Brighter is better: bill fluorescence increases social attraction in a colonial seabird and reveals a potential link with foraging.

Crested auklets (Aethia cristatella) are colonial seabirds with brilliant orange bills during the breeding season. We characterized the bill pigment with spectroscopy methods (resonance Raman, fluorescence, absorbance). We excluded carotenoids as a possible chromophore and showed that the pigment most closely resembles pterins. Like pterins the bill pigment fluoresces, and it occurred in two phenotypes that may differ geographically, perhaps due to environmental heterogeneity. The pigment is unique in the Genus Aethia, and its spectra did not match any known molecule. The UV-Vis absorbance spectrum of the bill pigment overlaps with the extracted pigment of euphausiids, a favored food of crested auklets. A color preference associated with prey may have favored characteristics of the crested auklet's accessory bill plates. Crest size, a signal of dominance, tended to correlate positively with highest fluorescence in the single-band phenotype. Brighter bills may function in self-advertisement and verify the status signal of the crest ornament. We tested for a behavioral preference using identical decoys that differed only in bill fluorescence. Crested auklets approached models with fluorescent bills at a higher frequency. In cases where sex of crested auklets was known, males responded at a higher frequency to fluorescent bills, but females did not. In an evolutionary context, bill fluorescence could have conferred an advantage in social interactions, e.g., in dimly lit rock crevices. Bill brightness and color may communicate success in foraging and may function as an honest signal of mate quality.

Skin carotenoid status measured by resonance Raman spectroscopy as a biomarker of fruit and vegetable intake in preschool children.

BACKGROUND/OBJECTIVE: Dietary assessment in children is difficult, suggesting a need to develop more objective biomarkers of intake. Resonance Raman spectroscopy (RRS) is a non-invasive, validated method of measuring carotenoid status in skin as a biomarker of fruit/vegetable intake. The purpose of this study was to examine the feasibility of using RRS in preschool children, to describe inter-individual variability in skin carotenoid status and to identify factors associated with the biomarker in this population. SUBJECTS/METHODS: We conducted a cross-sectional study of 381 economically disadvantaged preschoolers in urban centers in Connecticut (USA). In all, 85.5% were black non-Hispanic or Hispanic/Latino, and 14.1% were obese and 16.9% were overweight by age- and sex-specific body mass index (BMI) percentiles. Children had their skin carotenoid status assessed by RRS in the palm of the hand. Fruit/vegetable consumption was assessed by a brief parent/guardian-completed food frequency screener and a liking survey. RESULTS: We observed inter-individual variation in RRS values that was nearly normally distributed. In multiple regression analysis, higher carotenoid status, measured by RRS, was positively associated with fruit/vegetable consumption (P=0.02) and fruit/vegetable preference (P<0.01). Lower carotenoid status was observed among younger children, those participating in the US Supplemental Nutrition Assistance Program, and those with greater adiposity (P<0.05 for all). CONCLUSIONS: We observed wide variability in skin carotenoid status in a population of young children, as assessed by RRS. Parent-reported fruit/vegetable intake and several demographic factors were significantly associated with RRS-measured skin carotenoid status. We recommend further development of this biomarker in children, including evaluating response to controlled interventions.

Resonance Raman detection of carotenoid antioxidants in living human tissue.

Increasing evidence points to the beneficial effects of carotenoid antioxidants in the human body. Several studies, for example, support the protective role of lutein and zeaxanthin in the prevention of age-related eye diseases. If present in high concentrations in the macular region of the retina, lutein and zeaxanthin provide pigmentation in this most light sensitive retinal spot, and as a result of light filtering and/or antioxidant action, delay the onset of macular degeneration with increasing age. Other carotenoids, such as lycopene and beta-carotene, play an important role as well in the protection of skin from UV and short-wavelength visible radiation. Lutein and lycopene may also have protective function for cardiovascular health, and lycopene may play a role in the prevention of prostate cancer. Motivated by the growing importance of carotenoids in health and disease, and recognizing the lack of any accepted noninvasive technology for the detection of carotenoids in living human tissue, we explore resonance Raman spectroscopy as a novel approach for noninvasive, laser optical carotenoid detection. We review the main results achieved recently with the Raman detection approach. Initially we applied the method to the detection of macular carotenoid pigments, and more recently to the detection of carotenoids in human skin and mucosal tissues. Using skin carotenoid Raman instruments, we measure the carotenoid response from the stratum corneum layer of the palm of the hand for a population of 1375 subjects and develop a portable skin Raman scanner for field studies. These experiments reveal that carotenoids are a good indicator of antioxidant status. They show that people with high oxidative stress, like smokers, and subjects with high sunlight exposure, in general, have reduced skin carotenoid levels, independent of their dietary carotenoid consumption. We find the Raman technique to be precise, specific, sensitive, and well suitable for clinical as well as field studies. The noninvasive laser technique may become a useful method for the correlation between tissue carotenoid levels and risk for malignancies or other degenerative diseases associated with oxidative stress.

