The chemistry of electric discharge driven oxygen iodine lasers (EOIL) has long been believed to have O₂(a¹▵_g) as the sole energy carrier for excitation of the lasing state I(²P_1/2), and O(³P) as the primary quencher of this state. In many sets of experimental measurements over a wide range of conditions, we have observed persistent evidence to the contrary. In this paper, we examine comparisons of kinetics analysis and model predictions to experimental results from a supersonic EOIL research reactor. This analysis leads to identification of important additional production and loss terms for the lasing species, I(²P_1/2), in the EOIL reaction mechanism. These mechanisms are also relevant to the catalytically enhanced EOIL excitation mechanism. Exploitation of this chemistry can lead to substantial increases in gain and power extraction efficiency in larger-scale EOIL systems. The analysis points to a significantly higher level of understanding of this energetic chemical system, which can support application of advanced concepts in power scaling investigations.

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(a¹▵) production at higher discharge operating pressure at higher system flow rates. O₂(a¹▵) 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(²P_1/2) → I(²P_3/2) transition at 1315 nm. 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 (CW) 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.

The exciplex pumped alkali laser (XPAL) system has been demonstrated in mixtures of Cs vapor, Ar, with and without ethane, by pumping Cs-Ar atomic collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (exciplexes or excimers). The blue satellites of the alkali D₂ lines provide an advantageous pathway for optically pumping atomic alkali lasers on the principal series (resonance) transitions with broad linewidth (>2 nm) semiconductor diode lasers. The development of a simple theoretical analysis of continuous-wave XPAL systems is presented along with predictions as a function of temperature and pump intensity. The model predicts that an optical-tooptical efficiency in the range of 40-50% can be achieved for XPAL.

In this paper we present experimental results on several features of optically excited alkali atoms. We describe small signal gain measurements including spatially-resolved gain in atomic Cs. We discuss observations of numerous near- to mid-IR emissions from states that are higher in energy than the pump beam photons. Finally we outline a measurement scheme to determine the threshold pump intensities for two types of optically excited alkali lasers.

Heat loads in Diode Pumped Alkali Lasers (DPAL) have been investigated using a diode laser to probe the radial dependence of the absorbance. A TiS pump laser heats the medium in a T=50-100°C cesium heat pipe with 5 Torr nitrogen used for quenching. A tunable diode laser probes the spectral absorbance of the cesium cell. Local alkali concentration, temperature, and saturation broadening modify Voigt lineshapes in the wing of the hyperfine split lines. The temperature within the pumped volume exceeds the wall temperature by almost 200 C.

Metastable excited rare gas atoms are currently being considered for use in optically pumped laser systems. Understanding the collisional relaxation kinetics of the relevant excited states is of central importance for this application. In the present study, collisional deactivation rate constants for excited states of Kr(4p⁵5p) atoms colliding with ground state rare gas atoms Rg (=He, Ne, and Kr) have been determined from time- and wavelengthresolved fluorescence measurements. Metastable Kr(4p⁵5s) atoms were generated using a pulsed electrical discharge. A pulsed laser was then used to excited transitions states that correlated with the Kr(4p⁵5p) configuration. Total removal rate constants and intramultiplet state-to-state energy transfer rate constants were derived from the wavelength- and time-resolved fluorescence data by computational modeling. The data were simulated by fitting to numerical solutions of a set of coupled differential equations describing the full set of collisional transfer processes. The results indicate that Kr(4p⁵5p) + He and Kr(4p⁵5p) + Ne mixtures are suitable for use in optically pumped lasers.

Diode pumped alkali vapor lasers (DPAL's) rely on collisional energy transfer to move population from the optically pumped level (²P_3/2) to the upper level of the laser transition (²P1/2). Small hydrocarbon molecules such as methane and ethane have proved to be very effective transfer agents. It is thought that the primary mechanism is electronic-to-rotational (E-R) energy transfer, but this has yet to be proven. In the present study we use electronic structure calculations to determine the potential energy surfaces for Rb(²P) and Cs(2P) interacting with methane. These surfaces may be used to estimate the probabilities for transfer by E-R exchange and by surface hopping at the seams of intersection between potential energy surfaces. We have also examined the influence that interactions with CH₄ have on the ²P-²S transition moments. This is a preliminary step towards understanding the enhanced far-wing optical absorption cross-sections that have been observed in alkali metal/ rare gas/ hydrocarbon mixtures.

Average power scaling of 308nm excimer lasers has followed an evolutionary path over the last two decades driven by diverse industrial UV laser microprocessing markets. Recently, a new dual-oscillator and beam management concept for high-average power upscaling of excimer lasers has been realized, for the first time enabling as much as 1.2kW of stabilized UV-laser average output power at a UV wavelength of 308nm. The new dual-oscillator concept enables low temperature polysilicon (LTPS) fabrication to be extended to generation six glass substrates. This is essential in terms of a more economic high-volume manufacturing of flat panel displays for the soaring smartphone and tablet PC markets. Similarly, the cost-effective production of flexible displays is driven by 308nm excimer laser power scaling. Flexible displays have enormous commercial potential and can largely use the same production equipment as is used for rigid display manufacturing. Moreover, higher average output power of 308nm excimer lasers aids reducing measurement time and improving the signal-to-noise ratio in the worldwide network of high altitude Raman lidar stations. The availability of kW-class 308nm excimer lasers has the potential to take LIDAR backscattering signal strength and achievable altitude to new levels.

