Abstract:
A compact and inexpensive laser apparatus capable of obtaining laser beams of multiple wavelengths from a single solid crystal at the same time and excelling in reliability and efficiency is to be provided. A laser apparatus  1  uses a solid crystal consisting of a Raman effect substance as a laser medium  10 , and is equipped with a laser oscillator  12  for exciting the laser medium  10  to generate laser beams, a reflector  16 , a laser output mirror  18 , for resonating the laser beam generated from the laser medium  10  and a harmonic element  22  for enabling by angle adjustment a single wavelength to be extracted out of multiple oscillation wavelengths.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a laser apparatus capable of selectively taking out a single wavelength out of multiple wavelengths including Stokes light and anti-Stokes light and the second harmonic oscillation of Raman light resulting from Raman conversion simultaneously with laser oscillation.  
         [0003]     2. Description of the Related Art  
         [0004]     Various laser apparatuses are conventionally used as light sources for instruments for chemical measurement, micro-detectors using infrared absorption, isotope separation and so forth.  
         [0005]     As a laser apparatus having a broad wavelength-variable range and providing high-output coherent light in a wide band, a variable-wavelength laser apparatus using a method of wavelength conversion by induced Raman scattering is proposed in JP5-249513A.  
         [0006]     As shown in  FIG. 7 , a variable-wavelength laser apparatus  50  shapes a laser beam emitted from a variable-wavelength solid laser  52 , which serves as the excitation light source, into a parallel beam with a parallel beam generating mechanism  54  consisting of a plurality of lenses, subjects this parallel beam to wavelength conversion by a high-pressure Raman cell  56 , and subjects the wavelength-converted laser beam to further wavelength conversion by a multi-reflection type Raman cell  58 . The high-pressure Raman cell  56  and the multi-reflection type Raman cell  58  are filled with hydrogen or heavy hydrogen as a Raman effect substance.  
         [0007]     However, this variable-wavelength laser apparatus  50  requires selection of the wavelength of the laser beam emitted from the variable-wavelength solid laser  52  according to the desired wavelength. This factor results in greater complexity and larger size of the variable-wavelength laser apparatus  50 , with a consequent increase in cost. Also, the Raman effect substance filling the high-pressure Raman cell  56  and the multi-reflection type Raman cell  58  is gaseous hydrogen or heavy hydrogen, which is susceptible to deterioration by leaking or otherwise, accordingly unreliable and also poor in oscillation efficiency.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention, attempted to solve the problems noted above, is to provide a compact and inexpensive laser apparatus capable of obtaining laser beams of multiple wavelengths from a single solid crystal at the same time and excelling in reliability and efficiency.  
         [0009]     In order to achieve the object stated above, the invention is embodied in the following configuration. A laser apparatus according to the invention comprises an excitation light source unit for exciting a laser medium to generate a laser beam, a resonance unit for resonating the laser beam generated by the light source unit, and a harmonic element for modulating the wavelength of the laser beam, the laser apparatus being enabled to carry out multi-wavelength laser oscillation at the same time by forming the laser medium of a solid crystal of a Raman effect substance or forming the laser medium of a solid crystal of a non-Raman effect substance and providing the resonance unit with a solid crystal of a Raman effect substance, wherein a single wavelength is selectively extracted out of multiple wavelengths for oscillation of a visible region by adjusting the angle of the harmonic element relative to the optical axis. The solid crystal of the Raman effect substance may be a tungstate. The harmonic element may be one of LBO (LiB 3 O 5 ), KTP (KTiOPO 4 ), PPKTP (periodically poled KTiOPO 4 ), KDP (KH 2 PO 4 ) and BBO (BaB 2 O 4 ).  
         [0010]     In the laser apparatus according to the invention, for instance by using a Raman crystal KGd(WO 4 ) 2  as the solid crystal of the laser medium and having this solid crystal contain Nd, Yb, Er, Pr, Eu, Tb, Sm or the like as a laser-active substance, it is made possible to achieve simultaneous oscillation of the laser beam from the solid crystal, Stokes light having undergone Raman conversion of 901 cm −1  in Raman shift quantity and anti-Stokes light.  
         [0011]     Where Nd is used as a laser-active substance, fundamental wavelengths of 900 nm, 1067 nm, 1350 nm and so forth can be generated, and the simultaneous oscillation of Stokes light having undergone Raman conversion of 901 cm −1  in Raman shift quantity from these fundamental wavelengths and anti-Stokes light takes place.  
