Fengting Sang

Experimental investigation of an unstable ring resonator with 90-deg beam rotation for a chemical oxygen iodine laser

We report the experimental results of an unstable ring resonator with 90-deg beam rotation for a kilowatt class chemical oxygen iodine laser (COIL). The distributions of near-field phase and far-field intensity were measured. A beam quality of 1.6 was achieved when the COIL average output power was approximately 5 kW.

Chemical Oxygen–Iodine Laser Diluted by CO2/N2 Buffer Gases with a Cryosorption Vacuum Pump

Experiments were carried out on a verti-chemical oxygen-iodine laser (COIL), which was designed for N-2 and energized by a square-pipe jet singlet oxygen generator (JSOG). A cryosorption vacuum pump was used as the pressure recovery system for CO2 and N-2 buffer gases. The output power with CO2 was 27.3% lower than that with N-2, but the zeolite bed showed an adsorption capacity threefold higher for CO2 than for N-2 in the continuous operation with a Cl-2 flow rate of 155 mmol/s and a total flow rate of 430 +/- 3 mmol/s. [DOI: 10.1143/JJAP.47.8446]

Output beam analysis of an unstable resonator with a large Fresnel number for a chemical oxygen iodine laser

During the operation of a laser in an unstable resonator with a large Fresnel number, as the output power of a chemical oxygen iodine laser (COIL) is increased, instability in the output laser beam will occur, behaving mainly as far-field beam spot drift and deformation. To interpret this phenomenon, a simulation of the output beam mode of this kind of laser was developed by using the method of fast Fourier transform. From the result of calculation, we propose that the presence of the nonuniform gain in the COIL produces a skewed output intensity distribution, which causes the mirror to tilt and bulge due to thermal expansion. As the output power is increased, the mirror surface, especially the back of the scraper mirror, will absorb more and more heat, causing thermal expansion of the mirror front surface to occur more seriously, thus resulting in the tilting and deformation of the far-field beam spot. The initial misalignment of the direction is also an important factor leading to far-field beam spot drift and deformation.

Output beam drift and deformation in high-power COIL

Abstract During the operation of a chemical oxygen iodine laser (COIL) with an unstable resonator of a large Fresnel number, as the output power increases, an instability of the output laser beam will appear, behaving mainly as far-field beam spot drift and deformation. In order to interpret this phenomenon, thermal expansion analysis on the scraper with finite element analysis method and a simulation of the output beam mode of this kind of laser by the method of Fast Fourier Transform were developed. From the experimental measurement and the calculation, we proposed that the presence of the nonuniform temperature distribution of scraper causes the front surface of the scraper to tilt and bulge due to thermal expansion. As the output power is increasing, all the mirror surfaces, especially the scrapers, will absorb more and more heat, causing thermal expansion of the mirror front surface to occur more seriously, thus resulting in the tilting and deformation of the far-field beam spot. The initial misalignment of the direction is also an important factor leading to the far-field beam spot drift and deformation.

A 2-kW COIL with a square pipe-array JSOG and nitrogen buffer gas

A 2-kW-class chemical oxygen-iodine laser (COIL) using nitrogen buffer gas has been developed and tested since industrial applications of COIL devices will require the use of nitrogen as the buffer gas. The laser, with a gain length of 11.7 cm, is energized by a square pipe-array jet-type singlet oxygen generator (SPJSOG) and employs a nozzle bank with a designed Mach number of 2.5. The SPJSOG has advantages over the traditional plate-type JSOG in that it has less requirements on basic hydrogen peroxide (BHP) pump, and more important, it has much better operational stability. The SPJSOG without a cold trap and a gas-liquid separator could provide reliable operations for a total gas flow rate up to 450 mmol/s and with a low liquid driving pressure of around 0.7 atm or even lower. The nozzle bank was specially designed for a COIL using nitrogen as the buffer gas. The cavity was designed for a Mach number of 2.5, in order to provide a gas speed and static temperature in the cavity similar to that for a traditional COIL with helium buffer gas and a Mach 2 nozzle. An output power of 2.6 kW was obtained for a chlorine flow rate of 140 mmol/s, corresponding to a chemical efficiency of 20.4%. When the chlorine flow rate was reduced to 115 mmol/s, a higher chemical efficiency of 22.7% was attained. Measurements showed that the SPJSOG during normal operation could provide a singlet oxygen yield Y/spl ges/55%, a chlorine utilization U/spl ges/85%, and a relative water vapor concentration w=[H/sub 2/O]/([O/sub 2/]+[Cl/sub 2/])/spl les/0.1.

Measurements of the yield and chlorine utilization of singlet oxygen generator by use of Raman spectroscopy

A Raman scattering system was used to measure the O2 (a1delta) yield end the chlorine utilization in a singlet oxygen generator of chemical oxygen iodine laser with nitrogen diluent. We present the results from the tests that conducted on a 0.1-mol/s jet-type singlet oxygen-iodine generator. On the basis of the current reported uncertainty of the Raman cross section, the error in the yield measurement is calculated to be less than 8%, and the error of the chlorine utilization is 12%.

Temporal and 2-D small-signal gain measurements in a supersonic COIL

A dedicated CW chemical oxygen iodine mini-laser is constructed and used to probe the two-dimensional (2-D) distribution of small-signal gains in a supersonic CW chemical oxygen iodine laser (CW COIL). The uneven lateral gain distribution may possibly be explained by boundary layer effects.

Efficient chemical oxygen-iodine laser powered by a uniform droplet singlet oxygen generator

A uniform droplet singlet oxygen generator (SOG) has been developed and used to power chemical oxygen-iodine laser (COIL). The uniform droplets images have been caught by a camera. The chlorine utilization, O2(1&Dgr;) yield, H2O concentration, and laser power have been measured. The maximum power density through the nozzle is 121.3 W/cm2.

Measurement of chemical oxygen-iodine laser singlet oxygen generator parameter using Raman spectroscopy

Using a doubled Nd: YAG laser as a spontaneous vibrational Raman scattering source, and a single intensified CCD array at the exit of an imaging monochromator, the Raman scattering system is used to directly measure the concentrations of the O2(a1(Delta) ) and the O2((Chi) 3(Sigma) ) in the chemical oxygen-iodine laser singlet oxygen generator in real time. We present the results from the tests that conducted on a 0.1-mol singlet oxygen-iodine generator. With the current reported uncertainty of the Raman cross-section, the error in the yield measurement is calculated to be less than 8 percent.

Phase-interfacial stimulated Raman scattering generated in strongly pumped water.

We have observed unusual blue-shifted radiations in water pumped by a strong 532-nm nanosecond laser. Properties including divergence, polarizations, and pulse shapes of the unusual radiations are measured and compared with those of the regular stimulated Raman scattering (SRS) in water. The unusual radiations are attributed to the parametric anti-Stokes SRS that occurs on the interface of water and ionization plasma (or gas) formed in the laser-induced breakdown of water.