JPH11354897A - Laser beam output device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light intensity distribution suitable for light trap without sacrificing the output from a laser beam output device by combining the beams from a plurality of units and increasing the cross-section of the beam intensity gradually from the central region toward the periphery thereof. SOLUTION: Exciting light from a semiconductor laser 13 is condensed through a condensing optical system 14 to a laser crystal 15 and amplified through resonators 16, 17 to produce a laser beam being emitted from a mirror 18. The polarization directions of a solid laser crystal are regulated such that the laser beams from two resonators 16, 17 are polarized perpendicularly to each other. A beam 20 from the resonator 17 is deflected by 90 deg. through a mirror 7 and two beams 19, 20 emitted from the resonators 16, 17 are combined through a polarization beam splitter 8 to produce a single laser beam which is outputted 5 while reducing the spreading angle through an output lens 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam device used for optical manipulation and trapping, which has a function of capturing, moving or cutting a minute object by laser light.

[0002]

2. Description of the Related Art In recent years, techniques for capturing and moving a minute object by irradiating a laser beam and applying pressure (a phenomenon in which momentum moves from the laser beam to the object due to absorption, reflection, and refraction) have been developed. It is called trap or light manipulation technology, and has recently come into the spotlight. Such a technique is attracting attention especially as a tool in basic research in biology and micromachine engineering. For example, in combination with a microscope, a laser beam is guided into the microscope, and then squeezed by an objective lens to capture and move macromolecules such as DNA, cells, biological tissues, etc. near the focal point (optical tweezers), or to cut or destroy them. (Light scalpel). Microscopes used for such light manipulation are being developed by various research institutions, and are entering a practical stage.

[0003] On the other hand, various types of laser beam output devices are being actively researched and developed, and the fields of application are expanding. Many types of laser beam devices such as semiconductor lasers, gas lasers, and solid-state lasers have been put to practical use. Research and development using these laser devices as light sources for optical traps and optical manipulations are being actively conducted.

[0004] However, the cross-sectional light intensity distribution of the output beam of the laser beam output device is a circular normal distribution (Gaussian distribution), and the intensity is highest at the center. Therefore, when irradiating a small object with the output beam as it is and performing optical trapping or optical manipulation, it is easy to move the object, but the object receives force only from one direction, so it is captured. There is a problem that is difficult. Therefore, an efficient light trap,
For the purpose of optical manipulation operation, the light intensity distribution of the output beam from the laser beam output device is corrected using a filter, galvanometer mirror, etc., and the ring-shaped intensity distribution suitable for the optical trap, that is, the light intensity at the beam center Has been conventionally used such that the light intensity is smaller than the ambient light intensity.

FIG. 7 shows a galvanomirror 1 as a prior art.
The configuration of an apparatus using 0 and 11 is shown. The circular Gaussian beam 5 emitted from the laser beam output device 4 includes a galvanomirror 10 that vibrates at a constant amplitude in the horizontal direction,
The light is reflected by the galvanomirror 11 which vibrates in the vertical direction, and its traveling direction is controlled. Galvanometer mirrors 10 and 1
If the oscillation period and amplitude of 1 are made constant and a phase difference of 90 degrees is provided, the beam will rotate around a circle having a certain radius in the vertical plane of the reflected beam. By making the oscillation period of the galvanometer mirror short enough,
An apparently ring-shaped beam is obtained. Further, it is necessary to arrange a correction lens 12 for making the inclination angle of the beam closer to parallel to the optical axis. After that, it is configured to input to the optical trap device 6 for capturing the target.

[0006]

In the prior art using the galvanomirror shown in FIG. 7, the momentum from the outside for maintaining the capture of a minute object is due to the fact that the beam is rotating at a high speed. The light approximately acts on the object as pulsed light, and its output is smaller than in the case of continuous light. This can be considered to be equivalent to the effect of lowering the laser output value. Thus, in the galvanomirror type,
At the same time as the device was complicated, there was a limit to increase the output.

It is also possible to convert a Gaussian laser beam into a ring shape by a filter having a distribution in which the transmittance near the center is lower than that around the center. However,
In this case, since the laser beam is partially cut, there is a problem that the output is reduced, the device is complicated, and the conversion efficiency is reduced. In the conventional method for obtaining a ring-shaped beam as described above, it is necessary to add a device for correcting a laser beam emitted from a laser beam output device, and at the same time, it generally causes a decrease in output.
There were two serious problems.

