High power 1.5 μm integrated superluminescent light source with tilted ridge waveguide

In order to further suppress the F–P lasing and increase the superluminescent power, the tilted ridge waveguide was introduced to the integrated superluminescent device [monolithic integration of the superluminescent diode (SLD) with semiconductor optical amplifier (SOA)[. By this means, high power 1.5 m integrated superluminescent light source has been fabricated without anti-reflection (AR) coating. The F–P oscillations between the two cleaved facets were suppressed successfully compared with the device without ridge waveguide. More than 200 mW peak pulsed power was obtained under quasi-CW condition (0.1 ms pulse width, 10% duty cycle) by co-operation of the two integrated sections. The spectral FWHM is 25 nm.     

Q-switched Yb 3+ :YVO 4 laser with Raman self-conversion

We report the efficient continuous-wave (CW) and Q-switched laser operation of a diode-pumped Yb:YVO₄ laser. A CW output power of 1 W with a slope efficiency of 59% with respect to absorbed pump power was demonstrated. Passively Q-switched with a Cr⁴⁺:YAG saturable absorber, a Yb:YVO₄ laser with Raman conversion was demonstrated. Q-switched 18.7- J pulses with a pulse duration of 17 ns and a peak power up to 1 kW were obtained at 1018-nm fundamental wavelength and 3.6- J pulses with a pulse duration of 6 ns and a peak power of about 0.6 kW were obtained at 1119.5-nm first-Stokes wavelength.This revised version was published online in March 2005. In the previous version, the published online date was missing     

High efficiency cw far infrared lasers at 119 μm and 127 μm

The optically pumped FIR laser lines at 119 m from CH₃OH and at 127 m from¹³CD₃OH are known to be the most powerful in the far infrared spectral region. We report on efficiency measurements for our waveguide laser system. The effect of various parameters was investigated, resulting in the highest efficiency ever reported for the 119 m line. The Stark effect and others parameters of the 127 m were measured, and a new¹³CD₃OH laser line at 175 m discovered, with the same pump transition. These measurements are helpful for completing the assignment already proposed for the 127 m line.     

Analysis of the effects of doping and barrier design on the small-signal modulation characteristics of long-wavelength multiple quantum well lasers

This theoretical work has modelled the small signal response of InGaAsP and InGaAlAs multiple quantum well (MQW) lasers based on an ambipolar carrier transport model. The MQW parameters such as barrier bandgap, barrier width and the number of quantum wells have been optimized for high-speed modulation. The effect of the p-type doping and the strain of the InGaAs well have also been investigated.For the InGaAsP-based system, the optimization for maximum 3 dB bandwitdth shows that the optimum width is about 5 nm for 1.1 m barriers and 7 nm for 1.2 m barriers. The optimum barrier bandgap wavelength is about 1.1 m for the barrier width of 6 nm, about 1.15 m for 8 nm and 10 nm barriers. The p-doped MQW exhibits a higher modulation bandwidth because of its high differential gain and improved carrier distribution among the MQWs. The compressively strained InGaAs quantum well system has the potential for a higher modulation bandwidth. For the InGaAlAs-based system, the optimization for maximum 3 dB bandwidth shows that the optimum width is about 4 nm for a barrier wavelength of 1.10 m, and 6 nm for 1.2 m. The optimum barrier bandgap wavelength is about 1.1 m for a barrier width of 4 nm, and about 1.2 m for 6, 8 and 10 nm.     

Waveguide CW 118.6 μm H2O laser

This paper reports results of an experimental study of a cw 118.6 m H₂O waveguide laser. The laser cavity is a 3 cm inner diameter, 3.2 m long Pyrex tube, with plane reflectors against its ends, one of them being a copper mesh coupler. The active medium is a H₂O:H₂ gas mixture. Successive optimizations lead to a reliable output power of 50 mW, for the EH₁₁ mode. The power density is the highest ever reported, and the stability is such that the power drifts by less than 2% per hour. This laser is competitive with the optically pumped 118.8 m CH₃OH laser.     

