We present an overview of our on-going work in the domain of optical choppers with rotational shafts, which we proposed and patented. The different constructive solutions are presented and discussed referring to the shape of the shafts and of the slits. Our Finite Element Analyses (FEA), developed as a multi-parameter approach considering all the material, constructive and functional characteristics of the devices is briefly presented – regarding both the structural integrity and the level of deformation of fast rotational shafts with multiple holes. The potential of this novel type of optomechanical choppers is pointed out, in comparison to classical solutions of choppers with rotational disks.
Optical choppers are common components utilized in a wide variety of systems, for the modulation of light, including for generating controlled laser impulses, of as high as possible frequencies and with certain (required) profiles. Classical choppers have rotational disks, but such configurations are limited in terms of chop frequencies to 10 kHz, although issues already appear from around 3 kHz. Solutions to overcome this drawback include the development of Micro-Electro-Mechanical Systems (MEMS) or of macro-choppers with rotational shafts. To our knowledge, we have introduced the latter solution (patent pending). Our previous studies on choppers with cylindrical and spherical shafts are briefly pointed out in this work, while we approach a third possible solution, of choppers with conical shafts. Optomechanical aspects are discussed, performing the Finite Element Analysis (FEA) of the rotational shafts, for a certain range of constructive parameters, and for rotational speeds of up to 60 krpm. The possible limits of the rotational speed at which choppers with such conical shafts are obtained–from the point of view of their structural integrity and level of deformations.
Choppers are widely used in optical sensing, including for radiometry and photometry, spectrometry, biomedical applications, and telescopes. While classical choppers are built with rotational disk, we have introduced and patented a novel device, with rotational shafts, which has the capability to surpass the maximum limit of around 10 kHz chopping frequency that characterizes choppers with disks. The main issue of such choppers with shafts comes from the high rotational speeds they can employ. This is an advantage in terms of the high chopping frequency they can produce, but it imposes the necessity to perform a Finite Element Analysis (FEA) of the fast rotational shafts. While in previous studies we approached cylindrical shafts for the chopper, in the present one we consider spherical shafts. Optical aspects of such devices – regarding the transmission functions produced – have been presented in previous studies. In the present one we focus on the FEA of these choppers. Different dimensions and a range of rotational speeds of up to 60 krpm are considered. The main working conditions that are imposed are the structural integrity and the acceptable level of (elastic) deformations of the chopper shafts. Limits of the rotational speed at which the choppers can (still) work are discussed from these two points of view – with regard to the characteristics of the device.
Optical choppers are used in a large range of applications in sensing, from radiometry to telescopes and laser setups. Classical macro-devices comprise of a rotating disk with windows with linear margins. While we have introduced, for the first time to our knowledge, a novel type of chopper disks, with windows with non-linear margins, outward or inward (the latter as a patent), in the present study we approach another type of chopper: with rotating shafts (patent pending). Different types of shafts (cylindrical, spherical, or conical) are possible, in combination with different shapes of slits, but in the present paper cylindrical shafts with a certain profile of slits are considered. The paper is focused on the possibility to reach much higher chop frequencies than with disks choppers. In order to achieve this, a Finite Element Analysis (FEA) is performed on shafts with four slits (two perpendicular channels). A range of geometrical parameters of the shafts and of the slits are considered, as well as two possible materials, i.e. structural steel and an aluminium alloy. A discussion on the structural integrity and of the deformations of the fast rotating shafts is performed, based on the FEA, with regard to the materials used and to the limits of the rotational speed of the device.
Optical choppers are widely used in laser systems – for light modulation and/or attenuation. In their most used and wellknown configuration, they are built as a rotational wheel with windows, which transforms a continuous-wave laser beam into a series of impulses with a certain frequency and profile. We briefly present the analysis and design we have completed for the classical chopper wheels (i.e., with windows with linear margins) for both top-hat and Gaussian laser beams. Further on, novel chopper wheels configurations, with outward or inward semi-circular (or with other non-linear shaped) margins of the windows is pointed out; we completed for them both analytic functions and simulations, for both top-hat and Gaussian beams, in order to deduce their transmission functions (i.e., the time profile of the laser impulses generated by the device). The stress of the presentation is put on the novel choppers with shafts (patent pending); their transmission functions are pointed out for top-hat laser beams. Finally, an example of such choppers is considered, with regard to the necessary Finite Element Analysis (FEA) that has to be performed for their rotational shaft. Both the mechanical stress and the deformations in the shaft have to be taken into account, especially at high rotational speeds of the mobile element.
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