As described above, when a laser beam output device that emits a Gaussian beam is used as an optical trap or a light source for an optical manipulation device with high working efficiency,
In order to convert or correct the light intensity distribution of the laser beam from the Gaussian distribution to the ring shape, an optical system added to the laser device is added, and the entire system becomes complicated, and the output is reduced. The present invention has been made in view of such circumstances, and provides a mechanism for obtaining a ring-shaped laser beam having a light intensity distribution suitable for an optical trap without causing a decrease in output in a laser beam output device. The problem of the prior art is solved by incorporating.

[0009]

In order to efficiently capture a minute object, the cross-sectional shape of the beam intensity is low in the central region.
It just needs to get stronger as you go around. However, a beam emitted from an ordinary laser beam output device has a Gaussian distribution in which the light intensity peaks at the center. Therefore, there are two methods of generating a beam having a distribution other than the Gaussian distribution directly from the laser resonator, or changing the distribution of the Gaussian beam into a ring shape using various optical elements.

However, when these two methods are simply applied, the laser output is reduced. The reason is briefly described. First, a method of directly generating a laser beam from a laser resonator is known. A Gaussian beam is known as a beam mode that theoretically has the least diffraction loss and a high output from a laser resonator. Therefore, when a beam having a distribution other than the Gaussian beam is directly extracted from the laser resonator under the same excitation condition, the beam output is inevitably reduced. In addition, the method of correcting the distribution of the Gaussian beam into a ring-shaped distribution using various optical elements involves a decrease in light output due to reflection, absorption, refraction, scattering, etc. as described in the description of the related art. .

In the present invention, therefore, a plurality of laser beam output units are assumed, and attention has been paid to the fact that a ring-shaped shape should be obtained at the time of combining beams from the plurality of units. By assuming a plurality of laser beam output units, the output is roughly doubled by the number of units, so that a higher output can be achieved at the same time. FIG. 1 shows the principle configuration of the present invention. Before performing beam combining, the internal configuration of each laser beam output unit 1 is changed to A
As shown by the points, the laser beams 2 and 2 'of the transverse mode TEM01 having two intensity distributions on the upper and lower sides and the transverse mode TEM10 having two intensity distributions on the left and right of the point B are output. By combining these two beams 2 and 2 'by the optical beam combining means 3, a beam 5 having a ring-shaped light intensity distribution can be obtained.

As a method of obtaining the transverse modes TEM01 and TEM10, for example, there is a method of adjusting the tilt angle of the laser resonator mirror. There is also a method in which the distribution of the excitation energy applied to the laser generating medium (for example, a laser crystal or the like) in the laser resonator matches the intensity distribution of the laser beam in the transverse mode TEM01 or TEM10. Further, there is a method of inserting an aperture having the same loss distribution as the intensity distribution of the laser beam in the transverse mode TEM01 or TEM10 into the laser resonator. Either of them can be applied without any problem in practicing the present invention.

Next, specific conditions for combining beams will be described. In order to combine two beams, for example, a mirror (half mirror) having a transmittance and a reflectance of about 50% can be used. However, due to the reflection loss and transmission loss due to the half mirror, the output from each of the two laser beam output units is reduced by about half, and the combined output is limited to the output of one laser unit. Difficult to obtain.

FIG. 2 shows a basic configuration of a system according to the present invention as a method for specifically realizing beam combining without impairing the output. The laser resonators 1 and 1 'are set so that the polarization directions of the beams 2 and 2' are orthogonal to each other.
And the beams 2 and 2 ′ are synthesized by using the polarization beam splitter 8 as an optical beam synthesis means. The polarization beam splitter 8 is an optical element that can generally combine beams of two polarization directions perpendicular to each other without loss. Therefore, it is possible to secure an output about twice as large as the laser output from one resonator, and at the same time, it is possible to make the beam cross-sectional shape 5 into a ring shape. Note that the beams from the laser resonators 1 and 1 'do not necessarily have to have a sectional shape having two intensity distributions divided vertically or horizontally, as long as the division directions are two beams and are orthogonal to each other. Good. Similarly, the polarization directions need only be orthogonal to each other.

