JPH0674866A - Infrared ray mtf measuring device - Google Patents

Abstract

PURPOSE:To determine the position of a laser beam spot and the beam diameter on a focal surface of an infrared ray sensor which is a measurement specimen in the measurement of MTF (Modulation Transfer Function) of an infrared ray sensor. CONSTITUTION:The title device is provided with two optical systems, namely the first optical system irradiates an infrared ray laser beam and a second one irradiates a visible light laser beam. Both optical systems are led onto a same light axis of a focusing lens 8 and focus beams to a specimen on a movable stage 10 or onto a beam profile detector 15. The beam profile detector 15 measures the beam profile near the focal point of each laser beam and the relative relation position. On the other hand, the reflection light of a laser spot on the sensor focal point surface is projected on an output monitor 12 and then the diameter of beam on the specimen focal point surface is determined from the relative relation positions of both beam profiles and the spot size of the visible light beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an infrared MTF (MOD
ULATION TRANSFER FUNCTION
N) It relates to a measuring device.

[0002]

2. Description of the Related Art As is well known, an infrared MTF device is used to evaluate the spatial resolution of an infrared sensor such as crosstalk by irradiating the light receiving surface of an infrared sensor, which is a measurement sample, with spot light having a narrowed beam diameter. A measuring device,
This is particularly effective in a situation where it is difficult to accurately know the position and spot diameter of the spot on the focal plane of the sensor, such as a cooled infrared sensor, in which the measurement sample is housed in the cooling dewar.

Therefore, for more accurate measurement,
Needless to say, spot light having a smaller beam diameter is required, and it is also necessary to accurately grasp the spot position and spot diameter on the focal plane.

An example of a conventional infrared MTF measuring device is shown in FIG. In the figure, an infrared HeNe laser 1 having a central wavelength of 1523 nm is used as a light source of spot light. The laser light passes through the beam expander 2, is guided to the condenser lens 8 by the full mirror 5, and is condensed on the focal plane of the infrared sensor housed in the cooling dewar 9 on the movable stage 10.

By using a condenser lens with an F number of about 5, spot light with a diameter of about 20 μm can be obtained.
By moving the movable stage 10 in a plane perpendicular to the optical axis, the irradiation position of the sensor focal plane can be controlled, and the spot diameter of the focal plane can be changed by moving in the front-back direction on the optical axis. Conventionally, the MTF of the infrared device is measured in this manner.

[0006]

As described above, in the infrared MTF measuring device, it is important to accurately grasp the beam diameter on the focal plane of the sample. In this respect, the conventional infrared MTF measuring device has the following problems.

That is, since many infrared sensors have good characteristics at low temperatures, they are operated in the state of being housed in the cooling dewar 9. At this time, it is difficult to mount the sample sensor 1 at a strict fixed position in the cooling dewar 9, and it is extremely difficult to accurately know the spot position on the sensor focal plane and the distance from the condenser lens 8 to the sensor focal plane. is there.

Since the beam diameter changes in the optical axis direction, an error in measuring the distance in the optical axis direction makes it difficult to estimate the beam diameter. Particularly, in the infrared MTF evaluation device, a lens having a small F number is usually used to narrow the beam diameter, and the error in the beam diameter is large.

As described above, it is difficult for the conventional infrared MTF measuring device to detect the beam spot position and accurately grasp the beam diameter.

An object of the present invention is to provide an infrared MTF measuring device for measuring the position and beam diameter of a laser beam spot on the focal plane of an infrared sensor which is a measurement sample.

[0011]

To achieve the above object, in an infrared MTF measuring apparatus according to the present invention, a first optical system, a second optical system, a movable stage, a beam profile detector, Infrared M with monitor
In the TF measuring device, the first optical system focuses the infrared laser on the focal plane of the sample, and the second optical system uses the movable laser light as the same as the first optical system. It guides light onto the optical axis and focuses it on the focal plane of the sample.The movable stage fixes the measurement sample and the beam profile detector, and its movement is adjustable. The beam profile detector is an infrared laser. And a detector with sensitivity to both visible laser and slit,
The light receiving surface is mounted on the movable stage in a direction perpendicular to the optical axis, and the beam profile near the focal point of each laser beam and its relative positional relationship are measured, and the monitor measures the focal plane of the measurement sample. The image is taken.

[0012]

The relative position of the beam profile of each laser light measured in advance and the spot image on the focal plane of the visible light laser displayed on the output monitor are used to determine the position and beam of the spot on the sensor focal plane of the infrared laser light. You can know the diameter.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The following examples describe the configuration of an infrared MTF detection device of the present invention and a beam profile measuring method using a beam profile detector.

