Increasing the Q-factor of Fabry-Perot etalons using focused Bessel beam illumination

Sensing and filtering applications often require Fabry-Perot (FP) etalons with an Interferometer Transfer Function (ITF) having high visibility, narrow Full Width at Half Maximum (FWHM), and high sensitivity. For the ITF to have these characteristics, the illumination beam must be matched to the modes of the FP cavity. This is challenging when a small illumination element size is needed, as typical focused beams are not matched to the FP cavity modes. Bessel beams are a potential alternative as their structure resembles the FP cavity modes while possessing a focused core. To study the feasibility of using Bessel beam illumination, in this Letter, ITFs of an FP etalon were measured using Bessel and Gaussian illumination beams. A Bessel beam with core size of 28 µm provided an ITF with visibility 3.0 times higher, a FWHM 0.3 times narrower, and a sensitivity 2.2 times higher than a Gaussian beam with waist 32 µm. The results show that Bessel beam illumination can provide ITFs similar to that of collimated beam illumination while also having with a focused core.

Numerical model of light propagation through Fabry-Perot etalons composed of interfaces with non-planar surface topography

We present a model that calculates optical fields reflected and transmitted by a Fabry-Perot (FP) etalon composed of interfaces with non-planar surface topography. The model uses the Rayleigh-Rice theory, which predicts the fields reflected and transmitted by a single interface, to account for the non-planar surface topography of each interface. The Rayleigh-Rice theory is evaluated iteratively to account for all round trips that light can take within the FP etalon. The model predictions can then be used to compute Interferometer transfer function (ITF)s, by performing wavelength or angle resolved simulations enabling predictions of the bandwidth, peak transmissivity, and sensitivity of FP etalons. The model was validated against the Pseudospectral time-domain (PSTD) method, which resulted in good agreement. Since the model accuracy is expected to reduce as the Root mean square (RMS) of the topographic map increases, the error in the model's predictions was studied as a function of topographic map RMS. Finally, application of the model was exemplified by predicting the impact of roughness on ITFs and computing the changes in FP etalon transmissivity as cavity thickness is modulated by an ultrasonic wave.

ABCD transfer matrix model of Gaussian beam propagation in Fabry-Perot etalons

A numerical model of Gaussian beam propagation in planar Fabry-Perot (FP) etalons is presented. The model is based on the ABCD transfer matrix method. This method is easy to use and interpret, and readily connects models of lenses, mirrors, fibres and other optics to aid simulating complex multi-component etalon systems. To validate the etalon model, its predictions were verified using a previously validated model based on Fourier optics. To demonstrate its utility, three different etalon systems were simulated. The results suggest the model is valid and versatile and could aid in designing and understanding a range of systems containing planar FP etalons. The method could be extended to model higher order beams, other FP type devices such as plano-concave resonators, and more complex etalon systems such as those involving tilted components.

Angular Airy function: a model of Fabry-Perot etalons illuminated by arbitrary beams

Fabry-Perot (FP) etalons are used as filters and sensors in a range of optical systems. The reflected and transmitted fields associated with an FP etalon have traditionally been predicted by the Airy function, which assumes a plane wave illumination. FP etalons are, however, often illuminated by non-collimated beams, rendering the Airy function invalid. To address this limitation, we describe the angular Airy function which calculates the reflected and transmitted fields for arbitrary illumination beams, using angular spectrum decomposition. Combined with realistic models of the experimental illumination beams and detection optics, we show that the angular Airy function can accurately predict experimental wavelength resolved intensity measurements. Based on the angular Airy function, we show that the fundamental operating principle of an FP etalon is as an angular-spectral filter. Based on this interpretation we explain the asymmetry, broadening and visibility reduction seen on wavelength resolved intensity measurements from high Q-factor FP etalons illuminated with focused Gaussian beams.

