JPH0729238A - Reproducing method for optical recording - Google Patents

Abstract

PURPOSE:To enable stable recording and reproducing by detecting a fluctuation in use environment temp. and laser power and controlling the laser power, pulse width, etc., by using the result thereof. CONSTITUTION:Films are successively formed and laminated by a sputtering method continuously without breaking vacuum to produce recording media. The surface of the produced magneto-optical recording medium is coated with a UV curing resin 5 and two sheets of disk substrates 1 are stuck to each other. Magnetic characteristics change by a temp. rise and the reproducing power is decreased by as much as the increased component of amplitude, i.e., by 0.35mW in this case, if test reproduction is executed and the reproducing power is controlled to 0.85mW in such a manner that the output of the signal amplitude attains the same output of standard conditions. C/N attains 45dB when the same patterns as before are recorded and are then reproduced. The laser power for reproduction is controlled to a preferable value by previously executing the test reproduction, by which the domains of the same regions as the standard conditions are magnetically transferred and the dependency on the environmental temp. does not arise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing method for recording, reproducing, or erasing using a laser beam, and is particularly suitable for magneto-optical recording having ultrahigh density and high reliability. Regarding playback method.

[0002]

2. Description of the Related Art With the progress of the advanced information society in recent years, there is an increasing need for a high-density and large-capacity file memory. Optical recording is attracting attention as a memory that meets this demand. Recently, magneto-optical recording has been put to practical use as a rewritable optical disk in addition to the conventional compact disk and write-once optical disk.

More recently, many research institutions are conducting research and development aiming at higher performance, and one of them is further improvement of recording density. As a technique for realizing this high-density recording, research is being conducted from both sides of the disk and the device, and one of them is the magnetic super-resolution method.

In the magnetic super-resolution method, two kinds of magnetic films which are magnetically coupled and have different magnetic characteristics are used as recording films. A reproducing layer is formed on the side where the recording / reproducing laser beam (reproducing light) is incident, and a recording layer on which user information is recorded is formed on the back side thereof. Then, at room temperature, the magnetization state of the recording layer on which the user information is recorded is not transferred to the reproducing layer on the side where the light is incident. On the other hand, when reproducing light is irradiated, the temperature of the irradiated magnetic film (reproducing layer) rises, and the magnetization state of the recording layer is transferred to the reproducing layer due to the temperature change of the magnetic characteristics. Thereby, the information recorded in the recording layer can be reproduced based on the magneto-optical effect of the reproducing layer. Here, since information is not magnetically transferred to the part of the reproducing layer which is not irradiated with the reproducing light, information is not reproduced. With this effect, crosstalk in the track direction and the radial direction of the disk can be greatly suppressed, so that the resolution can be greatly increased.

[0005] In addition, as a thing related to this technique,
For example, SPII, Volume 1499, Optical Data Storage, '91, pages 209 to 215 [SPI
E 1499 Optical Data Strage '91 209-215].

[0006]

However, in the above-mentioned prior art, when the recording conditions such as the operating environment temperature and the laser power change, the magnetic transfer does not completely function,
There have been problems that the temperature of the recording film becomes high and a sufficient magneto-optical effect cannot be obtained, and a certain resolution cannot be obtained.

For example, if the ambient temperature rises and the ambient temperature rises, the temperature of the recording film rises.
If the laser power is considered to be constant, the area of the portion where magnetic transfer occurs becomes large, and there arises a problem that crosstalk in the track direction, the disk radial direction, or both directions increases.

As a result, there is a case where a highly reliable magneto-optical disk cannot be obtained, for example, an intended constant reproduction signal output cannot be obtained, and crosstalk may cause an error or noise. . In addition, when the recording / reproducing laser power fluctuates, the problem was the same as when the above-mentioned operating environment temperature fluctuated. In order to realize ultra-high density optical recording, it was necessary to be able to perform stable recording and reproduction, and particularly to be able to perform stable reproduction in realizing optical recording using magnetic super-resolution technology.

Therefore, an object of the present invention is to improve the reproduction of an optical record which always enables stable reproduction by detecting the fluctuation of the recording conditions such as the operating environment temperature and the laser power prior to the recording and reproduction. To provide a method.
Another object of the present invention is to provide a recording medium for realizing an optical recording reproducing method using such magnetic super-resolution technology and a magneto-optical recording apparatus for realizing ultra-high density recording / reproducing. It is in.

