DD147153A1 - Arrangement for measuring the spatial power distribution of laser radiation - Google Patents

Arrangement for measuring the spatial power distribution of laser radiation Download PDF

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Publication number
DD147153A1
DD147153A1 DD21642279A DD21642279A DD147153A1 DD 147153 A1 DD147153 A1 DD 147153A1 DD 21642279 A DD21642279 A DD 21642279A DD 21642279 A DD21642279 A DD 21642279A DD 147153 A1 DD147153 A1 DD 147153A1
Authority
DD
German Democratic Republic
Prior art keywords
arrangement
laser
laser beams
measuring
energy distribution
Prior art date
Application number
DD21642279A
Other languages
German (de)
Inventor
Hartmut Lucht
Edgar Klose
Original Assignee
Hartmut Lucht
Edgar Klose
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hartmut Lucht, Edgar Klose filed Critical Hartmut Lucht
Priority to DD21642279A priority Critical patent/DD147153A1/en
Publication of DD147153A1 publication Critical patent/DD147153A1/en

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Abstract

The invention relates to the field of laser technology. The aim of the invention is to ensure a high spatial resolution and an exact energy measurement over a large dynamic range in the spatial distribution of energy of laser beams. The invention has for its object to provide such an arrangement in which the linear relationship between radiant energy and photocurrent for semiconductor photodetectors is utilized in a wide range. According to the invention, this is achieved by arranging an optical shutter arrangement having a variable diameter light passage in the beam path of the laser light source at a selected distance from the photodetector displaceable in the direction of the optical axis, and the whole assembly is formed by two in-plane drives is movable perpendicular to the beam path. The invention is applicable in the exploration of nonlinear optical processes, in interaction studies in plasma, in the adjustment of resonators as well as in the focusing of laser beams for metal working.

Description

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Arrangement for measuring the spatial energy distribution of laser beams

Field of application of the invention

The arrangement finds application in science and technology whenever the spatial energy distribution of laser beams is of interest; for example, in the study of non-linear optical processes or interaction studies in plasma.

Characteristic of the known technical solutions

The determination of the spatial energy distribution of laser beams is necessary for many scientific and technological purposes. Examples include the investigation of non-linear optical processes, the processing of materials by laser beams and the interaction studies in plasma. A common method is to measure the radiation divergence using long focal length lenses. However, it has the disadvantage that the determination of the focal plane is difficult and the results obtained allow only an inaccurate indication of the radiation divergence. The specification of an exact spatial energy distribution is not possible. This is usually obtained by photographic means. A single laser pulse is gradually attenuated by multiple reflection, and the graded intensities of the laser beam expose a photosensitive film.

422 2

The developed film shows a series of two-dimensional blackening distributions which have graduated blackening maxima and are measured by a photometer. The maximum blackening is determined as a function of the relative irradiation energy.

The result is the Hurter-Driffield diagram, which is used to determine the two-dimensional density distributions from the two-dimensional blackening distributions. The total energy of the laser pulse is measured with a calorimeter and is equal to the integral of the energy drawn over the irradiated area. On the basis of this information, the absolute spatial energy density of the laser beam can be calculated.

The advantage of the photographic process is its reliability and suitability for a wide spectral range. The precision is not satisfactory due to the complicated conversion of the blackening of the film into relative irradiation energy, especially since at low intensities the blackening of the film increases only weakly with the logarithm of the irradiation energy. The main drawback is the tedious and cumbersome evaluation of the photographic images.

Also known is the measurement of the spatial energy distribution of laser beams by means of silicon vidicon. A significant advantage of silicon photodetectors is the achievable in a large intensity range Linitätität the photosensitivity. Consequently, no Hurter Driffield conversions are required. The silicon vidicon consists of a photodiode matrix which is charged or blocked by an electron beam.

The photo-electron-hole pairs generated by the laser beam discharge the diodes as a function of the irradiation energy. By a new, the photodiode array charging electron beam is simultaneously queried the discharge state of the diodes and the analog information, which is an image of the spatial irradiation energy, recorded as a so-called video data frame in a video recorder * The video data frame is then by a digitizer in digitally

216 422

converted to a basic form and usually fed to a small computer with the required peripherals. To determine the absolute. Energy density distribution is comparable to the photographic method requires a calorimeter. The signals from the calorimeter are also fed to the small computer via an AD converter. This method allows an extremely fast determination of the spatial energy distribution of the laser beam. The disadvantage is the required great effort, which is unacceptable for many development laboratories. Furthermore arise in the query and simultaneous blocking of Fotodiodenkapazitäten new. Charges which have a strongly weakened proportionality to the previous charges. This leads to distortions of the measurement results.