FIG. 1 shows an embodiment of the infrared MTF measuring device of the present invention. In the figure, 1 is an infrared HeNe laser having a central wavelength of 1523 nm, and 3 is a visible light HeNe laser having a central wavelength of 632.8 nm.

After passing through the beam expanders 2 and 4, the respective laser lights are guided to the same optical axis passing through the condenser lens 8 by the full mirror 5 and the half mirror 6, respectively, and the cooling dewar on the movable stage 10. The light is focused on the focal plane of the infrared sensor housed in 9. By moving the movable stage 10, the spot irradiation position on the sensor focal plane can be controlled. Next, the beam profile detector 15
A method of obtaining a beam profile near the focal point of each laser beam will be described using.

FIG. 2A shows a beam profile detector 15, which is a Ge avalanche photodiode 14 having sensitivity to both oscillation wavelengths of the lasers 1 and 3 and a width of about 1 μm arranged in front of the light receiving surface thereof. It is constituted by the slit 13. Here, the light receiving surface of the Ge avalanche photodiode has an area sufficient to cover the diffracted light behind the slit. Beam profile detector 15
Is fixed on the movable stage 10 in FIG. 1 in a direction in which the light receiving surface is perpendicular to the optical axis.

A method of operating the beam profile detector 15 will be described with reference to FIG. By controlling the movable stage,
The detector is moved in the diameter direction of the condenser lens 8, and the intensity distribution of the laser light near the focus is examined. Operate the beam profile detector 15 in the directions indicated by 16a and 16b to
The intensity distributions of 7a and 17b were obtained. From the intensity distribution, F
WHM (full width at half maximum) values Δωa and Δωb are obtained.

By repeating this operation in the optical axis direction 18 of the condenser lens and plotting the FWHM value, a beam profile can be created. By the above-mentioned method, a unique beam profile can be obtained in each of the infrared laser and the visible light laser, and at the same time, the relative positional relationship between the two beam profiles can be known through this measurement.

The spot position and the spot diameter on the sensor focal plane of the infrared laser can be known by using the relative positional relationship of the beam profiles. This will be described below.

The visible light HeNe laser 3 and the infrared light He
Since the optical axis of the Ne laser 1 coincides with that of the sensor focal plane, the spot position of the infrared HeNe laser on the sensor focal plane can be known by observing the reflected light of the spot of the visible HeNe laser. You can In FIG. 1, 11 and 12 are C for detecting the reflected light of the laser spot on the sensor focal plane of the visible light HeNe laser 3.
In the CD camera 11 and the output monitor 12, the half mirror 7 is for guiding the reflected light on the focal plane to the CCD camera 11. The method of observing the reflected light is not limited to the above embodiment, and a method of arranging the fiber bundle obliquely in front of the cooling dewar 9 and observing the reflected light of the laser spot on the sensor focal plane from the oblique direction is also possible.

Further, the beam diameter of the infrared laser light on the sensor focal plane is known from the relative positional relationship between the beam profiles of the two laser lights obtained above and the spot size of the visible light laser projected on the output monitor 12. be able to.

[0022]

As described above, according to the present invention,
The effect is that the beam profile of the infrared laser light can be grasped, and the position of the beam spot on the focal plane of the infrared sensor and the beam diameter can be known.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an infrared MTF measuring device of the present invention.

FIG. 2A is a diagram showing a configuration of a beam profile detector, and FIG. 2B is a diagram showing a method for measuring a beam profile.

FIG. 3 is a diagram showing a conventional example of an infrared MTF measuring device.

[Explanation of symbols]

 1 Infrared HeNe Laser 2 Beam Expander for Infrared HeNe Laser 3 Visible Light HeNe Laser 4 Beam Expander for Visible Light HeNe Laser 5 Full Mirror 6 Half Mirror 7 Half Mirror 8 Condensing Lens 9 Cooling Dewar 10 Infrared Sensor Movable Stage 11 CCD Camera 12 Output monitor 13 Slit 14 Ge avalanche photodiode 15 Beam profile detector 16a, 16b Detector operating direction 17a, 17b Intensity distribution output result 18 Optical axis direction of condenser lens

Claims (1)

[Claims] 1. An infrared MTF measuring device having a first optical system, a second optical system, a movable stage, a beam profile detector, and a monitor, wherein the first optical system is an infrared laser. Is focused on the focal plane of the sample, and the second optical system guides the movable laser light on the same optical axis as the first optical system to focus on the focal plane of the sample. The movable stage fixes the sample to be measured and the beam profile detector and can be moved and adjusted.The beam profile detector has a slit in the detector that is sensitive to both infrared lasers and visible lasers. Is mounted on the movable stage with the light receiving surface perpendicular to the optical axis, and measures the beam profile near the focal point of each laser beam and its relative positional relationship. An infrared MTF measuring device, characterized in that the focal plane of the measurement sample is to imaging.