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The effect of antimicrobial use on the gastrointestinal microbiota of food animals is of increasing concern as bacteria accumulate resistance to multiple antimicrobials. Only a small fraction of the gastrointestinal microbiome is culturable, complicating characterisation of the swine gastrointestinal ecosystem. The objective of this study was to determine the effect of a growth promotion dose (50g/ton) of chlortetracycline on the phylogenetic diversity of bacteria from swine faeces using a culture-independent method. Four freshly weaned pigs were provided a grower ration of primarily corn (63.7%) and soybean meal (25.2%) for 21 days; on Day 21 for 4 weeks the diet of two pigs was medicated with 50g/ton chlortetracycline. Faecal material was collected from each pig on Days 0, 14, 23, 28, 35, 42 and 49 for 454-pyrosequencing of the 16S rRNA gene. UniFrac analysis of pyrosequencing data showed no significant difference in bacterial diversity based on diet and among pigs (P>0.05) fed the low-level dose of chlortetracycline. The most abundant phyla in both treatment groups were Firmicutes, Bacteroidetes, Proteobacteria and Spirochaetes. Higher concentrations of chlortetracycline (e.g. 200g/ton or 400g/ton) may be required to observe a shift in the gastrointestinal flora in swine faeces compared with the low-level dose in this study. Studies of broader scope are needed to understand thoroughly how growth-promoting antimicrobials influence the gut microflora and benefit food animal growth efficiency., (Published by Elsevier Ltd.)

Because challenge models to infect peripheral lymph nodes (PLNs) with Salmonella have not been reported, we performed a series of experiments to develop and refine challenge models to evaluate an intervention applied at the animal level and to provide initial estimates of efficacy of an intervention (i.e., a vaccine) to aid in the design of future studies. In each of four experiments, steers (control or vaccinated) were inoculated with Salmonella strains Montevideo or Newport, and in experiment IV, Salmonella Senftenberg was also used. Calves were euthanized 14 to 42 days postinoculation, and PLNs were collected. In the first experiment, calves were challenged with ∼10¹⁰ Salmonella cells, and few treatment differences were observed 14 days postchallenge. However, by day 21, Salmonella Newport was recovered from fewer vaccinated calves than control calves (P < 0.05). In experiment II, calves were challenged with ∼10⁷ Salmonella cells and, after two necropsies (14 and 28 days postchallenge), only one lymph node was Salmonella positive; therefore, the study was terminated. In experiment III, calves were again challenged with ∼10¹⁰ Salmonella cells, and no significant effect of vaccine was observed in calves challenged with Montevideo or Newport strains. A transdermal route of challenge was explored in experiment IV, using a 10-lancet, allergy testing instrument. Sixteen steers were challenged with either Salmonella Newport or Salmonella Montevideo (Salmonella Newport right legs; Salmonella Montevideo left legs), and all steers were challenged on the lower abdomen with Salmonella Senftenberg. Transdermal inoculation resulted in predictably Salmonella-positive PLNs, and a modest vaccine effect was detected. Because it is well tolerated by the calves and results in predictable and regionally specific Salmonella recovery from PLNs, the transdermal route of challenge may be preferred by researchers wishing to evaluate the impact of interventions designed to reduce the carriage of Salmonella in PLNs.

Previous research conducted in our laboratory found a significant prevalence of multi-drug resistant (MDR) Salmonella and MDR Escherichia coli (MDR EC) in dairy calves and suggests that the MDR EC population may be an important reservoir for resistance elements that could potentially transfer to Salmonella. Therefore, the objective of the current research was to determine if resistance transfers from MDR EC to susceptible strains of inoculated Salmonella. The experiment utilized Holstein calves (approximately 3 weeks old) naturally colonized with MDR EC and fecal culture negative for Salmonella. Fecal samples were collected for culture of Salmonella and MDR EC throughout the experiment following experimental inoculation with the susceptible Salmonella strains. Results initially suggested that resistance did transfer from the MDR E. coli to the inoculated strains of Salmonella, with these stains demonstrating resistance to multiple antibiotics following in vivo exposure to MDR EC. However, serogrouping and serotyping results from a portion of the Salmonella isolates recovered from the calves post-challenge, identified two new strains of Salmonella; therefore transfer of resistance was not demonstrated under these experimental conditions.