The operation of the silicon vidicon in the form described is intended for the measurement of small light energies. For the measurement of large energies, as they occur in the lasers, it is unsuitable due to the low charge storage capacity of the diodes. The intense laser light is therefore to be weakened by several orders of magnitude. This is usually only possible with multiple neutral filters.

Object of the invention

The aim of the invention is to determine the spatial energy distribution of laser beams with less effort than before so that a high spatial resolution and an accurate energy measurement over a wide dynamic range are guaranteed.

Explanation of the nature of the invention

• l

The object of the invention is to provide an arrangement for the high-resolution measurement of the spatial energy distribution of laser beams, in which the linear relationship between radiant energy and photocurrent for semiconductor photodetectors is utilized in a wide range.

According to the invention, this is in an arrangement for measuring the spatial energy distribution of laser beams with a large dynamic range in terms of energy and high spatial resolution, in which a control unit and a high voltage pulse generator and a laser light source and a photodetector are arranged, which an integrator and an XY writer with downstream of a staircase generator, characterized in that an optical aperture arrangement having a light passage having a variable cross section is arranged in the beam path of the laser light source in a distance of the photodetector selected before the measurement as a function of the intensity of the laser light, v / obei the distance proportional to the Laser intensity is that the photodetector is mounted near the optical axis or in the optical axis of the light cone of the diffracted light, and the distance to the optical aperture is provided by propulsion in the direction of the optical axis tion is adjustable, and that the entire arrangement is movable by two drives in the plane perpendicular to the beam path.

The laser beam is scanned by the optical shutter arrangement. Delayed in time to the laser pulse, the control unit triggers the control of the drives of the optical aperture arrangement such that after each laser pulse and their registration, the aperture is moved by an adjustable interval until the entire laser beam is scanned. Registration is accomplished by receiving the laser light diffracted by the optical shutter assembly from the photodetector, converting it to an electrical signal, and then detecting it in a known manner for amplification and storage via a recorder. A special embodiment of the optical diaphragm arrangement consists of two crossed micrometer slots of a double-slit arrangement that can be closed up to the order of magnitude of the light wave. In high intensity laser beams, the gap widths are on the order of the wavelength, while in the case of low intensity laser beams, the gap widths are large in relation to the wavelength.

21ό 422

With decreasing gap widths of the double slit, the achievable spatial resolution becomes greater. At the same time the diffraction increases at the columns. This causes a weakening of the energy density behind the gap, which greatly increases with gap widths in the order of magnitude of the wavelength. Particularly focused laser light has very high radiation energy density and requires large attenuation of the light at the highest spatial resolution, that is, small gap widths. The photodetector is spatially fixed to the double-slit arrangement and is moved with this through the described drives in the plane perpendicular to the laser beam. Due to the small dimensions, semiconductor photodiodes, for example, silicon photodiodes in the visible spectral range, are preferably used.

The photodetector is chosen as small as possible, for example 100 χ 100 yum. By a further propulsion of the potentiometer is movable in the direction of the optical axis. This makes it possible to set a desired radiant energy density at the potentiometer detector or a desired sensitivity of the entire arrangement by changing the distance from the double slit.

The dependence of the irradiation energy density on the distance is particularly strong if the gap width has the order of magnitude of the wavelength. In the case of pulse lasers, the potentiometer measures the radiation energy arriving per pulse in the blanked area. Sampling the spatial energy distribution gives a graph indicating the relative energy density of the radiation as a function of location. With continuous lasers only a constant measurement time is given and otherwise proceeded in the same way. The maximum measurable energy density is determined by the onset of the thermal destruction of the material of the gap forming surfaces. In order for destruction to occur only at high energy densities, the gap-forming surfaces are provided with an Al or Au layer in the order of a few tenths of a micrometer.

'2.1 6'422 6

The main advantages of the described arrangement consist in comparison to the photographic method in the simplification of the evaluation of the results and compared to the use of a silicon vidicon in a much lower equipment cost, since no vidicon with the appropriate control and no weakening by neutral filters are required. Furthermore, with the arrangement according to the invention, a spatial resolution is achieved, which is superior to the Siliconicon and the photographic method. ·

embodiment

The invention will be explained in more detail below using an exemplary embodiment. In the accompanying drawings, Figure 1 shows the schematic diagram of the arrangement for measuring the spatial energy distribution of a laser beam and Figure 2 is a block diagram of the arrangement, which illustrates the measurement of the spatial 'energy distribution according to the method.