[0010]

In order to achieve the above object, at least two magnetic layers, that is, a reproducing layer provided on the light incident side and a recording layer provided on the back side thereof for recording information. When reading the information by transferring the recording magnetic domain (information) recorded in the recording layer to the reproducing layer on the basis of the change in the magnetic characteristics by irradiating the reproducing layer with the reproducing light, the magneto-optical recording medium having , A reference signal is recorded in a predetermined area of the recording layer under standard temperature conditions, this reference signal is reproduced at a fixed time interval during reproduction, and the reproduction reference signal amplitude at that time is measured to obtain The laser power that is the reproduction light is controlled so as to compensate (reduce) the difference between the signal amplitude obtained and the reference signal amplitude input under the standard temperature condition, and the magnetic characteristics of the magnetic characteristics due to the external temperature during reproduction are controlled. Exclude changes , In which stable reproduction output with a constant and reduced to be obtained.

That is, in the reproducing method of the optical recording by the magnetic super-resolution method, the change amount of the magnetic characteristics affected by the external temperature condition at the time of reproducing is reproduced from the reference signal which is inputted in the recording layer in advance, and the output thereof. The signal amplitude is measured and compared with the original reference signal amplitude, and based on the signal output difference (“deviation” from the input reference signal), the level is the same as or close to the original reference signal amplitude. The laser power as the reproduction light is controlled so as to reproduce the signal of (1) and the temperature is compensated at the time of reproduction, whereby reproduction can be always performed under preferable conditions.

More specifically, by regenerating a domain whose signal amplitude is known and calibrating the power so as to obtain a certain signal amplitude, the temperature change of the magnetic film such as the temperature change of the operating environment can be prevented. Can be corrected. The magneto-optical recording medium having a two-layer magnetic film used here is a magnetic super-resolution technique using magnetic transfer as described above.
A film in which the magnetic films of the layers are magnetically coupled to each other is used.
In this case, what is important in performing the above control is how stably the recorded information is reproduced, and it is understood that the present invention is important for that purpose.

That is, magneto-optical recording is very sensitive to changes in the temperature of the magnetic film such as environmental temperature, and in order to realize high density recording, it is necessary to finally grasp the changes in the temperature of the magnetic film. is important. It should be noted that this will cause noise and errors especially when recording the mark length and when recording the pit position when the reproduction signal output fluctuates due to temperature changes.

At the time of reproduction, it is preferable to control the laser power for reproduction so as to transfer to a range where optical interference does not occur due to the adjacent recording domains. For example, when the reproduction laser power is increased, the recorded information is transferred in a wide range, so that the domain recorded next is also reproduced by the transfer, so that crosstalk occurs. In particular, in order to realize ultra-high density recording, recording is performed with a bit interval narrowed, so reduction of crosstalk is an issue. Therefore, it is important to control the area of the magnetically transferred portion.

By the way, it is effective to use a multi-pulse composed of an assembly of minute pulses as the laser light for reproducing the information recorded on the magneto-optical recording medium. This is to arbitrarily control the area to be magnetically transferred.
That is, by using the multi-pulse, the effective spot diameter can be controlled mainly by controlling the pulse width, and as a result, the temperature distribution on the magnetic film can be controlled. In particular, since the area where magnetic transfer can be performed, the length in the circumferential direction and the length in the radial direction can be obtained, only the domain in the limited area can be reproduced.

Here, for example, when a domain larger than the standard is formed in the recording layer at the time of recording, an error or noise is generated by the normal method due to the track direction or crosstalk between tracks. However, when the reproducing system of the present invention is used, the area transferred to the reproducing layer can be made constant regardless of the domain size recorded in the recording layer even in such a domain, so that crosstalk or the like is prevented. Does not occur.

