Taro Uchiyama

Laser produced 3D display in the air

Taro Uchiyama and Burton Inc. noticed a phenomenon that, when laser beams are strongly focused, air plasma emission can be induced only near the focal point. Thereby, they succeeded in the experimental fabrication of a device displaying 2D-images in the air, which are constructed from dot arrays produced using a technique combining a laser light source and galvanometric mirrors. To further form 3Dimages in the air, the scanning of the focal point in the depth direction along the laser optical axis is essential. However, for such a purpose, the quality of the laser and the technique for varying the position of the focal point must be improved, and thus as yet there are no 3D display devices.

Output Power Enhancement of a Chemical Oxygen-Iodine Laser by Predissociated Iodine Injection.

Output power enhancement of a chemical oxygen-iodine laser (COIL) by an injection of predissociated iodine was studied. Iodine molecules were dissociated into atoms by the microwave discharge prior to injection. It was determined that predissociation caused a negative effect on the output power enhancement when this technique was applied to a conventional supersonic COIL. Model calculations revealed that the existence of atomic iodine at the plenum caused the dissipation of stored energy. It was demonstrated that decreasing the mixing point pressure was crucial to obtain output power enhancement by the predissociation technique. For this purpose, a low-pressure transonic mixing scheme with a grid nozzle array was developed. A 9% enhancement of output power was demonstrated.

Critical Power of Stimulated Brillouin Scattering in Multimode Optical Fibers.

A set of coupled-wave equations for stimulated Brillouin scattering (SBS) in multimode optical fibers excited by single-mode laser light is derived. The analytical solution of the critical pump power is also derived. The solution explains the experimental results well.

A highly efficient, compact chemical oxygen-iodine laser

The dependence of the laser output power on the flow velocity at a cavity for a compact chemical oxygen–iodine laser is reported. The flow velocity is changed by using two vacuum pumps (3000 and 15 000 l/min). It becomes experimentally clear that the laser output power is proportional to the flow velocity and the extractable O2(1Δ) concentration. Output power in excess of 100 W has been extracted efficiently. The maximum overall reaction efficiency of 16.8% with the chlorine flow rate of 413 mmol/min is obtained.

Characteristics of interelectrode flashover in air with the existence of a weakly ionized plasma channel induced by a KrF laser (248 nm)

The irradiation of a KrF laser (248 nm) into the interelectrode space affects the electric flashover characteristics there. The results obtained show that negative oxygen ions dominate formation of the interelectrode arc in air. A laser beam is introduced parallel to the interelectrode axis and the equipment is arranged to prevent the occurrence of photoelectric effects on the electrode surfaces. The time separation between laser firing and application of the interelectrode voltage is varied from 10 ns to 10 ms. The interelectrode spacing is set in the range 2–12 cm. The arc formation time and the flashover probability are measured. The initial ion number density is estimated experimentally to be on the order of 1011 cm−3 throughout the channel.

Numerical simulation of the w-axicon type optical resonator for coaxial slab CO2 lasers

The numerical simulation of the optical resonator for a coaxial slab CO2 laser is conducted. The resonator consists of a toric mirror, a w-axicon, and a plane output coupler. To hold the two slabs coaxially, struts exist in the annular gap region. The effects of the struts on the output power and beam quality for the given resonator are discussed. It is found that varying the vertex of the toric mirror can control the oscillation mode between the E00 fundamental mode and the E01 first azimuthal mode. It is revealed that the resonator loss of the fundamental mode can be smaller than the first azimuthal mode by shifting the vertex inward, and this results in single-mode oscillation at the E00 fundamental mode. On the other hand, the maximum output is obtained under conditions where the resonator oscillates at the E01 mode, because the nodes of the mode coincide with the position of the struts. Loss measurement of each eigenmode well describes the aforementioned phenomena.

Singlet oxygen generator using a porous pipe

The results of a study of an improved new method for generating O2(1Δ) for use in a chemical oxygen‐iodine laser are presented. The generator, using a porous pipe, was found to produce O2(1Δ) with an excitation efficiency of more than 80% and a maximum production of O2 molecules from the unit surface area of 2.2 mmol min−1 cm−2 has been attained.

Development of Hybrid Simulation for Supersonic Chemical Oxygen-Iodine Laser

DOI: 10.2514/1.20339 A numerical simulation method for a supersonic chemical oxygen–iodine laser is developed. The model is a combination of a three-dimensional computational fluid dynamics code without kinetics and a detailed onedimensional,multiple-leaky-stream-tubeskineticscode.Intheproposedmethod,thedetailed flowfieldcharacteristic is calculated by solving a full Navier–Stokes equation that does not involve chemical reactions, and the resultant temperature, velocity, and mixing characteristics are input to the kinetics code as its boundary conditions. A “nonuniform coefficient” is introduced to transform the fluid-dynamic mixing to the diffusive mixing term of the kinetics code. As a result, precise predictions of the gain distribution and laser output are given with a reasonable computational cost. The developed model is applied to the X-wing-type supersonic mixing chemical oxygen–iodine laser, which we have developed, and the calculated gain and output power are compared with the experimental results. The excellent agreements of calculated and experimental results show the validity of the developed method.

Chemical oxygen-iodine laser using rf-discharge dissociation of I2

The gain of COIL is so small (about 0.13%/cm) that scaling up is necessary to achieve high power but considering practical use, reduction of system size is needed. Now, new type of small size COIl using RF discharge dissociation of I2 is presented. The output power of RFCOIL was obtained two or three times higher power than that of normal COIL and chemical efficiency was 12% at 340 mmol/min chlorine flow rate.

Numerical simulation of an all gas-phase iodine laser based on NCl3 reaction system

A numerical simulation code for an all gas-phase iodine laser based on the NCl3 reaction system is developed. The model is a one-dimensional, multiple-leaky-stream-tubes kinetics code combined with all the known rate equations to date. To confirm the validity of this simulation code, the calculated results are compared with the experimental results obtained in other laboratories. The results of computer calculations utilizing this model are in good agreement with those experimental results. This agreement shows that the code is capable of precisely predicting the small signal gain and laser output for a given set of flow conditions. Using this simulation code, we defined the flow rates and the nozzle configuration that should allow laser oscillation based on NCl3 reaction system to be achieved. The calculations suggest that a laser output power of 410 mW can be obtained under optimum conditions with facilities available in our laboratory.