Systematic study of muon transfer to sulphur dioxide

In a systematic study of the transfer process to sulphur dioxide, in seven different H₂ + SO₂ gas mixtures, the time spectra of the muonic sulphur X-rays yield muon transfer rates to the SO₂ molecule, deduced from the lifetimes of the p atoms, which agree all well with each other. The muonic oxygen time spectra show an additional structure as if p atoms of another kind were present. Reduced transfer rates_O are reproducible if one uses the model of ephemeral p atoms. The intensity ratios between the different kinds of p atoms are also discussed in the framework of this model and the one of black and white p atoms.     

Threshold conditions for 800 nm pumping of 2 μm Tm : Ho lasers

Pumping requirements of pulsed and continuous wave (CW) 2 m Tm : Ho lasers are investigated experimentally and theoretically for excitation at 800 nm. The influence of the pulse duration on threshold is measured using a chopped Ti : Al₂O₃ laser. Based on the experimental and simulated results the spatial and temporal pump requirements in future quasi-CW high-power diode-pumped 2 m Tm : Ho lasers are determined. The experiments and the model allow the evaluation of different loss mechanisms and indicate significant 540 nm emitting loss mechanisms.     

1.55 μm AlGaInAs/InP polarization-insensitive optical amplifier with tensile strained wells grown by MOCVD

Polarization-insensitive AlGaInAs'InP semiconductor optical amplifier is realized at wavelength of 1.55 . The active layer consists of three tensile strained wells with strain of 0.40%. The amplifier is fabricated to ridge waveguide structure. The testing result shows the amplifiers have excellent polarization insensitivity (less than 0.8dB). The 1540 nm wavelength optical gain is 20 dB at the bias current of 200 mA.     

Near Field Observation of a Refractive Index Grating and a Topographical Grating by an Optically-Trapped Gold Particle

We observed the near field for a refractive index grating fabricated on a planar light waveguide circuit (PLC) by scanning an optically-trapped 100 nm diameter gold particle. We demonstrate that stable trapping and scanning occur with a Gaussian laser beam at the scan velocity of 1.6 m/s and Nd:YAG laser power of 25mW. The scattered Ar laser light from the gold particle is strong at high refractive indexes of the grating with periods of 1.06 m and 0.53 m both by s and p polarized illumination. In addition, we observed the surface profile of the optical disk tracking groove with and without the gold particle. © 2004 The Optical Society of Japan     

Optimization and Maximum Output Power of CW DCN Laser

A high power CW 195 m DCN laser has been developed for fusion plasma diagnostics. Optimization of various parameters (such as the rate of N₂:CD₄:He gas mixture, the gas pressure and the discharge current, the wall temperature and the output couple) for maximum output power at the DCN laser were performed and reported in this paper. Output power of about 220 mW on the 195 m line has been obtained with 3.4 m long and 54 mm inner diameter discharge-pumped wave-guide laser. A new mixture gas of N₂:CD₄:D₂ was used in producing a stable high-power discharge and preventing the deposition of brown polymer with lower wall temperature and discharge current.     

Induced geometry and confinement

A classical, Poincaré invariant dynamical system is developed which contains, besides the natural metric _v , an induced metricg _v that is generated by a real scalar dynamical field. It is shown that scalar fields whose dynamics are governed by the induced metric can be consistently introduced. Also, point particles which follow timelike quasi-geodesic trajectories can be introduced. The reaction forces acting ong _v due to the presence of these fields and particles are computed. A discussion of causality and geometrical confinement is given.     

High-power 1.625-μm strained multiple-quantum-well lasers as a light source for optical time-domain reflectometers

An optical output power of 160 mW has been successfully achieved in 1.625-m strained multiple-quantum-well lasers at a forward current of 800 mA under pulsed operation. Such a high output power has been achieved by optimizing the separated confinement heterostructure layer thickness. The operating life of high-power 1.625-m lasers has been estimated from the results of accelerated ageing at an ambient temperature of 45°C and 500 mA under continuous-wave operation. No significant change in the optical output power was observed up to 2000 hours. The mean time to failure is estimated to be about 4.5×10⁴ hours at 500 mA and 45°C.     

