Optical: systems and elements – Single channel simultaneously to or from plural channels – By refraction at beam splitting or combining surface
Patent
1992-05-27
1994-08-16
Henry, Jon W.
Optical: systems and elements
Single channel simultaneously to or from plural channels
By refraction at beam splitting or combining surface
356358, 359834, G02B 2710, G02B 504, G01P 368
Patent
active
053391969
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optical device, in particular for measuring the speed of a moved surface, by means of a measuring light beam from a laser, this beam being split into two part beams which are directed in a transmitting prism to converge through prisms towards the moved surface.
In a known optical device of the above type for measuring lengths and speeds, a light beam from a laser--the term "laser" is used for a laser resonator for the sake of simplicity--is split into two part beams which are directed at different angles to the moved surface, in particular that of an object whereof the speed or length is to be measured continuously. The laser light reflected and scattered by this surface is detected by optical means and supplied to a photodetector for evaluation. Since both part beams arrive at the same location on the surface of the object to be measured, the scattered light waves which are Doppler-shifted to a different extent are overlaid. This results in a beat whereof the frequency is proportional to the speed of the moved surface. The speed or length sought can be determined continuously from the modulation frequency and represented or displayed.
In a known optical device of this type, the two part beams, either parallel or diverging, enter two prisms which are arranged mirror-symmetrically with respect to one another, and there the part beams are deflected outwards with reference to their center plane to intensify beam splitting. They leave the prisms in a parallel alignment, in the case of part beams which enter parallel through correspondingly parallel reflection surfaces of the prisms. In order that the part beams intersect at a predetermined point of intersection, each part beam is then guided through a wedge-shaped prism which, for the angular adjustment of the part beam concerned, is arranged to be adjustable on a mounting, in particular to be rotatable about an axis of rotation parallel to the center plane between the two prisms. Consequently, for precise angular adjustment of the part beams a very precise adjustment has to be set and in particular this has also to be maintained in all the circumstances of practical operation. On the one hand, the input prisms each have to be adjusted with respect to the succeeding wedge prisms, and on the other hand the angular adjustment of the wedge prism has to be adjusted with respect to the angle of intersection of the emerging part beam with the center plane between the prism arrangements. In other words, four individual prisms have to be matched precisely to one another as regards the position and angle of their reflective and refractive surfaces. This is because the Doppler frequency for example depends in a crucial way on the angle of intersection of the two part beams, and this angle of intersection is established by the transmitting prism.
It is particularly problematic to maintain an adjustment of the prisms by gluing the prisms, which, in particular in the case of heat expansion to which the individual prisms are exposed, cannot prevent the mutual position of the reflective and also the refractive surfaces of the prisms and thus also the angle of intersection of the part beams emerging from the wedge prisms with the center plane from altering accordingly.
The expense for the production of four individual prisms and their adjustable arrangement with respect to one another is also considerable and makes the production of the device correspondingly more expensive.
In another known optical device, two prisms are glued to one another, and the measuring light beam enters these prisms unsplit and is split by an appropriate arrangement of the reflective and refractive surfaces into two part beams which are guided outwards--in relation to the center plane--for beam splitting in the prisms and emerge parallel from the prisms. Downstream of the two prisms there is arranged a lens which deflects the part beams to converge so that they meet at the predetermined point of intersection. This optical arrangement also requires a high level of expense f
REFERENCES:
patent: 1253137 (1918-01-01), Brewster
patent: 1579806 (1926-04-01), Ball et al.
patent: 2265264 (1941-12-01), Bunger et al.
patent: 4787710 (1988-11-01), Durell
patent: 4916529 (1990-04-01), Yamamoto
patent: 4948257 (1990-08-01), Kaufman et al.
Henry Jon W.
Mesacon Gesellschaft fur Messtechnik mbH
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