JPH01312426A - Light beam profile measuring apparatus - Google Patents

Abstract

PURPOSE:To measure a dynamic beam profile of a light beam simply by engaging an optoelectro transducer means with a light shielding plate having one set or more of openings and the openings corresponding to a direction of main scanning. CONSTITUTION:Laser light L1 outputted from a laser diode 2 is reflected on a reflecting surface 6a of a galvanometer mirror 6 oscillating through a collimator 4 to irradiate almost perpendicularly to slits 54a and 54b on a light shielding plate 56 through an ftheta lens 8. The laser light L1 passing through the slits 54a and 54b is converted to electricity from light with an optoelectro transducer section 58 and an current signal corresponding to the intensity of the laser light L1 is introduced into a current/voltage conversion circuit 90. The current signal is converted into a voltage signal to be introduced into an oscilloscope 94 through an amplifier 92. An interval is measured corresponding to a beam diameter at a point where an interval and amplitude value of a waveform correspond to 1/e<2>(e 2.72) from the waveform on a tube surface of the oscilloscope. This simplifies measurement of a dynamic beam profile of the light beam.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a light beam profile measuring device, and more specifically, a light beam deflecting beam to scan an object to be scanned to record or read an image. The present invention relates to a light beam profile measurement device that enables a beam scanning device to measure a beam shape during scanning of the light beam, a so-called dynamic beam profile.

[Background of the Invention] Conventionally, an object to be scanned is main-scanned by a light beam deflected in a one-dimensional direction by an optical deflection means such as a galvanometer mirror, a rotating polygon mirror, or a hologram scanner, and the object to be scanned is generally scanned in the main scanning direction. Orthogonal direction (sub-scanning direction)
Light beam scanning devices configured to move relative to each other and two-dimensionally scan an object to be scanned are widely used in various recording devices and scanning/reading devices.

FIG. 1 shows a light beam scanning recording apparatus equipped with a mechanism that operates in this manner. In this light beam scanning recording device, a laser beam L1 output from a recording laser diode 2 is made into a parallel beam by a collimator 4, and a galvanometer mirror 6 and an fθ lens 8 swing in the direction of the arrow.
Main scanning is performed on the rotating drum 10 in six directions indicated by arrows. The drum 10 has a pair of nip rollers 12a, 12b on which the film F to be sub-scanned and conveyed in the direction of arrow B is attached.
Sliding contact is made while being held between the two.

On the other hand, the synchronizing laser beam L2 output from the synchronizing laser diode 14 driven by the synchronizing laser diode drive circuit 13 is made into a parallel beam by the collimator 16 and is irradiated onto the grid 18 via the galvanometer mirror 6 and the θ lens 8. In this case, grid 18
Transmissive portions 20a and non-transmissive portions 20b are alternately formed along the main scanning direction (six directions of arrows), and a condensing rod 22 is arranged on the back side of this grid 18. Note that photodetectors 24a and 24b are arranged at both ends of the condensing rod 22, and these photodetectors 24a,
The output signal from 24 b is sent to the frequency multiplication PLL circuit 26
supplied to The output signal of the frequency multiplication PLL circuit 26 is supplied as a synchronization signal to an image signal generation circuit 28 that converts image information read from a document into a binarized halftone image signal.

A recording laser diode drive circuit 30 is driven based on the halftone image signal from the image signal generation circuit 28, and the recording laser diode 2 is driven by the output signal of the recording laser diode drive circuit 30. Therefore, the recording laser beam L1 outputted from the recording laser diode 2 is deflected by the galvanometer mirror 6 and main-scans the film F, thereby providing predetermined image information at the position of the scanning line P on the film F. recorded.

By the way, in the light beam scanning device configured as described above, the laser beam L1 that main scans the film F by the swinging operation of the galvanometer mirror 6 is accurately focused at all points of the scanning line P on the film F. Therefore, it is desirable to control the beam diameter so that it becomes the same diameter on the scanning line P. In this way, by controlling the beam diameter of the radar light L1 as a light beam to be the same diameter on the scanning HP, a high quality image without uneven exposure can be formed on the film F.

