Transition Of Atomic Iodine Research Articles

Determination of the fraction of excited iodine atoms produced by dissociation of iodides in a self-sustained pulsed discharge

Based on the measured absorption coefficient for the atomic iodine transition in the mixtures of iodides with helium we have determined the fractions of the excited atomic iodine produced by dissociation of CH3I, CF3I, i-C3F7I, C2F5I and C2H5I molecules in a self-sustained pulsed discharge. In the 1: (3 – 15) mixtures of iodides with helium at the pressure 133 – 400 Pa these fractions amount to 0.29 for CF3I and CH3I, 0.2 for i-C3F7I, and 0.31 for C2F5I and C2H5I. The accuracy of determining the excited iodine fraction is 10%. The numerical modelling is carried out for the mixtures containing CF3I. The calculated values of the excited iodine fraction for the mixture with CF3I agree well with the experimental data.

High steady-state column density of I((2)P3/2) atoms from I2 photodissociation at 532 nm: Towards parity non-conservation measurements.

Steady-state column densities of 1017 cm−2 of I(2P3/2) atoms are produced from photodissociation of I2 vapour at 290.5 K using 5 W of 532 nm laser light. Recombination of the I(2P3/2) atoms at the cell walls is minimized by coating the cell surface with a hydrophobic silane (dimethyldichlorosilane/DMDCS). Operation at room temperature, and at an I2 vapour pressure of ~0.2 mbar, without using a buffer gas, allows relatively low Lorentz and Doppler widths of ~2π × 1.5 (FWHM) and ~2π × 150 (HW at 1/e2) Mrad/s, respectively, at the M1 transition of atomic iodine at 1315 nm. These high column densities and low linewidths are favorable for parity nonconservation optical rotation measurements near this M1 transition. Furthermore, as the cell is completely sealed, this method of production of high-density 127I(2P3/2) atoms is also compatible with using iodine radioisotopes, such as for the production of high-density 129I(2P3/2).

Calculation of parity-nonconserving optical rotation in iodine at 1315 nm

We examine the feasibility of a parity non-conserving (PNC) optical rotation experiment for the $^2$P$_{3/2}\rightarrow ^2$P$_{1/2}$ transition of atomic iodine at 1315 nm. The calculated $E1_{\rm PNC}$ to $M1$ amplitude ratio is $R=0.80(16)\times 10^{-8}$. We show that very large PNC rotations (greater than 10 $\mu$rad) are obtained for iodine-atom column densities of $\sim 10^{22}$ cm$^{-2}$, which can be produced by increasing the effective interaction pathlength by a factor of $\sim 10^4$ with a high-finesse optical cavity. The simulated signals indicate that measurement of the nuclear anapole moment is feasible, and that a 1% PNC precision measurement should resolve the inconsistency between previous measurements in Cs and Tl.

Superlinear Enhancement of Discharge Driven Electric Oxygen-Iodine Laser by Increasing $g_{0}{L}$

Continuing experiments with electric oxygen-iodine laser (ElectricOIL) technology have significantly increased laser power output by increasing the product of gain and gain-length, g0L. The authors report on progress with recent ElectricOIL devices utilizing a new concentric discharge geometry with improved O2(a1Δ) production at higher discharge operating pressure at higher system flow rates. O2(a1Δ) produced in flowing radio-frequency discharge in O2-He-NO gas mixture is used to pump I(2P1/2) by near-resonant energy transfer, and laser power is extracted on the I(2P1/2)→ I(2P3/2) transition at 1315 nm. Advancements in heat exchanger design reduce O2(a1Δ) wall loss without sacrificing significant cooling efficiency improving best gain performance from 0.26 to 0.30% cm-1. Modeling of recent data is presented. By increasing the gain length (system size) by a factor of 3, a 5-fold increase in laser output on the 1315-nm transition of atomic iodine was achieved. Flow conditions with g0L = 0.042 were used to extract a continuous wave average total laser power of 481 W. A low frequency ±11.9% oscillation in the total power was observed giving a peak outcoupled power of 538 W.

Discharge-driven electric oxygen-iodine laser superlinear enhancement via increasing g_0L

The authors report the development of an electric oxygen-iodine laser with higher output using a larger product of gain and gain length, g0L. A factor of 4.4 increase in laser power output on the 1315 nm atomic iodine transition was achieved with a factor of 3 increase in gain length. I(2P1/2) is pumped using energy transferred from O2(a1Δ) produced by flowing a gas mixture of O2-He-NO through three coaxial geometry radio-frequency discharges. Continuous wave (CW) average total laser power of 481 W was extracted with g0L=0.042.

The influence of radio-frequency discharge geometry on O2(a 1Δ) production

Experiments and modelling have led to continued enhancements in the electric oxygen–iodine laser system. This continuous wave laser operating on the 1315 nm transition of atomic iodine is pumped by the production of O2(a) in a radio-frequency discharge in an O2/He/NO gas mixture. New discharge geometries have led to improvements in O2(a) production and efficiency. Studies of electrode gap continue to improve O2(a) production at high pressures, and measurements of species exiting the discharge have expanded the understanding of this system. Some of these improvements have already been applied to the laser system, and other advances will be utilized to continue scaling the system to higher laser powers. Over 1 kW of power stored in O2(a) has been demonstrated in both the rectangular cross-section and multi-circular tube discharges.

Enhancement of electric oxygen-iodine laser performance using larger mode volume resonators

Herein the authors report on the demonstration of an 87% enhancement in cw laser power on the 1315 nm transition of atomic iodine via a 100% increase in the resonator mode volume. O(2)(a1Delta) is produced by a single rf-excited electric discharge sustained in an O(2)-He-NO gas mixture flowing through a rectangular geometry, and I(P2(1/2)) is then pumped using energy transferred from O(2)(a1Delta). A total laser output power of 102.5 W was obtained using a Z-pass resonator configuration.

Laser transition in atomic iodine for passive and active SETI

It is proposed to use the wavelength 1.315 μm of the laser transition 2P 1/2→ 2P 3/2 in atomic iodine both for passive and active SETI. The search for an extraterrestrial signal at this wavelength is promising because an active quantum filter (AQF) with a quantum sensitivity limit and with strong fixing in the spectrum luminescence line of the width less than 0.01 cm −1, has been developed for the noted wavelength. Such AQF is capable of receiving the laser signals, consisting of only a few photons, against the background of emission from a star under study. In addition, the high-energy iodine lasers emitting diffraction-limited nanosecond pulses of energy of 2 kJ in a single beam at the wavelength 1.315 μm have been created. The spectral tuning of radiation of these lasers allows one to compensate the frequency Doppler shift. A weak absorption of the 1.315 μm radiation in the Earth atmosphere allows the search for extraterrestrial signals by using the ground optical telescopes equipped with adaptive optical systems.

Demonstration of an iodine laser pumped by an air–helium electric discharge

Herein the authors report on the demonstration of gain and a continuous-wave laser on the 1315 nm transition of atomic iodine using the energy transferred to I(2P1/2) from O2(a 1Δ) produced by both radio-frequency and microwave electric discharges sustained in a dry air–He–NO gas mixture. Active oxygen and nitrogen species were observed downstream of the discharge region. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow. Gain of 0.0062% cm−1 was obtained and the laser output power was 32 mW in a supersonic flow cavity.

Enhancement of electric oxygen-iodine laser performance using a rectangular discharge and longer gain length

Herein the authors report on the demonstration of a 95% enhancement in continuous-wave laser power on the 1315 nm transition of atomic iodine via a 50% increase in gain length, flow rates, and discharge power. O2(a Δ1) is produced by a single radio-frequency-excited electric discharge sustained in an O2–He–NO gas mixture flowing through a rectangular geometry, and I(P21/2) is then pumped using energy transferred from O2(a Δ1). A gain of 0.26% cm−1 was obtained and the total laser output power was 54.8 W.

Iodine photodissociation laser SOFIA with MOPO-HF as a solid-state oscillator

The hybrid iodine photodissociation laser SOFIA has been constructed. The pulse feeding the amplifier chain is the idler wave of an optical parametric oscillator (OPO) tuned to the atomic iodine transition at 1315 nm. This solid-state oscillator enables ps-synchronization to other laser systems. A homemade automatic stabilization of the OPO idler wave as to wavelength and pointing ensures long-term stable operation of the whole system. The active medium of the SOFIA amplifiers is a mixture of C3F7I and He. The SOFIA pulses are frequency-tripled in two KD*P crystals and then serve as the driver in a two-stage optical parametric amplification scheme in which chirped broadband Ti:sapphire laser pulses are amplified (OPCPA).

Gain and continuous-wave laser oscillation on the 1315nm atomic iodine transition pumped by an air-helium electric discharge

Herein the authors report on the demonstration of gain and a continuous-wave laser on the 1315nm transition of atomic iodine using the energy transferred to I(P1∕22) from O2(aΔ1) produced by a radio-frequency-excited electric discharge sustained in a dry air-He–NO gas mixture. Active oxygen and nitrogen species were observed downstream of the discharge region. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow. Gain of 0.0062%cm−1 was obtained and the laser output power was 32mW in a supersonic flow cavity.

Gain and continuous-wave laser power enhancement with a multiple discharge electric oxygen-iodine laser

Herein the authors report on the demonstration of a 70% enhancement in gain and 98% enhancement in continuous-wave laser power on the 1315nm transition of atomic iodine via an increase in flow rates and pressure using multiple discharges in an electric oxygen-iodine laser. O2(aΔ1) is produced by two parallel radio-frequency-excited electric discharges sustained in an O2–He–NO gas mixture, a secondary discharge predissociated the molecular iodine, and I(P1∕22) is then pumped using energy transferred from O2(aΔ1). A gain of 0.17%cm−1 was obtained and the total laser output power was 12.3W.

Gain and continuous-wave laser power enhancement with a secondary discharge to predissociate molecular iodine in an electric oxygen-iodine laser

Herein the authors report on the demonstration of a 50% enhancement in gain and 38% enhancement in continuous-wave laser power on the 1315nm transition of atomic iodine through the addition of a secondary discharge to predissociate the molecular iodine in an electric oxygen-iodine laser. In the primary discharge the O2(aΔ1) is produced by a radio-frequency-excited electric discharge sustained in an O2–He–NO gas mixture, and I(P1∕22) is then pumped using energy transferred from O2(aΔ1). A gain of 0.10%cm−1 was obtained and the total laser output power was 6.2W.

O2(1Δ) production and gain in plasma pumped oxygen–iodine lasers: consequences of NO and NO2 additives

The 1.315 µm [I(2P1/2) → I(2P3/2)] transition of atomic iodine in the chemical oxygen–iodine laser (COIL) is pumped by sequential reactions of I2 and I with O2(1Δ). In electrically pumped systems (eCOILs), electron impact excitation of O2 produces the O2(1Δ) and also produces O atoms through dissociative excitation. The O atoms, through reactions with I2, I(2P1/2) and I(2P3/2), lead to dissociation of I2, quenching of the upper laser level and removal of the lower laser level. While dissociating I2 is potentially beneficial, quenching of the upper laser level is detrimental and so management of the O atom density is necessary to maximize laser gain. In this regard, NO and NO2 additives have been used to manage the O atom density by cyclically reacting with O and I. In this paper, results from a computational investigation of eCOIL systems using plug flow and two-dimensional models are discussed where NO and NO2 additives are used. The system is a flowing plasma sustained in He/O2/NO mixtures with downstream injection of NO2 followed by injection of I2. We found that addition of NO and NO2 is effective in managing the density of O atoms and maximizing gain by minimizing quenching of the upper laser level. We found that by optimizing the additives, laser gain can be maximized even though O2(1Δ) densities may be lower due to the management of quenching and dissociation reactions.

The 2P1/2 → 2P3/2 laser transition in atomic iodine and the problem of search for signals from extraterrestrial intelligence

It is proposed to search for signals from extraterrestrial intelligence (ETI) at a wavelength of 1.315 μm of the laser 2P1/2 → 2P3/2 transition in the atomic iodine, which can be used for this purpose as the natural frequency reference. The search at this wavelength is promising because active quantum filters (AQFs) with the quantum sensitivity limit have been developed for this wavelength, which are capable of receiving laser signals, consisting of only a few photons, against the background of emission from a star under study. In addition, high-power iodine lasers emitting diffraction-limited radiation at 1.315 μm have been created, which highly developed ETI also can have. If a ETI sends in our direction a diffraction-limited 10-ns, 1-kJ laser pulse with the beam diameter of 10 m, a receiver with an AQF mounted on a ten-meter extra-atmospheric optical telescope can detect this signal at a distance of up to 300 light years, irrespective of the ETI position on the celestial sphere. The realisation of the projects for manufacturing optical telescopes of diameter 30 m will increase the research range up to 2700 light years. A weak absorption of the 1.315-μm radiation in the Earth atmosphere (the signal is attenuated by less than 20%) allows the search for ETI signals by using ground telescopes equipped with adaptive optical systems.

O 2 ( Δ 1 ) production in high pressure flowing He∕O2 plasmas: Scaling and quenching

Chemical oxygen-iodine lasers (COILs) oscillate on the P1∕22→P3∕22 transition of atomic iodine at 1.315μm by a series of excitation transfers from O2(Δ1). In electrically excited COILs (eCOILs), the O2(Δ1) is produced in a flowing plasma, typically He∕O2, at a few to tens of Torr. Many system issues motivate operating eCOILs at higher pressures to obtain larger absolute densities of O2(Δ1) for a given yield and to provide higher back pressure for expansion. In this paper, we discuss results from a computational investigation of O2(Δ1) production in flowing plasmas sustained at moderate pressures (⩽50Torr). Power deposition and flow rates were scaled such that in the absence of second order effects, yield should be constant and absolute O2(Δ1) production should scale linearly with pressure. We found in many cases that absolute O2(Δ1) production scaled sublinearly with pressure. Ozone is found to be one of the major quenchers of O2(Δ1) and its production increases with pressure. Gas heating also increases with increasing pressure due to exothermic three-body reactions. The gas heating reduces O3 production, increases O3 destruction and, for certain conditions, restores yields. With increasing pressure and increasing absolute densities of atomic oxygen and pooling reactions of O2(Δ1), quenching by these species also becomes important, though the influence of O-atom quenching can be controlled by managing the density of O atoms with additives. The yield of O2(Δ1) is also determined by discharge stability which becomes problematic at higher pressure.

Oxygen Discharge and Post-Discharge Kinetics Experiments and Modeling for the Electric Oxygen−Iodine Laser System

Laser oscillation at 1315 nm on the I(2P1/2)-->I(2P3/2) transition of atomic iodine has been obtained by a near resonant energy transfer from O2(a1Delta) produced using a low-pressure oxygen/helium/nitric oxide discharge. In the electric discharge oxygen-iodine laser (ElectricOIL) the discharge production of atomic oxygen, ozone, and other excited species adds levels of complexity to the singlet oxygen generator (SOG) kinetics which are not encountered in a classic purely chemical O2(a1Delta) generation system. The advanced model BLAZE-IV has been introduced to study the energy-transfer laser system dynamics and kinetics. Levels of singlet oxygen, oxygen atoms, and ozone are measured experimentally and compared with calculations. The new BLAZE-IV model is in reasonable agreement with O3, O atom, and gas temperature measurements but is under-predicting the increase in O2(a1Delta) concentration resulting from the presence of NO in the discharge and under-predicting the O2(b1Sigma) concentrations. A key conclusion is that the removal of oxygen atoms by NOX species leads to a significant increase in O2(a1Delta) concentrations downstream of the discharge in part via a recycling process; however, there are still some important processes related to the NOX discharge kinetics that are missing from the present modeling. Further, the removal of oxygen atoms dramatically inhibits the production of ozone in the downstream kinetics.

266 nm photolysis of CF3I and C2F5I studied by diode laser gain FM spectroscopy

Frequency modulated diode laser based absorption at 1.315 microm has been used to measure the Doppler lineshapes of the I((2)P(1/2)-(2)P(3/2)) transition in atomic iodine produced from the 266 nm photolysis of both CF(3)I and C(2)F(5)I. Wavelength resolved laser gain is seen following photolysis as excited iodine atoms ((2)P(1/2)) are produced with a quantum yield close to unity from photolysis of both parent molecules. Time resolved measurements were made and the nascent speed distribution and translational anisotropy parameter, beta were determined. Mean atomic speeds of 800 and 850 ms(-1), which correspond to 83 and 68% of the maximum possible kinetic energy release into the iodine photofragment, were determined for photolysis of CF(3)I and C(2)F(5)I, respectively. The nascent translational anisotropy parameter was found to be beta = 1.77 +/- 0.05 for CF(3)I and beta = 1.69 +/- 0.05 for C(2)F(5)I. These values are explicable in terms of parent rotational motion and non-adiabatic processes in the exit channel.

Continuous-wave laser oscillation in subsonic flow on the 1315nm atomic iodine transition pumped by electric discharge produced O2(aΔ1)

Herein the authors report on the demonstration of a continuous-wave laser in subsonic flow on the 1315nm transition of atomic iodine using the energy transferred to I(P1∕22) from O2(aΔ1) produced by a radio-frequency-excited electric discharge. The electric discharge was sustained in an O2–He–NO gas mixture. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow to shift the equilibrium of atomic iodine in favor of the I(P1∕22) state. The laser output power was 540mW in a stable cavity with two 99.993% reflective mirrors.