The objective of the current research was to determine if feeding the citrus by-products(D) -limonene (DL) and citrus molasses would reduce the concentration and prevalence of Salmonella in weanling pigs experimentally infected with Salmonella Typhimurium. Twenty crossbred weanling pigs (average body weight [BW], 19.9 kg) were randomly assigned to one of four treatments: control, low-dose DL (1.5 ml/kg of BW per day), high-dose DL (3.0 ml/kg of BW per day), and citrus molasses (0.05 kg/kg of BW per day). Treatments were administered in the feed (twice daily) for 7 days, with one-half of the dose administered at each feeding. Fecal samples were collected twice daily (prior to administration of treatment) and cultured for quantitative and qualitative determination of the challenge strain of Salmonella. Upon termination of the study, pigs were euthanized and tissues from the stomach, ileum, cecum, spiral colon, and rectum, as well as luminal contents, were collected. In addition, the popliteal and ileocecal lymph nodes and liver, spleen, and tonsil tissue were collected for qualitative Salmonella culture. No significant treatment differences (P > 0.05) were observed among treatments for fecal concentration or prevalence of Salmonella throughout the 7-day collection period. Likewise, no treatment differences (P > 0.05) were observed for any of the tissue or luminal content samples collected. Salmonella was not cultured from the muscle-bound popliteal lymph node but was cultured from the mesenteric ileocecal lymph nodes. While there were no effects in the current experiment, future research may examine the effect of a lower challenge dose and/or different administration (dose or duration) of the citrus by-products.

Three experiments were conducted to evaluate the influence of vitamin D on fecal shedding of Escherichia coli O157:H7 in cattle. In the first experiment, two groups of cattle (beef and dairy) were assigned to a control treatment or to receive 0.5 × 10(6) IU vitamin D per day via oral bolus for 10 days. Fecal samples were collected before and throughout the dosing period for culture of E. coli O157:H7. No differences were observed for fecal shedding of E. coli O157:H7 among treatments for either beef or dairy animals. Serum concentrations of vitamin D were markedly higher (P < 0.0001) in treated beef cattle but only tended to be higher (P = 0.09) in the dairy cattle. In the second experiment, three successive vitamin D dosages (2,400, 4,800, and 9,600 IU/day; 14 days each) were administered to 14 dairy steers (7 steers served as controls), fecal samples were collected daily, and serum samples were collected weekly throughout the 42-day experimental period. No significant differences in fecal prevalence or serum vitamin D concentrations were observed for any of the vitamin D dosages. A third experiment sampled feedlot cattle (winter and summer) to determine whether serum vitamin D concentrations were correlated with fecal shedding of E. coli O157:H7. A fecal sample and a blood sample were obtained in each season from 60 randomly selected animals (total of 120 fecal samples and 120 corresponding blood samples). As expected, season was highly correlated (r = 0.66) with serum vitamin D concentration with higher concentrations (P < 0.01) observed in the summer. E. coli O157:H7 prevalence (percentage of positive samples) was not highly correlated (r = 0.16) with season, although the correlation tended to be significant (P = 0.08). The proportion of cattle shedding E. coli O157:H7 was 16.7 and 6.7% for the summer and winter collections, respectively. Results of this research do not support a correlation between vitamin D intake and E. coli O157:H7 shedding in cattle.

We employ picosecond dual-broadband pure-rotational coherent anti-Stokes Raman spectroscopy (CARS) in a one-dimensional (1D) imaging configuration. Temperature and O(2):N(2) concentration ratios are measured along a 1D line of up to 12 mm in length. The images consist of up to 330 individual rotational CARS (RCARS) spectra, corresponding to 330 spatially resolved volume elements in the probe volume. Signal levels are sufficient for the collection of single-laser-pulse images at temperatures of up to approximately 1200 K and shot-averaged images at flame temperatures, demonstrated at 2100 K. The precision of picosecond pure-rotational 1D imaging CARS is assessed by acquiring a series of 100 single-laser-pulse images in a heated flow of N(2) from 410 K-1200 K and evaluating a single volume element for temperature in each image. Accuracy is demonstrated by comparing temperatures from the evaluated averaged spectra to thermocouple readings in the heated flow. Deviations from the thermocouple of <30 K in the evaluated temperature were found at up to 1205 K. Accuracy and single-shot precision are compared to those reported for single-point nanosecond dual-broadband pure-RCARS and nanosecond 1D vibrational CARS., (© 2011 Optical Society of America)