By the way, the standard information (reference signal) is previously recorded on the magneto-optical recording medium at least on the innermost track and outermost track of the disc, and on the intermediate track between them. To advantage, it is preferable to use the results of these three points to determine the reproduction conditions of the tracks in between. This is because in an optical recording device that is driven at a constant number of rotations, the recording conditions differ depending on the disc position and do not necessarily change linearly depending on the disc position. Since this depends on the laminated structure of the disc and the material used, the disc characteristics are measured at typical positions, and the recording conditions at other positions are determined by extrapolation from the points sandwiching the positions. However, the most thermally severe condition is the innermost circumference of the disc. Considering this point, at least the track near the innermost circumference should be used as the standard position for recording the monitor information on the magneto-optical recording medium. It is necessary to provide a signal. Then, before recording the user information in the information area of the magneto-optical recording medium, the previously recorded reference signal is reproduced, and the recording condition is determined based on the result.

The present invention is most effective when the mark length recording method for recording information on the edge portion of the recording mark is used. When using the mark length recording method,
When the length of the short pattern of the reference signal is 1, it is practical that the length of the long pattern is about 4 to 5 times the length. Besides this,
To record user information in the information area on the magneto-optical recording medium, a circular domain is formed, and the center position of the formed recording domain is detected to demodulate the signal.
It goes without saying that it can also be applied to the "pit position recording method".

As a preferable thickness of the magnetic film of the magneto-optical recording medium, it is desirable from the viewpoint of the signal output-to-noise ratio that the thickness of the magnetic film is such that it penetrates the magnetic film consisting of at least two layers at the wavelength of the reproducing light. This is because it is possible to use both the Faraday effect (detects transmitted light) and the Faraday effect (detects transmitted light) in addition to the Kerr effect (detects reflected light).

In this case, a light reflecting layer may be provided on the side opposite to the light incident side, or a recording layer on the side opposite to the light incident side may be used as a reflective film. In that case, the thickness of the layer on the light incident side (reproduction layer) may be set so that light can pass therethrough. in this way,
It goes without saying that it is effective to increase the magneto-optical effect. As information (reference signal) to be recorded in advance on the magneto-optical recording medium, it is preferable to record a pattern having the highest recording density in the modulation method used. This is because in the case of this close-packed pattern, reproducing the information is the most severe condition.

As a timing for inputting the reference signal to the magneto-optical recording medium, it is practical that the manufacturer side inputs it when the magneto-optical recording medium is completed.
It may be input in advance at the time of recording / reproducing information on the user side.
Alternatively, a method may be used in which a reference pattern is recorded when user data is recorded and the pattern is first reproduced and then compared with the reference signal when reproducing.

As a magneto-optical recording apparatus for realizing the reproducing method of this optical recording, as a temperature compensating means, a memory section for fetching and storing the same signal as a reference signal inputted in advance to the magneto-optical recording medium, and this storage. It is necessary to have means for comparing the amplitudes of the reference signals actually measured at the time of reproduction with reference to the thus-generated signal amplitude and controlling the irradiation output of the laser beam based on the deviation amount. For example, if the ambient temperature during playback is higher than the temperature at the time of inputting the reference signal, the amplitude will increase when playback is performed without control,
On the contrary, it becomes smaller under the low temperature condition. Therefore, in the former case, the beam intensity is lowered so that the reproduction output becomes a constant value, and in the latter case, the laser beam is controlled so as to raise the beam intensity and irradiate the laser beam. In this way, it is indispensable to provide a means for reproducing the reference signal, monitoring it, and controlling the laser light under appropriate irradiation conditions.

[0023]

According to the present invention, a monitor signal serving as a reference is recorded in advance at a predetermined position of a magneto-optical recording medium (abbreviated as disk), and this reference signal is recorded before recording, reproducing or erasing user information. By reproducing and controlling the laser power so that the obtained signal amplitude becomes a constant value, the effects of environmental temperature fluctuations and laser power fluctuations can be canceled, so stable recording / reproducing is possible. High density recording can be realized.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. Example 1 (1) Fabrication of Magneto-Optical Recording Medium FIG. 1 is a schematic view showing the cross-sectional structure of a disc prototyped in this example. Although the magneto-optical recording medium is actually provided on both sides of the disk, this figure shows the cross-sectional structure of one side thereof for the sake of simplifying the explanation.

First, a silicon nitride film 2 having a film thickness of 75 nm was formed on a glass or plastic substrate 1 having a diameter of 5.25 "having an uneven guide groove by a sputtering method. Then, a GdFeCo film having a film thickness of 20 nm was formed as a reproducing layer 3-1 by a sputtering method, and a GdTbFeCo film having a film thickness of 12 nm was formed as an exchange coupling control layer 3-2. Finally, a TbFeCo film having a film thickness of 50 nm was formed as the recording layer 3-3 by a sputtering method.

