JP2023140463A - Light-emitting module and method for driving light-emitting module - Google Patents

Abstract

To obtain a light-emitting module that can change the oscillation wavelength and optical output of a laser beam with a relatively simple configuration.SOLUTION: A light-emitting module 100 comprises a semiconductor laser 11, and a collimator lens 12 collimating a light beam L emitted in a state of divergent light from the semiconductor laser 11, and the light-emitting module is provided with temperature adjustment means 10, 30 that can set the temperature of the semiconductor laser 11 to a temperature higher than room temperature, a semiconductor laser driving circuit 31 that can change the driving current of the semiconductor laser 11 to change the optical output of the semiconductor laser 11; and an attenuator 5 that can attenuate the light beam L emitted from the semiconductor laser 11.SELECTED DRAWING: Figure 1

Description

The present invention relates to a light emitting module that emits a light beam, and particularly relates to a light emitting module that uses a semiconductor laser as a light source. Furthermore, the invention relates to a method of driving such a light emitting module.

Conventionally, analytical devices and instruments that measure and analyze the structure, properties, number, etc. of a specimen by irradiating a light beam onto a microscopic specimen such as cells or bacteria, and detecting the scattered light and fluorescence generated by the light beam with a photodetector. Various types of vessels are known. In this type of analysis device, a module is often used in which optical elements such as a light source and a lens for converging a light beam emitted from the light source are assembled into a module. Patent Document 1 shows an example of a light emitting module configured in this way.

When miniaturization is desired in the above-mentioned light emitting module, a semiconductor laser (laser diode) is often used as a light source. Further, in many cases, the light beam emitted from this type of light emitting module is set to a desired wavelength or optical wavelength. A semiconductor laser device disclosed in Patent Document 2 has been known as a semiconductor laser device that satisfies such requirements.

The semiconductor laser device disclosed in Patent Document 2 includes means for detecting the optical output and oscillation wavelength of the semiconductor laser, and controlling the optical output and oscillation wavelength of the semiconductor laser based on the outputs of the optical output and oscillation wavelength detection means. The invention is characterized in that it has means for.

JP2020-42061A Japanese Unexamined Patent Publication No. 7-15078

The semiconductor laser device shown in Patent Document 2 has a simple structure at first glance, but when put into practical use, it tends to cause dew condensation and has problems such as difficulty in controlling the oscillation wavelength over a sufficient area. is recognized. Note that these problems will be explained in detail in comparison with the embodiments of the present invention later when the embodiments of the present invention are described.
SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a light emitting module that can change the oscillation wavelength of a laser beam and optical output over a wide range, and a method for driving the same.

The light emitting module according to the present invention includes:
A light emitting module comprising a semiconductor laser and a collimating lens that converts a light beam emitted from the semiconductor laser in a diverging state into parallel light,
temperature control means capable of setting the semiconductor laser to a temperature higher than room temperature;
a semiconductor laser drive circuit that can change the optical output of the semiconductor laser by changing the drive current of the semiconductor laser;
an attenuator capable of attenuating the light beam emitted from the semiconductor laser;
It is characterized by the provision of.
Note that the above-mentioned "room temperature" refers to the temperature of the place where the semiconductor laser is installed, and means the temperature when there is no influence from temperature adjustment. Specifically, as an example, the temperature is often about 20°C to 25°C.

In the light emitting module of the present invention having the above configuration, it is preferable that an aperture plate is provided that blocks at least a portion of the return light that is emitted from the semiconductor laser and then reflected outside and travels toward the semiconductor laser. . Note that the above-mentioned "external" means outside the semiconductor laser, and does not necessarily mean outside the light emitting module.

Further, it is preferable that the temperature adjustment means is composed of a temperature detection element that detects the temperature in the vicinity of the semiconductor laser, and a heating element that increases the temperature of the semiconductor laser according to the temperature detected by the temperature detection element. .

Furthermore, the light emitting module of the present invention having the above configuration is provided with a light beam branching means for branching a part of the light beam emitted from the semiconductor laser, and a photodetector for detecting the optical output of the branched light beam. is,
a semiconductor laser drive circuit configured to change the drive current of the semiconductor laser based on the output of the photodetector;
This is desirable.

On the other hand, the method for driving a light emitting module according to the present invention is as follows:
A method for driving a light emitting module comprising a semiconductor laser and a collimating lens that converts a light beam emitted from the semiconductor laser in a diverging state into parallel light, the method comprising:
Set the semiconductor laser to a temperature higher than room temperature,
Changing the optical output of the semiconductor laser by changing the drive current of the semiconductor laser,
Attenuates the light beam emitted from the semiconductor laser to a predetermined optical output using an attenuator.
It is characterized by this.

The method for driving a light emitting module according to the present invention includes:
Set the semiconductor laser to a temperature higher than room temperature,
Changing the optical output of the semiconductor laser by changing the drive current of the semiconductor laser,
The light beam emitted from the semiconductor laser is attenuated to a predetermined optical output by an attenuator, so by setting the semiconductor laser to a temperature higher than room temperature, the oscillation wavelength is shifted to the longer wavelength side, and the semiconductor laser is By lowering the optical output, the oscillation wavelength can be shifted to the shorter wavelength side, and the oscillation wavelength can be changed over a wide range.

The method for driving a light emitting module according to the present invention is particularly suitable for a system where the oscillation wavelength is limited to a narrow range and stability of the oscillation wavelength is required. That is, in conventional semiconductor laser modules, the oscillation wavelength changes depending on temperature and output, and the oscillation wavelength becomes unstable due to return light. Precision measurements using Raman scattering instruments and the like are very sensitive to wavelengths, such as the Raman intensity changing depending on the excitation wavelength, and as a result, the sensitivity of the measurement system changes significantly. Therefore, such a system requires that the wavelength be a constant value and that the wavelength does not fluctuate. In conventional semiconductor laser modules, the signal strength fluctuated due to the factors mentioned above, deteriorating the S/N of the system, but according to the present invention, this problem has been resolved and the S/N has improved, resulting in high reliability. It becomes possible to build a system.

Then, it is possible to maintain the oscillation wavelength at a desired value by canceling out the shift to the long wavelength side and the shift to the short wavelength side, and also to set the optical output and the temperature of the semiconductor laser to the desired values. . Furthermore, since the light beam emitted from the semiconductor laser is attenuated to a predetermined light output by the attenuator, the light output can be varied over a wide range from this point as well.

On the other hand, the light emitting module according to the present invention is
temperature control means capable of setting the semiconductor laser at a temperature higher than room temperature;
a semiconductor laser drive circuit that can change the optical output of the semiconductor laser by changing the drive current of the semiconductor laser;
an attenuator capable of attenuating the light beam emitted from the semiconductor laser;
, the light emitting module driving method according to the present invention described above can be carried out.