Resonant Raman detection of macular pigment levels in the living human retina.

We have used resonant Raman scattering as a novel, noninvasive in vivo optical technique to measure the concentration of macular carotenoid pigments in the living human retina. Using a backscattering geometry and resonant molecular excitation in the visible, we measure the Raman peaks that originate from the single- and double-bond stretch vibrations of the p -conjugated molecule's carbon backbone. The Raman signals scale linearly with carotenoid content, whereas the required laser excitation is well under safety limits for macular exposure. The Raman technique is objective and quantitative and may lead to a new method for rapid screening of carotenoid pigment levels in large human populations that are at risk for vision loss from age-related macular degeneration, the leading cause of blindness of the elderly in the United States.

Resonance Raman detection of carotenoid antioxidants in living human tissues.

We have used resonance Raman scattering as a novel noninvasive optical technology to measure carotenoid antioxidants in living human tissues of healthy volunteers. By use of blue-green laser excitation, clearly distinguishable carotenoid Raman spectra superimposed on a fluorescence background are obtained. The Raman spectra are obtained within less than a minute, and the required laser light exposure levels are well within safety standards. Our technique can be used for rapid screening of carotenoid levels in large populations and may have applications for assessing antioxidant status and the risk for diseases related to oxidative stress.

Non-invasive raman spectroscopic detection of carotenoids in human skin.

Carotenoids are thought to play a significant part in the skin's anti-oxidant defense system, and may help prevent malignancy. Inability to measure skin carotenoid content readily has, however, made it difficult to establish the relationship between carotenoid concentration and the occurrence of cutaneous malignancy. We have measured in vivo carotenoid concentration using a noninvasive optical method, Raman spectroscopy. To validate our instrumentation, abdominoplasty skin was evaluated by both Raman spectroscopy and high-performance liquid chromatography determination for carotenoid content. Evaluation of the Raman signal in specific carotenoid solutions was also performed. Precision of Raman measurements within skin sites, within subjects, and between subjects was measured. Sensitivity of the method was evaluated as a function of anatomical region and the distribution of carotenoids within the stratum corneum. Lastly, we evaluated the Raman signal in actinic keratosis and basal cell carcinoma lesions and perilesional skin and compared this with region-matched sites in healthy subjects. Our results indicate that the Raman scattering method reflects the presence of carotenoids in human skin and is highly reproducible. Evaluation of five anatomical regions demonstrated significant differences in carotenoid concentration by body region with the highest carotenoid concentration noted in the palm. Comparison of carotenoid concentrations in basal cell carcinomas, actinic keratosis, and their perilesional skin demonstrate a significantly lower carotenoid concentration than in region-matched skin of healthy subjects. These results represent the first evidence that carotenoid concentration in the skin correlate with the presence or absence of skin cancer and precancerous lesions.

Raman detection of macular carotenoid pigments in intact human retina.