Here, the characteristics of the magnetic film 3 for writing information are as follows: the reproducing layer 3-1 is Curie temperature: Tc> 300 ° C., coercive force: Hc = 0.1 kOe (rare earth element rich, Gd in this example). is there. The exchange coupling control layer 3-2 has a Curie temperature: Tc = 120 ° C.,
Coercive force: Hc <0.1kOe (Rare earth element rich, GdT in this example)
b). The recording layer 3-3 has a Curie temperature: Tc = 220.
℃, coercive force: Hc> 10kOe (Rare earth element rich, G in this example
d).

Next, the silicon nitride film 4 was again formed to a film thickness of 150 nm by the sputtering method. For the production of the recording medium, the films were successively formed by the sputtering method and laminated without breaking the vacuum. The surface of the thus-produced magneto-optical recording medium was coated with the ultraviolet effect resin 5. Then, the two disk substrates 1 were aligned so that the surfaces having the recording medium face each other, and by irradiating with ultraviolet rays, the two were adhered with the ultraviolet effect resin 5 and bonded together.

(2) Input of reference signal Near the innermost circumference (radius r = 30 mm) and middle circumference (r = 4) of this disk
A pattern in which the shortest pattern and the longest pattern were repeated was recorded as reference information on the outermost circumference (near 5 mm) and the outermost circumference (near r = 60 mm). The schematic diagram is shown in FIG. here,
The (1,7) RLL method, which is a mark length recording method, was used as the modulation method for inputting the reference signal. The length of the shortest pattern of the domain in which the reference signal was recorded on the recording layer was 0.75 μm, the length of the longest pattern was 3.2 μm, and the ratio of the long / short patterns was slightly more than 4 times. It has been confirmed that this ratio is practically preferably 4 to 5 times. Here, an example of the mark length recording method is shown as the recording method of the reference signal, but it goes without saying that the above-mentioned pit position recording method is preferable.

The rotation speed of the disk is 3000 rpm, the wavelength of the laser used is 680 nm, the reproduction power is 1.2 mW, and the zone CA is used.
Recording was performed using the V method. The reproduction signal amplitude at that time was 380 mV for the shortest pattern and 950 mV for the longest pattern at the innermost position. The domain size is 0.45 μm in width, 0.45 μm in the shortest pattern, and 2.3 μm in the longest pattern. In addition, the domain interval was set to be the same as the domain length. This is a value at 25 ° C., and was recorded as a memory on a disk and a recording / reproducing device as standard conditions.

(3) Optical Recording Reproduction Test Results This disc and recording / reproducing apparatus were left in an environment of 50 ° C. Drive the disc, read the standard condition (reference signal) recorded in the previous memory, and based on that information, reproduce the area in which the reference information of the disc is recorded and measure the signal amplitude at that time. did.

As a result, first, the standard condition (reproduction power 1.
The signal amplitude of the reference signal when reproduced at 2 mW) was 1030 mV for the longest pattern (950 mV under standard conditions) and 403 mV for the shortest pattern (380 mV under standard conditions). This is because the temperature of the magnetic film 3 changes from 25 ° C when the reference signal is input to when reproducing.
It is considered that this is because the area where magnetic transfer can be performed is widened due to the high temperature of 50 ° C.

Therefore, for the purpose of comparison, the repetition of the shortest pattern in the (1,7) RLL modulation system is recorded without performing the test reproduction, and when it is reproduced, the carrier-to-noise ratio (C
/ N) was 39 dB. On the other hand, test reproduction was performed and the reproduction power was controlled to 0.85 mW so that the signal amplitude output would be the same as the standard condition. In other words, the read power corresponding to the change in the magnetic characteristics and the increase in the amplitude due to the temperature rise is
Reduced by 0.35mW (= 1.2mW-0.85mW). When the same pattern as the above was recorded and reproduced, the carrier-to-noise ratio (C / N) was 45 dB. As described above, by performing test reproduction in advance and controlling the reproduction laser power to a preferable value, the domain in the same region as the standard condition can be magnetically transferred, so that stable reproduction can be performed without depending on the environmental temperature.

