Testicular volumetry and prediction of daily sperm output in stallions by orchidometry and two- and three-dimensional sonography.

Accurate determination of the testes volume and prediction of the daily sperm output (DSO) is valuable information for reproductive management of a stallion. The aim of this study was to compare different methods for measuring the testes volume, including caliper, 2D and 3D ultrasound. Special emphasis was on feasibility of 3D volume analysis. First, 22 castrated testes were measured and derived volumes were compared with volumes determined via volume displacement in a graded cylinder with saline solution. Then, during the breeding season, testes sizes of 52 stallions were measured in vivo and analyzed. With the derived volumes, predicted DSO (pDSO) values were calculated which were compared with actual values (aDSO) determined from semen evaluation. Analyses of castrated testes revealed a discrepancy between volume assessments via the caliper and ultrasound methods and actual volumes as found via volume displacement. The smallest difference was found for 3D volume analysis, followed by caliper and 2D ultrasound. Testicular volumes of breeding stallions were highest if determined via 3D ultrasound, followed by measurements using 2D ultrasound and caliper. Correlation between the total testicular volume (TTV) and aDSO was high with volume assessment via ultrasound (2D: r = 0.639, p < 0.001, and 3D: r = 0.604, p < 0.001), and moderate for using caliper (r = 0.46, p < 0.01). Linear regression analyses of TTV and aDSO values revealed that changes in aDSO in part could be explained by differences in testes volume: 32% and 27% in case of 3D and 2D ultrasound, and 12% with caliper. pDSO values that were predicted from testicular measurements correlated best with aDSO values from semen collection protocols in case of using 3D ultrasound (r = 0.56, p < 0.001), followed by 2D ultrasound (r = 0.52; p < 0.001) and caliper (r = 0.34, p = 0.01). In conclusion, 3D ultrasound can be performed on equine testes for more accurate volume predictions, which in turn may increase precision when determining the breeding potential of a stallion.

Generalized retarded response of nonlinear media and its influence on soliton dynamics.

We demonstrate by means of numerical simulations of the generalized Nonlinear Schrödinger Equation that the retarded response of a nonlinear medium embedded in a single hole of a photonic crystal fiber crucially affects the spectrum generated by ultrashort laser pulses. By introducing a hypothetic medium with fixed dispersion and nonlinearity and with a variable retarded response, we are able to separate the influence of the retarded response from other effects. We show that the fission length of a launched higher-order soliton dramatically increases if the characteristic time of the retarded response is close to the input pulse duration. Furthermore, we investigate the effect of the retarded response on the soliton self-frequency shift and find that the optimum input pulse duration for maximizing the spectral width has to be shortened for a larger characteristic retarded response time. Our work has important implications on future studies of spatiotemporal solitons in selectively liquid-filled photonic crystal fibers.

Ultrafast nonlinear optofluidics in selectively liquid-filled photonic crystal fibers.

Selective filling of photonic crystal fibers with different media enables a plethora of possibilities in linear and nonlinear optics. Using two-photon direct-laser writing we demonstrate full flexibility of individual closing of holes and subsequent filling of photonic crystal fibers with highly nonlinear liquids. We experimentally demonstrate solitonic supercontinuum generation over 600 nm bandwidth using a compact femtosecond oscillator as pump source. Encapsulating our fibers at the ends we realize a compact ultrafast nonlinear optofluidic device. Our work is fundamentally important to the field of nonlinear optics as it provides a new platform for investigations of spatio-temporal nonlinear effects and underpins new applications in sensing and communications. Selective filling of different linear and nonlinear liquids, metals, gases, gain media, and liquid crystals into photonic crystal fibers will be the basis of new reconfigurable and versatile optical fiber devices with unprecedented performance. Control over both temporal and spatial dispersion as well as linear and nonlinear coupling will lead to the generation of spatial-temporal solitons, so-called optical bullets.

Tapering fibers with complex shape.

We present a model which allows us to accurately simulate the fabrication process of complex-shaped tapered fibers. The range of possible profiles is only limited by the properties of the heat source used to shape the fiber. The model takes into account the motion of the heat source relative to the fiber as well as its temperature distribution. Our measurements and corresponding finite element method (FEM) simulations have shown a strong dependency of the temperature distribution along the fiber axis on the actual diameter of the fiber. The inclusion of this relation in the model proved to be crucial for the accuracy of the results. Our model has been verified experimentally by fabricating tapered fibers with a sinusoidally modulated waist. A comparison to the profile predicted by our model reveals an excellent agreement.

Coherence of subsequent supercontinuum pulses generated in tapered fibers in the femtosecond regime.

We measure the degree of coherence of supercontinua generated in tapered fibers by subsequent fs pulses. By means of interference experiments we study its dependence on the input pulse duration and power. We also present numerical simulations that allow us to explain the experimental observations which show a decreasing degree of coherence with increasing input power. We attribute this loss of coherence to phase noise due to the cross-phase modulation by several solitons with randomly varying parameters due to quantum noise.

Compact portable 20 MHz solid-state femtosecond whitelight-laser.

We demonstrate a new and extremely compact design for a directly diode-pumped Yb:glass laser oscillator that is used as femtosecond light source for supercontinuum generation. The laser is capable of generating femtosecond pulses of 150 fs and pulse energies up to 39 nJ at a repetition rate of 20 MHz. By using a Herriott-type multi-pass cell, 70 % of the total resonator length are folded to only 30 cm. With off-the-shelf components, our setup has a footprint of 62x23 cm(2). Using smaller mechanical components, the size can easily be further decreased. In combination with a tapered fiber, the laser forms a cheap, stable, and compact femtosecond supercontinuum source with up to 400 mW of average whitelight power.