Composition dependence of indentation deformation and indentation cracking in glass

International audienceAbstract Crack initiation and deformation behaviors of oxide glasses belonging to different chemical systems were studied using the Vickers indentation test. The crack initiation resistance is chiefly governed by the extents to which densification and isochoric shear flow develop in a process zone beneath and within the contact area. Densification is favored in glasses with relatively small Poisson's ratio (ν), whereas shear is favored at large ν. Glasses were ranged according to their resistance to the formation of corner cracks as follows: Resilient, for 0.15 ⩽ ν ⩽ 0.20; Semi-Resilient, for 0.20 ⩽ ν ⩽ 0.25; and Easily-Damaged for 0.25  <  ν  <  0.30. Radial-median cracks occur at low load (⩽50 mN) in Easily-Damaged glasses, while cone cracks predominate in Resilient glasses under higher loads. A critical value for ν (∼0.22 depending on the Young's modulus/hardness ratio) was identified, at which the intensity of the indentation stress field tends to vanish, preventing crack formation on loading, while the driving force on unloading remains very small

Corrigendum to: Composition dependence of indentation deformation and indentation cracking in glass (vol 61, pg 5949, 2013)

International audienceThe authors regret that a typographic error has slipped into one of the numerical values of the coefficients needed to get a sigmoidal curve fitting using Eq. (11). In sub-section 3.2 on page 5958 of the original paper, the βR coefficient should read 0.0008 instead of 0.008

Development of broadband infrared single-mode fibers for the DARWIN mission

A vital function of the space interferometer foreseen in the DARWIN mission is the so-called "nulling" operation. The challenge of nulling is making the null in the interferometric signal sufficiently deep to cancel the light from the bright star during the collection of light from its surrounding planets. The performance of the nulling is limited by the wavefront quality of the beams. The wavefront error can be reduced by filtering. One promising concept for nulling wavefront filtering is using a single mode fiber. For the wavefront filtering in the DARWIN mission, the fiber has to cover the operational wavelength range of 4-20 μm. Furthermore, a minimal insertion loss is required to ensure a minimum exposure time. This results in the separation of the complete wavelength range into several separate wavelength bands in the nulling system. Within an ESA project, a chalcogenide glass fiber based on the Te-As-Se (TAS) composition is selected to be used for the short wavelength band. TNO has designed and tested several TAS fibers that have been manufactured by the University of Rennes. Single mode operation is demonstrated. Furthermore, the effect of bending the fiber and light coupling are investigated. For the long wavelength band up to 20 μm, Tellurium based glass is proposed. Different samples of various composition based on Te glass are manufactured. Accurate temperature control to avoid crystallization is found to be essential for the manufacturing process. For the bulk material, a transmission window up to 20 μm is measured

Test results of the infrared single-mode fiber for the DARWIN mission

Nulling interferometry is the baseline technique for the DARWIN planet finding mission of the European Space Agency. Using this technique it will be possible to cancel, by destructive interference, the light from the bright star and look directly at its surrounding planets and eventually discover life on them. To achieve this goal wavefront errors need to be reduced to a very high degree in order to achieve the required nulling quality. Such a high wavefront quality can only be achieved with adequate wavefront filtering measures. Single mode fibers in general have excellent mode filtering capabilities, but they were not recently available for the broad infrared wavelength region of Darwin (4-20 um). Within an ESA technology development project, TNO has designed and tested an infrared single mode fiber based on chalcogenide glasses that has been manufactured by the University of Rennes. Several tests are carried out to characterize the materials used and the IR single mode fiber. Far field intensity distribution measurement at 10.6 um reveals the single mode operation of the manufactured fiber. Influence of coating, length, light coupling and bending of the fiber are also investigated

Development of infrared single-mode fibers for 2 wavelength bands of the Darwin mission: test results of prototypes

Various space telescope array systems are being considered to investigate other terrestrial planets orbiting around nearby stars in order to find extra-terrestrial life. One of them is the DARWIN mission of the European Space Agency (ESA). The required technology is the nulling interferometer. The challenge of nulling is making the null in the interferometric signal sufficiently deep to cancel the light from the bright star during the collection of light from its surrounding planets. The performance of the nulling is limited by the wavefront quality of the beams. The wavefront error can be reduced by filtering using a single mode fiber. For the DARWIN mission, the operational wavelength range is 6.5-20μm. Within the current ESA project, this is covered by a dual-band fiber system. A chalcogenide glass fiber based on the Te-As-Se (TAS) composition is selected to be used for the short wavelength band. For the long wavelength band up to 20 μm, Tellurium based glass is proposed. Different samples of various composition based on Te glass are manufactured and tested. The fibers are designed by TNO and different prototypes have been manufactured by the University of Rennes. Test setups are developed to demonstrate/investigate the single mode operation. Cladding modes are found to disturb the single mode operation. The effect of cladding modes is modeled. Solutions to eliminate the cladding modes are investigated and tested. © 2009 SPIE

Infrared single mode chalcogenide glass fiber for space.

International audienceAn important measuring technique under study for the DARWIN planet finding mission, is nulling interferometry, enabling the detection of the weak infrared emission lines of an orbiting planet. This technique requires a perfect wavefront of the light beams to be combined in the interferometer. By using a single mode waveguide before detection, wavefront errors are filtered and a virtually perfect plane wavefront is obtained. In this paper the results on the development and the optical characterisation of suitable infrared transmitting chalcogenide glasses and mid-IR guiding optical fibers are reported. Two different perform techniques for manufacturing core-cladding chalcogenide fibers are described. Two types of step index fibers, prepared with Te(2)As(3)Se(5) chalcogenide glasses, offer single mode guidance at 10.6 mum