[0015]

FIG. 3 shows an embodiment of the present invention. In this embodiment, a wavelength of 669 n
m, Broad output red semiconductor laser 1 with rated output 1W
3 and 1.5% Cr concentration, 3 × 3
A × 5 mm Cr: LiSAF (Cr: LiSrAlF ₆ ) single crystal 15 was used. As shown in FIG. 3, two resonators 16 and 17 are used. The laser cavity length is 95 mm and the cavity mirror 18
Has a radius of curvature of 100 mm. Resonator 17 on laser output side
A mirror 7 and a polarizing beam splitter 8 that bend the path of the beam from the mirror are arranged. Finally, a plano-convex lens 9 was arranged as an output lens, and the beam 5 was output.

Excitation light emitted from the semiconductor laser 13 is focused on a laser crystal 15 by a focusing optical system 14. The laser light amplified and oscillated in the resonators 16 and 17 becomes a laser beam and is emitted from the mirror 18. The direction of the polarized light oscillated by the solid-state laser crystal is defined so that the polarization directions of the laser beams from the two resonators 16 and 17 are perpendicular to each other. The beam 20 from the resonator 17 has its 90 ° path bent by the mirror 7, and the two beams 19 and 20 emitted from the resonator 16 and the resonator 17 are combined by the polarization beam splitter 8 into one laser beam. . The output lens 9 reduced the beam divergence angle to obtain an output beam 5.

Laser oscillation was performed in the above optical system. The drive current in the semiconductor laser 13 is 1540 mA, and the pump output is 860 mW. At the time of laser oscillation, the position of each optical component was adjusted so that the transverse mode of the laser resonator beam was TEM01.

The output value of the beam 5 after combining with the driving current of the semiconductor laser of 1540 mA was 305 mW. This is resonator 1
High power is achieved as compared with the values of 151 mW and 158 mW of 6 and 17 alone. FIG. 6 shows the result of measuring the light intensity distribution of the output beam 5 at a semiconductor laser drive current of 1540 mA.
4 and 5 show the beams before the combination of the resonators 16 and 17, respectively. The intensity distribution of the beams from the resonators 16 and 17 is a distribution in the TEM01 and TEM10 modes as described above, and the intensity distribution of the combined beam has a target ring shape. In this embodiment, a Cr: LiSrAlF ₆ crystal is used as the solid-state laser crystal.
Exactly the same result can be obtained by using d: Y ₃ Al ₅ O ₁₂ single crystal or Nd: YVO ₄ .

[0019]

According to the present invention, when a laser device is used as a light source for an optical trap, it is not necessary to add an optical system for adjusting the light intensity distribution of the beam. It is possible to obtain a laser beam having a ring-shaped shape with higher output than the laser output by the set of laser resonators. Therefore, it can be expected that the optical trap and the optical manipulation system can be significantly reduced in size and work efficiency of the optical trap and the optical manipulation can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a basic configuration of a system according to the present invention.

FIG. 3 is another embodiment according to the present invention.

FIG. 4 is a TEMOI mode distribution.

FIG. 5 is a TEM10 mode distribution.

FIG. 6 is a distribution of a combined beam according to the present invention.

FIG. 7 is a schematic diagram showing a conventional technique.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 laser resonator, 2 laser beam, 3 optical beam combining means, 4 laser beam output device, 5 output beam, 6 optical manipulation device, 7 reflection mirror,
Reference Signs List 8 polarization beam splitter, 9 output lens, 10 horizontal galvanometer mirror, 11 vertical galvanometer mirror, 12 correction lens, 13 semiconductor laser, 14 focusing optics, 15 Cr: LiSrAlF ₆ single crystal, 16 laser resonator A, 17 Laser resonator B, 18 Output mirror, 19
Laser beam A, 20 Laser beam B, 21 Semiconductor laser drive power supply and crystal temperature controller

Claims (4)

[Claims] 1. A laser beam device for generating a laser beam by exciting a laser medium inside a resonator by an excitation light source, wherein the laser beam device has at least two or more units for outputting a laser beam. A laser beam output device, wherein a laser beam from a unit is synthesized by an optical means, and a cross-sectional light intensity of a synthesized output beam is larger at a peripheral portion than at a central portion. 2. The laser beam of the laser unit is Cr.
Claims, characterized in that it is obtained by exciting the doped LiSrAlF ₆ laser single crystal of a semiconductor laser
2. The laser beam output device according to 1. 3. The laser beam of the laser unit is
(0,1) next transverse mode TEM01 or (1,0) next transverse mode T
3. The laser beam output device according to claim 1, wherein the laser beam output device is EM10. 4. The laser beam output device according to claim 1, wherein said optical means uses a polarization beam splitter.