A partially cutaway side view showing the overall shape of the light emitting module according to the first embodiment of the present invention A schematic perspective view (a) and a vertical cross-sectional view (b) showing the semiconductor laser used in the light emitting module of FIG. Schematic diagram explaining the action of the beam conversion unit used in the light emitting module of FIG. 1 Graph showing an example of the relationship between the set temperature and oscillation wavelength of a semiconductor laser Graph showing an example of the relationship between optical output and oscillation wavelength of a semiconductor laser Schematic diagram showing an example of the relationship between the set temperature, optical output, and oscillation wavelength of a semiconductor laser Cross-sectional view showing the mechanism that holds the semiconductor laser and collimating lens A schematic diagram illustrating how the holding mechanism in Figure 7 changes its state depending on temperature. Graph showing the relationship between laser beam propagation distance and beam diameter for multiple set temperatures A graph showing the relationship shown in FIG. 9 when different semiconductor lasers are used. A schematic diagram illustrating how the holding mechanism in Figure 7 changes its state depending on temperature. A schematic side view (a) and a schematic plan view (b) showing the main parts of a light emitting module according to a second embodiment of the present invention A schematic perspective view showing a laser diode chip used in the light emitting module of FIG. 4 Schematic diagram showing four examples of beam profiles in the fast axis direction of laser beams emitted by semiconductor lasers Schematic diagram illustrating the operation of the light emitting module according to the third embodiment of the present invention Schematic diagram explaining the operation of the light emitting module according to the fourth embodiment of the present invention

Embodiments of the present invention will be described below with reference to the drawings.
<First embodiment>
FIG. 1 is a partially cutaway side view of a light emitting module 100 according to a first embodiment of the present invention. As shown in the figure, this light emitting module 100 includes a base plate 1, a casing 3 mounted on the base plate 1 via a Peltier element 2 for temperature adjustment, a cover 4 covering the casing 3, and a cover 4 extending from the casing 3 to the right in the figure. It has an attenuator 5 that attenuates the emitted laser beam (light beam) L and reflects a part of it upward in the figure, and a terminator 6 that absorbs the laser beam L reflected by the attenuator 5. A terminator 6 is attached to the inner surface of the cover 4.

The laser beam L emitted from the cover 4 in the direction of arrow A may be reflected by some member and generate reflected light LR (indicated by a dashed-dotted line in the figure) that attempts to return to the semiconductor laser 11 side as a light source, which will be described later. . An aperture plate (diaphragm plate) 7 is attached to the outer surface of the cover 4 to block this reflected light LR. A similar aperture plate 8 is also attached to the outer surface of the housing 3. Both of these aperture plates 7 and 8 are made of light-blocking plates having openings that allow the laser beam L traveling rightward in the figure to pass through well. Compared to the laser beam L, the reflected light LR has a light intensity distribution that is wider and weaker extending from the beam center to the outside, so that it can be effectively blocked by the portions around the openings of the aperture plates 7 and 8.

Next, the configuration inside the housing 3 will be explained. Inside the housing 3, there is a semiconductor laser 11 as a light source, a collimating lens 12 that converts a laser beam (light beam) L emitted from the semiconductor laser 11 in a diverging state into a parallel beam, and a laser beam that has been converted into a parallel beam. A first prism 13 and a second prism 14 are arranged in sequence on the optical path of the beam L, and a rotation stage 15 on which these prisms 13 and 14 are fixed are arranged.

Although the semiconductor laser 11 is shown schematically in FIG. 1, its detailed external shape and vertical cross-sectional shape are shown in FIGS. 2(1) and 2(2), respectively. As shown in the figure, the semiconductor laser 11 is basically protected by a metal stem 11a whose bottom portion is roughly disk-shaped, a roughly cylindrical metal cap 11b disposed on the metal stem 11a, and this metal cap 11b. The laser diode chip 11c is fixed to the upper part of a metal stem 11a in a state where the laser diode chip 11c is fixed to the top of a metal stem 11a.

The laser beam L emitted from the laser diode chip 11c passes through a disc-shaped cover glass 11d fixed to the upper part of the metal cap 11b, and passes through the central circular hole of the annular low-melting glass 11e disposed thereon. The light passes through a central circular hole 11f formed at the upper bottom of the metal cap 11b and is emitted to the outside of the metal cap 11b. Further, the metal stem 11a includes a plurality of leads 11g for feeding power to the laser diode chip 11c, and a rear emitted light beam for controlling the optical output of the laser beam (front emitted light) L emitted from the laser diode chip 11c. A photodiode 11h is attached to detect the .

Returning to FIG. 1, the explanation will be continued. Both the first prism 13 and the second prism 14 are so-called triangular prisms formed in a roughly triangular plate shape using optical glass, and the laser beam L is passed through and refracted between two end faces sandwiching one apex angle. let These prisms 13 and 14 constituting the prism pair are sequentially arranged in the optical path of the collimated laser beam L with the directions of the apex angles being opposite to each other.

In other words, one prism, the first prism 13, has one apex angle located at the lower side in the figure with respect to the optical path of the laser beam L, whereas the other second prism 14 has the same apex angle as described above. One apex angle of is located at the upper side in the figure with respect to the optical path of the laser beam L. In other words, in the second prism 14, the bottom side facing the one apex angle is located on the lower side in the figure with respect to the optical path of the laser beam L. Note that, contrary to the above configuration, in the first prism 13, the one apex angle is located on the upper side in the figure with respect to the optical path of the laser beam L, and in the second prism 14, the one apex angle is located in the upper side of the figure with respect to the optical path of the laser beam L. The optical path may be located at the lower side in the figure with respect to the optical path.

The rotation stage 15 on which the prism pair is fixed is rotatable in the direction R in the figure around the rotation axis C. The rotation axis C is, for example, an axis that extends between the prisms 13 and 14 in a direction perpendicular to the display surface of the figure (or the paper surface if printed; the same applies hereinafter). The rotation stage 15 is mechanically connected to, for example, a rotation knob or a gear (not shown), and can be rotated forward or backward in the R direction by manually rotating the rotation knob. Note that in order to rotate the rotation stage 15, a known mechanism other than the above may be used. Further, in this embodiment, the shape of the rotation stage 15 is a rectangular plate shape with four rounded corners, but the shape is not particularly limited and may be, for example, a disk shape.

Specifically, the mechanism for rotatably holding the rotary stage 15 is to move from one surface of the rotary stage 15 (the surface opposite to the surface on which the prisms 13 and 14 are fixed) concentrically with the notation point of the rotation axis C in the figure. A mechanism in which a cylindrical holding shaft is protruded in the shape of a cylinder and held by a bearing fixed to the housing 3 side, or a mechanism in which a cylindrical holding shaft is provided concentrically with the notation point of the rotational axis C in the figure on the rotation stage 15 is used. Various known mechanisms can be applied, such as a mechanism in which a cylindrical holding shaft is formed through the through hole and the holding shaft is held on the housing 3 side.

The first prism 13 and the second prism 14 are fixed on a rotation stage 15 while maintaining a predetermined angular positional relationship with each other. Note that the first prism 13 and the second prism 14 may not be fixed to the rotation stage 15, but may be attached to the rotation stage 15 with their respective orientations adjustable. In such a case, after the first prism 13 and the second prism 14 are attached, they can be adjusted to have a predetermined angular positional relationship. Note that hereinafter, the mechanism consisting of the prisms 13 and 14 and the rotation stage 15 may be referred to as a "beam conversion unit."

