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Further distribution of this work must maintain attribution to the author s and the published article's title, journal citation, and DOI This media kit contains background information of use to journalists and reporters covering the LISA Pathfinder mission. ESA uses cookies to track visits to our website only, no personal information is collected. By continuing to use the site you are agreeing to our use of cookies. OK Find out more about our cookie policy.

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Publication archive. In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. The Letter presents the measured differential acceleration noise figure, which is at 1. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency.

Spatium Gravitational waves: the sound of the Dark Universe. It is devoted to gravitational waves, their sources and the marvellous technologies required for observing them. Over and above, this issue renders homage to Albert Einstein and the scientists of his time, who laid the cornerstone for our understanding of gravitational waves. LISA Pathfinder appreciably constrains collapse models. Spontaneous collapse models are phenomological theories formulated to address major difficulties in macroscopic quantum mechanics.

Dispersive IR Spectrometers

We place significant bounds on the parameters of the leading collapse models, the continuous spontaneous localization CSL model, and the Diosi-Penrose DP model, by using LISA Pathfinder's measurement, at a record accuracy, of the relative acceleration noise between two free-falling macroscopic test masses. In particular, we bound the CSL collapse rate to be at most 2. This competitive bound explores a new frequency regime, 0. Moreover, we bound the regularization cutoff scale used in the DP model to prevent divergences to be at least Thus, we rule out the DP model if the cutoff is the size of a fundamental particle.

Detailed measurements of the charge-induced electrostatic forces exerted on free-falling test masses TMs inside the capacitive gravitational reference sensor are the first made in a relevant environment for a space-based gravitational wave detector. Employing a combination of charge control and electric-field compensation, we show that the level of charge-induced acceleration noise on a single TM can be maintained at a level close to 1.

Using dedicated measurements that detect these effects in the differential acceleration between the two test masses, we resolve the stochastic nature of the TM charge buildup due to interplanetary cosmic rays and the TM charge-to-force coupling through stray electric fields in the sensor. All our measurements are in good agreement with predictions based on a relatively simple electrostatic model of the LISA Pathfinder instrument.

Experimental bounds on collapse models from gravitational wave detectors. Wave function collapse models postulate a fundamental breakdown of the quantum superposition principle at the macroscale. Therefore, experimental tests of collapse models are also fundamental tests of quantum mechanics. We consider the most widely used collapse model, the continuous spontaneous localization CSL model.

We show that these experiments exclude a huge portion of the CSL parameter space, the strongest bound being set by the recently launched space mission LISA Pathfinder. Here excitation and recombination of modes is carried out with permanent and stable splices which does not degrade with time and temperature.

However, it is to be noted that the length of the collapse region depends upon the arc power and arc time of the fusion splicer. These parameters can be precisely tuned to control the length of the collapsed region. So the method is highly reliable and repeatable.


The position of the glue has been optimized and is placed in such a way that the cladding modes of PCF do not get affected so that the interference pattern is well retained. Before utilizing the probe for flow measurement, the response of the probe to the input vibrational frequency is first studied using a piezo-actuator. This is due to the fact that the presence of a bluff body in the pipe in which flow velocity is to be measured results in the generation of vortex shedding frequency and the response of the probe to this frequency is to be measured.

Further, the objective of this experiment is to evaluate the response of the optical probe for wide range of frequency.

Micro- and Nanoelectromechanical Systems | NIST

Since, the amplitude and frequency of vortex shedding is unknown a prior, hence the tests are conducted with a piezo actuator, which is excited at a known frequency and amplitude. This test is necessary to characterize the probe for wide range of frequency and amplitudes of vibrations before using it in an unknown environment.

The two ends of the probe are fixed between two stationary stages and a plastic sheet with adequate stiffness is attached to the piezo as shown in Fig. The plastic sheet is kept just below the mid part of the probe i. The piezo is connected to a signal generator that can be operated at different amplitude and frequencies. The probe is subjected to different amplitudes and frequencies through the piezo-actuator to evaluate the response of the probe.