First, reference is made to FIG. Starting from a laser light source 1, the laser beam 2 impinges on the slit arrangement 3. The slit arrangement consists of two crossed micrometer gaps whose surfaces are vapor-deposited with a gold layer a few tenths of a micrometer thick and which are moved by two advances in the indicated arrow direction and in the direction perpendicular to the plane of the drawing. The gaps can be closed reproducibly up to a gap width of 1 / um. The diffused and diffracted by the gap arrangement light 4 strikes the silicon photodiode 5, the distance to the double-slit arrangement is controlled by a drive and is simultaneously displaced by the two propulsions of the slit assembly. The diode used detects at sufficient distance to the double-slit arrangement only a small portion of the diffracted light 4. At low energy of the laser beam can be selected by choosing a small distance to the gap arrangement

216 422

the entire diffracted light is detected by the diode. At very high energy densities, depending on the time course of the laser pulse, the destruction of the fissile material begins, which as a rule consists of stainless steel. Stainless steel has a visible reflectance of about 55%.

This reflectivity is increased by a few tenths of a micrometer thick gold coating to about 90 % , so that the light absorption and thus the thermal heating in the fissile material leads to destruction at significantly higher light intensities. FIG. 2 illustrates the performance of the measurement by means of the arrangement according to the invention. A control unit 8 triggers the pulsed laser 1 via a high-voltage pulse generator 9. The laser beam strikes the double slit arrangement 3, which has two drives.

Delayed in time to the laser pulse, the control unit 8 triggers the control of the drives so that after each laser pulse and its registration, the gap opening is displaced by an adjustable interval and scanned the entire laser beam v / ird.

The diffracted at the double slit laser light is received by the photodiode 5 and converted into an electrical signal, the electrical signal is amplified in the integrator 6 and da3 stored maximum of the electrical signal. The stored signal generates the Y deflection of an XY recorder 7 ·

The integrator 6 is cleared after registration of the electrical signal by the trigger pulse of the control unit. The X-stroke of the recorder is generated via a staircase generator 10 triggered by the control unit 8. After registration of the signal by the recorder, the laser is triggered again and the registration of the laser light with subsequent displacement of the gap opening is repeated. The laser beam is scanned line by line,

Claims (5)

216 422 β Breakthrough claim
1. Arrangement for measuring the spatial energy distribution of laser beams with a control unit and a high voltage generator and a laser light source and a photodetector, which an integrator and an XY writer are connected to a staircase generator, characterized in that one, a light passage having a variable cross-section , optical diaphragm arrangement (3) is arranged in the beam path of the laser light source (1) in a distance from the photodetector (5) selected before the measurement as a function of the intensity of the laser light, the distance being proportional to the laser intensity that the photodetector (5) in the vicinity of the optical axis or in the optical axis of the light cone of the diffracted
  , Attached light and by a propulsion in the direction of the optical axis, the distance to the optical diaphragm assembly (3) is adjustable, and that the entire assembly is movable by two propulsions in the plane perpendicular to the beam path.
'2 \ 6 422
2. Arrangement for measuring the spatial energy distribution of laser beams according to item 1,
characterized in that the, having a light passage with variable cross-section having optical Bleridenanordnung consists of two closable to the order of the light wave crossed micrometer column of a double-slit order.
3. Arrangement for measuring the spatial energy distribution of laser beams according to item 1 and 2, characterized in that are at high-intensity laser beams, the gap widths of the order of the wavelength and laser beams of low intensity, the gap widths are large in relation to the wavelength.
4 «arrangement for measuring the spatial energy distribution of laser beams according to items 1 to 3, characterized in that the gap-forming surfaces are provided with an Al or Au layer in the order of a few tenths of a micrometer.
5. Arrangement for measuring the spatial energy distribution of laser beams according to item 1 to 4, characterized in that a semiconductor diode is used as the photodetector (5).
See ".. 2 .._." Soaps Zeichnungea
DD21642279A 1979-10-24 1979-10-24 Arrangement for measuring the spatial power distribution of laser radiation DD147153A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DD21642279A DD147153A1 (en) 1979-10-24 1979-10-24 Arrangement for measuring the spatial power distribution of laser radiation

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DD21642279A DD147153A1 (en) 1979-10-24 1979-10-24 Arrangement for measuring the spatial power distribution of laser radiation

Publications (1)

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DD147153A1 true DD147153A1 (en) 1981-03-18

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010053323B3 (en) * 2010-12-02 2012-05-24 Xtreme Technologies Gmbh Method for the spatially resolved measurement of parameters in a cross section of a beam of high-energy, high-intensity radiation

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010053323B3 (en) * 2010-12-02 2012-05-24 Xtreme Technologies Gmbh Method for the spatially resolved measurement of parameters in a cross section of a beam of high-energy, high-intensity radiation
JP2012118061A (en) * 2010-12-02 2012-06-21 Xtreme Technologies Gmbh Method for measuring spatial decomposition of parameter on beam cross section of high-energy radiation light of high intensity
US8686372B2 (en) 2010-12-02 2014-04-01 Ushio Denki Kabushiki Kaisha Method for the spatially resolved measurement of parameters in a cross section of a beam bundle of high-energy radiation of high intensity

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