<Embodiment 2> Next, another embodiment will be described. A multi-pulse was used as the reproduction light beam used in this example. By using this pulse,
When magnetically transferring information on the recording layer to the reproducing layer during reproduction,
The area to be transferred can be arbitrarily selected. In particular, since it is possible to transfer minute areas, crosstalk can be greatly reduced,
The resolution can be greatly improved. Therefore, an attempt was made to reproduce by multipulse using the disc having the laminated structure shown in FIG.

The same information as that in the first embodiment was previously recorded on the disc. That is, the innermost circumference (radius r = 30 mm), the middle circumference (r = 45 mm), and the outermost circumference (r = 60 mm) of the disc are each a repeating pattern of the shortest pattern and the longest pattern. Recorded as information. The schematic diagram is as shown in FIG. Here, the (1,7) RLL method is used as the modulation method. This modulation method is advantageous in terms of S / N (signal-to-noise ratio) for high density recording. The disk rotation speed was 3000 rpm, the laser light wavelength used was 680 nm, the reproduction laser power was 1.2 mW (continuous light), and recording was performed using the zone CAV method. The signal amplitude at that time is 315m at the innermost position and the shortest pattern.
V and the longest pattern was 890 mV. Also,
The domain size has a width of 0.45 μm and a shortest pattern
0.45μm, the longest pattern is 2.3μm. In addition, the domain interval was set to be the same as the domain length.

This prerecorded signal was reproduced using multi-pulses. The pulse used here has a laser power of 1.5 mW, a pulse width of 60 ns, and a pulse-to-pulse interval of 20 ns. Here, the pulse shape used is
The selection may be made according to the laminated structure of the recording medium used, the constituent material, the width of the magnetic domain to be transferred, and the like. The reproduction using the multi-pulse becomes more advantageous as the laser light having a shorter wavelength is used. This is because the shorter the wavelength of light, the higher the power density, which is effective in preventing the destruction of recorded data during reproduction. Then, the portion in which the reference information is recorded is subjected to test reproduction, and the result is used to control the pulse width, the interval between pulses, or the reproduction laser power so that the reproduction signal output becomes equal to the reference value. Good. That is, so that the average power is always constant, for example, the pulse width and the pulse interval are constant and the power is changed, or the power is constant and the pulse width and the pulse interval are changed. In the example, the former method was adopted.

The operating environment temperature was 25 ° C., and the signal amplitude was recorded in a certain area of the recording / reproducing device and the disk under this temperature as a standard condition. The device and the disc were left in an environment of 0 ° C. for a reproduction test. Under this condition, the standard data previously recorded on the disc was reproduced. As a result, the shortest pattern is 295mV at the innermost position.
(315 mV under standard conditions), and the longest pattern is 8
It was 55 mV (890 mV under standard conditions). It is considered that this is because the temperature of the magnetic film was lowered and the region to be magnetically transferred was narrowed.

Then, for comparison, the reproduction light is set under the standard condition (in this case, a pulse laser of 1.5 mW),
Record and replay that information to carrier-to-noise ratio (C / N)
Was measured, it was 43 dB. In addition, C / N when continuous light is used for reproducing light is 41 dB as in the first embodiment,
The resistance to temperature change was improved with the multi-pulse method.
Then, using the reproduction result of the above standard conditions, the pulse width and the pulse interval are fixed so that the signal amplitudes are equal, and the laser power is controlled (output is increased from 1.5 mW to 2 mW).
The shortest pattern was recorded and the C / N was measured. As a result, the same C / N (= 45 dB) as recorded under standard conditions was obtained.

[0038]

As described above in detail, according to the present invention, the intended purpose can be achieved. That is, it is possible to cancel the influence of the environmental temperature fluctuation and the laser power fluctuation by detecting the fluctuation of the operating environment temperature and the laser power and controlling the laser power or the pulse width using the result, so that stable recording can be performed. Playback is possible. Further, the minute recording magnetic domain can be reproduced stably and with high resolution. Furthermore, ultra high density optical recording can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a cross-sectional structure of a disc.

FIG. 2 is a schematic diagram showing domain shapes of a shortest pattern and a longest pattern, which are reference signals recorded on a disc, and corresponding reproduction signal waveforms.