Further, inside the housing 3, a photodetector 9 such as a photodiode for detecting the optical output of the semiconductor laser is attached. One light beam passing end surface of the first prism 13, that is, the passing end surface on the downstream side in the passing direction of the laser beam L is used as a reflecting surface that guides the laser beam L reflected by the end surface to the photodetector 9. . Furthermore, a thermistor 10 is attached to the casing 3 to detect the temperature inside the casing 3. A signal indicating the temperature detected by the thermistor 10 is input to a temperature adjustment circuit 30 arranged outside the cover 4. Further, a signal indicating the optical output of the semiconductor laser detected by the photodetector 9 is input to a semiconductor laser drive circuit 31 which is also arranged outside the cover 4. In addition to the thermistor 10, a thermocouple or the like can also be used as the temperature detection element. Further, a temperature regulating element other than the Peltier element 2 may be used, but this element only needs to be capable of heating, so a heater or the like can also be used.

Next, the effect of the light emitting module 100 of this embodiment will be explained. When the rotation stage 15 is rotated in either of the R directions, the angle of incidence of the laser beam L on the first prism 13 gradually changes as the rotation stage 15 rotates. Whether this angle of incidence gradually increases or decreases depends on the rotation direction of the rotation stage 15. When the angle of incidence of the laser beam L on the first prism 13 changes in this way, the angle of emission of the laser beam L from the first prism 13 changes, so the angle of incidence of the laser beam L on the second prism 14 changes, Eventually, the emission angle of the laser beam L from the second prism 14 changes. The above situation is schematically shown in FIG. The laser beam L before the emission angle from the first prism 13 is changed is shown by a solid line in the figure, and the laser beam L after the emission angle is changed is shown by a broken line in the figure. Note that in FIG. 3, the rotation stage 15 is shown as having a generally disk shape.

The light emitting module 100 of this embodiment is used in an optical scanning recording device that uses the laser beam L emitted from the cover 4 in the direction of arrow A in FIG. It can be applied to processing equipment used as a light source, analysis equipment used as light for analysis, and the like. When applied to an optical scanning recording device or an optical scanning reading device, the light emitting module 100 is mounted on a scanning mechanism. The laser beam L emitted from the light emitting module 100 is often passed through a converging lens (not shown in FIGS. 1 and 3) to converge it into a small spot.

It is desired that the convergence position of the spot is set at a predetermined position with high precision, for example, in order to improve the precision of optical scanning and processing. If such control of the convergence position is desired in the vertical direction in FIGS. ), the convergence position can be set with high precision. Note that the light emission of this embodiment can be used not only when controlling the convergence position of the spot as described above, but also when changing the direction of the laser beam L emitted from the light emitting module 100 itself is the final requirement. The module 100 is of course compatible.

Regarding the spot to be converged, in addition to controlling the convergence position to a predetermined position, there is also a requirement to set and maintain the spot diameter at a predetermined value. This spot diameter is, in other words, the beam waist diameter of the laser beam L focused by the converging lens, and depends on the beam diameter of the laser beam L before entering the converging lens. Therefore, even if the direction of the laser beam L is changed as described above, if the beam diameter of the laser beam L changes accordingly, the beam waist diameter, that is, the spot diameter also changes. If this is the case, the adjustment to set and maintain the spot diameter at a predetermined value becomes complicated, so in order to prevent this, it is required that the beam diameter does not change even if the direction of the laser beam L is changed. It will be done.

The light emitting module 100 of this embodiment can also satisfy such requirements. In other words, as described above, the first prism 13 and the second prism 14 constituting the prism pair are located on the side where the apex angle is located in one prism and on the side where the apex angle is located in the other prism with respect to the optical path of the laser beam L passing through them. The bottom is located. Therefore, when the beam diameter of the laser beam L emitted from the first prism 13 gradually decreases (expands) as the rotation stage 15 rotates, the beam diameter of the laser beam L emitted from the second prism 14 gradually increases. (descend. In this way, the change in beam diameter caused by the rotation of the rotary stage 15 is substantially canceled out between the two prisms 13 and 14, so that the beam diameter of the laser beam L emitted from the second prism 14 becomes substantially constant. It is maintained. Note that the beam diameter of the laser beam L, which is kept substantially constant, can be set to a desired value by changing the relative angular positional relationship between the first prism 13 and the second prism 14.

Details such as the beam diameter of the laser beam L will be described in detail below, with specific examples also shown. In this embodiment, the oscillation wavelength of the laser beam L emitted from the semiconductor laser 11 shown in FIG. 1 is 505 nm. Although this laser beam L is a diverging light, it is made into parallel light by the collimating lens 12. The beam diameters of the collimated laser beam L in the direction parallel to and perpendicular to the display surface in FIG. 1 are 1.6 mm and 0.6 mm, respectively. In this embodiment, the directions parallel to and perpendicular to the display surface in FIG. 1 are the fast axis direction and the slow axis direction of the semiconductor laser 11, respectively. That is, the rotation axis C extends in a direction parallel to the slow axis of the semiconductor laser 11. Furthermore, the beam diameter described here and the beam waist diameter described later are defined as a 1/ ^e2 diameter.

The collimated laser beam L then enters the first prism 13, is refracted within the display plane of FIG. 1, and exits from the first prism 13. The two illustrated apex angles of the prisms 13 and 14 are each 45°, and their base material is quartz. The laser beam L emitted from the first prism 13 enters the second prism 14, is refracted, and exits from the second prism 14, but the beam diameter in the direction parallel to the display surface in FIG. It exits from the second prism 14 after being reduced in size compared to before it enters the second prism 13 . Specifically, the beam diameter in the above direction of the laser beam L emitted from the second prism 14 is 0.6 mm, so the beam diameter magnification is 0.38 (=0.6/1.6) times.

On the other hand, the beam diameter of the laser beam L in the direction perpendicular to the display surface in FIG. 1 is not reduced or expanded, and is maintained at the beam diameter of 0.6 mm before entering the first prism 13. That is, the laser beam L after passing through the second prism 14 is a perfect circular beam, and if this laser beam L is passed through the aforementioned converging lens and converged to a small spot, that spot becomes a perfect circular spot. As described above, if the rotation stage 15 is rotated while the laser beam L is passing through the prisms 13 and 14, the direction of the laser beam L emitted from the second prism 14 changes.

Note that the incident angle of the laser beam L to the first prism 13 is, for example, 12° in a state in which the azimuth adjustment of the laser beam L is completed. Furthermore, an antireflection coating (AR coating) with a transmittance of 99.5% or more is applied to the end surface of the first prism 13 on which the laser beam L is incident. On the other hand, the end surface of the first prism 13 from which the laser beam L is emitted is a non-coated surface. Therefore, a part of the laser beam L is reflected at this emission end face with a reflectance of 17%, and the reflected light is guided to the photodetector 9 as described above. The output of this photodetector 9 is used to monitor the amount of light from the semiconductor laser 11.