         [0012]     In order to achieve high conversion efficiency in a laser apparatus, the phase vector of the input beam and that of the generated beam should be coincident with each other, and phase mismatching represented by Equation (1) below should be zero:  
                     Δ   ⁢           ⁢   k     =       k   3     -     k   2     -     k   1                   =       2   ⁢           ⁢   π   ⁢           ⁢       n   3     /     λ   3         -     2   ⁢           ⁢   π   ⁢           ⁢       n   2     /     λ   2         -     2   ⁢           ⁢   π   ⁢           ⁢       n   1     /     λ   1                         (   1   )             
        where Δk is the phase mismatch; k i , the phase vector at the wavelength λ i  and n i , the refractive index at the wavelength λ i .        
 
         [0014]     The angle which makes Δk zero is known as a phase-matching angle. Where the output is low, the relationship between conversion efficiency and phase matching is represented by Equation (2) below: 
 
{sin(ΔkL)/ΔkL} 2   (2) 
        where η is the conversion efficiency, and L, the crystal length.        
 
         [0016]     There is a phase-matching angle for each wavelength. In the case the fundamental wavelength is 1067 nm, by aligning the harmonic element with each phase-matching angle of 1181 nm and 1250 nm resulting from Raman scattering, it is possible to generate a green wavelength (534 nm), a yellow wavelength (591 nm) and a red wavelength (660 nm), which are ½ wavelengths respectively. Thus, it is possible to selectively extract various wavelengths out of the resonance unit. An increase in phase mismatching would entail a sharp drop in conversion efficiency. If phase matching is achieved by adjusting the angle of the harmonic element relative to the optical axis, conversion efficiency will rise. Adjustment of the angle of the harmonic element is simple to accomplish and therefore advantageous compared to a case of achieving phase matching by adjusting temperature or the like. The phase-matching angle when the angle formed between the optical axis and the direction of beam propagation is 90 degrees or 0 degree is known as a non-critical phase-matching (NCPM) angle, and any other phase-matching angle, a critical phase-matching (CPM) angle.  
         [0017]     It is possible to generate Raman wave by forming the laser medium of a solid crystal of a non-Raman effect substance such as Y 3 Al 5 O 12  (YAG), YVO 4  or LiYF 4  (YLF) and combining with it a solid crystal of a Raman effect substance such as Al 2 (WO 4 ) 3 , CaWO 4 , CsLa(WO 4 ) 2 , Gd 2 (WO 4 ) 3 , KY(WO 4 ) 2 , KEr(WO 4 ) 2 , KGd(WO 4 ) 2 , KLu(WO 4 ) 2 , NaY(WO 4 ) 2 , NaLa(WO 4 ) 2 , NaGd(WO 4 ) 2 , NaBi(WO 4 ) 2 , PbWO 4 , ZnWO 4 , RbNd(WO 4 ) 2 , SrWO 4 , CdWO 4 , LiNbO 3 , KH 2 PO 4 , NaClO 3  or Ba(NO 3 ) 2 .  
         [0018]     Using a solid crystal of a Raman effect substance for the laser medium contributes to increasing the oscillation efficiency. It is preferable to use a tungstate as the solid crystal of a Raman effect substance. Available tungstates include, for instance Al 2  (WO 4 ) 3 , CaWO 4 , CsLa(WO 4 ) 2 , Gd 2 (WO 4 ) 3 , KY(WO 4 ) 2 , KEr(WO 4 ) 2 , KGd(WO 4 ) 2 , KLu(WO 4 ) 2 , NaY (WO 4 ) 2 , NaLa(WO 4 ) 2 , NaGd(WO 4 ) 2 , NaBi(WO 4 ) 2 , PbWO 4 , ZnWO 4 , RbNd(WO 4 ) 2 , SrWO 4  and CdWO 4 .  
         [0019]     Using LBO, KTP, PPKTP, KDP or BBO as the solid crystal of the harmonic element also contributes to increasing the oscillation efficiency.  
         [0020]     Using a tertiary harmonic or a quartic harmonic from a higher-order harmonic element would give a laser beam of a shorter wavelength.  
         [0021]     Therefore, where laser beams of multiple wavelengths are to be obtained at the same time, no extra equipment other than a laser oscillation apparatus is needed.  