Analysing the impact of non-parallelism in Fabry-Perot etalons through optical modelling

Fabry-Perot (FP) etalons, composed of two parallel mirrors, are used widely as optical filters and sensors. In certain applications, however, such as when FP etalons with polymer cavities are used to detect ultrasound, the mirrors may not be perfectly parallel due to manufacturing limitations. As little is known about how the mirrors being non-parallel impacts upon FP etalon performance, it is challenging to optimize the design of such devices. To address this challenge, we developed a model of light propagation in non-parallel FP etalons. The model is valid for arbitrary monochromatic beams and calculates both the reflected and transmitted beams, assuming full-wave description of light. Wavelength resolved transmissivity simulations were computed to predict the effect that non-parallel mirrors have on the sensitivity, spectral bandwidth and peak transmissivity of FP etalons. Theoretical predictions show that the impact of the non-parallel mirrors increases with both mirror reflectivity and incident Gaussian beam waist. Guidelines regarding the maximum angle allowed between FP mirrors whilst maintaining the sensitivity and peak transmissivity of a parallel mirror FP etalon are provided as a function of mirror reflectivity, cavity thickness and Gaussian beam waist. This information, and the model, could be useful for guiding the design of FP etalons suffering a known degree of non-parallelism, for example, to optimize the sensitivity of polymer based FP ultrasound sensors.

Modelling Fabry-Pérot etalons illuminated by focussed beams

Fabry-Pérot (FP) etalons are used as filters and sensors in a range of optical systems. Often FP etalons are illuminated by collimated laser beams, in which case the transmitted and reflected light fields can be calculated analytically using well established models. However, FP etalons are sometimes illuminated by more complex beams such as focussed Gaussian beams, which may also be aberrated. Modelling the response of FP etalons to these beams requires a more sophisticated model. To address this need, we present a model that can describe the response of an FP etalon that is illuminated by an arbitrary beam. The model uses an electromagnetic wave description of light and can therefore compute the amplitude, phase and polarization of the optical field at any position in the system. It can also account for common light delivery and detection components such as lenses, optical fibres and photo-detectors, allowing practical systems to be simulated. The model was validated against wavelength resolved measurements of transmittance and reflectance obtained using a system consisting of an FP etalon illuminated by a focussed Gaussian beam. Experiments with focal spot sizes ranging from 30 µm to 250 µm and FP etalon mirror reflectivities in the range 97.2 % to 99.2 % yielded excellent visual agreement between simulated and experimental data and an average error below 10% for a range of quantitative comparative metrics. We expect the model to be a useful tool for designing, understanding and optimising systems that use FP etalons.

Sleep Quality Assessment and Daytime Sleepiness of Liver Transplantation Candidates

OBJECTIVE

The goal of this study was to evaluate the sleep quality and daytime sleepiness of patients eligible for liver transplants.

METHODS

A cross-sectional prospective study was conducted on liver transplant candidates from a transplant center in the interior of São Paulo State. The Pittsburgh Sleep Quality Index and Epworth Sleepiness Scale questionnaires were applied to obtain demographic and clinical characteristics and to assess sleep quality and daytime sleepiness.

RESULTS

The mean (±SD) score on the Epworth Sleepiness Scale of the 45 liver transplantation candidates was 7.00 ± 2.83 points, with 28.89% having scores >10 points, indicating excessive daytime sleepiness. The mean score on the Pittsburgh Sleep Quality Index was 6.64 ± 4.95 points, with 60% of the subjects showing impaired sleep quality, with scores >5 points. The average sleep duration was 07:16 h. Regarding sleep quality self-classification, 31.11% reported poor or very poor quality. It is noteworthy that 73.33% of patients had to go to the bathroom, 53.33% woke up in the middle of the night, and 40.00% reported pain related to sleeping difficulties. Comparison of subjects with good and poor sleep quality revealed a significant difference in time to sleep (P = .0002), sleep hours (P = .0003), and sleep quality self-classification (P = .000072).

CONCLUSION

Liver transplant candidates have a compromised quality of sleep and excessive daytime sleepiness. In clinical practice, we recommend the evaluation and implementation of interventions aimed at improving the sleep and wakefulness cycle, contributing to a better quality of life.