Normally, when such light amount monitoring is performed, the laser beam L is often split by a beam splitter and the split laser light is used as monitor light. On the other hand, in this embodiment, the laser beam L is branched by using one end surface of the first prism 13 as a non-coated surface, so that a light emitting module is realized at low cost and compact because there is no beam splitter. When splitting the light in this way, the laser beam incident end face of the first prism 13 may be used as the end face for branching the light beam, or furthermore, the incident end face or the output end face of the second prism 14 may be used. It's okay.

Next, the rotation of the rotation stage 15 will be explained in detail. In this embodiment, when the rotation stage 15 is rotated by ±1° in the R direction shown in FIG. 3, the direction of the laser beam L emitted from the second prism 14 can be changed by ±2°. Therefore, unless there are any other requirements, it is desirable to change the orientation of the laser beam L within this range of ±2° and adjust the orientation so that it is parallel to the base plate 1. In this way, the laser beam L can be propagated to the subsequent optical system with a constant beam height, which facilitates optical design. Alternatively, the direction of the rotation axis C can be set to be changed by 90 degrees from the display state in FIG. The light may be propagated parallel to the plate 1.

The laser beam L that is emitted from the second prism 14 as a perfect circular beam with a diameter of 0.6 mm can change its direction by about ±2° as described above, but this laser beam L passes through the aperture plate 8. The laser beam L passes through the aperture plate 8, but at this time the outer periphery of the beam is slightly kicked (the loss is about 5 to 10%). This aperture plate 8 is provided to prevent return light, which will be described later, from returning to the semiconductor laser 11.

The laser beam L that has passed through the aperture plate 8 is incident on the attenuator 5 with a transmittance of 50%, and 50% of the beam is reflected and absorbed by the terminator 6, which is a metal block with a hole of 2 mm in diameter. The laser beam L transmitted through the attenuator 5 enters an aperture plate 7 attached to the cover 4. This aperture plate 7 has an opening diameter of 1.0 mm, and the loss of the laser beam L there is less than 1%. Like the aperture plate 8, this aperture plate 7 is also provided to prevent the returned light from returning to the semiconductor laser 11.

Here, the oscillation wavelength of the semiconductor laser 11 will be explained with reference to FIG. Basically, the light emitting module 100 of this embodiment drives the semiconductor laser 11 with an optical output lower than its rated optical output, and the expected shift of the oscillation wavelength to the shorter wavelength side is caused by the temperature increase of the semiconductor laser 11. The oscillation wavelength is compensated for by the shift to the longer wavelength side, and as a result, the oscillation wavelength is maintained approximately constant. Note that the reason why the semiconductor laser 11 is driven with an optical output lower than its rated optical output is mainly to ensure the product life of the semiconductor laser 11. Alternatively, the oscillation wavelength may be largely shifted to the shorter wavelength side or the longer wavelength side without performing the above compensation.

As an example, the semiconductor laser 11 shown in FIG. 1 has a rated optical output of 80 mW at a temperature of 25° C. within the room temperature range, an oscillation wavelength of 505.0 nm at a center wavelength λc (wavelength width at half maximum Δλ, maximum wavelength of _FWHM λMAX, If the minimum wavelength is λMIN, the center wavelength λc=(λMAX+λMIN)/2 (the same applies hereinafter). Therefore, this semiconductor laser 11 is first driven at a set temperature of 45°C. The temperature adjustment circuit 30 in FIG. 1 changes the drive current value of the Peltier element 2 based on the temperature detection signal input from the thermistor 10 so that the set temperature is reached. Specifically, the temperature control circuit 30 in this example increases the drive current value until the set temperature reaches 45°C, and then uses automatic control to slightly increase or decrease the drive current value to maintain that temperature. The temperature, that is, the temperature of the semiconductor laser 11 is kept constant at 45°C.

Here, the temperature coefficient, that is, temperature dependence, of the oscillation wavelength of the semiconductor laser 11 is +0.03 nm/°C, so when the semiconductor laser 11 is driven at a temperature of 45°C, the oscillation wavelength is compared to when it is driven at room temperature, for example, 25°C. and shifts to the longer wavelength side by 0.6 nm{=(45-25)°C×0.03nm/°C} (see FIG. 4). In order to compensate for this shift, the semiconductor laser 11 is used with its optical output reduced to 50 mW. The purpose of lowering the wavelength is twofold, as described above, to ensure the lifetime of the semiconductor laser 11 and to adjust the oscillation wavelength.

The semiconductor laser drive circuit 31 shown in FIG. 1 receives a signal indicating the optical output of the semiconductor laser 11 detected by the photodetector 9, and controls the driving current value of the semiconductor laser 11 so that this optical output becomes a desired value. do. Note that the optical output of the semiconductor laser 11 changes depending on the temperature of the semiconductor laser 11. Therefore, in this example, when the temperature of the semiconductor laser 11 is 45° C., the drive current value is controlled so that the optical output of the semiconductor laser 11 becomes a desired value.

Since the optical output dependence of the oscillation wavelength is +0.02 nm/mW (see Figure 5), when the semiconductor laser 11 is driven with an optical output of 50 mW, the oscillation wavelength is 0.6 nm {= (80-50) mW×0.02 nm/mW} Shift to short and long wavelength side. Note that if the semiconductor laser 11 is continued to be driven in a state where the rated optical output of 80 mW is obtained, its lifetime will be shortened.

As explained above, according to the driving method of the light emitting module in this embodiment, the semiconductor laser 11 is driven with an optical output lower than its rated optical output, and the expected shift of the oscillation wavelength to the shorter wavelength side is caused by By compensating for the shift to the longer wavelength side due to the temperature rise of the laser 11, the oscillation wavelength can be maintained without shift, that is, at a substantially constant 505.0 nm.

Incidentally, in the semiconductor laser device disclosed in Patent Document 2, when the oscillation wavelength and optical output are adjusted by changing the temperature setting, changing the temperature setting may cause condensation, which poses a problem. Typical products are often able to operate even under severe operating conditions such as temperature and humidity of 45° C. and 80%. Therefore, there is little room for adjusting the temperature by lowering it. This is because if the set temperature falls below 41°C, condensation will begin and the optical system will no longer function. On the other hand, when adjusting the temperature to 45° C. or higher, it is virtually impossible to control the oscillation wavelength by temperature in general products, since the product life of semiconductor lasers is shortened at high temperatures. For example, in a semiconductor laser product with specifications of a temperature of 25° C., an oscillation wavelength of 505±2 nm, and an optical output of 80 mW, when used at an optical output of 20 mW, the optical output is lowered from 80 mW to 20 mW, so the oscillation wavelength is shortened by 1.2 nm.