As can be seen from the Fig. This flat response is advantageous in the present application as the flow rate is inferred from the frequency shift and the present technique is not based on amplitude tracking. Here, the change in vibrational amplitude of the peak can be neglected due to the variation in second decimal. Further, large variation in amplitude may lead to error in tracking of interference peaks. This is due to the fact that in order to track a given peak of the interference pattern, a particular amplitude limit is fixed in IMON interrogator.

If the change in amplitude becomes very high, then other peaks may come into picture and this may lead to misleading readings and hence negatively impact the reliability of the measurements.

How an FTIR Spectrometer Operates

From the above discussions, it can be concluded that the change in amplitude of peak corresponding to applied frequency is insignificant. Therefore, we proceed to use this probe for flow sensing based on wavelength interrogation. The use of SLED is advantageous considering its high power and low divergence.

This is due to the fact that the fabrication of the probe involves splicing of different types of fibers SMF-PCF and the splicing junction of the fibers lead to more losses. The output is analyzed using an interrogator IMON which acted as a spectrometer. The broadening of the mode results in the excitation of core and cladding modes in PCF as shown in Fig. These modes again combine at the second collapsed region at the other end of PCF and subsequently filtered through the core of SMF. Due to the different propagation constants, the core and cladding mode accumulate phase difference and this leads to the formation of interference pattern upon combination of these modes.

Considering the intensity of core and cladding modes as I 1 and I 2 , the resultant intensity I T of the probe can be written as. Any external perturbation that affects the effective index of either the core mode or the cladding mode, will ultimately affect the resulting interference pattern as can be realized from Equation 1. In our case, the vibration of piezo leads to the vibration of the plastic sheet which in turn vibrates the PCF. This results in the formation of a microbend and subsequent shift in the wavelength of the peak of the interference pattern. The shift in interference pattern may be attributed to the shift in cladding mode of the PCF towards outer region and subsequent change in effective index of cladding mode.

The experimental setup for the flow measurement is shown in Fig. As can be seen from the figure, a centrifugal pump 0. The inner diameter of the pipe is In order to regulate the flow of water, a gate valve is connected to the main line section of pipe through which flow is to be monitored.


Further, the mechanical vibration caused due to the pump is nullified using dampers on both upstream and downstream of the main line. A trapezoidal bluff body with blockage ratio of 0. The probe kept in the steel pipe is attached to the pipe vertically as shown in Fig. The length of PCF considered for this is nearly equal to the inner diameter of pipe One end of the probe is connected to SLED and the other to the interrogator. The resulting interference pattern of the probe is shown in Fig. As evident from the figure, there are two peaks corresponding to wavelengths of The numbers refer to various parts of the experiment as follows. Usually, the flow condition of fluids or the type of fluid flow can be predicted using a parameter called Reynolds number and this can be defined as:.

Further, for the same condition, the dynamic viscosity of water is 0. Therefore, the variation in volume flow rate affects the flow velocity which in turn changes the Reynolds number. In order to see the variation in Reynolds number with velocity of flow, we varied the velocity from 0. Several industrial applications demands metering of the flow at low Reynolds number, presently convention vortex flowmeter use a reduced bore design, which are capable of measuring low Reynolds number flows.

However, the major disadvantage of such design is permanent pressure loss, which impose financial burden and hence, are not preferable in industrial application. Hence, the present design has significant merit as the design is capable of measuring low Reynolds number without addition pressure loss and cost escalation. It is interesting to note that flow measurement using vortex flow meters at high Reynolds number is relatively easier since the signal strengths are sufficiently high. Hence, in the present study the focus is restricted to measure low Reynolds numbers.

Further, when the water flows through the pipe, the trapezoidal bluff body acts as an obstacle and as a consequence of this vortices are created downstream of the bluff body. These vortices shed at a fixed rate f , which is directly proposal to the velocity of the flow.