Adenosine A(2A) receptors are necessary and sufficient to trigger memory impairment in adult mice

BACKGROUND AND PURPOSE

Caffeine (a non-selective adenosine receptor antagonist) prevents memory deficits in aging and Alzheimer's disease, an effect mimicked by adenosine A2 A receptor, but not A1 receptor, antagonists. Hence, we investigated the effects of adenosine receptor agonists and antagonists on memory performance and scopolamine-induced memory impairment in mice.

EXPERIMENTAL APPROACH

We determined whether A2 A receptors are necessary for the emergence of memory impairments induced by scopolamine and whether A2 A receptor activation triggers memory deficits in naïve mice, using three tests to assess short-term memory, namely the object recognition task, inhibitory avoidance and modified Y-maze.

KEY RESULTS

Scopolamine (1.0 mg·kg(-1) , i.p.) impaired short-term memory performance in all three tests and this scopolamine-induced amnesia was prevented by the A2 A receptor antagonist (SCH 58261, 0.1-1.0 mg·kg(-1) , i.p.) and by the A1 receptor antagonist (DPCPX, 0.2-5.0 mg·kg(-1) , i.p.), except in the modified Y-maze where only SCH58261 was effective. Both antagonists were devoid of effects on memory or locomotion in naïve rats. Notably, the activation of A2 A receptors with CGS 21680 (0.1-0.5 mg·kg(-1) , i.p.) before the training session was sufficient to trigger memory impairment in the three tests in naïve mice, and this effect was prevented by SCH 58261 (1.0 mg·kg(-1) , i.p.). Furthermore, i.c.v. administration of CGS 21680 (50 nmol) also impaired recognition memory in the object recognition task.

CONCLUSIONS AND IMPLICATIONS

These results show that A2 A receptors are necessary and sufficient to trigger memory impairment and further suggest that A1 receptors might also be selectively engaged to control the cholinergic-driven memory impairment.

Delayed deficits in behavior after transection of the olfactory tracts in hamsters

This study compared the effects of transection of the lateral olfactory tracts (LOT) and the accessory olfactory tracts (AOT) in male hamsters on nest building, food piling, and sexual behavior. Autoradiographic tracing of amino acids injected into the olfactory bulbs allowed accurate determination of the location and extent of the transections. Animals with complete bilateral transection of the projections to the amygdaloid targets of the accessory olfactory bulbs and to the main olfactory targets posterior to the olfactory tubercle showed no sexual behavior postoperatively; they did not exhibit extensive genital investigation and did not mount females. In contrast, most of the animals with partial sparing of accessory olfactory bulb efferents to the amygdala did exhibit investigatory and copulatory behaviors postoperatively, although half of the animals with this partial sparing developed delayed deficits in these sexual behaviors. Almost all animals without detectable main olfactory bulb efferents to posterior targets showed delayed deficits in nest building and food piling. This was true whether or not there was partial sparing of accessory olfactory bulb efferents to the amygdala. The animals with LOT transections typically built nests and piled food during the first postoperative week, but stopped building nests and piling food by the fourth postoperative week. Cold stress enhanced these two behaviors in control animals but did not obviate the deficits in experimental animals. Caudally placed transections, which spared a larger portion of the main olfactory projections than rostally placed transections, did not spare more behavior. In fact, the caudally placed transections produced shorter delays in the appearance of deficits in nest building and food piling. These results indicate that the accessory olfactory bulb efferents to the amygdala are more important for sexual behavior than for nest building and food piling in male hamsters. Nest building and food piling are not directly dependent on normal ongoing or sensory evoked activity in the main or accessory olfactory bulb efferents which project through the LOT and AOT. The deficits in nest building and food piling may represent a deterioration in the ability of the animals to organize their living space. The observed delays in the appearance of deficits in behavior may also reflect slow degenerative processes or humoral changes associated with loss of input from the main olfactory bulbs to posterior olfactory target areas, and possibly with interruptions of projections to targets of the accessory olfactory system.