Therefore, when a semiconductor laser with the lower limit wavelength of 503 nm is in stock, and the wavelength specification of the system using the semiconductor laser is 505 ± 2 nm, which is the same as the semiconductor laser, the oscillation wavelength will be 501.8 nm, which is the lower limit of the system wavelength specification. The wavelength becomes less than 503 nm (see FIG. 5). In other words, a semiconductor laser with an oscillation wavelength of 503 nm cannot be used. As a result, a problem arises in that the yield of semiconductor lasers deteriorates and, as a result, the price of light emitting modules using semiconductor lasers increases.

Next, the optical output considering the loss of the laser beam L will be explained with reference to FIG. 6 as well. The laser beam L with an optical output of 50 mW, whose wavelength was maintained at 505.0 nm as described above, is heated as described above by raising the set temperature from 25 °C to 45 °C, as shown by the arrow in the upper part of Fig. 6. As a result, the oscillation wavelength shifts to the longer wavelength side by 0.6 nm. At this time, the optical output is 80 mW, but if the semiconductor laser 11 is then driven from this state with an optical output of 50 mW as shown by the arrow in the lower part of the figure, the oscillation wavelength will be shifted to the shorter wavelength side by 0.6 nm. shift.

Next, when the laser beam L passes through an attenuator 5 (denoted as ATT in FIG. 6) having a transmittance of 50%, the optical output decreases to 25 mW. Furthermore, the total loss due to branching for the photodetector 9 at the first prism 13, loss due to the AR coating, and loss due to the aperture plates 7 and 8 is approximately 20%. As a result, the optical output is about 20 mW, which is about 80% of the above 25 mW. In this way, the desired relatively low output laser beam L of 20 mW can be obtained.

In other words, to summarize the changes in optical output shown by the arrows in the middle lower part of Figure 6, when a semiconductor laser with a set temperature of 25°C, an optical output of 80 mW, and an oscillation wavelength of 505.0 nm is set to a temperature of 45°C and an optical output of 50 mW, By inserting an attenuator with a transmittance of 50% and reducing the loss due to the optical system to 20%, it is possible to obtain a light emitting module with a desired optical output of 20 mW and an oscillation wavelength of 505.0 nm.

Next, a structure for holding the semiconductor laser 11 will be explained. The structure in which the laser diode chip 11c of the semiconductor laser 11 is mounted on the metal stem 11a is as described above with reference to FIG. 2(2). A typical structure in which such a semiconductor laser 11 is held in the housing 3 together with the collimating lens 12 in the light emitting module 100 shown in FIG. 1 is shown in a sectional view in FIG. In this figure, the semiconductor laser 11 is simply shown with only its laser diode chip 11c, metal stem 11a, and submount 11s (the same applies to FIGS. 8 and 11). In addition, in the figures from FIG. 7 onwards, the same numbers are given to elements equivalent to those in FIGS. ).

In the structure shown in FIG. 7, the metal stem 11a of the semiconductor laser is fixed to the reference surface of an LD holder 50, and this LD holder 50 is integrated with a ring 51. A lens holder 52 holding the collimating lens 12 is attached to this ring 51. Further, the laser diode chip 11c is welded to a submount 11s, and the submount 11s is welded to a metal stem 11a.

In the conventional structure shown in FIG. 7, the metal stem 11a is often made of gold-plated iron, the LD holder 50 is made of brass, and the ring 51 and lens holder 52 are made of SUS (stainless steel). The problems occurring in such a conventional example will be explained with reference to FIG. As shown in (1) of the same figure, for example, when the distance between the collimating lens 12 and the laser diode chip 11c is adjusted and fixed with the laser beam L spread out at a room temperature of 23°C, the temperature inside the housing 3 is reduced to 36°C. When the temperature is increased to 45°C, the amount of expansion of the ring 51 holding the collimating lens 12 and the lens holder 52 becomes larger than the amount of expansion due to thermal expansion of the metal stem 11a on which the laser diode chip 11c is mounted. The distance between the laser diode chip 11c and the collimating lens 12 increases (see (2) and (3) in the figure). In this way, the laser beam L, which was spread out at an initial temperature of 23°C, changes to become a parallel beam at a temperature of 36°C, and becomes a convergent beam at a temperature of 45°C.

Specific beam propagation data at this time is illustrated in FIG. The horizontal axis represents the propagation distance of the laser beam L from the collimating lens 12 (indicated in 100 mm increments with the tip as zero), and the vertical axis represents the beam diameter at each propagation distance. (1) shows the beam diameter in the slow axis direction of the semiconductor laser 11, and (2) shows the beam diameter in the fast axis direction. The beam diameter of the semiconductor laser 11 in the fast axis direction has a large temperature dependence and changes greatly due to the characteristics of the laser diode chip 11c. That is, the light emitted from the semiconductor laser 11 has a large divergence angle in the fast axis direction, and changes in the beam diameter with respect to changes in the propagation distance are more sensitive than in the slow axis direction. Therefore, when the set temperature of the semiconductor laser 11 is set to 45° C., there is a problem that the beam diameter changes greatly in one direction, making it impossible to obtain a good collimated beam.

Note that the beam propagation data shown in FIG. 9 is for the case where, as an example, a semiconductor laser 11 with an oscillation wavelength of 505 nm and an optical output of 80 mW is used. Also, α brass: coefficient of linear expansion of brass, αSUS: coefficient of linear expansion of SUS, α iron: coefficient of linear expansion of iron, L brass: thickness of the LD holder 50, L iron: metal from the reference plane shown in Figure 7. Assuming that the length of the stem 11a is LSUS: the length of the ring 51 and the lens holder 52, the change ΔL in the distance between the laser diode chip 11c and the collimating lens 12 when the temperature changes from 23°C to 45°C is as follows. Calculation using the formula yields 0.7 μm.
ΔL = (α brass x L brass + α SUS x LSUS) - α iron x L iron = 0.7 μm

On the other hand, in this embodiment, the ring 51 and lens holder 52 have the same shape as the conventional example, but the material is changed to Invar (registered trademark). As for its configuration, when the laser beam L is collimated by the collimating lens 12, the state of beam propagation becomes almost the same between temperatures of 23° C. and 45° C. That is, in (1) and (2) of FIG. 10, the two graphs almost overlap, for example, the measurement point at 23° C. and the measurement point at 45° C. match.

Actual beam propagation data in this case is shown in (1) and (2) of FIG. The display method in FIG. 10 is the same as the display method in FIG. 9 described above. It can be seen that the beam diameter in the fast axis direction, which had a large change in the conventional example, remains almost the same at temperatures of 23° C. and 45° C. in this embodiment, and is well collimated in both cases. At this time, the change in distance ΔL between the laser diode chip 11c and the collimating lens 12 is calculated to be 0.3 μm using the following formula. Note that α invar is the linear expansion coefficient of invar, and using 0.5 × 10 ^-6 /K ΔL = (α brass × L brass + α invar × L invar) - α iron × L iron = 0.3 μm

It can be inferred that the above results are due to the fact that the distance between the laser diode chip 11c and the collimating lens 12 did not change even if there was a temperature change, as shown in FIG. The actual beam propagation data is as shown in FIG. 10, and the data at 23° C. and 45° C. are in good agreement. In the calculation, there should be a distance change Δ of 0.3 μm as described above, but the difference with this calculation is that due to the heat generated by the laser diode chip 11c, the metal stem 11a directly below it extends in the beam propagation direction, causing the laser diode This is thought to be due to the relatively shortening of the distance between the chip 11c and the collimating lens 12.