         [0022]     A laser apparatus according to the invention, which can provide laser beams of multiple wavelengths from single solid crystal, excel in reliability and oscillation efficiency, and is compact and inexpensive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIGS. 1A and 1B  show the configuration of a laser apparatus according to the present invention;  
         [0024]      FIGS. 2A and 2B  show the configuration of a laser apparatus which is a variation of the invention;  
         [0025]      FIG. 3  is a spectral diagram of oscillation having a yellow wavelength;  
         [0026]      FIG. 4  is a spectral diagram of oscillation having a green wavelength;  
         [0027]      FIG. 5  is a spectral diagram of oscillation having a red wavelength;  
         [0028]      FIG. 6  is a spectral diagram of oscillation having multiple wavelengths; and  
         [0029]      FIG. 7  shows the configuration of a conventional variable-wavelength laser apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     A preferred embodiment of the present invention will be described below with reference to  FIGS. 1A and 1B .  
         [0031]     A laser apparatus  1  comprises a laser medium  10 , a laser oscillator  12 , a condenser lens  14 , a reflector  16 , a laser output mirror  18 , a Q switch  20  and a harmonic element  22 .  
         [0032]     The laser medium  10  is a solid crystal consisting of a Raman effect substance. As the Raman effect substance, a single crystal of KGd(WO 4 ) 2  is used for instance. It is also possible to use some other tungstate than KGd(WO 4 ) 2  or another Raman effect substance as the solid crystal of the laser medium  10 .  
         [0033]     Also, as in the variation shown in  FIGS. 2A and 2B , it is also possible to generate a Raman wave by forming the laser medium  10  of a solid crystal of a non-Raman effect substance, such as Y 3 Al 5 O 12  (YAG), YVO 4  or LiYF 4 (YLF) and combining with it a solid crystal  11  of a Raman effect substance such as Al 2 (WO 4 ) 3 , CaWO 4 , CsLa(WO 4 ) 2 , Gd 2 (WO 4 ) 3 , KY(WO 4 ) 2 , KEr(WO 4 ) 2 , KGd(WO 4 ) 2 , KLu(WO 4 ) 2 , NaY(WO 4 ) 2 , NaLa(WO 4 ) 2 , NaGd(WO 4 ) 2 , NaBi(WO 4 ) 2 , PbWO 4 , ZnWO 4 , RbNd(WO 4 ) 2 , SrWO 4 , CdWO 4 , LiNbO 3 , KH 2 PO 4 , NaClO 3  or Ba(NO 3 ) 2 .  
         [0034]     The laser medium  10  contains as the laser-active substance, for instance, 5 mol % of Nd. Instead of Nd, Yb, Er, Pr, Eu, Tb, Sm or the like may as well be used as the laser-active substance.  
         [0035]     It is generally preferable for the laser medium  10  to have a greater content of the laser-active substance because the conversion efficiency will be correspondingly higher. However, if the concentration of the laser-active substance surpasses 20 mol % in a single crystal of KGd(WO 4 ) 2 , it will become difficult to cut, grind or otherwise machine that single crystal. If the concentration of the laser-active substance further rises beyond 25 mol %, no single crystal structure can be formed. Or if the concentration of the laser-active substance is less than 0.01 mmol %, no laser oscillation can take place. Therefore, it is required to keep the concentration of the laser-active substance in the single crystal of KGd(WO 4 ) 2  not more than 20 mol % and not less than 0.01 mol %, and preferably not more than 15 mol % and not less than 0.05 mol %.  
         [0036]     The face  10   a  of the laser medium  10  to be irradiated with the excitation light is coated for the prevention of reflection against 809 nm, which is the oscillation wavelength of the excitation light and the absorption wavelength of Nd. The optical axis face of the laser medium  10  is coated for the prevention of reflection against 1067 nm, the oscillation wavelength of Nd, and 1181 nm and 1321 nm, the oscillation wavelengths of Stokes lights resulting from Raman scattering.  
         [0037]     Incidentally, if the laser-active substance in the laser medium  10  is not Nd, the face  10   a  of the laser medium  10  will have to be coated for the prevention of reflection against the oscillation wavelength of the excitation light, and the optical axis face should also be coated for the prevention of reflection against the oscillation wavelength of that laser-active substance and against the oscillation wavelengths of the Stokes lights resulting from Raman scattering.  
