We have recently shown that Alkali atoms contained in a vapor cell can serve as a highly accurate standard for microwave electric field strength as well as polarization using the principles of Rydberg atom electromagnetically induced transparency. Here, we show, for the first time, that Rydberg atom electromagnetically induced transparency can be used to image microwave electric fields with unprecedented precision. The spatial resolution of the method is far into the sub-wavelength regime. The electric field resolutions are similar to those we have demonstrated in our prior experiments. Our experimental results agree with finite element calculations of test electric field patterns.Atomic standards are important because they enable stable and uniform measurements and often link physical quantities to each other via universal constants [1]. We have demonstrated in our prior work that atoms contained in a vapor cell can be used for a practical and, in principle, portable microwave (MW) electric field standard using Rydberg atom electromagnetically induced transparency (EIT) [2, 3]. The accurate measurement of MW electric field strength and polarization can lead to advances in applications such as antenna design, device development, characterization of electro-magnetic interference, advanced radar applications and materials characterization [4-9], including metamaterials [10][11][12].To our knowledge, no other work exists on imaging MW electric fields with atoms in vapor cells. Even in the field of magnetometry, where vapor cell magnetometers have played a central part [13], absorption imaging for vapor cell MW magnetometry has only been recently reported [14, 15]. Many of the technical issues of imaging a MW magnetic field as opposed to an electric field with a vapor cell are different. Knowledge of both fields is important. Despite the rather straightforward connection between the electric and magnetic fields in free space, there is not always a simple relation between them in the near field. The absolute measurement of MW electric fields at sub-wavelength resolutions and in the near field is necessary for many MW applications.To meet the need for sub-wavelength imaging of MW electric fields, we demonstrate a scheme for subwavelength MW electrometry using Rydberg atom EIT [16, 17] in Cesium (Cs) atomic vapor cells at room temperature. In contrast to scanning probe technology [18, 19], our approach avoids cryogenics and eliminates the presence of conducting materials near the sample, therefore minimizing field disturbances. We achieve a 2-dimensional spatial resolution of ∼ λ MW /650, ∼ 66 µm at ∼ 6.9 GHz, using a test MW electric field in the form of a standing wave and image the MW electric field di- * Corresponding author: shaffer@nhn.ou.edu rectly above a co-planar waveguide (CPW) to demonstrate near field imaging. The electric field resolution is ∼ 50 µV cm −1 limited by our detection setup. The measurements are compatible with our prior work where we attained a minimum detectable electric field amplitude of ...
Despite recent developments and new treatments in ophthalmology there is nothing available to cure retinal degenerations like Retinitis Pigmentosa (RP) yet. One of the most advanced approaches to treat people that have gone blind due to RP is to replace the function of the degenerated photoreceptors by a microelectronic neuroprosthetic device. Basically, this subretinal active implant transforms the incoming light into electric pulses to stimulate the remaining cells of the retina. The functional time of such devices is a crucial aspect. In this paper the laboratory and clinical reliability of the two active subretinal implants Alpha IMS and Alpha AMS is presented. Based on clinical data the median operating life of the Alpha AMS is estimated to be 3.3 years with a one-sided lower 75 % confidence level of 2.0 years. This data shows a significant improvement of the device lifetime compared to the previous device Alpha IMS which shows a median lifetime of 0.6 years with a lower confidence bound (75 %) of 0.5 years. The results are in good agreement with laboratory data from accelerated aging tests of the implant components, showing an estimated median lifetime for Alpha IMS components of 0.7 years compared to the improved lifetime of Alpha AMS of 4.7 years.
We present a very sensitive and scalable method to measure the population of highly excited Rydberg states in a thermal vapor cell of rubidium atoms. We detect the Rydberg ionization current in a 5 mm electrically contacted cell. The measured current is found to be in excellent agreement with a theory for the Rydberg population based on a master equation for the three level problem including an ionization channel and the full Doppler distributions at the corresponding temperatures. The signal-to-noise ratio of the current detection is substantially better than purely optical techniques.PACS numbers: 32.80. Rm, 03.67.Lx, 42.50.Gy Coherent phenomena involving strongly interacting Rydberg atoms have recently led to the demonstration of first quantum devices like quantum logic gates [1][2][3] and single photon sources [4] based on ultracold atoms. All these experiments require precise control over the highly excited states populations, which can be probed directly by field ionization [5,6] or by fluorescence techniques involving Rydberg shielding [7]. Since the strong vdW interaction has recently also been observed in vapor cells [8], scalable quantum devices based on the Rydberg blockade in above room temperature ensembles seem to be also within reach [9]. However, ion detectors as electron multipliers or multi-channel plates cannot be used in dense thermal vapors. For this reason, in thermal cells, most studies today use an indirect measurement of the excited state population by analyzing light fields leaving the atomic ensemble. Nevertheless, it is desirable to study not only the back-action of the vapor on the light, typically via electromagnetically induced transparency (EIT) [10], but also to measure directly the number of excited Rydberg states. One method, developed almost a century ago [11,12], makes use of thermionic diodes [13][14][15]. There, one of the electrodes is heated to emit electrons, which produce space charge limited gain for the amplification of ionized Rydberg atoms. The need of long ion trapping times requires large geometries for the space charge region, and an additional shielded excitation region to minimize the effect of disturbing electric fields during excitation of the highly polarizable Rydberg atoms. Despite its high sensitivity, this drawback sets a practical limitation for further applications where size and scalability play a role.Here we demonstrate that, in a symmetric configuration of atomic vapor between two transparent field plates, sizable currents in the nA regime reflect directly the Rydberg population and can be used as a probe with very good signal-to-noise ratio. This opens unique possibilities to probe very efficiently small spectroscopic features involving Rydberg states in thermal vapor but also might be used to stabilize lasers. By extending this concept to an array of pixel-wise arranged electrodes, high resolution spatial information on the Rydberg population can be obtained.The experiments were performed with the setup schematically shown in Fig. 1. The Rb va...
Electronic retinal implants have been developed and are marketed as a therapeutic option for blind people suffering from degenerative retinal diseases such as retinitis pigmentosa. The functionality of subretinal implants depends heavily on the performance of the electronic interface to the retina. For the RETINA IMPLANT Alpha AMS device, this interface consists of a subretinally implanted chip that samples the retinal image, like a camera chip, and stimulates the adjacent retina simultaneously at the corresponding locations. The technical functionality of the RETINA IMPLANT Alpha AMS is described and compared with the outcome of two clinical trials over an observation period of one year. The discrimination of different grey levels observed in these clinical trials confirms that the sensitivity of the implanted CMOS chip can be varied over the range of relevant light intensities. We show that accelerated aging lifetime measurements of implant components in a laboratory environment match implant lifetimes observed during clinical trials for the predecessor device, the RETINA IMPLANT Alpha IMS. By using the same model for the current technically advanced device, the RETINA IMPLANT Alpha AMS, the predicted clinical lifetime of the implant is about 5 years.
We demonstrate the use of electrically contacted vapor cells to switch the transmission of a probe laser. The excitation scheme makes use of electromagnetically induced transparency involving a Rydberg state. The cell fabrication technique involves thin-film-based electric feedthroughs, which are well suited for scaling this concept to many addressable pixels like in flat panel displays.
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