Deformable mirrors are becoming more and more important elements in the astronomical field, both for development of active and adaptive optics. PCDMs behave in a completely different way respect to the traditional ones, since a pattern of light creates virtual actuators, whose size and density can be freely modulated. PCDMs consist in a slab of photoconductive material with a reflective membrane placed at a certain distance from the photoconductor, creating a capacitor. In this paper will be presented the mechanical solution adopted in order to realize a prototype and the setup used in order to start the characterization of the different component. A critical analysis will be performed on the sensitivity of the system to the different dimension that characterize the system itself, like the distance between the membrane and the photoconductor and the membrane tension. The result presented will be relate to the static deformation of the membrane using the DC current.
Deformable mirrors are key optical elements in modern astronomical telescopes and instrumentation both for active and adaptive optical systems. Different technological approaches have been exploited for the realization of the deformable mirrors, especially for adaptive optics devices. A new approach is here presented, namely the photo-controlled deformable mirrors, where the size and density of actuators is set by an illumination pattern projected on the back side of a photoconductor. The working principle and an electric model are presented highlighting the features of the material that affect the performances of the mirror in terms of dynamic range and response time. Based on these results, a prototype exploiting ZnSe as photoconductor is reported together with its characterization.
The progress in the field of organic photodetectors has recently led to the development of very fast and efficient devices, but their spectral sensitivity is mainly limited to the visible, without covering the regions of the spectrum of greater interest for telecommunications. One of the major issues when dealing with long wavelength organic photodetectors is the usually poor environmental stability of low bandgap organic semiconductors. A possible exception to this scenario is represented by coordination complexes with organic ligands. We employ as photosensitive materials transition metal dithiolene and dioxolene complexes which combine high thermal and photochemical stabilities with high molar extinction coefficients in the near infrared. Taking advantage of the broad tuning of electronic absorption spectra which can be exerted by changing the oxidation state of the complexes, we develop planar metal-semiconductor-metal phostodetectors which are spectrally matched to the optical fiber windows and which can detect light pulses with repetition rates in the range of hundreds of kbit/s.
This investigation demonstrates the existence of organic materials of potential telecom interest and that the detection of infrared light pulses is feasible, thus representing a first step toward organic photodetectors for telecommunications.
A new class of photodetectors, whose active material is an organic semiconductor, has been developed. Thanks to the ease of deposition on any dielectric surface, the device may be built directly on the cleaved surface of an optical fiber, therefore realizing an on-fiber-detector (OFD). The photodetector is based on an organic semiconductor belonging to a new general class of neutral dithiolenes deposited onto a quartz substrate with microlithographically defined gold electrodes so to realize a metal-semiconductor-metal surface structure. First experimental results on a photodiode made of (monoreduced imidazolidine-2,4,5-trithione) having peak responsivity at 1014nm, have shown a time response down to 100microseconds, at present limited by the leakage current noise due to the poorly rectifying contacts. Differently from the vast majority of organic semiconductor materials, dithiolenes have shown extremely high chemical and thermal stability. The photoresponse of the dithiolenes in the liquid phase is shown to be wavelength selective with an absorption peak about 150nm wide that can be chemically tailored so to shift from almost 1000nm to 1700nm. Experimental measurements to prove that the absorption property is maintained in the solid state also at wavelengths around 1500nm, thus covering with a photodetector the spectrum of possible telecom applications, are under way.
In the framework of trap-free steady-state space-charge-limited single-carrier currents, exact equations are derived for the evaluation of arbitrary field-dependent mobility. A differential method, which simply needs first and second derivatives of measured current-voltage (I-V) curves, is put forward. No a priori assumptions are required, other than those which are typical for space-charge-limited currents. An extension to the mixed case of exponentially distributed traps and field-dependent mobility is briefly outlined. The extraction of mobility from measurements can be a valuable tool for the theoretician: theoretical predictions on mobility field-dependence can be easily compared to the real field-dependence, thus permitting an improvement of the model and stimulating the development of transport theory. This method can be of particular relevance for organic semiconductors, whose field-dependent mobility has recently attracted so much theoretical and experimental work.
The paper describes the use of noise current analysis to sense variations of the microscopic conduction process in organic Light Emitting Diodes and to track their evolution through time. The monitoring of current fluctuations has been made both in time and frequency domain and is of great value when one wants to correlate the conduction properties of the charge carriers and the changes in current flow with the corresponding changes in the microscopic morphology of the organic layers. The method reveals itself to be very effective also in sensing the initial state and the growth of catastrophic degradation of oLEDs in large advance with respect to current monitoring or other techniques. Microscopic damages within the device, as a result of microshorts and/or thermal breakdown, are shown to reveal a neat increase of the white noise component of about three orders of magnitude in the power spectral density, that can therefore be detected with very good time precision. This would allow to study the sources that may give reason of degradation, through structural or spectroscopic investigations for example, before the microscopic damages have sum up to a visible and irreversible macroscopic failure.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.