Vomeronasal pump: significance for male hamster sexual behavior

Vomeronasal chemoreceptors segregated within the vomeronasal organ are important for male hamster sexual behavior. An autonomically controlled vascular pump, previously demonstrated in anesthetized animals, can transport stimuli to the receptors. Interruption of the efferent nerves controlling the pump results in behavioral deficits similar to those produced by interruption of the afferent nerves carrying information from the vomeronasal organ to the brain. Pump activation is thus a prerequisite for normal vomeronasal stimulation in behaving animals.

Sagittal knife cuts in the far-lateral hypothalamus reduce sexual receptivity in female hamsters

We have previously shown that hypothalamic knife cuts confined to the sagittal plane lateral to the medial anterior hypothalamus-ventromedial nucleus can disrupt sexual receptivity in female golden hamsters. In the present study we have compared the effects of varying the lateral position of sagittal cuts located at this same rostral-caudal level. Near-lateral (NL) cuts were placed at or just lateral to the fornix, while far-lateral (FL) cuts were placed at the lateral edge of the medial forebrain bundle. Ovariectomized, estradiol benzoate plus progesterone-treated females were given weekly tests for lordosis before and after hypothalamic cuts. Changes in body weight and agonistic behavior were also recorded. Both NL and FL cuts reduced lordosis in response to both manual stimulation and a sexually active male. Postoperatively, it was more difficult to elicit lordosis from these females, and if elicited, the duration of the response was reduced. NL, but not FL, cuts also increased agonistic behavior, and produced obesity. Since both NL and FL cuts severed axons traveling in the region of the supraoptic commissures (SOC), these data support our hypothesis that these SOC connections are critical for sexual receptivity. The SOC carrys both efferents and afferents of the ventromedial hypothalamus. Sagittal-plane cuts which interrupt the SOC may disrupt lordosis by cutting either or both types of connection.

Effects of perilymphatic perfusion with neomycin on the cochlear microphonic potential in the guinea pig

The effects of three concentrations of neomycin, administered by a method of acute perilymphatic perfusion of the guinea pig cochlea, on the cochlear microphonic potential (CM) at 4 kHz and 500 Hz are described. A concentration-dependent reduction in CM occured during the 60 minute perfusion period. Neomycin at 10-4 M did not change the CM magnitude, while at 10-3 and 102 M it caused 4 kHz (and 500 Hz) CM reductions which began within 24 (for both frequencies) minutes and 10 (and 12) minutes of drug application respectively. CM reduction proceeded at a higher rate for greater neomycin concentration. The perfusion technique, the implication of the frequency indifference, and the potential of the perfusion technique for inner ear biochemical analysis are discussed.

Individual differences in aggressiveness of female hamsters: response to intact and castrated males and to females

The aggressive behaviour of female hamsters was studied while they were housed in large enclosures with males and in brief tests with males or females. Some females are not aggressive with any male, whereas others are very aggressive toward all males in both testing conditions. Females that are not aggressive toward intact males may be very aggressive toward castrated males or females. When the animals are housed together for long periods of time, males dominate only if they are much heavier. Male dominance takes a relatively long time to establish and often there is an equivocal period characterized by reversals of dominance. Female dominance is rapidly established. Unless the male is much heavier, the female determines the presence or absence of agonistic behaviour.

Another hamster paradox: more males carry pups and fewer kill and cannibalize young than do females

The response of virgin male and female golden hamsters to young was studied. In contrast to most species, males are more likely to carry pups than are females. All males carried pups, but approximately 50% of females cannibalized the young. The females that did not cannibalize the pups carried them with less hesitation and after shorter latencies than did the males. The response of females to young was not correlated with the aggressiveness displayed toward adult males during separate tests. Tests with gonadectomized females indicated that the maintenance of pup-killing behavior is not dependent on concurrent gonadal hormones. Progesterone injections did not significantly increase pup killing in males that had previously carried young. Speculations on the adaptive significance of the male and female hamster's response to pups are presented.