         [0038]     The laser oscillator  12  is, for instance, a semiconductor laser oscillator of a type generating a pulse of 100 to 10000 Hz, so configured as to constitute the excitation light source unit for the laser medium  10  and to be able to generate the excitation light. Incidentally, the laser oscillator  12  can as well be a continuous oscillation type semiconductor laser oscillator.  
         [0039]     The condenser lens  14 , positioned between the laser oscillator  12  and the laser medium  10 , so configured as to be able to irradiate the laser medium  10  with the excitation light generated by the laser oscillator  12 . The direction of irradiating the laser medium  10  by the excitation light is at an angle of 90 degrees to the optical axis. Incidentally, though the direction of irradiating the laser medium  10  by the excitation light is not limited to what forms an angle of 90 degrees to the optical axis, a substantially greater angle than 90 degrees would increase reflection by the irradiated face, which means a disadvantage of greater loss of irradiated energy. It is preferable for the direction of irradiating the laser medium  10  by the excitation light to be within a range of 90°±45° relative to the optical axis. Obviously, irradiation in the direction of the optical axis, which is the usual way of exciting the laser medium  10 , would pose no problem.  
         [0040]     The reflector  16  and the laser output mirror  18  constitute a resonance unit, configured to be capable of resonating the beam generated by the laser medium  10 .  
         [0041]     The Q switch  20  and the harmonic element  22  are positioned on the optical axis between the laser medium  10  and the laser output mirror  18 , with the Q switch  20  on the laser medium  10  side and the harmonic element  22  on the laser output mirror  18  side. The Q switch  20 , intended for amplifying the output, is an AOQ switch using a SiO 2  crystal. The harmonic element  22 , consisting of an LBO crystal for instance, is so configured as to permit adjustment of its angle relative to the optical axis. Incidentally, it is also possible to compose the Q switch  20  of a Cr:YAG crystal, which is a supersaturated absorbent, a supersaturated coloring matter and a semiconductor MQW type supersaturated absorbent element.  
         [0042]     Next, the actions of this apparatus will be described.  
         [0043]     An electric current is fed to the laser oscillator  12  and the laser medium  10  is irradiated with a laser-generated excitation light through the condenser lens  14 .  
         [0044]     Nd, which is the laser-active substance contained in the laser medium  10 , can oscillate in fundamental wavelengths of 900 nm, 1067 nm, 1350 nm and so on, and generate Stokes lights and anti-Stokes lights resulting from the Raman conversion of the fundamental wavelengths by 901 cm −1 , which is the extent of Raman shift. The generable wavelengths of Stokes lights and anti-Stokes lights resulting from the Raman conversion of the fundamental wavelength 1067 nm by a Raman shift of 901 cm −1  are shown in Table 1.  
                                                   TABLE 1                                       Raman wave                Wavelength (nm)   No. of waves (cm −1 )                        10th order anti-Stokes light   544   18382       9th order anti-Stokes light   572   17481       8th order anti-Stokes light   603   16580       7th order anti-Stokes light   638   15679       6th order anti-Stokes light   677   14778       5th order anti-Stokes light   721   13877       4th order anti-Stokes light   771   12976       3rd order anti-Stokes light   828   12075       2nd order anti-Stokes light   895   11174       1st order anti-Stokes light   973   10273       Fundamental wavelength   1067   9372       1st order Stokes light   1181   8471       2nd order Stokes light   1321   7570       3rd order Stokes light   1499   6669       4th order Stokes light   1734   5768       5th order Stokes light   2055   4867       6th order Stokes light   2521   3966       7th order Stokes light   3263   3065       8th order Stokes light   4621   2164       9th order Stokes light   7918   1263       10th order Stokes light   27624   362                  
 
         [0045]     Adjustment of the angle of the harmonic element  22  relative to the optical axis enables a single wavelength to be extracted out of multiple wavelengths that are simultaneously generated. The laser apparatus  1  shown in  FIG. 1A  is in a state in which the angle of the harmonic element  22  relative to the optical axis is 0 degree, and that shown in  FIG. 1B  is in a state in which the harmonic element  22  is inclined relative to the optical axis. The same is true of the variation of the laser apparatus  1  shown in  FIGS. 2A and 2B . The laser apparatus  1  shown in  FIG. 2A  is in a state in which the angle of the harmonic element  22  relative to the optical axis is 0 degree, and that shown in  FIG. 2B , in a state in which the harmonic element  22  is inclined relative to the optical axis.  