However, in an optical deflector such as a galvanometer mirror 6 that deflects a light beam, the mirror surface is distorted by inertial force on the peripheral surface of its reflective surface 6a, causing so-called dynamic distortion. The light beam L1 reflected by the reflective surface 6a with such dynamic strain and irradiated onto the film F becomes more influenced by the dynamic strain as it approaches both ends of the film F in the main scanning direction. That is, the beam diameter of the light beam L1 increases on both end sides in the main scanning direction, resulting in so-called beam thickening, and when an image, etc. is displayed, the image quality is significantly degraded due to the beam thickening, which is an inconvenience. has been pointed out.

Therefore, in order to improve these disadvantages, a reinforcing member is fixed to the back surface 6b of the galvanometer mirror 6, or the material of the galvanometer mirror 6 itself is made of a material with a small Young's modulus.

By the way, a light beam profile measurement device according to the prior art irradiates a stationary light beam onto a two-dimensional sensor consisting of an image pickup device such as a CCD, which has hundreds of thousands of photoelectric conversion units corresponding to pixels, for example. The beam profile is then measured from the light intensity distribution obtained from this two-dimensional sensor. That is, only the beam profile corresponding to when the optical deflector is stationary can be measured.

However, by only measuring the profile of a stationary light beam, it is impossible to confirm the effects of dynamic distortion due to the inertial force mentioned above. Improvement of the deflector and associated confirmation work have become extremely complicated. Moreover, it is extremely difficult to grasp quantitative numerical values of the degree of improvement, and for these reasons, measuring the dynamic light beam profile in a light beam scanning device has become an important technical issue in this field.

[Object of the Invention] The present invention has been made to solve the above-mentioned technical problem, and provides a light shielding device having at least two openings, for example, a rectangular slit, on the scanning line of the deflected light beam. After arranging a plate and arranging a photoelectric converter on the opposite side of the light beam scanning surface of the light shielding plate to photoelectrically convert the optical energy of the light beam transmitted through the two slits,
The output signal after the photoelectric conversion is introduced into a waveform measuring device such as an oscilloscope, and the beam diameter of the dynamic light beam is accurately determined from the waveform shape corresponding to the light intensity distribution observed by the waveform measuring device and the slit interval. To reproduce a high-quality image by adjusting the scanning optical system such as a light deflector so that the dynamic beam profile on the scanning line of the light beam that scans the object to be scanned has an optimal shape based on the measurement results. An object of the present invention is to provide a light beam profile measuring device that enables the following.

[Means for achieving the object] In order to achieve the above object, the present invention provides a light shielding plate having two or more openings on the scanning line of the light beam, and a surface of the light shielding plate scanned by the light beam. It is characterized by comprising a photoelectric conversion means disposed on the opposite surface of the device so as to face the two or more openings.

Furthermore, the present invention provides a structure in which the distance between at least two adjacent apertures among the two or more apertures formed in the light shielding plate is at least twice the beam diameter of the light beam. It is characterized by

Furthermore, the present invention is characterized in that the aperture lengths of two adjacent apertures in the scanning line direction are each less than the beam diameter of the light beam.

[Embodiments] Next, preferred embodiments of the optical beam profile measuring device according to the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 2, reference numeral 50 indicates a light beam profile measurement system including a light beam profile measurement device according to the present invention. In FIG. 2, the same components as those of the prior art shown in FIG. 1 are denoted by the same reference numerals, and the structure thereof will be schematically explained.

Therefore, this light beam profile measurement system 50 includes a scanning optical system 52, a light shielding plate 56 having slits 54a and 54b formed in parallel at the center thereof, and a light shielding plate 56 that detects the Rede light L1 that has passed through the slits 54a and 54b. The beam profile measuring device 60 includes a photoelectric conversion section 58 that performs photoelectric conversion, and a beam profile measuring device 60 that includes a photoelectric conversion section 58 that performs photoelectric conversion. In this case, the scanning optical system 52 includes the recording laser diode 2 driven by the recording laser diode drive circuit 30, as described above.
, a collimator 4 that converts the laser beam L1 outputted from the recording laser diode 2 into a parallel beam, a galvanometer mirror 6 that reflects the laser beam L1 that has been converted into a parallel beam by the collimator 4, and this galvanometer mirror 6.
fθ to keep the scanning speed of the laser beam L1 reflected at constant
It is composed of a lens 8.