PURPOSE: To develop and test a novel noninvasive optical technique suitable for the objective measurement of macular carotenoid levels in human retina. METHODS: A resonance Raman scattering apparatus was constructed to measure carotenoid levels in flat-mounted human retinas and eyecups and in experimental animal eyes. Light from an argon laser was used to resonantly excite the electronic absorption of the carotenoid pigments, and scattered light was collected and analyzed by a Raman spectrometer. After carotenoid Raman measurements were completed on the retinal samples, macular carotenoid levels were determined by high-performance liquid chromatography (HPLC). RESULTS: Carotenoid resonance Raman scattering proved to be a highly sensitive and specific method for the noninvasive measurement of macular pigments in the human retina. Signal strength scaled linearly with actual macular carotenoid content as measured by HPLC. Our apparatus was also used to record resonance Raman signals from xanthophyll carotenoids stored in the retinal pigment epithelium of intact frog eyes. CONCLUSIONS: This new noninvasive optical method will facilitate studies of ocular carotenoid distributions and their role in degenerative diseases of the eye and may allow for the rapid screening of carotenoid levels in large populations at risk for vision loss from age-related macular degeneration, the leading cause of blindness in the elderly in the United States. A prototype clinical instrument is under development.

Femtosecond fiber laser pulses amplified by a KCl:Tl+ color-center amplifier for continuum generation in the 1.5-microm region.

A diode-pumped stretched-pulse additive-pulse mode-locked Er-doped fiber laser is used to seed a KCl:Tl + color-center amplif ier crystal. The initial l-nJ chirped pulses are double passed through the amplif ier, which is pumped by a 1-kHz Q-switched Nd:YAG laser. The resulting 10-microJ pulses are then chirp compensated to 250-fs duration and are used to generate a spectral continuum. A few high-n(2) materials are investigated for continuum generation, and spectral slicing of the continuum is demonstrated.

Passive stabilization of a synchronously mode-locked NaCl color-center laser by coherent photon seeding.

We use coherent photon seeding to passively stabilize a synchronously mode-locked NaCl color-center laser. This results in the generation of essentially transform-limited picosecond pulses with average power levels of as high as 1.3 W in the 1.5-1.7-microm range. In addition, the pulse energy fluctuations are reduced by as much as 1 order of magnitude.

Optical and laser properties of (F(2)(+))(H) centers in sulfur-doped NaCl.

We report the production and main optical and laser properties of (F(2)(+))(H) color centers in sulfur-doped NaCl crystals. Using a 1.06-microm Nd:YAG laser as the pump source, we realize continuous-wave and synchronously mode-locked laser operation. The laser is tunable over a remarkably large wavelength range of 1.43-2.0 microm. Output power levels are as much as ~800 mW near 1.6 microm; mode-locked pulse durations are typically 4-7 ps.

Subpicosecond and continuous-wave laser operation of (F(2)(+))(H) and (F(2)(+))(AH) color-center lasers in the 2-microm range.

We report synchronously mode-locked subpicosecond and continuous-wave color-center laser operation in the 1.8-2.4-microm wavelength range. For active materials we use (F(2)(+))(H) centers in KBr:O(2)(-) and (F(2)(+))(AH) centers in KBr:Na(+):O(2)(-) crystals. When the lasers are pumped with a continuous-wave or mode-locked NaCI (F(2)(+))(H)-center laser in a cascaded configuration, laser operation is obtained over the combined tuning range of 1.8-2.4 microm, with output powers as high as 150 mW. When synchronously mode locked with ~5-ps pump pulses, both KBr lasers yield typically ~1-ps pulse widths over the entire tuning range. Pulses as short as ~400 fs could be obtained at the expense of higher noise levels.

Femtosecond pulses with high energies from a coupled-cavity saturable-absorber mode-locked KCl F(A)(Tl) color-center laser.

By using a bulk InGaAsP saturable absorber, we passively mode lock a KCl F(A)(Tl) color-center laser in a resonator configuration where the gain material is placed in a main cavity and the saturable absorber is placed in a weakly coupled external cavity. We obtain self-starting and self-stabilized resonant passive mode-locked laser operation, either with pulses as short as ~320 fs or average output power as high as ~380 mW. The pulse width-bandwidth product is ~0.47, with pulse energies of as much as 2.5 nJ. By temperature tuning the saturable absorber band edge, we realize laser operation with similar performance over the wavelength range of 1.50-1.55 microm. When compared with mode-locked KCl F(A)(Tl) laser operation, where both the gain material and the saturable absorber are placed in a common single cavity, the resonant passive mode-locking technique yields pulses with only moderately increased widths (by ~50 fs) but significantly higher energies (by a factor of ~4).