On the other hand, the reflected light LR generated as described above (indicated by a chain line in FIG. 1) returns around the optical path of the laser beam L from the semiconductor laser 11 toward the analyzer or the like. This reflected light LR enters the collimating lens 12 in a direction opposite to that described above, is focused near the active layer of the semiconductor laser 11, is reabsorbed by the active layer, and affects oscillation. It is known that the oscillation wavelength of the semiconductor laser 11 changes due to this small amount of returned light. When performing precision measurements using a semiconductor laser as an excitation light source in Raman scattering spectroscopy, fluorescence analysis, etc., there is a problem in which the Raman scattering intensity changes or the fluorescence intensity changes depending on a slight change in the oscillation wavelength of the semiconductor laser. may invite

Aperture plates 7, 8 are arranged to prevent this problem. Of the returned light, a component that follows exactly the same optical path in the opposite direction as the laser beam L traveling toward the use position is probabilistically rare and the amount thereof is very small. Therefore, by arranging the two aperture plates 7 and 8 at two different locations, it is possible to substantially cut out the peripheral return light component at a different angle from the laser beam L traveling toward the use position. In order to effectively block the return light, one aperture plate is not sufficient, and it is necessary to arrange the aperture plate in at least two places, and it is also possible to arrange the aperture plate in three places. For example, one location may be provided immediately after the collimating lens 12. The greater the distance between the plurality of arrangement locations, the higher the effect of blocking the return light. Further, the opening diameter of the aperture plate 8 may be 0.5, 0.6, 0.7, 0.9, 1.0 mm, etc. other than 0.8 mm. The loss of the laser beam L increases as the aperture diameter becomes smaller with respect to the beam diameter=0.6 of the laser beam L traveling toward the use position, but the return light blocking effect becomes higher. The same applies to the aperture plate 7, and its opening diameter may be 0.8 mm, 1.2 mm, etc.

Note that in this embodiment, the beam diameter of the laser beam L is reduced in one direction by the beam conversion unit, but on the contrary, it may be expanded in one direction. Furthermore, the beam diameter may be reduced in one direction and enlarged in the other direction perpendicular to this one direction. Furthermore, in this embodiment, the beam diameter is reduced in one direction in order to make the laser beam L into a perfect circular beam, but in order to make the laser beam L into an elliptical beam, the beam diameter is reduced or expanded in one direction. You may.

<Second embodiment>
FIG. 12 shows a light emitting module 200 according to a second embodiment of the present invention, and FIGS. 12(a) and 12(b) show a schematic side and planar shape of a beam conversion unit thereof, respectively. The light emitting module 200 of this embodiment includes two beam conversion units that change the direction of the laser beam L, and each beam conversion unit changes the direction of the laser beam L in directions that are 90 degrees apart from each other. . This light emitting module 200 also uses one semiconductor laser 11 as a light source, and FIG. 13 shows a schematic perspective view of the semiconductor laser 11, more specifically, the laser diode chip 11c thereof. As an example, the laser diode chip 11c emits a laser beam L having a wavelength of 488 nm and has an output of 60 mW.

As shown in FIG. 13, the laser diode chip 11c emits a laser beam L in a diverging state from the active layer 11A toward the emission end face 11B. The laser beam L has a divergence angle θ// in the slow axis direction parallel to the active layer 11A, and diverges in the fast axis direction perpendicular to the active layer 11A, that is, the direction in which the layers overlap. A laser beam L is emitted at an angle θ⊥. Note that θ//<θ⊥, and the latter is usually about 2 to 3 times the former. The side and planar shapes shown in FIGS. 12(a) and 12(b) respectively correspond to the axes of the output end surface 11B, with the slow axis direction indicated by arrow S and the fast axis direction indicated by arrow F. The state in which the light emitting module 200 is viewed from a direction perpendicular to the figure is shown.

As shown in FIG. 12, the light emitting module 200 of this embodiment is applied to a flow cytometer. The flow cytometer has a fine conduit 20 made of a glass capillary or the like, and in this conduit 20, a plurality of particles 21 as a specimen are arranged in a line in the length direction of the conduit and flowed therethrough. The flow cytometer then irradiates these particles 21 with a laser beam L from the side of the flow, and detects the resulting scattered light (forward scattered light or side scattered light) or fluorescence with a photodetector. An electrical signal is obtained, and based on this electrical signal, particles 21 are measured and analyzed individually or as a group. The light emitting module 200 according to this embodiment is used to irradiate the particles 21 flowing in the conduit 20 with the laser beam L as described above.

As shown in FIG. 12, the light emitting module 200 of this embodiment includes a collimating lens 12 that converts the laser beam L emitted in a diverging state from the semiconductor laser 11 into parallel light, and a collimator lens 12 that sequentially converts the laser beam L that has been made into parallel light into parallel light. It has prisms 13, 14, 16, and 17 to pass through, and a converging lens 19 to converge the laser beam L emitted from the prism 17 in the conduit 20. Note that the collimating lens 12 uses an aspherical lens. Compared to a spherical lens, an aspherical lens can provide a beam that is closer to a Gaussian beam, so double counting can be more effectively prevented.

Prisms 13 and 14 are fixed on a rotation stage 15 that can be rotated in the direction of arrow R, forming a prism pair. Prisms 16 and 17 are similarly fixed on a rotation stage 18 that can be rotated in the direction of arrow R, forming a prism pair. The prism pair consisting of prisms 13 and 14 together with the rotation stage 15 constitute a first beam conversion unit. The prism pair consisting of prisms 16 and 17 together with the rotation stage 18 constitute a second beam conversion unit. These beam conversion units have the function of deflecting (changing the direction) the laser beam L. It also has the function of changing the beam diameter of the laser beam L depending on each prism that makes up the prism pair, but as mentioned above, this beam diameter hardly changes when comparing before it enters the prism pair and after it exits. That's right.

To explain in more detail, the prism pair consisting of prisms 13 and 14 maintains the beam diameter ds in the slow axis direction of the laser beam L, which has been made into a parallel beam by the collimating lens 12, and the beam diameter df in the fast axis direction. Reduce it and emit it. Further, the prism pair consisting of prisms 13 and 14 deflects the laser beam L so as to change the traveling direction (azimuth) in a plane including the fast axis, and emits the laser beam L.

On the other hand, the prism pair consisting of prisms 16 and 17 expands the beam diameter in the slow axis direction of the laser beam L emitted from the prism 14 while maintaining the beam diameter ds in the slow axis direction after passing through the collimating lens 12. However, the beam diameter in the fast axis direction is maintained as it is and is emitted. Further, the prism pair consisting of prisms 16 and 17 deflects the laser beam L so as to change the traveling direction (azimuth) in a plane including the slow axis, and emits the laser beam L.

