Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1997-10-20
2000-04-11
Westin, Edward P.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
250214VT, 250374, H01J 3150, G04F 1302
Patent
active
060490799
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for detecting a photon pulse as a function of time, for instance a streak camera, comprising a pulse converter for converting a photon pulse for detecting into an electron stream, first deflection means for deflecting the electron stream as a function of time and a position-sensitive detector for determining the deflection of the electron stream.
Such an invention is known from a publication by R. Yen, P. M. Downey, C. V. Shank and D. H. Auston in "Appl. Phys. Lett.", Vol. 44, No. 8, (1984), pp. 718-720. In this publication a streak camera is described, the streak tube (image-converter tube) of which contains a photocathode, a collimator plate provided with micro-channels, deflection plates and a phosphor screen. The output image of this streak tube is coupled via a reducing bundle of optical fibres to an image amplifier, the output of which is coupled using a fibre optic to a silicon image amplifier, the output signal of which is displayed on the screen of an optical multi-channel analyzer (OMA).
A photon pulse incident on the photocathode generates an electron beam which is deflected by the deflection plates, to which is applied a voltage which rapidly increases synchronously with the incidence of the photon pulse. The deflected electron beam strikes the phosphor screen, on which is displayed a line segment progressing in time, the intensity of which corresponds to the intensity of the incident photon pulse. This image is further processed by the relevant fibre optics, image amplifiers and OMA, whereafter an image of the intensity of the incident photon pulse as a function of time is finally obtained.
The known streak camera has the drawback that the wavelength range of photons of which the pulse intensity can be displayed is bounded on the long-wave side of the spectrum at a wavelength of approximately 1.5 .mu.m (infrared), while on the other side photons from the X-ray region (i.e. the part of the spectrum having very short wavelengths) occur in many practical applications in non-monochromatic pulses, of which no sharp image can be made using an apparatus of the above described type.
The object of the invention is to provide an apparatus for detecting as a function of time a photon pulse which has a wavelength shorter than that of visible light or longer than that of infrared light and for making a sharp image of such a pulse.
This object is achieved with an apparatus of the type stated in the preamble, wherein according to the invention the pulse converter comprises a gaseous medium for absorbing the photon pulse to be detected and for emitting the electron stream.
In an apparatus wherein according to the invention the pulse converter comprises a gaseous medium the spectral range of a photon pulse for detecting is not limited to the visible light and the infrared region, but the spectral range can be extended as required to the wavelength region of far-infrared light or the wavelength region of X radiation.
In an embodiment of an apparatus according to the invention for detecting a photon pulse in the far- infrared region the apparatus is provided with excitation means for bringing particles into an excited electron state and the gaseous medium contains particles for bringing into this excited electron state in order in this state to absorb the photon pulse and to emit the electron stream.
The excited electron state is for instance a Rydberg state.
By bringing particles, for instance atoms, into an excited electron state, for instance a Rydberg state, a pulse converter is obtained for converting a (far) infrared and therefore low-energy photon pulse into an electron stream. An atom in a Rydberg state, referred hereinafter to as Rydberg atom, has a high value of the main quantum number n, and therefore a relatively low binding energy E (E=-13.6
.sup.2 eV). As a consequence the relatively low energy of a far-infrared photon is sufficiently high to cause photo-ionization of an atom in a Rydberg state and to liberate a weakly bonded electron from that atom. Moreover,
REFERENCES:
patent: 4814599 (1989-03-01), Wang
patent: 4958231 (1990-09-01), Tsuchiya
patent: 4988859 (1991-01-01), Tsuchiya et al.
patent: 5311010 (1994-05-01), Kruger
Applied Physics Letters, Apr. 15, 1984, USA vol. 44, No. 8, ISSN 0003-6951, pp. 718-720, XP002004345 Yen R et al: "Low jitter streak camera triggered by subpicosecond laser pulses" cited in the application.
Lankhuijzen Marcelis Dominicus
Noordam Lambertus Dominicus
Bednarek Michael D.
Hanig Richard
Stichting Voor Fundamenteel Onderzoek der Materie
Westin Edward P.
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