[Explanation of symbols]

1 ... Disk substrate, 2 ... Silicon nitride film, 3 ...
Magnetic film, 3-1 ... GdFeCo layer, 3-2 ... GdTbFeCo
3-3 ... TbFeCo layer, 4 ... Silicon nitride film 5 ... UV curable resin layer.

Claims (13)

[Claims] 1. A magneto-optical recording medium having at least two magnetic layers, that is, a reproducing layer provided on the light incident side and a recording layer provided on the back side of the recording layer, on which information is recorded. In a reproducing method of optical recording using a magnetic super-resolution method, information is read by transferring a recording magnetic domain recorded as information on a recording layer to a reproducing layer based on a change in magnetic characteristics,
A reference signal was recorded in a predetermined area of the recording layer under a standard temperature condition, the same signal information was stored in a recording / reproducing device, and the reference signal was preliminarily monitored and reproduced at the time of reproduction. A reproducing method of optical recording, which comprises comparing a reproduction signal amplitude with a reference signal amplitude recorded under the standard temperature condition and controlling an irradiation power of reproduction light so as to reduce the difference. 2. A domain recorded with a reference signal to be stored in a recording / reproducing apparatus while being input to a magneto-optical recording medium under the standard temperature condition has a shortest pattern length of 1, and a longest pattern is a shortest pattern. The method for reproducing optical recording according to claim 1, wherein the length is 4 to 5 times. 3. A reproducing method for optical recording according to claim 1, wherein said at least two magnetic layers are magnetically coupled to each other. 4. The reproducing light is composed of laser light, and the irradiation power of the reproducing light is set so as to transfer the information of the recording layer to the reproducing layer within a range where optical interference due to adjacent recording domains does not occur. The method for reproducing optical recording according to claim 1 or 2, which is controlled. 5. The multi-pulse laser light comprising the aggregate of minute pulses as the reproduction light.
A method for reproducing the optical recording described. 6. A reproducing method for optical recording according to claim 1, wherein, when the reference signal is recorded on a magneto-optical recording medium, it is recorded on a track at least near the innermost circumference of the disk. 7. When recording the reference signal on a magneto-optical recording medium, there are three points of an innermost track and an outermost track of the disk and an intermediate track between them, and based on the reproduction results of these three points. 2. The optical recording reproducing method according to claim 1, wherein the reproducing condition of a track between these reference signals is determined. 8. A recording signal is reproduced based on a reference signal recorded in advance before the user information is recorded in the information area of the magneto-optical recording medium, and the recording condition is determined based on the result. Item 8. An optical recording reproducing method according to any one of Items 1 to 7. 9. When the user information is recorded in the information area of the magneto-optical recording medium, a circular domain is formed and the center position of the formed recording domain is detected to demodulate the signal. Item 9. The reproducing method for optical recording according to any one of Items 1 to 8. 10. A reproducing method for optical recording according to claim 1, wherein at least two layers of magnetic films constituting the magneto-optical recording medium have a film thickness capable of transmitting a wavelength of recording / reproducing light. . 11. A reproducing method for optical recording according to claim 1, wherein a pattern having the highest recording density in the modulation method used is recorded as a reference signal to be recorded in advance on the magneto-optical recording medium. 12. A reproducing layer provided on the light incident side, and a recording layer provided on the back side of the recording layer on which information is recorded have at least two magnetic layers, and the reproducing layer is irradiated with light. Is a magneto-optical recording medium using a magnetic super-resolution method in which information is read by transferring a recording magnetic domain recorded as information in a recording layer to a reproducing layer, and recording is performed on at least a track in the vicinity of the innermost circumference of the disc. A magneto-optical recording medium having a predetermined reference signal recorded under standard temperature conditions as a monitor during reproduction. 13. A memory unit for fetching and storing at least a same signal as a reference signal inputted in advance to a magneto-optical recording medium under a standard temperature condition as a monitor signal, and a reference measured during reproduction with reference to the stored signal amplitude. A magneto-optical recording apparatus comprising a temperature compensating means at the time of recording / reproducing, which comprises a means for comparing the amplitude of a signal and controlling the irradiation output of a laser beam based on the amount of deviation, and including this means.