A Master Oscillator - Power Amplifier (MOPA) carbon monoxide laser system emitting nanosecond pulses was developed on the basis of the wide-aperture pulsed electron-beam-sustained-discharge CO-laser facility. Amplification parameters including gain and saturation intensity of amplifying media consisted of gas mixtures CO : He or CO : Ar were measured. The MOPA system emitted a train of nanosecond pulses with peak power up to ~0.1MW on a single spectral line and up to ~0.4MW with multiline spectrum.

HF chemical laser with MOPA configuration is a good solution to achieve high output power with high reliability. Kinetic models for HF amplifier are important for prediction and optimization of the performance of MOPA chemical lasers. In this paper, a simplified model for HF chemical laser amplifier is presented. The main processes which are included in the model are: (a) chemical pumping of HF (v=2) and HF (v=1), (b) stimulated transitions and spontaneous emission. (c) relaxation of vibration excited HF molecule by H2,N2 and HF. Some assumptions are taken in this model: (a) the density of H₂, N₂, HF, translational temperature and velocity of gas mixture are averaged across the laser cross section, (b) only two vibration-rotational transitions (2P6, 1P7) occurs in the amplifier, (c) gas temperature does not change during the lasing process in the amplifier. Based on these assumptions, a set of three-level rate equations is formulated and then solved by an iterative technique. Comparison is made with recent experimentally obtained data from a low power discharge-driven CW HF laser with MOPA configuration. It is shown that experimental results are consistent with the calculation from the simplified model.

Using a three-aperture scintillometer system (TASS) to measure irradiance fluctuations along a slant path, it is possible to create a C_n² profile model as a function of altitude up to (and possibly beyond) the maximum altitude of a laser beam along the propagation slant path. This technique was demonstrated recently in June 2011 on a beacon beam transmitted between Hollister Airport in California and Fremont Peak at a slant range of 17 km. Although the primary experiment was to test a hybrid optical RF communication system (FOENEX), the beacon signal at the transmitter was intercepted by the TASS from which weighted path-average values of C_n², inner scale l₀, and outer scale L₀ were determined. Path-average values were then entered into an algorithm that determines the parameters of the HAP C_n² profile model (a variation of the HV profile model). In this paper we report on these recent measurements and how this method of constructing the HAP model can be used over other propagation paths.

The cesium (Cs) Diode Pumped Alkali Laser (DPAL) operates near 894 nm, in the vicinity of atmospheric water vapor absorption lines. An open-path Tunable Diode Laser Absorption (TDLAS) system composed of narrow band (~300 kHz) diode laser fiber coupled to a 12" Ritchey-Chrétien transmit telescope has been used to study the atmospheric transmission characteristics of Cs DPALs over extended paths. The ruggedized system has been field deployed and tested for propagation distances of greater than 1 km. By scanning the diode laser across many free spectral ranges, many rotational absorption features are observed. Absolute laser frequency is monitored with a High Finesse wavemeter to an accuracy of less than 10 MHz. Phase sensitive detection is employed with an absorbance of less than 1% observable under field conditions.

Measurements of the intensity of a light beam produced by a laser source, reflected from a Spatial Light Modulator (SLM) and propagating in a weakly turbulent maritime atmosphere have been carried out in a recent campaign on the grounds of the US Naval Academy. The effect of the degree of spatial coherence in the beam at the source plane (right after the reflection from the SLM) on the Probability Density Function (PDF) of the intensity of the propagating beam at a single fixed position in space is studied in detail. The measured intensity histogram of the fluctuating intensity is compared with the Gamma-Laguerre analytical model for the intensity PDF.

Proper operation of an adaptive optics (AO) system requires the laser beacon to be on or near the image-resolved target along the line of site. Characterization of the wave returned from the beacon spot (the references wave) allows for the derivation of wavefront perturbations along the beacon-to-receiver range - data that can then be used to solve two problems: (i) restoration of the turbulence-corrupted image; and (ii) pre-distortion of the outgoing laser beam for turbulence effect compensation and beam focusing on the target. Implementation of this technique is based on the assumption that propagation of the beacon wave and the outgoing beam are reciprocal. This paper presents results of studies done on the effects associated with beacon formation on an image-resolved target, laser-illuminated from the detector site. In this method, the target-returned wave measured at the detector site is formed as a result of laser light scattering on a rough-surface target and is a superposition of multiple target-sourced spherical waves. Consequently, the returned reference wave's structure substantially differs from the structure of the illuminating wave on the target surface; therefore, for these two contra-propagated waves, the reciprocity conditions are not satisfied. This makes conventional AO approaches not directly applicable to such propagation geometry and instead requires essential modifications to the AO implementation for correct operation.

A scintillation-resistant sensor that allows retrieval of an input optical wave phase using a multi-aperture phase reconstruction (MAPR) technique is introduced and analyzed. The MAPR sensor is based on a low-resolution lenslet array in the classical Shack-Hartmann arrangement and two high-resolution photo-arrays for simultaneous measurements of pupil- and focal-plane intensity distributions which are used for retrieval of wavefront phase in a two stage process: (a) phase reconstruction inside the sensor pupil sub-regions corresponding to lenslet sub-apertures, and (b) recovery of sub-aperture averaged phase components (piston phases). Numerical simulations demonstrate the efficiency of the MAPR technique in conditions of strong intensity scintillations and presence of wavefront branch points.

This PDF file contains the front matter associated with SPIE Proceedings Volume 8238 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.