Strategies aimed at reducing fecal shedding of Salmonella and other foodborne pathogens may be effective for limiting transmission of pathogens from food animals to humans. The objective of this study was to determine the effectiveness of gallium maltolate (GaM) against Salmonella in vitro and to determine whether oral administration of GaM would reduce fecal shedding of Salmonella in cattle. Gallium is a semimetal exhibiting antimicrobial properties against some pathogenic bacteria, including Salmonella, by exploiting their need for iron to survive and replicate. In vitro growth studies were performed in pure cultures of Salmonella and in mixed cultures from ruminal fluid. Inclusion of GaM in culture medium or in mixed cultures of ruminal fluid resulted in a significant reduction in growth of Salmonella, suggesting that GaM may be effective for limiting growth and survival in vivo. Therefore, we subsequently administered two doses of GaM to Holstein steers, experimentally infected them with Salmonella, and quantitatively and qualitatively monitored fecal shedding at 12-h intervals. Sixty hours after beginning treatment, cattle were euthanized, and luminal contents and tissue were aseptically harvested from the rumen, jejunum, spiral colon, cecum, and rectum. The luminal contents were processed for quantitative and qualitative analysis of the challenge strains of Salmonella, and tissue samples were enriched and plated for qualitative analysis. We found no significant differences between control and treated animals in quantitative levels of Salmonella in the feces or the luminal contents. Likewise, we observed no pattern between control and treated animals in the frequency of positive or negative results from enriched feces, luminal contents, or tissue samples. These results suggest that GaM was not effective for reducing Salmonella in cattle.

The objectives of the current research were to determine the effect of weaning on fecal shedding of Salmonella and Escherichia coli O157:H7 in dairy calves and to examine cultured isolates (to include Enterococcus) for antimicrobial susceptibility. This research was conducted on one large commercial dairy (>3000 head) in the southwestern United States. Two collections were made, during the winter (January 2009) and summer (July 2009) seasons. For the winter collection, two groups of calves were sampled (group 1: n = 18 pens, 69 head, ∼12 weeks of age; group 2: n = 19 pens, 75 head, ∼10 weeks of age). Fecal samples were collected from all calves via rectal palpation 2 days pre- and again 2 days postweaning. For the summer collection, one group of calves housed in 40 pens were utilized and 79 and 76 calves sampled 7 days pre- and 5 days postweaning, respectively. Fecal samples were collected into sterile palpation sleeves, placed on ice, and shipped to our laboratory for bacterial culture of E. coli O157:H7, Salmonella, and Enterococcus. Antimicrobial susceptibility was determined on select isolates. No differences (p > 0.10) in prevalence of Salmonella or E. coli O157:H7 were observed due to weaning in the winter collection. In the summer collection, more (p < 0.01) fecal samples were Salmonella positive preweaning (15.2%) as compared to postweaning (2.6%). No differences were observed for antimicrobial susceptibility in isolates collected pre- as compared to postweaning in either winter or summer collections, with the exception that multidrug-resistant Enterococcus faecium isolates preweaning were resistant to six antibiotics compared to seven or eight antibiotics postweaning (summer collection). Results of the current research indicate that the weaning of dairy calves does not increase the prevalence of pathogenic bacteria or substantially modify antimicrobial susceptibility profiles of these bacteria.

