Brian T. Anderson

Results of small-signal gain measurements on a supersonic chemical oxygen iodine laser with an advanced nozzle bank

High-resolution diode laser spectroscopy has been used to probe the gain in the active medium formed by an advanced supersonic chemical oxygen iodine laser (COIL), ejector nozzle bank. The probe beam was directed through the medium at 90/spl deg/ (normal) to the flow velocity and at an angle of 27.5/spl deg/ away from normal incidence. Analysis of the small-signal gain spectrum allowed for the determination of the gain, average gas velocity, static pressure, and temperature. The dependence of gain, temperature, and gas velocity on the primary nitrogen molar flow rate and basic hydrogen peroxide temperature was obtained. A maximum small-signal gain of 7 /spl times/ 10/sup -3/ cm/sup -1/, average gas velocity of 575 m/s, static temperature of 172 K were measured for flow rates of 270 mmole/s of primary nitrogen, 39.2 mmole/s of chlorine, 11 mmole/s of secondary nitrogen, and 0.8 mmole/s of iodine. Estimation of the static pressure in the flow core from spectroscopic data is very close to the static sidewall pressure. The role of transverse velocity components in the gas flow and their effect on the interpretation of gain profiles is discussed.

The Measurement of Gain on the 1.315 Micrometers Transition of Atomic Iodine in a Subsonic Flow of Chemically Generated NCl(a(1) delta)

Abstract Gain is measured on the electronic I( 2 P 3/2 )– I ∗ ( 2 P 1/2 ) transition of atomic iodine at 1.315 μm when hydrazoic acid HN 3 is injected into a flow of iodine and chlorine atoms. The inversion was generated in a transverse subsonic flow device that produced electronically excited I ∗ ( 2 P 1/2 ) atoms from the efficient energy transfer reaction between NCl(a 1 Δ ) metastable and ground state I ( 2 P 3/2 ) atoms. The population inversion was directly observed using a 1.315 μm tunable diode laser that scanned the entire line shape of the (3,4) hyperfine transition of iodine.

Experimental and theoretical investigation of a coaxial pumped photolytic atomic bromine laser

This paper describes the results from a combined experimental theoretical investigation of a coaxial pumped photolytic bromine laser. A 532-nm pump was used to photodissociate IBr and produce Br*(/sup 2/P/sub 1/2/) with subsequent lasing on the (/sup 2/P/sub 1/2/)/spl rarr/(/sup 2/P/sub 3/2/) transition. Experimental results are presented for output energy, mode buildup time and small-signal gain as a function of pump energy and mirror outcoupling fraction. A simplified rate equation model was developed to predict the laser performance parameters and shows good agreement with the laser output energy and small-signal gain.

Multi-kilowatt diffractive coherent combining of pseudorandom-modulated fiber amplifiers

Abstract. We report efficient coherent beam combining of five kW-class fiber amplifiers seeded with pseudorandom phase-modulated light, using a 1×5 diffractive optical element (DOE). Each fiber amplifier channel was path length matched, actively polarized, and provided approximately 1.2 kW of near diffraction-limited output power (M2<1.1). A low-power sample of the combined beam after the DOE provided an error signal for active phase stabilization. After phase stabilization, the beams were coherently combined via the DOE. Notably, a total output power of ∼5  kW was achieved with 82% combining efficiency and excellent beam quality (M2<1.1). The intrinsic DOE splitter loss was 5%. Additional losses due in part to nonideal polarization, amplified spontaneous emission content, uncorrelated wavefront errors, and fractional beam misalignments contributed to the efficiency reduction. Overall, multi-kW beam combining of pseudorandom-modulated fiber amplifiers was demonstrated for the first time.

Measurement of gain on the 1.315-μm transition of atomic iodine as produced from the NCl(a1Δ) + I(2P3/2) energy transfer reaction

A direct measurement of gain on the electronic I (2P3/2) - I*(2Pi/2) transition of atomic iodine at 1.315 jam using tunable diode laser is demonstrated. The population inversion results from the efficient energy transfer between NCI (alA) metastables and I (2P3/2) atoms. Ground state iodine atoms and NCI (a1 A) metastables are produced in a transverse subsonic flow device from the stepwise reaction of Cl atoms with HI followed by the reaction of Cl with azide (N3) radicals, respectively. Under current experimental conditions, a gain of 0.020%/cm is obtained and appears to be limited by reagent number density. A kinetic model was constructed to simulate the experimental gain profile using a mechanism consisting of fully coupled finite rate chemistry and 1-D fluid dynamics. Good agreement with experimental and theoretical calculations are obtained. Keywords: Gain, population inversion, atomic iodine, NCI (a*A) metastables, azides, energy transfer

Progress report on the development of a repetitively pulsed frequency-shifted COIL laser

This paper summarizes recent progress that has occurred in several research areas related to the development of a repetitively-pulsed, frequency-shifted chemical oxygen iodine laser (COIL). COIL gain- switch experiments at 10 kHz pulse rates are described using a novel solid state pulsed magnetic field system. Raman conversion experiments in hydrogen using a pulsed photolytic iodine laser as a COIL surrogate are also described.

The direct observation of gain on the 1.315 μm transition of atomic iodine produced by the energy transfer from NCl(a1Δ) to I(2P3/2)

Gain between the I(2P3/2) and I*(2P1/2) states of atomic iodine at 1.315 μm was detected in a transverse subsonic flow reactor that produced electronically excited I*(2P1/2) atoms from the efficient energy transfer reaction between NCl(a1Δ) metastables and ground state I(2P3/2) atoms. The population inversion was directly observed using a 1.315 μm tunable diode laser that scanned across the entire I(2P3/2)−I*(2P1/2) hyperfine transition with complete resolution.

Short-pulse photolytic iodine laser

A compact, short pulse photolytic iodine laser (PIL) system designed for use as a source in Raman conversion experiments is described. The single-shot, flashlamp-pumped laser outputs 10 Joules in a 3 microsecond(s) FWHM pulse at a wavelength of 1.315 micrometer and uses n-C3F7I as the renewable laser fuel. Laser design and performance characteristics are presented.

Zeeman spectra of atomic iodine in a 0- to 400-gauss B field

A high-resolution, continuously tunable 1.3 micrometers diode laser is used as a small signal probe to investigate the Zeeman spectra of atomic iodine. A heated quartz cell containing a small amount of I2 is placed in a 0 to 400 gauss B field transverse to the axis of the laser probe. Hyperfine spectral scans are recorded as a function of B- field strength and laser polarization and are compared to theory with very good agreement.