Laser processing device

1. A laser processing device comprising:

a laser beam source which emits a laser beam;

a collimating unit which collimates rays of the laser beam emitted from the laser beam source to parallel rays;

a condensing optical system which condenses the parallel rays of the laser beam in a medium;

a first lens group which is arranged in the parallel rays between the collimating unit and the condensing optical system and moves along the optical axis direction of parallel rays, the first lens group including one or more lenses;

a second lens group which is securely arranged in the parallel rays between the first lens group and the condensing optical system, and includes one or more lenses; and

a moving unit which moves the first lens group in accordance with the refractive index of the medium in which the laser beam is condensed and the distance from a surface of the medium to a position where the laser beam is condensed, wherein

a rear side focal length of the second lens group is arranged at least in the vicinity of an entrance pupil position of the condensing optical system.

2. The laser processing device according to claim 1 , further comprising

an observation optical system which is provided in coordination with the condensing optical system and maintains a predetermined distance from a bottom face of the condensing optical system to the surface of the medium, wherein

the observation optical system includes an autofocus detecting unit or an autofocus mechanism.

3. The laser processing device according to claim 2 , wherein

the relative distance in the optical axis direction between the condensing optical system and the surface of the medium is constant.

4. The laser processing device according to claim 1 , wherein

when |f| is the combined focal distance of the first lens group and the second lens group, the moving unit moves the first lens group to a position which satisfies the following equation

1/| f |<0.01.

5. The laser processing device according to claim 1 , wherein

when f 2 is the focal distance of the second lens group, the second lens group satisfies the following equation

f2>0.

6. The laser processing device according to claim 1 , wherein

when f 1 is the focal distance of the first lens group and f 2 is the focal distance of the second lens group, the first lens group and the second lens group satisfy the following equations.

f1<0.

and 1≦| f 1 /f 2|≦5.

7. The laser processing device according to claim 1 , wherein

when f 1 is the focal distance of the first lens group and f 2 is the focal distance of the second lens group, the first lens group and the second lens group satisfy the following equations

f1>0

and 0.5≦| f 1 /f 2|≦2.

8. A laser processing device comprising:

a laser beam source which emits a laser beam;

a condensing optical system which condenses the laser beam in a medium; and

a laser condensing optical system wherein, in accordance with the refractive index of the medium where the laser beam is condensed and the distance from a surface of the medium to a position where the laser beam is condensed, a plurality of lenses satisfying the following equation arc exclusively inserted/removed to/from a path of divergent rays and/or convergent rays of the condensing optical system.

2( d 2 +l×f−l×d ) NA=f×a

where d is the distance from an entrance pupil position of a condensing optical system to the plurality of lenses,

l is the distance from the entrance pupil position of the condensing optical system to the beam source position,

f is the focal length of the plurality of lenses,

NA is the numerical aperture of the beam source (the numerical aperture seen from a condensing lens), and

a is the entrance pupil diameter of the condensing optical system.

9. A laser processing device comprising:

a laser beam source which emits laser rays parallel to an optical axis;

an optical system which condenses the laser rays in a medium; and

a laser condensing optical system wherein, in accordance with the refractive index of the medium where the laser beam is condensed and the distance from a surface of the medium to a position where the laser beam is condensed, a plurality of lenses satisfying the following equation are exclusively inserted/removed to/from the laser rays

b ( f−d )/ f=a

where b is the diameter of the collimated beam from the beam source,

d is the distance from an entrance pupil position of a condensing optical system to the plurality of lenses,

f is the focal length of the plurality of lenses, and

a is the entrance pupil diameter of the condensing optical system.

10. A laser processing device comprising:

a laser beam source which emits a laser beam;

a condensing optical system which is arranged between the laser beam source and a medium and condenses the laser beam in the medium;

a laser divergence point moving unit which moves a position of a laser divergence point of the laser beam along an optical axis of the laser beam; and

a controller which controls the laser divergence point moving unit, wherein the controller includes:

an input unit into which a refractive index of the medium in which the laser beam is condensed, and a distance from a surface of the medium to a position where the laser beam is condensed, are input; and

a calculator which calculates an amount of movement of the laser divergence point based on the refractive index and the distance, and wherein

the laser divergence point moving unit moves the laser divergence point based on the amount of movement calculated by the calculator.

11. A laser processing device comprising:

a laser beam source which emits a laser beam;

a condensing optical system which is arranged between the laser beam source and a medium and condenses the laser beam to a position inside the medium; and

a laser divergence point moving unit which moves the position of a laser divergence point of the laser beam along an optical axis of the laser beam, wherein

the laser divergence point moving unit sets the position of the laser divergence point in accordance with the refractive index of the medium in which the laser beam is condensed, the distance from a surface of the medium to a position where the laser beam is condensed, and wavefront data of the condensing optical system measured beforehand.

12. A laser processing device comprising:

a laser beam source which emits a laser beam;

a condensing optical system which is arranged between the laser beam source and a medium and condenses the laser beam to a position inside the medium;

a laser divergence point moving unit which moves the position of a laser divergence point of the laser beam along an optical axis of the laser beam in accordance with the refractive index of the medium in which the laser beam is condensed and the distance from a surface of the medium to a position where the beam is condensed; and

an observation optical system which is provided in coordination with the condensing optical system and maintains a predetermined distance from the condensing optical system to the surface of the medium, wherein

the observation optical system includes an autofocus detecting unit or an autofocus mechanism.

13. The laser processing device according to claim 12 , wherein the autofocus detecting unit or the autofocus mechanism performs focusing on the surface of the medium, and offsets an auto focusing point by a predetermined amount in accordance with the position inside the medium, where the laser beam is condensed.

14. The laser processing device according to claim 12 , wherein the autofocus detecting unit or the autofocus mechanism controls so as to maintain a relative distance in the optical axis between the condensing optical system and the surface of the medium, to be constant.