CW Discharge‐Pumped DCN Laser with Novel Mixture Gas

This paper describes a CW submillimeter waveguide dischargepumped DCN laser operating on 190 and 195m lines with novel mixture gas(N₂, CD₄, and D₂). No brown polymer deposit was found after long time discharge even at low wall temperature. The laser discharge length is 3 m, and the resonator length is 3.4 m. The resonator cavity consists of a pyrex tube of 54 mm diameter and two plane reflectors against its ends, one is a plane mirror, the other is a metal mesh. After optimization of various parameters, such as the N₂:CD₄:D₂ gas mixture, the discharge current and the wall temperature, this laser delivers 150 and 160mW on the 190 and 195m lines, respectively, for EH₁₁ mode.     

Excited states of the molecular ion (H2μ)+

The rotation-vibration spectrum of (H₂ )⁺ is computed. Radiative lifetimes of the excited states are of order 10^–4 s or more. These times can be considered infinite compared to the lifetime of ⁺. For the ion in a crystal the lifetimes are significantly decreased by interaction with polarized molecules of the lattice. Transition rates to the ground state are calculated for (H₂ )⁺ in a hydrogen crystal. The results make it possible to interpret the experimental data from SR investigations of hydrogen, deuterium and hydrogen-deuterium mixtures.     

Efficient multiple-longitudinally diode laser pumped Nd:YAG slab laser

The operation of an eightfold longitudinally diode laser pumped 1.06m cw Nd:YAG slab laser is demonstrated. The 809 nm diode radiation is focused through a dichroic coating into each laser channel starting from the reflection points of the 1.06m beam in the slab crystal. At an absorbed pump power in the crystal of 2830 mW a maximum cw TEM₀₀ output of 1075 mW was achieved with a corresponding slope efficiency of 42.5%.     

Slow and monoenergetic (3Heμ−)+ beam production and novel applications

Based upon the recent discovery at UT MSL/KEK, a new idea is proposed for producing a slow and monoenergetic (3.2 keV) (³He^–)⁺ ion beam by using particle decay of the (d³He) muon molecule formed during the (d) to³He transfer reaction. The proposed intense (³He) beam as well as the less intense (⁴He) beam will open up way to various new types of important CF experiments.     

Laser-induced CVD of rhodium

Stripes of rhodium metal were deposited by focusing an Ar⁺ laser (514.5 nm) onto glass and polyimide substrates in a heated vacuum cell that contained Rh(CO)₂acac vapor. Stripes were characterized by scanning profilometry, electrical resistivity, SEM and Auger measurements. Most stripes were 100–200 m wide and 1–3 m high. Very broad stripes (>500 m) were deposited when the Rh(CO)₂acac vapor pressure was greater than 1 Torr and when the laser power was more than 200 mW. Stripe resistivities were in general around 30 times that of the bulk material. Auger spectra show the presence of carbon in the stripes.     

Non-resonant zeugmatography with muons (μSI) and radioactive isotopes

The procedure of zeugmatographic imaging — hitherto implemented only with nuclear magnetic resonance to form the well known MRI technique — is examined with the aim of utilizing it also in combination with non resonant phenomena. It is shown that in principle, one may indeed use zeugmatographic schemes with Perturbed Angular Correlations (PAC) or with muon spin rotations (SR) to obtain image information from material bodies. The preliminary experimentation with zeugmatographic Spin Imaging scheme, (SI), will be described. SomeSI imaging results will be presented and the inherent limitations of the method will be discussed.     

Tunable CW laser oscillation of NdP5O14 at 1.3 μm

Low-threshold tunable cw laser oscillation is achieved at the⁴ F _3/2⁴ I _13/2 transition of NdP₅O₁₄. Continuous tunign over 1.8% of the central wavelenght is possible with 55 mW of absorbed pump power. At gain line maximum near 1.32 , the output power exceeded 1 mW. Pump threshold as low as 8 mW was observed. Reliable cw operation of the 1.3 m NdP₅O₁₄ laser pumped by a 15 mW AlGaAs laser diode is demonstrated.