Photoelectron spectroscopic measurements have the potential to provide detailed mechanistic insight by resolving chemical states, electrochemically active regions and local potentials or potential losses in operating solid oxide electrochemical cells (SOCs), such as fuel cells. However, high-vacuum requirements have limited X-ray photoelectron spectroscopy (XPS) analysis of electrochemical cells to ex situ investigations. Using a combination of ambient-pressure XPS and CeO(2-x)/YSZ/Pt single-chamber cells, we carry out in situ spectroscopy to probe oxidation states of all exposed surfaces in operational SOCs at 750 °C in 1 mbar reactant gases H(2) and H(2)O. Kinetic energy shifts of core-level photoelectron spectra provide a direct measure of the local surface potentials and a basis for calculating local overpotentials across exposed interfaces. The mixed ionic/electronic conducting CeO(2-x) electrodes undergo Ce(3+)/Ce(4+) oxidation-reduction changes with applied bias. The simultaneous measurements of local surface Ce oxidation states and electric potentials reveal the active ceria regions during H(2) electro-oxidation and H(2)O electrolysis. The active regions extend ~150 μm from the current collectors and are not limited by the three-phase-boundary interfaces associated with other SOC materials. The persistence of the Ce(3+)/Ce(4+) shifts in the ~150 μm active region suggests that the surface reaction kinetics and lateral electron transport on the thin ceria electrodes are co-limiting processes.

We use photo-electrons as a non-contact probe to measure local electrical potentials in a solid-oxide electrochemical cell. We characterize the cell in operando at near-ambient pressure using spatially-resolved X-ray photoemission spectroscopy. The overpotentials at the interfaces between the Ni and Pt electrodes and the yttria-stabilized zirconia (YSZ) electrolyte are directly measured. The method is validated using electrochemical impedance spectroscopy. Using the overpotentials, which characterize the cell's inefficiencies, we compare without ambiguity the electro-catalytic efficiencies of Ni and Pt, finding that on Ni H(2)O splitting proceeds more rapidly than H(2) oxidation, while on Pt, H(2) oxidation proceeds more rapidly than H(2)O splitting.

We describe a fixture that allows electrochemical devices to be studied under electrical bias in the type of vacuum systems commonly used in surface science. Three spring-loaded probes provide independent contacts for device operation and the characterization in vacuum or under in situ conditions with reactive gases. We document the robustness of the electrical contacts over large temperature changes and their reliability for conventional electrochemical measurements such as impedance spectroscopy. The optical access provided to the device enables the analysis by many techniques, as we demonstrate using x-ray photoelectron spectroscopy to measure local electrical potentials on a solid-oxide electrolyte device operating at high temperature in near-ambient pressure.

The current research examined the inclusion of 20% wet distiller's grains (WDG) fed with steam-flaked corn (SFC) or dry-rolled corn (DRC) in diets fed to feedlot cattle on fecal prevalence of Escherichia coli O157:H7 and Salmonella. Crossbred beef heifers (n = 272; average initial body weight (BW) = 354 kg) were blocked by BW and pen size and randomly assigned to treatment. Fecal samples from freshly voided fecal pats were collected from each pen on the day cattle shipped for slaughter (237 fecal samples: 72, 125, and 40 from cattle 132, 160, and 181 days on feed, respectively). Fecal samples were cultured quantitatively and qualitatively for the above pathogens. Populations of E. coli O157:H7 and Salmonella were generally low with very few samples containing quantifiable populations. Similarly, after enrichment, few samples were E. coli O157:H7 positive in any collection with no treatment differences (p > 0.10). More samples were Salmonella positive during the first collection with an increased (p < 0.05) prevalence observed in the SFC and DRC treatments compared with DRC + WDG treatment. No other treatment differences were observed for Salmonella. Putative fecal coliform isolates (18 per treatment; first collection) were examined for antimicrobial susceptibility, and the majority were susceptible to all of the antibiotics examined. Most of the resistance was observed in the SFC (n = 3) and DRC (n = 4) treatments, and only one isolate in each of the two WDG treatments demonstrated resistance (one antibiotic each, streptomycin and tetracycline). All multidrug resistance (2-4 antibiotics) was observed in isolates cultured from the DRC and SFC treatments (n = 2 isolates in each treatment). Results of the current research found no significant effect of feeding WDG to feedlot cattle on fecal prevalence, at time of shipment for slaughter, of E. coli O157:H7, and only modest differences (decreases) in Salmonella prevalence with no apparent affect on antimicrobial susceptibility of fecal coliform isolates.

Bioelectrical impedance technology (BIA) is capable of providing an objective method of beef carcass yield estimation with the rapidity of yield grading. Electrical resistance (Rs), reactance (Xc), impedance (I), hot carcass weight (HCW), fat thickness between the 12th and 13th ribs (FT), estimated percentage kidney, pelvic, and heart fat (KPH%), longissimus muscle area (LMA), length between electrodes (LGE) as well as three derived carcass values that included electrical volume (EVOL), reactive density (XcD), and resistive density (RsD) were determined for the carcasses of 41 commercially fed cattle. Carcasses were subsequently fabricated into salable beef products reflective of industry standards. Equations were developed to predict percentage salable carcass yield (SY%) and percentage trimmable fat (FT%). Resulting equations accounted for 81% and 84% of variation in SY% and FT%, respectively. These results indicate that BIA technology is an accurate predictor of beef carcass composition., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Ractopamine HCl and zilpaterol HCl, beta-agonists recently approved for use in feedlot cattle to improve performance traits and carcass leanness, were examined for their effects on fecal shedding of Escherichia coli O157:H7 in feedlot cattle. Fecal samples (n = 2,454) were obtained from four experiments (one ractopamine HCl, three zilpaterol HCl) over the course of a 3-year period, either by rectal palpation (ractopamine HCl experiment) or from pen-floor fecal pats. Samples were cultured quantitatively and qualitatively for E. coli O157:H7. No significant treatment differences were detected for fecal prevalence of E. coli O157:H7 in the ractopamine HCl experiment. Zilpaterol HCl feeding had no effect (P > 0.20) on fecal shedding in the first or second experiments, with overall E. coli O157:H7 prevalence relatively low (<7%). In the third zilpaterol HCl experiment, the percentage of fecal samples that were E. coli O157:H7 positive following qualitative culture was higher (P < 0.05) in the zilpaterol HCl treatment (10.3%) than for the control (6.1%). The current research showed minimal effects of beta-agonists on fecal shedding of E. coli O157:H7 and indicated that these compounds (fed immediately prior to slaughter) are not a cause for concern from a food safety standpoint.

The objective of the current research was to determine if exogenous melatonin would exert a "protective" effect on the gastrointestinal tract of sheep and prevent or reduce the horizontal transfer of Escherichia coli O157:H7 from experimentally infected to noninfected or "naïve" sheep. Sixteen cross-bred ewes were housed indoors and adapted to a high concentrate ration. Ewes were randomly assigned to one of four rooms and treatment (three ewes/room, six ewes/treatment) and received either control (gelatin capsule only) or melatonin (5.0 mg/kg body weight [BW]/d). Four additional ewes served as "carrier" sheep (one/room) and were experimentally infected via oral gavage with E. coli O157:H7. Three days post-challenge, carrier ewes were housed with naïve sheep and remained with them for the remainder of the experimental period. Treatments were administered to the naïve sheep 1 day prior to introduction of the carrier sheep and on each of the remaining 7 days of the experimental period. Fecal samples were collected via rectal palpation from the carrier sheep daily throughout experiment and from the naïve sheep daily for 5 days, starting 2 days following introduction of the carriers. On day 8 of the experiment, all ewes were euthanized and tissues from the rumen, ileum, cecum, colon, and rectum as well as their respective lumen contents collected. The carrier sheep quickly infected the naïve ewes, which had similar fecal concentrations as the carrier animals throughout the 5-day sampling period. Melatonin treatment had no effect (p > 0.10) on daily fecal shedding, luminal content concentrations, or in the percentage of gastrointestinal tract tissue positive for the inoculated strain of E. coli O157:H7.

Eighty-seven grain-finished steers were harvested, evaluated, and fabricated into wholesale cuts to determine what measured composition indicators most accurately describe the percentage of closely trimmed salable meat yield. Indicators of lean and fat composition present at the cross-section between the 12th and 13th ribs were objectively evaluated using Assess image analysis software. Salable meat yield ranged from 50.18% to 72.92%, trimmable fat yield ranged from 12.87% to 36.69%, and bone yield ranged from 10.07% to 19.21%. Regression models were developed to estimate percentage of total salable meat yield. Composition indicators chosen to predict salable meat yield included hot carcass weight (HCW), perinephric fat weight, longissimus muscle area (LMA), subcutaneous fat thickness (SFT), ratio of LMA to subcutaneous fat area, and ratio of subcutaneous fat depth to HCW. These results indicate that prediction of beef carcass salable meat yield can be improved via modification to current measures used in the USDA yield grade equation and addition of new measures.

Acyl-homoserine-lactone autoinducer (AHL) produced by nonenterohemorrhagic Escherichia coli species in cattle appears to be required for enterohemorrhagic E. coli (EHEC) colonization of the gastrointestinal tract (GIT). The current research aimed to examine the effect of season, diet, EHEC shedding, and location within the GIT on AHL prevalence in the ruminant. Luminal content samples were collected from the rumen and rectum of feedlot cattle at slaughter in the spring, summer, fall, and winter for culture of E. coli O157:H7 and AHL determination. During the spring collection, samples were additionally collected from the cecum and small intestine, but these samples all were AHL negative and therefore not examined again. To assess the influence of diet on AHL prevalence, 14 lambs were fed either 100% forage or 80% concentrate diets and experimentally inoculated with EHEC. At 8 days after infection, all the lambs were killed, and necropsies were taken, with luminal contents collected from the GIT. The collections from the feedlot cattle had AHL in 100% of the rumen content samples from the spring, summer, and fall, but not in any of the winter samples. No other GIT samples from feedlot cattle were AHL positive, and all the samples from the sheep study were AHL negative. The cattle seemed to show a weak correlation between ruminal AHL and EHEC prevalence. This research found AHL only in the rumen and not in the lower GIT of feedlot cattle. However, it is unclear whether this is because the pH of the lower gut destroys the AHL or because a lack of certain bacteria in the lower gut producing AHL.

With the adoption of visual instrument grading, the calculated yield grade can be used for payment to cattle producers selling on grid pricing systems. The USDA beef carcass grading standards include a relationship between required LM area (LMA) and HCW that is an important component of the final yield grade. As noted on a USDA yield grade LMA grid, a 272-kg (600-lb) carcass requires a 71-cm(2) (11.0-in.(2)) LMA and a 454-kg (1,000-lb) carcass requires a 102-cm(2) (15.8-in.(2)) LMA. This is a linear relationship, where required LMA = 0.171(HCW) + 24.526. If a beef carcass has a larger LMA than required, the calculated yield grade is lowered, whereas a smaller LMA than required increases the calculated yield grade. The objective of this investigation was to evaluate the LMA to HCW relationship against data on 434,381 beef carcasses in the West Texas A&M University (WTAMU) Beef Carcass Research Center database. In contrast to the USDA relationship, our data indicate a quadratic relationship [WTAMU LMA = 33.585 + 0.17729(HCW) -0.0000863(HCW(2))] between LMA and HCW whereby, on average, a 272-kg carcass has a 75-cm(2) (11.6-in.(2)) LMA and a 454-kg carcass has a 96-cm(2) (14.9-in.(2)) LMA, indicating a different slope and different intercept than those in the USDA grading standards. These data indicate that the USDA calculated yield grade equation favors carcasses lighter than 363 kg (800 lb) for having above average muscling and penalizes carcasses heavier than 363 kg (800 lb) for having below average muscling. If carcass weights continue to increase, we are likely to observe greater proportions of yield grade 4 and 5 carcasses because of the measurement bias that currently exists in the USDA yield grade equation.

We present an experimental and theoretical analysis of four-wave mixing in nanosecond pulsed amplifiers based on double-clad ytterbium-doped fibers. This process leads to saturation of the amplified pulse energy at 1064 nm and to distortion of the spectral and temporal profiles. These behaviours are well described by a simple model considering both Raman and four-wave-mixing contributions. The role of seed laser polarization in birefringent fibers is also presented. These results point out the critical parameters and possible tradeoffs for optimization.

We have numerically investigated the behavior of the fundamental mode of a step-index, multimode (MM) fiber as the optical power approaches the self-focusing limit (P(crit)). The analysis includes the effects of gain and bending (applicable to coiled fiber amplifiers). We find power-dependent, stationary solutions that propagate essentially without change at beam powers approaching P(crit) in straight and bent fibers. We show that in a MM fiber amplifier seeded with its fundamental eigenmode at powers <

We report a pulsed, fiber-amplified microchip laser providing widely tunable repetition rate (7.1 - 27 kHz) with constant pulse duration (1.0 ns), pulse energy up to 0.41 mJ, linear output polarization, diffraction-limited beam quality (M(2) < 1.2), and < 1% pulse-energy fluctuations. The pulse duration was shown to minimize nonlinear effects that cause temporal and spectral distortion of the amplified pulses. This source employs passive Q-switching, single-stage single-pass amplification, and cw pumping, thus offering high efficiency, simplicity, and compact, rugged packaging for use in practical applications. The high peak power and high beam quality make this system an ideal pump source for nonlinear frequency conversion, and we demonstrated efficient harmonic generation and optical parametric generation of wavelengths from 213 nm to 4.4 mum with Watt-level output powers.

We investigate the accuracy of temperature measurements by coherent anti-Stokes Raman spectroscopy (CARS) of O(2) and use measurements taken with N(2) CARS and a thermocouple for comparison. Scanning vibrational CARS spectra of O(2) and N(2) were recorded over a broad range of temperatures: between 294 K and 1900 K in air that was heated in a tube furnace and at approximately 2450 K in a fuel-lean CH(4)-O(2)-N(2) flame. Temperatures were derived from least-squares fits of simulated and experimental spectra. Both the fundamental vibrational band and the first hot vibrational band were included in fitting. In the case of the tube furnace, the N(2) and the O(2) CARS temperature measurements agreed to within 3%, and results were similar with the thermocouple; in the flame the agreement was to within 1%. We conclude that, for cases in which O(2) is present in sufficient concentrations ( approximately 10% or greater), the accuracy of O(2) thermometry is comparable with that of N(2).

Dual-pump coherent anti-Stokes Raman scattering (CARS) has been demonstrated for the simultaneous measurement of gas-phase temperature and concentrations of molecular nitrogen and oxygen. A polarization technique was used to vary the relative intensities of the two CARS signals and expand the dynamic range of the relative concentration measurements. Detailed temperature and oxygen mole fraction measurements were performed in the stabilization region of a hydrogen-nitrogen jet diffusion flame. These results indicate that there is a region below the nozzle exit where significant amounts of oxygen are found on the fuel side of the peak flame temperature profile.

We report the spatially resolved detection of methyl radicals in a methane-air flat flame, using degenerate four-wave mixing (DFWM). A frequency-tripled dye laser pumped with a frequency-doubled Nd:YAG laser was used to access the Herzberg beta(1) band of methyl near 216 nm. Using a nearly phase-conjugate geometry, we detected methyl with high spatial resolution [0.2 mm (0.3 mm) vertical (horizontal) and ~6 mm longitudinal] and with good signal-to-noise ratio in a rich (ø = 1.55) flame. Compared with laser absorption spectra, DFWM spectra were much less influenced by a broad featureless background. From the absorption data, we measured the peak methyl concentration to be 650 parts in 10(6), resulting in an estimated DFWM detection limit of 65 parts in 10(6).

Spectroscopies that make use of laser light have provided an important tool to modern researchers for the nonintrusive analysis of chemical systems. The strengths and limitations of these spectroscopic techniques often determine the viability of scientific investigations. The unique properties of degenerate four-wave mixing, a nonlinear optical technique, have recently been found to provide powerful capabilities for a wide range of applications.

Degenerate four-wave mixing is used to produce two-dimensional images of OH distributions in atmosphericpressure flames. The phase-conjugated images from single laser pulses exhibit excellent signal-to-noise ratios and illustrate that degenerate four-wave mixing has outstanding potential as a multidimensional diagnostic for combustion environments.

We have compared high-resolution coherent anti-Stokes Raman spectroscopy measurements of the Q(1) transition of H(2) with theoretical line shapes incorporating both Doppler broadening and motional narrowing. Least-squares fits varying the motional narrowing coefficient for both the hard- and soft-collision model yielded line shapes that agreed well with observed spectra at 295 K for pressures between 50 and 3050 Torr. However, the narrowing coefficient for the hard-collision model was pressure dependent, whereas the narrowing coefficient for the soft-collision model was independent of pressure and yielded an optical diffusion coefficient that agreed with previously measured values.

High-resolution coherent anti-Stokes Raman spectroscopy spectra of the N(2) Q branch at 294 K have been obtained at 1, 5, and 10 atm. Even at 1-atm pressure, disagreements with spectra calculated using the isolated line approximation were observed, indicating the importance of collisional narrowing effects in describing these spectra. A method of using the full G-matrix approach for the calculation of these spectra that is both exact and computationally efficient (requiring only one matrix diagonalization and inversion per spectrum) is discussed. Excellent agreement with experimental data is obtained using this method and a simple exponential gap model for the off-diagonal G-matrix elements.

The effects of intensity fluctuations in the frequency-doubled output of a multimode Nd:YAG pump laser on coheren anti-Stokes Raman spectroscopy (CARS) signal generation have been investigated in a crossed-beam, twocolor CARS experiment. Measurements of signal intensity as a function of time delay (small compared with pulse length) in one pump beam show a maximum at zero delay. In measurements on a single unresolved transition, however, the nonresonant signal is enhanced by almost a factor of 2 more than the resonant signal. Our results demonstrate the non-Gaussian nature of the laser field statistics and introduce new considerations into the analysis of experimental CARS spectra.

Coherent anti-Stokes Raman spectroscopy (CARS) has been used to obtain radial temperature profiles in an axisymmetric methane diffusion flame. Temperatures were obtained from analysis of background-free nitrogen Q- and O-branch spectra. The spectra were analyzed with a nonlinear least-squares CARS fitting program and compared to measurements from radiation- and conduction-corrected thermocouples. Excellent agreement was obtained in regions of relatively constant temperature, whereas improved CARS spatial resolution was required to obtain agreement near steep temperature gradients.

We propose a new approach to the analysis of stochastic processes (such as fluctuating laser fields) with super-Gaussian statistics: the expansion of stochastic processes in terms of first and higher powers of Gaussian components, which are used like a basis set. This approach is applied to treat the super-Gaussian correlation effects observed in coherent anti-Stokes Raman scattering experiments using frequency-doubled pump laser fields. Our results give much better agreement with experimental data than previous theories do.

This Letter describes the application of spatially resolved optical Stark-modulation spectroscopy for making point-absorption measurements in combustion environments by monitoring transitions between electronic energy levels. The technique is demonstrated in a study of atomic sodium aspirated into a flame.

Broadband rotational coherent and anti-Stokes Raman scattering (CARS) and vibrational CARS measurements have been performed to determine the N(2) temperature in a flame (1800-2000 K). Comparisons between these two CARS approaches indicate that, despite loss of signal strength with increasing temperature, rotational CARS is a potentially viable technique for flame-temperature measurements.

We report the first measurements to our knowledge of the effects of two-photon Raman saturation on fully resolved, homogeneously broadened coherent anti-Stokes Raman spectroscopy (CARS) line shapes. Saturation dips and line broadening were observed with a high-resolution scanning CARS experiment using a single-mode, frequency-doubled Nd:YAG laser and a pulse-amplified cw dye laser. Saturated line shapes are compared with the results of numerical solutions of the time-dependent density matrix equations.

We use high-resolution coherent anti-Stokes Raman spectroscopy to measure the temperature profile and pressure in a nitrogen-filled tungsten lamp. Using a modified exponential-gap model for the J-dependent collisional-broadening coefficients, we obtain good fits to the experimental spectra, yielding spatially resolved temperatures and pressures with an accuracy of +/-5%.

A new technique for obtaining point measurements in gases by infrared absorption is described. The method is based on a recently discovered quadratic Stark effect on vibrational and rotational molecular transitions that is induced by high-intensity optical fields. Detectivity calculations for CO, an important combustion gas, are presented together with a proof-of-principle demonstration of Stark-induced absorption in ammonia.