As shown in the partially exploded perspective view of FIG. 3, the light receiving surface 59 of the photoelectric conversion section 58 is attached to the back surface of the light shielding plate 56, and the other surface of the photoelectric conversion section 58 is attached to the holding member 62. be done. In this case, the holding member 62 is engaged with a vertical surface portion 66 of a slide plate 64 that slides in the direction of arrow C, and is held rotatably in the direction of arrow C. Therefore,
The light shielding plate 56 is held so as to be slidable in the vertical direction, and is also held so as to be rotatable in a clockwise or counterclockwise direction on a vertical plane. A key portion 68 is formed in the lower part of the slide plate 64, and this key portion 68 engages in a key groove 72 formed in the holding base 70.

On the other hand, a height adjustment screw 76 for the slide plate 64 is provided on the vertical side 75 of the holding table 70, so that the vertical position of the light shielding plate 56 can be adjusted and fixed. The base portion 78 of the holder 70 is inserted into the groove 82 of the stage 80 (see FIG. 2), and the holder 70 is slid in the same direction as the main scanning direction A. In this case, the light shielding plate 56 is placed on the same surface as the surface of the film F.

The output signal of the photoelectric conversion section 58 is sent to a current-voltage conversion circuit 90.
After being converted into a voltage signal, the signal is introduced into a vertical axis input terminal of a waveform measuring device, such as an oscilloscope 94, via an amplifier 92.

Note that the slit 54a on the light shielding plate 56.

The slit width WSL of 54b (see FIG. 4) is set to a value less than the beam diameter dl1 of the laser beam LI.

Moreover, the slit interval DSL between the slits 54a and 54b
is a value that is sufficiently proportional to fluctuations in the scanning speed of the scanning laser beam L1, for example, a value of several mm or less, and
It is necessary to set the beam diameters d at intervals that do not interfere with each other.

In this embodiment, since the beam diameter d of the laser beam L1 to be measured is approximately 30 μm, the slit width W S L is 3 μm, which is the value of l/10, and the slit interval I) st
is set to three times the beam diameter d, that is, 90 μm.

The light beam profile measurement system incorporating the light beam profile measurement device according to this embodiment is basically configured as described above, and its operation and effects will be explained next.

First, the laser beam output from the laser diode 2 is reflected by the reflecting surface 6a of the galvanometer mirror 6 which swings in the direction of the arrow via the collimator 4.
The slits 54a and 54b on the light-shielding plate 56 are irradiated with scanning laser light through the θ lens 8 so as to be substantially perpendicular to the slits 54a and 54b. The laser beam L1 that has passed through the slits 54a and 54b is photoelectrically converted by the photoelectric converter 58, and a current signal corresponding to the intensity of the laser beam L1 is introduced into the current-voltage conversion circuit 90. The current signal introduced into the current-voltage conversion circuit 90 is converted into a voltage signal and introduced into the oscilloscope 94 via the amplifier 92. Therefore, by appropriately setting the sweep time of the oscilloscope 94, two waveforms 100 and 102 having a Gaussian intensity distribution shape are displayed on the tube surface of the oscilloscope 94, as shown in FIG. In this state, by rotating the holding member 62 that is attached to the slide plate 64 in the direction indicated by the arrow, a waveform 100 corresponding to the beam profile displayed on the tube surface of the oscilloscope passes through the slits 54a and 54b. The holding member 62 is fixed so that the waveform width in the time axis T direction of .102 is minimized. By adjusting in this way, the slit 5 formed in the light shielding plate 56
4a154b is arranged in a direction exactly perpendicular to the laser beam L1.

Next, waveforms 100 and 102 on the oscilloscope tube surface
, the waveform interval LB and the amplitude value of the waveform are 1/e
'Measure the distance Ld corresponding to the beam diameter d at the point corresponding to (e#2.72).

In this case, the beam diameter dB of the laser beam is as follows (1)
Calculated by the formula.

do = (La/LB) ・DSL ・
(t) Here, the dimensions of the waveform interval La and the interval are the dimensions of "time/scale", so the value of La/L B is a non-dimension.

After all, the dimension of the beam diameter d is the slit interval D
The dimension of SL, in this case, will be equal to μm. In this way, by measuring the beam diameter d8 over the entire scanning area on the film F, as shown in FIG. 2, it is possible to easily check whether the beam diameter d is at a predetermined value. .