         [0046]     Using the harmonic element  22  makes it possible to take out many different wavelengths existing between the reflector  16  and the laser output mirror  18 .  
       EXAMPLE OF IMPLEMENTATION 1  
       [0047]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated.  
         [0048]     A current of 90 A was let flow into the laser oscillator  12 , and the laser medium  10  was irradiated with the resultant laser-generated excitation light. The irradiation energy of the excitation light was set to 28 mJ. Laser oscillation of 1067 nm in fundamental wavelength was confirmed within the resonance unit consisting of the reflector  16  and the laser output mirror  18 . It was confirmed that a Raman wave of 1181 nm and a Raman wave of 1321 nm were generated when the Q switch  20  was used. Then the harmonic element  22  was turned to vary the angle θ of the harmonic element  22  relative to the optical axis, and the resultant wavelength of oscillation was checked.  
         [0049]     As a result, when the angle θ was −1 degree, the oscillation of a blue wavelength (485 nm) was observed.  
         [0050]     When the angle θ was 0 degree, the oscillation of a yellow wavelength (590 nm) was observed.  
         [0051]     When the angle θ was 1 degree, the oscillation of a green wavelength (534 nm) and a yellow wavelength was observed.  
         [0052]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength, a yellow-green wavelength (560 nm), a yellow wavelength and a red wavelength (660 nm) was observed.  
         [0053]     When the angle θ was 2 degrees, the oscillation of a green wavelength was observed.  
         [0054]     When the angle θ was 3 degrees, the oscillation of a red wavelength was observed.  
         [0055]      FIG. 3  is a spectral diagram of oscillation having a yellow wavelength;  FIG. 4 , a spectral diagram of oscillation having a green wavelength;  FIG. 5 , a spectral diagram of oscillation having a red wavelength; and  FIG. 6 , a spectral diagram of oscillation having multiple wavelengths, i.e. yellow wavelength, yellow-green wavelength, green wavelength and red wavelength.  
       EXAMPLE OF IMPLEMENTATION 2  
       [0056]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a KTP crystal was used as the harmonic element  22 .  
         [0057]     As a result, when the angle θ was −1.5 degrees, the oscillation of a blue wavelength was observed.  
         [0058]     When the angle θ was 1 degree, the oscillation of a green wavelength was observed.  
         [0059]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0060]     When the angle θ was 2 degrees, the oscillation of a yellow wavelength was observed.  
         [0061]     When the angle θ was 2.5 degrees, the oscillation of a green wavelength, a yellow wavelength and a red wavelength was observed.  
         [0062]     When the angle θ was 3 degrees, the oscillation of a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 3  
       [0063]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a KDP crystal was used as the harmonic element  22 .  
         [0064]     As a result, when the angle θ was −1.5 degrees, the oscillation of a blue wavelength was observed.  
         [0065]     When the angle θ was 0 degree, the oscillation of a green wavelength was observed.  
         [0066]     When the angle θ was 1 degree, the oscillation of a yellow wavelength was observed.  
         [0067]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0068]     When the angle θ was 2 degrees, the oscillation of a red wavelength was observed.  
         [0069]     When the angle θ was 2.5 degrees, the oscillation of a green wavelength, a yellow wavelength and a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 4  
       [0070]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a BBO crystal was used as the harmonic element  22 .  
         [0071]     As a result, when the angle θ was −1.5 degrees, the oscillation of a blue wavelength was observed.  
         [0072]     When the angle θ was 0 degree, the oscillation of a green wavelength was observed.  
         [0073]     When the angle θ was 1 degree, the oscillation of a yellow wavelength was observed.  
         [0074]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0075]     When the angle θ was 2 degrees, the oscillation of a red wavelength was observed.  
         [0076]     When the angle θ was 2.5 degrees, the oscillation of a green wavelength, yellow wavelength and red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 5  
       [0077]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a PPKTP crystal was used as the harmonic element  22 .  
         [0078]     As a result, when the angle θ was −1.5 degrees, the oscillation of a blue wavelength was observed.  
         [0079]     When the angle θ was 0 degree, the oscillation of a green wavelength was observed.  
         [0080]     When the angle θ was 1 degree, the oscillation of a yellow wavelength was observed.  
         [0081]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0082]     When the angle θ was 2 degrees, the oscillation of a red wavelength was observed.  
         [0083]     When the angle θ was 2.5 degrees, the oscillation of a green wavelength, a yellow wavelength and a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 6  
       [0084]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that the concentration of Nd contained in the laser medium  10  was set to 15 mol %.  
         [0085]     As a result, when the angle θ was −1 degree, the oscillation of a blue wavelength was observed.  
         [0086]     When the angle θ was 0 degree, the oscillation of a yellow wavelength was observed.  
         [0087]     When the angle θ was 1 degree, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0088]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength, a yellow-green wavelength, a yellow wavelength and a red wavelength was observed.  
         [0089]     When the angle θ was 2 degrees, the oscillation of a green wavelength was observed.  
         [0090]     When the angle θ was 3 degrees, the oscillation of a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 7  
       [0091]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that the concentration of Nd contained in the laser medium  10  was set to 0.05 mol %.  
         [0092]     As a result, when the angle θ was −1 degree, the oscillation of a blue wavelength was observed.  
         [0093]     When the angle θ was 0 degree, the oscillation of a yellow wavelength was observed.  
         [0094]     When the angle θ was 1 degree, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0095]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength, a yellow-green wavelength, a yellow wavelength and a red wavelength was observed.  
         [0096]     When the angle θ was 2 degrees, the oscillation of a green wavelength was observed.  
         [0097]     When the angle θ was 3 degrees, the oscillation of a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 8  
       [0098]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a single crystal of KY(WO 4 ) 2  was used as the laser medium  10 , the concentration of Nd contained in the laser medium  10  was set to 5 mol % and a PPKTP crystal was used as the harmonic element  22 .  
         [0099]     As a result, when the angle θ was −1.5 degrees, the oscillation of a blue wavelength was observed.  
         [0100]     When the angle θ was 0 degree, the oscillation of a green wavelength was observed.  
         [0101]     When the angle θ was 1 degree, the oscillation of a yellow wavelength was observed.  
         [0102]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0103]     When the angle θ was 2 degrees, the oscillation of a red wavelength was observed.  
         [0104]     When the angle θ was 2.5 degrees, the oscillation of a green wavelength, a yellow wavelength and a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 9  
       [0105]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a single crystal of NaY(WO 4 ) 2  was used as the laser medium  10 , Yb was used as the laser-active substance, the concentration of Yb contained in the laser medium  10  was set to 5 mol % and a PPKTP crystal was used as the harmonic element  22 . Further, the wavelength of the excitation light radiating from the laser oscillator  12  was set to 980 nm.  
         [0106]     As a result, when the angle θ was −1.5 degrees, the oscillation of a blue wavelength was observed.  
         [0107]     When the angle θ was 0 degree, the oscillation of a green wavelength was observed.  
         [0108]     When the angle θ was 1 degree, the oscillation of a yellow wavelength was observed.  
         [0109]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0110]     When the angle θ was 2 degrees, the oscillation of a red wavelength was observed.  
         [0111]     When the angle θ was 2.5 degrees, the oscillation of a green wavelength, a yellow wavelength and a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 10  
       [0112]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a single crystal of LiNbO 3  was used as the laser medium  10 , the concentration of Nd contained in the laser medium  10  was set to 3 mol % and a PPKTP crystal was used as the harmonic element  22 .  
         [0113]     As a result, when the angle θ was −1.5 degrees, the oscillation of a blue wavelength was observed.  
         [0114]     When the angle θ was 0 degree, the oscillation of a green wavelength was observed.  
         [0115]     When the angle θ was 1 degree, the oscillation of a yellow wavelength was observed.  
         [0116]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0117]     When the angle θ was 2 degrees, the oscillation of a red wavelength was observed.  
         [0118]     When the angle θ was 2.5 degrees, the oscillation of a green wavelength, a yellow wavelength and a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 11  
       [0119]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a Cr:YAG crystal was used for the Q switch  20 .  
         [0120]     As a result, when the angle θ was −1 degree, the oscillation of a blue wavelength was observed.  
         [0121]     When the angle θ was 0 degree, the oscillation of a yellow wavelength was observed.  
         [0122]     When the angle θ was 1 degree, the oscillation of a green wavelength and a yellow wavelength was observed.  
         [0123]     When the angle θ was 1.5 degrees, the oscillation of a green wavelength, a yellow-green wavelength, a yellow wavelength and a red wavelength was observed.  
         [0124]     When the angle θ was 2 degrees, the oscillation of a green wavelength was observed.  
         [0125]     When the angle θ was 3 degrees, the oscillation of a red wavelength was observed.  
       EXAMPLE OF IMPLEMENTATION 12  
       [0126]     By using the laser apparatus  1  according to the invention described above, a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 1 except that a single crystal of PbWO 4 , 3 mm×3 mm×15 mm in size, was used as the laser medium  10 , the concentration of Nd contained in the laser medium  10  was set to 0.5 mol % and a laser beam of 808 nm in wavelength and 20 Hz in frequency was used as the excitation light radiating from the laser oscillator  12 .  
         [0127]     When the angle θ was varied, the oscillation of a green wavelength, a yellow-green wavelength, a yellow wavelength and a red wavelength was observed.  
         [0128]     Where a supersaturated coloring matter and a semiconductor MQW type supersaturated absorbent element were used for the Q switch  20 , varying the angle θ made observable the oscillation of a green wavelength, a yellow-green wavelength, a yellow wavelength and a red wavelength.  
         [0129]     Further, also where a continuous oscillation type semiconductor laser oscillator was used as the laser oscillator  12  and an excitation light of 808 nm in wavelength was continuously generated from the laser oscillator  12 , varying the angle θ made observable the oscillation of a green wavelength, a yellow-green wavelength, a yellow wavelength and a red wavelength.  
       EXAMPLE OF IMPLEMENTATION 13  
       [0130]     By using the laser apparatus  1  which is the variation of the invention shown in  FIGS. 2A and 2B , a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated.  
         [0131]     A current of 90 A was let flow into the laser oscillator  12 , and the laser medium  10  was irradiated with the resultant laser-generated excitation light. YAG (Y 3 Al 5 O 12 ) containing 1 mol % of Nd was used as the laser medium  10 , and LBO, as the harmonic element  22 . The irradiation energy of the excitation light was set to 20 mJ.  
         [0132]     Ba(NO 3 ) 2  was used as the solid crystal  11  of a Raman effect substance, and the laser oscillation of 1064 nm in fundamental wavelength was observed within the resonance unit consisting of the reflector  16  and the laser output mirror  18 . Using the Q switch made observable a Raman wave of 975 nm, a Raman wave of 1197 nm and a Raman wave of 1367 nm.  
         [0133]     Then the harmonic element  22  was turned to vary the angle θ of the harmonic element  22  relative to the optical axis, and the resultant wavelength of oscillation was checked.  
         [0134]     As a result, when the angle θ was −1 degree, the oscillation of a blue wavelength 487 nm was observed.  
         [0135]     When the angle θ was 1 degree, the oscillation of a yellow wavelength 598 nm was observed.  
         [0136]     When the angle θ was 0 degree, the oscillation of a green wavelength 534 nm was observed.  
         [0137]     When the angle θ was 2 degrees, the oscillation of a red wavelength 683 nm was observed.  
       EXAMPLE OF IMPLEMENTATION 14  
       [0138]     By using the laser apparatus  1  which is the variation of the invention shown in  FIGS. 2A and 2B , a wavelength was selectively extracted out of multiple wavelengths that were simultaneously generated in the same way as in Example of Implementation 13 except that YVO 4  of 0.5 mol % in Nd concentration was used as the laser medium  10 , KGd(WO 4 ) as the solid Raman crystal  11  and PPKPT as the harmonic element  22 .  
         [0139]     The laser oscillation of 1064 nm in fundamental wavelength was observed within the resonance unit consisting of the reflector  16  and the laser output mirror  18 . Using the Q switch made observable a Raman wave of 970 nm, a Raman wave of 1176 nm and a Raman wave of 1316 nm.  
         [0140]     As a result, when the angle θ was −1 degree, the oscillation of a blue wavelength 485 nm was observed.  
         [0141]     When the angle θ was 1 degree, the oscillation of a yellow wavelength 588 nm was observed.  
         [0142]     When the angle θ was 0 degree, the oscillation of a green wavelength 534 nm was observed.  
         [0143]     When the angle θ was 2 degrees, the oscillation of a red wavelength 658 nm was observed.