Prisms 13, 14, 16 and 17 each have an apex angle of 45°. As these prisms 13, 14, 16, and 17, for example, prisms made of optical glass BK7 can be suitably used, but prisms made of other materials such as fused silica are also applicable.

The laser beam L, which is emitted from the prism 17 and converged in the conduit 20 by the converging lens 19, irradiates a plurality of particles 21 flowing in a line in the conduit length direction in the conduit 20. The resulting scattered light (forward scattered light and side scattered light) or fluorescence is detected by a photodetector not shown. The flow cytometer measures and analyzes the particles 21 individually or as a group based on the electrical detection signal output by the photodetector.

In the flow cytometer laser emitting module 200 of this embodiment, the laser beam L converging in the conduit 20 is directed in the length direction of the conduit 20 (in the direction of the particle 21), as shown in FIG. 12(a). The inside of the conduit 20 is irradiated with the flow direction) aligned with the slow axis. This prevents one particle 21 from being double counted in the flow cytometer. This point will be explained in detail below.

In order to avoid double counting of the particles 21 that are aligned and flowing in the flow direction in the pipe 20, the beam waist diameter of the laser beam L at the convergence position in the pipe 20 must be It needs to be sufficiently small. Otherwise, when two particles 21 flow close to each other, they will be counted as one particle. On the other hand, the beam waist diameter in the direction perpendicular to the flow direction is required to be large to some extent in order to prevent counting failure from occurring due to the laser beam L not hitting the particles 21. For example, in many flow cytometers that use biological microparticles as specimens, the former beam waist diameter is required to be approximately 10 μm or less, and the latter beam waist diameter is required to be approximately 60 to 100 μm or more.

On the other hand, when the laser beam L is converged by the converging lens 19, the beam waist diameter becomes smaller as the beam diameter before entering the converging lens 19 increases. Specifically, when a laser beam with a wavelength λ is focused by a lens with a focal length f, the beam diameter 2ω is 2ω=4/π·fλ/D.

In view of the above, as can be seen from FIG. 13 described above, it is desirable to arrange the unconverged laser beam L in a state where the fast axis is aligned with the particle flow direction because it can simplify the optical system. . However, according to research conducted by the present inventors, it has been found that the beam profile of the laser beam in the fast axis direction tends to have disturbances such as bumps, which leads to the occurrence of double counting.

An example of the beam profile in the fast axis direction is shown in FIG. In the figures (a) to (d), the horizontal axis shows the position in the fast axis direction, and the vertical axis shows the beam intensity I. (a) of the figure shows an ideal Gaussian beam profile. On the other hand, (b), (c), and (d) respectively show a beam profile with two humps sandwiching the center of the profile, a beam profile with a shoulder at the end of the profile, and a beam profile with a shoulder at the end of the profile. This shows a beam profile with one hump.

In this way, if a disturbance such as a bump occurs in the beam profile of the laser beam L along the flow direction of the particles 21, the detection signal of the detector that detects the aforementioned scattered light or fluorescence will be affected by the disturbance. It will fluctuate. This variation is then interpreted as originating from non-existent particles 21, leading to double counting. For example, if two bumps occur in the beam profile of the laser beam L, one particle 21 may be determined to be two. Such double counting occurs even when there is a bump in intensity of about 1 to 2% of the original beam intensity I of the laser beam L.

Based on the above knowledge, in this embodiment, the laser beam L is converted into a pipe length in the pipe line 20 by a first beam conversion unit including prisms 13 and 14 and a second beam conversion unit including prisms 16 and 17. The slow axis direction is aligned in the horizontal direction (particle flow direction). Therefore, it is possible to prevent double counting caused by disturbances such as bumps in the beam profile in the fast axis direction.

Further, in this embodiment, the laser beam L that has been made into parallel light by the collimating lens 12 is reduced in beam diameter in the fast axis direction by the first beam conversion unit and the second beam conversion unit, and is converted into a parallel beam in the slow axis direction. After enlarging the diameter, it is passed through a converging lens 19 and converged in a conduit 20. Specifically, regarding the slow axis direction, the beam diameter ds of the laser beam L after passing through the collimating lens 12 is 0.56 mm, and this laser beam L is made incident on the prism 16 at an incident angle α = 56°, and the prism 17 with a beam diameter of 3 mm (magnification ratio Ms=5.4). In addition, since the laser beam L after passing through the collimating lens 12 is perpendicularly incident on the first beam conversion unit in the slow axis direction, the above beam diameter ds=0.56 mm in the first beam conversion unit is essentially will be maintained as is.

On the other hand, regarding the fast axis direction, the beam diameter df of the laser beam L after passing through the collimating lens 12 is 1.4 mm, and this laser beam L is made incident on the prism 13 at an incident angle β = 23°, The beam is emitted with a beam diameter of 0.5 mm (magnification ratio Ms=0.36). Note that, since the laser beam L after passing through the prism 14 is perpendicularly incident on the second beam conversion unit in the fast axis direction, the beam diameter = 0.5 mm in the second beam conversion unit is essentially It will remain as is.

That is, the laser beam L before entering the converging lens 19 with a focal length f=50 mm has a beam diameter of 3 mm in the slow axis direction and a smaller 0.5 mm in the fast axis direction. As a result, the beam waist diameter of the laser beam L after being focused by the converging lens 19 at the convergence position in the conduit 20 is set to a relatively small 10 μm in the slow axis direction and a relatively large 60 μm in the fast axis direction. It is said that

As described above, in this embodiment, it is easily realized that the beam waist diameter in the fast axis direction at the convergence position is approximately 60 to 100 μm or more as described above, and the beam waist diameter in the slow axis direction is approximately 10 μm or less as described above. ing. The first beam conversion unit and the second beam conversion unit, which can produce such an effect and prevent double counting as described above, each consist of a simple prism pair, so in this embodiment, the optical system is It is easy to design, manufacture, and adjust, and its cost can be kept low.

When a gas laser or the like other than a semiconductor laser is used as a light source and a laser beam with a beam cross-sectional shape of an approximately perfect circle is converged in the conduit 20, for example, by narrowing down the laser beam using a cylindrical lens, it is possible to It is also possible to change the beam waist diameter in the direction perpendicular to the beam waist diameter. However, cylindrical lenses are difficult to process and expensive, and require complicated adjustments when used.

Note that in this embodiment, since the prism pair (prisms 16 and 17) as the second beam conversion unit is fixed on the rotation stage 18, the rotation stage 18 is rotated in the direction of arrow R around the rotation axis C2. This allows the laser beam L emitted from the second beam conversion unit to be deflected in the slow axis direction. Similarly, the prism pair (prisms 13 and 14) as the first beam conversion unit is fixed on the rotation stage 15, so by rotating the rotation stage 15 in the direction of arrow R around the rotation axis C1, The laser beam L emitted from the first beam conversion unit can be deflected in the fast axis direction.

