa-aluminate La0.9Nd0.1MgAl11O19at room temperature. When a 1 cm long crystal is pumped by an Ar+ laser (514 nm) or a Kr+ laser (752 nm), CW emission is obtained with slope efficiencies of 10 and 26 percent, respectively. A four-plate Lyot filter in the cavity forces the LNA crystal to oscillate in either of the two major bands centered al 10 820 Å (tuning range 80 Å) and 10 545 Å (tuning range 35 Å).     

Operation of an Er:YLF laser at 1.73 µm

The performance, characterization, and optimization of an Er:YLF laser operating at 1.73 μm is described. The lifetimes of the upper and lower laser level were measured which allowed the optimum Er concentration and the ultimate performance to be predicted. In addition, the pulse-forming network and the mirror transmissivity were optimized. The laser output energy in the normal mode and theQ-switched mode as well as theQ-switched pulselength were measured. In a separate, more efficient, laser arrangement, an output energy of 55 mJ was obtained with an overall efficiency of 0.0024.     

Free electron laser small signal gain measurement at 10.6 µm

Small signal gain has been observed for 10.6 μm radiation using a constant (untapered) wiggler. The permanent magnet wiggler was 2.65 m long, had a period of 3.56 cm (75 periods) and a magnetic field on axis of 2.67 kG. The gain measured was 1.5 ± 0.4 percent agreeing well with the predicted gain corresponding to the experimental electron beam conditions (E = 25MeV,DeltaE/E = 0.75percent,epsilon = 8pimm . mrad, andI = 10A).     

The CW optically pumped 12.08µm Raman laser theory and experiments for high power-conversion efficiency

A model is developed to predict the performance of the continuous-wave CO2-pnmped 12.08 μm NH3laser which is operated by a two-photon or Raman-like process. The local gain and pump absorption are determined from a two-wave three-level treatment based on the density matrix formalism. A ring cavity configuration is considered and interaction of the two intensities inside the cavity are described using coupled wave equations. The subsequent 12.08μm output intensity is calculated for a wide range of operational parameters (injected pump intensity, NH3gas pressure, pump frequency offset, gain length, output coupling,... ). For a well optimized system, power-conversion efficiencies of 10-30 percent should be realistically obtained by pumping with a conventional CW CO2laser. Experiments illustrating the major conclusions are described.     

1.5 µm GaInAsP traveling-wave semiconductor laser amplifier

This paper presents a theoretical and experimental study in terms of small-signal gain, signal gain saturation, and noise characteristics of a 1.5 μm GaInAsP traveling-wave amplifier (TWA), realized through the application of SiOxfilm antireflection coatings. This TWA, having a residual facet reflectivity of 0.04 percent, exhibits a wide, flat signal gain spectrum and a saturation output power of +7 dBm at a 20 dB signal gain. The TWA also has a noise figure of 5.2 dB, which is the smallest value reported for semiconductor laser amplifiers. The experimental results are confirmed to be in good agreement with the theoretical predictions based on the multimode traveling-wave rate equations in conjunction with the photon statistic master equation analysis, which takes into account the amplifier material and device structural parameters. Signal gain undulation, saturation output power, and noise figure are also theoretically evaluated as functions of the facet reflectivity. The superior performance of the TWA demonstrates that the device is favorable for use in linear optical repeaters in fiber transmission systems.     

A study of the CW 28-µm water-vapor laser

The low signal gain of a CW water-vapor laser at 28 μm was measured as a function of the discharge current and pressure. Together with the measurement of other quantities such as the axial electric field and the concentration of OH, a partial interpretation of the mechanisms involved in pumping the 28-μm transition was possible. Thermal equilibrium between the ν0,2nu_{2}, and ν3vibrational levels will result in a large absorption at the elevated gas temperatures observed (800-1000 K). The strong dependence of gain on the electron temperature strongly suggests that the vibrational excitation proceeds through electron-impact excitation. Only the electron-impact excitation of H2O is quantitatively capable of overcoming the large thermally induced absorption. Although vibrational-excitation transfer from H2to H2O seems insufficient, by itself, to overcome this absorption, it may provide appreciable additional gain. Pumping of the 28-μm line through electron-ion recombination and by reactions involving OH can be ruled out.     

Distributed feedback laser emitting at 1.3 µm for gigabit communication systems

A distributed feedback (DFB) laser emitting at 1.3 μm for gigabit lightwave communication systems has been developed. The distributed feedback structure has been introduced in a newly developed buried heterostructure and designs for stable single-mode operation, high speed modulation, and low noise have been done. Threshold current of 10-15 mA, differential efficiency of around 0.28 mW/mA, low noise, small signal modulation bandwidth of 13.9 GHz, and satisfactory modulation waveform at 5-Gbit/s NRZ modulation have been attained with high single-mode operation yield.     

Hybrid bistable devices at 10.6 µm

We present a new hybrid bistable device which depends on the frequency of a modulation carried by the output optical beam. Experiments have been carried out with a CW CO2laser at 10.6 μm wavelength and an electrooptic CdTe amplitude modulator. The necessary nonlinearity for switching was provided by the tuning characteristics of a resonant circuit. This resonant driver circuit allows application of reduced voltages on the CdTe crystal to obtain bistability. Two feedback loops have been considered using either synchronous (at 0.117 MHz) or envelope detection (at 0.853 MHz).     

CW electrooptical properties of InGaAsP(λ = 1.3 µm) buried-heterostructure lasers

The fabrication procedure, electrical properties, optical-bean characteristics, spectral characteristics, and temperature dependence of emission wavelength and threshold of InGaAsP buried-heterostructure (BH) lasers emitting at 1.3 μm are described. The dimensional requirements for fundamental-transverse mode operation have been determined. BH devices are characterized by low threshold currents, fundamental transverse mode operation, linear light output, and narrow spectral width. For 380 μm long devices threshold currents of 40 mA, slope efficiencies of 18 percent, forward resistance of 5 Ω, and T0values of 75 K have been attained.     

High-efficiency CW thulium-sensitised holmium-doped fluoride fibre laser operating at 2.04 mu m

Laser oscillation at 2.04 mu m has been observed in a thulium-sensitised holmium doped singlemode fluorozirconate fibre. 52% slope efficiency and 250 mW output power were obtained with a pump at 0.82 mu m. Cross relaxation in thulium gives a pump quantum efficiency of 1.30.<>     

1.3 µm high-power BH laser on p-InP substrates

In our fabrication of a 1.3 μm band high-power BH laser on a p-type InP substrate, 79 mW CW laser output was obtained, and the spectrum width was 10 nm at 50 mW; it also obtained a high-power pulse output of more than 200 mW at 30 ns pulse width. It shows high-speed pulse response at 2 Gbits/s. These CW and pulse lasing characteristics are reported in this paper, and we also show the output and threshold current distribution of about 1000 samples from six wafers. This high-power laser is very useful for light sources of measuring instruments.     

Performances of a frequency offset locked He-Xe laser system at 3.51 µm

A highly stabilized frequency offset locked He-Xe laser system was constructed for high resolution laser spectroscopy of H2CO [5_{1,5}(upsilon = 0) rightarrow 6_{0,6}(upsilon_{5}= 1)] at 3.51μm. It is composed of three He-Xe lasers. The first laser is H2CO-stabilized and is used as a frequency reference in the system. The second laser is frequency offset locked to the first laser by using the beat frequency between these lasers, and is used as a local oscillator. The third laser is frequency offset locked to the second laser, and is used to observe the H2CO spectrum by slowly varying the beat frequency between these lasers. The frequency stability of the first laser, measured against a similarly stabilized and synchronously modulated laser, was1.0times10^{-14}attau = 100s, where τ represents the integration time. The frequency traceability of the second laser to the first laser was expressed as8.0times10^{-13} cdot tau^{-1}for 10 msleq tau leq 100s. It was found that this value of the traceability was independent of the frequency modulation of the first and second lasers. The frequency traceability of the third laser to the second laser was nearly equal to that of the second laser described previously. The variable range of the frequency of the third laser was 19 MHz. In this range, the frequency traceability of the third laser to the second laser was independent of the beat frequency between these two lasers. From these results, it was concluded that this system can be used for the observation of the H2CO spectrum.     

Modulated single-longitudinal mode semiconductor laser and fiber transmission characteristics at 1.55 µm

A laser light injection technique was studied to realize a semiconductor laser transmitter oscillating in a 1.55 μm single-longitudinal mode. When -15 dBm optical power was injected into the directly modulated laser, no dispersion degradation was observed in the error rate characteristics after transmitting through 44.3 km single-mode fibers at 100 Mbits/s. Effective gain coefficientg-alpha, measured by the light injection method, was 45 cm^-1near threshold. As this gain was sufficiently saturated at the -15 dBm injection power, undesired longitudinal modes in the modulated laser were suppressed.     

InGaAsP/InP buried crescent laser diode emitting at 1.3 µm wavelength

The fabrication procedure, designing of an active region and a p-n-p-n current blocking structure, characteristics and the aging results of an InGaAsP/InP buried crescent (BC) laser diode are described. The BC laser diodes exhibit high laser performances, such as a low-threshold current, a fundamental transverse mode oscillation with linear light output-current characteristics. CW operation at as high as 100°C is achieved with a junction up configuration as a result of the improvement in the current blocking structure. A stable CW operation at 80°C has been realized with a constant optical output power of 5 mW.