Note that by setting the slit width WSL of the slit formed in the light shielding plate 56 to a smaller value than the beam diameter d, as shown in FIG. 6 As shown in Figure 6, the laser beam L
Waveform 104 with an intensity distribution proportional to the beam shape of 1
will be displayed as . If the slit width WSL is larger than the beam diameter dB, as shown in Figure 6C, the waveform on the oscilloscope will be the same as the laser beam, as shown in Figure 6D. The waveform is different from the intensity distribution proportional to the shape, and in this case, the measurement error of the beam diameter becomes extremely large. This relationship is shown in the characteristic curve of FIG. That is, the allowed measurement error ε.

Although the necessary slit widths W and L are more determined, it is understood that they need to be set to at least less than the beam diameter do.

In this way, since the dynamic beam profile of the light beam can be easily measured, the effect of the reinforcing member attached to the galvanometer mirror 6 on dynamic strain and the effect of changing the material on the beam diameter can be extremely easily measured. is possible,
It has an extremely large effect on the design and confirmation of optical systems. Note that, of course, any photoelectric conversion element such as a photomultiplier, a photodiode, a bin photodiode, etc. may be employed as the photoelectric conversion section.

Furthermore, the light shielding plate, as shown in FIG. 8a,
There are apertures + 110 on both sides of the slits 54a and 54b.
a, 110b, and the aperture 110a.

Of course, it is also possible to accurately read the rising portions of the waveforms 100 and 102 related to the slits 54a and 54b by using the signal corresponding to the radar light L+ passing through the slit 110b as a trigger signal for the oscilloscope. (See Figure 8).

Furthermore, the slit M distance DSL and the slit width WSL
It is also possible to make the beam diameter measurement device variable by making it variable so as to correspond to the beam diameter of the light beam. Furthermore, the slit for passing the light beam need not have the shape of a slit, but may of course have the shape of a pinhole, as shown in FIG.

[Effects of the Invention] As described above, according to the present invention, there is provided a beam profile measuring device that includes a light shielding plate having one or more sets of openings corresponding to the main scanning direction and a photoelectric conversion means attached to the openings. It consists of

Therefore, as can be understood from equation (1), the beam diameter calculation method does not depend on the beam scanning speed, so it is suitable not only for optical systems with known scanning speeds, but also for optical systems with unknown scanning speeds. The dynamic beam profile of the light beam can be easily measured even for optical systems whose scanning speeds vary. Therefore, it is possible to accurately measure, for example, changes in the beam diameter during actual operation of the mirror-vibrating optical deflector, that is, during vibration, and this enables optical beam scanning using the mirror-vibrating optical deflector. It becomes possible to shorten the design period of the device.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
Of course, various improvements and changes in design are possible without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a general light beam scanning device, FIG. 2 is a schematic configuration diagram of a light beam profile measurement system incorporating a light beam profile measurement device according to the present invention, and FIG. 3 is shown in FIG. In the light beam profile measurement system, FIG. 4 is an explanatory diagram of the main part configuration of the device, FIG. 4 is a front explanatory diagram of a light shielding plate having two slits shown in FIGS. 2 and 3, and FIG. 6 and 7 are diagrams explaining the relationship between the slit width formed in the light shielding plate and the beam diameter measurement error. It is an explanatory view of other embodiments. 2...Laser diode 4...Collimation 6.
... Galvanometer mirror 8 ... fθ lens 50 ... light beam profile measurement system 54a,
54b...Slit 56...Shading plate 58
... Photoelectric conversion unit 60 ... Beam profile measurement device 90 ... Current-voltage conversion circuit 94 ... Oscilloscope A ... Main scanning direction Ll ... Laser light patent applicant
Fuji Photo Film Co., Ltd. (d) FIG, 7 γ □ s L Procedural amendment (spontaneous) 1. Indication of the case 1988 Patent Application No. 143371 2
, Title of the invention Light beam profile measuring device 3, Person making the correction Relationship with the matter Patent applicant 4, Agent

Claims (3)

[Claims] (1) A light-shielding plate having two or more openings on the scanning line of the light beam, and a surface of the light-shielding plate opposite to the surface scanned by the light beam so as to face the two or more openings. 1. A light beam profile measuring device comprising: a photoelectric conversion means provided therein. (2) In the device according to claim 1, among the two or more openings formed in the light shielding plate, the interval between at least two adjacent openings is at least twice the beam diameter of the light beam. A light beam profile measuring device characterized in that it is configured so that: (3) In the apparatus according to claim 2, the light beam profile measurement is characterized in that the aperture lengths of the two adjacent apertures in the scanning line direction are each less than the beam diameter of the light beam. Device.