Specifically, in this embodiment, by rotating the rotation stage 18 by ±1° in the direction of the arrow R, the laser beam is L can be deflected in the slow axis direction. This also applies to the amount of rotation of the rotation stage 15 and the direction of the laser beam L in deflection in the fast axis direction (see FIG. 3 of the first embodiment).

By deflecting the laser beam L in the fast axis direction as described above, the laser beam L can be adjusted to converge at the center position of the conduit 20. Furthermore, by deflecting the laser beam L in the slow axis direction, the convergence position of the laser beam L in the particle flow direction can be adjusted. As described above, by making the convergence position of the laser beam L adjustable both in the flow direction of the particles 21 and in the direction crossing this direction, the scattered light and fluorescence originating from the particles 21 can be made to have high intensity. can do. Therefore, since the intensity of the detection signal from the photodetector that detects these lights can also be increased, it is possible to eliminate signal variations between individual flow cytometers and obtain a highly reliable detection signal. Note that the laser beam L may be deflectable in only one direction, either the slow axis direction or the fast axis direction.

Further, also in the light emitting module 200 according to the second embodiment, the driving method for controlling the oscillation wavelength of the semiconductor laser 11 adopted in the first embodiment can be implemented. The same applies to the third and fourth embodiments described below.

<Third embodiment>
Next, referring to FIG. 15, a light emitting module according to a third embodiment of the present invention will be described. The light emitting module of this third embodiment is used as a processing light source in a laser processing device. The configuration of this light emitting module is the same as the configuration of the laser light emitting module 200 for flow cytometer shown in FIG. 12, but the target to be irradiated with the laser beam L is not the conduit 20 shown in FIG. This is the processing part of the laser processing equipment.

This laser processing device performs fine processing by two-dimensionally scanning a laser beam L over a processing portion. In FIG. 15, a partial processing area in the processing part is shown as Ap, and the laser beam L is scanned with respect to this processing area Ap in the main scanning direction and the sub-scanning direction shown by thick arrows X and Y, respectively. Ru. In addition, in the figure, the laser beam L is schematically shown by its beam profile. Further, arrows F and S shown in (a) and (b) of the figure indicate the fast axis direction and slow axis direction of the laser beam L, respectively.

In some types of laser processing equipment, when micromachining is performed with the fast axis aligned with the main scanning direction X as shown in FIG. sagging may occur. As the sub-scanning progresses, this sag becomes a linear erroneously processed portion as shown by G in the figure. According to the research conducted by the present inventor, the above-mentioned problems are considered to be caused by the above-mentioned hump in the beam profile of the laser beam L in the fast axis direction. This is because, if micromachining is performed with the slow axis aligned with the main scanning direction X, as shown in FIG. 4B, this problem will not occur.

Therefore, in this embodiment, the slow axis is controlled by a first beam conversion unit including a prism pair made up of prisms 13 and 14 shown in FIG. 12, and a second beam conversion unit including a prism pair made up of prisms 16 and 17. The laser beam L is aligned with the main scanning direction X, and the irradiation beam diameter is sufficiently small in the main scanning direction Set the direction and beam diameter. This makes it possible to prevent the above-mentioned problems from occurring.

<Fourth embodiment>
Next, with reference to FIG. 16, a light emitting module according to a fourth embodiment of the present invention will be described. The light emitting module of this fourth embodiment is used as a recording light source in a recording apparatus. The configuration of this light emitting module is the same as that of the laser light emitting module 200 for flow cytometer shown in FIG. 12, but the target to be irradiated with the laser beam L is not the conduit 20 shown in FIG. This is a recording medium, such as an optical disk, in which pits are formed for the purpose of recording.

A recording device that forms pits on a recording medium forms pits by two-dimensionally scanning the surface of the recording medium with a laser beam L emitted from a light emitting module. That is, as schematically shown in FIG. 16, the laser beam L scans the surface of the recording medium in the main scanning direction and the sub-scanning direction indicated by thick arrows X and Y, respectively. In addition, in the figure, the laser beam L is schematically shown by its beam profile. Further, an arrow F shown in the figure indicates the fast axis direction of the laser beam L.

In some types of recording media, when pits P are formed with the fast axis aligned with the main scanning direction may be formed. This partial pit Pf may lead to a reading error when reading the correct pit P from the recording medium. According to the research conducted by the present inventors, it is believed that the formation of the partial pits Pf is caused by the presence of the above-described hump in the beam profile of the laser beam L in the fast axis direction. This is because if the pits P are formed with the slow axis aligned with the main scanning direction X, no partial pits Pf will be formed.

Therefore, in this embodiment, the slow axis is controlled by a first beam conversion unit including a prism pair made up of prisms 13 and 14 shown in FIG. 12, and a second beam conversion unit including a prism pair made up of prisms 16 and 17. The laser beam L is aligned with the main scanning direction X, and the irradiation beam diameter is sufficiently small in the main scanning direction Set the direction and beam diameter. This makes it possible to prevent the above-mentioned partial pits Pf from occurring.

1 Base plate 2 Peltier element 3 Housing 4 Cover 5 Attenuator 6 Terminator 7, 8 Aperture plate 9 Photodetector 10 Thermistor 11 Semiconductor laser 12 Collimating lens 13, 16 First prism 14, 17 Second prism 15, 18 Rotation stage 19 Converging lens 20 Conduit 21 Particle 30 Temperature control circuit 31 Semiconductor laser drive circuit 50 LD holder 51 Ring 52 Lens holder L Laser beam LR Reflected light 100, 200 Light emitting module

Claims (5)

A light emitting module comprising a semiconductor laser and a collimating lens that converts a light beam emitted from the semiconductor laser in a diverging state into parallel light,
temperature control means capable of setting the semiconductor laser to a temperature higher than room temperature;
a semiconductor laser drive circuit that can change the optical output of the semiconductor laser by changing the drive current of the semiconductor laser;
an attenuator capable of attenuating the light beam emitted from the semiconductor laser;
A light emitting module characterized by being provided with. 2. The light emitting module according to claim 1, further comprising an aperture plate that blocks at least a portion of return light that is reflected from the outside and travels toward the semiconductor laser after being emitted from the semiconductor laser. 2. The temperature adjusting means includes a temperature detection element that detects a temperature near the semiconductor laser, and a heating element that increases the temperature of the semiconductor laser in accordance with the temperature detected by the temperature detection element. 3. The light emitting module according to 1 or 2. A light beam branching means for branching a part of the light beam emitted from the semiconductor laser and a photodetector for detecting the optical output of the branched light beam are provided,
the semiconductor laser drive circuit is configured to change the drive current based on the output of the photodetector;
The light emitting module according to any one of claims 1 to 3. A method for driving a light emitting module comprising a semiconductor laser and a collimating lens that converts a light beam emitted from the semiconductor laser in a diverging state into parallel light, the method comprising:
setting the semiconductor laser at a temperature higher than room temperature;
Changing the optical output of the semiconductor laser by changing the driving current of the semiconductor laser,
Attenuating the light beam emitted from the semiconductor laser to a predetermined optical output using an attenuator;
A method for driving a light emitting module, characterized in that: