GB2330199A - Wavelength measuring device for short duration laser pulses - Google Patents

Abstract

A device for measuring the wavelength of the narrow band low intensity stray light from short duration laser pulses (eg from laser range finders) wherein the light is split and directed along two light intensity measuring channels (FO1/2, ST1/2, Detector1/2) with differing spectral transmission characteristics (eg by a spectral filter 4). The wavelength of the light is then determined computationally from these two intensity measurements.

Description

Wavelength Measuring Device for Short Laser Pulses The invention relates to a wavelength measuring device for short laser pulses. In particular it relates to wavelength measuring device for short laser pulses of narrow-band stray light with low intensity whereby a specific visual field is simultaneously monitored by a supplementary optical element.

In the present state of the art, all tunable Fabry-Perot filters, graded interference filters, monochromators etc. are temporally always ready to receive only in one wavelength, and therefore the probability of detecting single short pulses is very small without temporal synchronisation.

Simultaneously measuring diode line spectrometers work with an on-chip integration of the measured signal, and with the long measurement times compared to the nanosecond pulses the background signal is problematic, since its noise covers the low intensity of the pulses to be measured. With the usual low pixel dimensions, moreover, it is difficult to simultaneously obtain a sufficiently large visual field and a large entrance pupil, since this leads to exactly opposed requirements for the focal length.

Preferably the present invention provides a measuring device of the aforementioned type, which enables and assures determination of the wavelength of narrow-band stray light generated by short laser pulses - e.g. by laser range finders.

Accordingly, the present invention provides wavelength measuring device for short laser pulses of narrow-band stray light with low intensity whereby a specific visual field is simultaneously monitored by a supplementary optical element, characterised in that the incident light is spatially split and distributed onto a specific number of measuring channels, these measuring channels having sensitivities differing spectrally from one another, which are generated by spectral filters arranged in the optical path of a collection optical system or different detectors, and the wavelength of the incident light is computationally determined from the measured values of the different measuring channels.

Configurations and further developments are specified in the sub-claims and an example is explained in the following description in conjunction with the figures of the drawings: Figure 1 shows the essential structure of an embodiment of a beam splitter with two detectors in schematic representation; Figure 2 is a diagram showing a transmission curve of a spectral filter.

An embodiment of a wavelength measuring device according to the invention for narrow-band light pulses such as those occurring in the case of stray light generated by laser range finders, for example, is described below. Both a short pulse duration and a very low intensity should be given as situation features.

The pulse duration typically lies in the ns range.

Furthermore, the instant of time of the pulse and the exact direction is unknown, and therefore all wavelengths in the spectral range of interest must preferably be monitored simultaneously and a specific visual field must preferably also be monitored with a suitable supplementary optical element.

The general concept of the invention therefore envisages spatially splitting the incident light pulse and distributing it onto a specific number - at least two - of measuring channels. These measuring channels are marked by spectrally different sensitivities and the sensitivity curves as a function of the wavelength are thereby assumed to be monotonically sloping upwards or downwards, ideally to be linear.

The wavelength of the respectively incident light may be computationally clearly determined from the individual measured values, at least by quotient formation. The suitable spectral sensitivity curves are formed by different spectral filters and different detectors.

An embodiment of the above-mentioned wavelength measuring device is sketched in Figure 1 and shows a light-collecting objective lens comprising mirror or lens elements with a spectral filter 4 arranged in its collection beam axis, which divides the collection beam into two part-beams ST1 and ST2 in a manner dependent on wavelength, which are respectively dIrected onto the detectors 1 and 2 allocated to them via a focussing optical system FOl and FO2.

The diagram in Figure 2 illustrates an example of a favourable transmission curve of the spectral filter used. It is evident from this that the detectors observe different signal strengths relative to one another depending upon the wavelengths. The signal I of detector 1 is: I = T * 1o and the signal of detector 2 is: I2 = R * I.

The wavelength X results, for example, from I1/I2 = T/R (\) independently of the intensity 1o of the incident light.

As a result of proposed measures not hitherto recognised by the prior art, determination of the wavelength of narrow-band stray light of short laser pulses is now assured in a surprisingly simple manner.

Claims (4)

1. Patent - Claims: 1. Wavelength measuring device for short laser pulses of narrow-band stray light with low intensity whereby a specific visual field is simultaneously monitored by a supplementary optical element, characterised in that the incident light is spatially split and distributed onto a specific number of measuring channels, these measuring channels having sensitivities differing spectrally from one another, which are generated by spectral filters arranged in the optical path of a collection optical system or different detectors, and the wavelength of the incident light is computationally determined from the measured values of the different measuring channels.
2. 2. Wavelength measuring device according to Claim 1, wherein a mirror or lens optical element is used as collection optical system.
3. 3. Wavelength measuring device according to Claim 1 or 2, wherein a focussing optical system and a corresponding detector are allocated to each measuring channel of spectrally different sensitivity generated by the spectral filter or filters.
4. 4. A wavelength measuring device substantially as any one embodiment herein described with reference to the accompanying drawings.