Laser-diode pumped solid-state laser apparatus, optical scanning apparatus, image forming apparatus and display apparatus

A laser-diode pumped solid-state laser apparatus comprises at least one laser diode producing a pumping laser light, and at least one laser light generator including a monocrystalline substance doped with a dopant element and pumped with the pumping laser light from at least one laser diode, the monocrystalline substance containing the dopant element with a concentration profile such that the dopant element increases a concentration thereof in a direction perpendicular to a laser oscillation direction gently in the form of a slope from a near zero concentration.

BACKGROUND OF THE INVENTION

The present invention generally relates to laser-diode pumped solid-state laser apparatuses, optical scanning apparatuses, image forming apparatuses and display apparatuses. More particularly, the present invention relates to a laser-diode pumped solid-state laser apparatus having a solid-state laser crystal in which pumping is caused by laser diode. Further, the present invention relates to any of an optical scanning apparatus, an image forming apparatus or a display apparatus that uses such a laser-diode pumped solid-state laser apparatus.

These days, lasers are used in various fields including laser printers and laser measuring instruments. Further, aiming practical application in future, investigation and development are being made with regard to laser display apparatus or the like. In such apparatuses that use laser light, there is an increasing demand for downsizing of laser source and improvement of laser light quality.

Various proposals have been made with regard to so-called solid-state lasers (see Patent References 1-11, for example).

For example, Patent Reference 1 discloses a solid-state laser oscillation apparatus that uses a laser medium having a doped part and undoped part. Further, Patent Reference 2 discloses a laser apparatus having a gain medium and a waveguide of pumping light, while Patent Reference 3 discloses a laser apparatus having a laser medium and a waveguide optical system.

Further, Patent Reference 4 discloses a method of manufacturing an oxide monocrystal (single crystal) having a core part and a cladding part, while Patent Reference 5 discloses an oxide monocrystal of fiber shape for optical applications formed of a fiber body of an oxide monocrystal and a liquid-phase epitaxial layer of an oxide monocrystal formed so as to cover the surface of the foregoing fiber body. Further, Patent Reference 6 discloses a solid-state laser crystal in which doping concentration of laser-activating ions is increased continuously or stepwise from an end surface where excitation is caused toward an end surface where cooling is made.

Further, Patent Reference 7 discloses a composite laser device having a transparent crystal body including therein a region where laser oscillation can take place and a second crystal body jointed to the transparent crystal body, wherein at least one of the transparent crystal body and the second crystal body is formed of a polycrystalline material. Further, Patent Reference 8 discloses a solid-state laser oscillator having a polycrystalline ceramic composite laser medium in which a polycrystalline transparent ceramic not containing active element and a polycrystalline transparent ceramic doped with an active element are jointed.

Further, Parent References 11 and Non-Patent Reference 1 disclose a composite monocrystal that has regions formed by so-called dual-die EFG (edge-defined film-fed growth) process with different compositions or components.

Patent Reference 1

Japanese Patent 3,503,588

Patent Reference 2

Japanese Laid-Open Patent Application 2004-356479

Patent Reference 3

Japanese Laid-Open Patent Application 2004-152817

Patent Reference 4

Japanese Patent 3759807

Patent Reference 5

Japanese Laid-Open Patent Application 8-278419

Patent Reference 6

Japanese Patent 3266071

Patent Reference 7

Japanese Laid-Open Patent Application 2005-327997

Patent Reference 8

Japanese Laid-Open Patent Application 2002-57388

Patent Reference 9

Japanese Laid-Open Patent Application 6-128089

Patent Reference 10

Japanese Laid-Open Patent Application 6-128076

Patent Reference 11

Japanese Laid-Open Patent Application 6-128078

SUMMARY OF THE INVENTION

However, with conventional laser optical source, it has been difficult to obtain a high-quality laser light without inviting increase of size of the laser optical source.

Thus, the present invention has been made in view of the foregoing problems and it is a first object of the present invention to provide a laser-diode pumped solid-state laser apparatus capable of providing high-quality laser output without inviting increase of size.

A second object of the present invention is to provide an optical scanning apparatus capable of scanning a surface with high precision.

A third object of the present invention is to provide an image forming apparatus capable of forming high-quality images.

A fourth object of the present invention is to provide a display apparatus capable of displaying information with high display quality.

In a first aspect, the present invention provides a laser-diode pumped solid-state laser apparatus, comprising:

at least one laser diode producing a pumping laser light; and

at least one laser light generator comprising a monocrystalline substance doped with a dopant element (optical emission center: rare earth element or transitional metal element) and pumped with said pumping laser light from said at least one laser diode,

said monocrystalline substance containing said dopant element with a concentration profile such that said dopant element increases a concentration thereof in a direction perpendicular to a laser oscillation direction gently in the form of a slope from a near zero concentration.

According to the present invention, in which at least one laser light generator used therein comprises the monocrystalline substance doped with the dopant element (optical emission center: rare earth element or transitional metal element) excited by the pumping laser light from the at least one laser diode, with the concentration profile such that the dopant element increases a concentration thereof from near zero concentration gently in the form of a slope in the direction perpendicular to the laser oscillation direction, it is easily possible to attain the desired distribution of optical absorption in the monocrystalline substance. Further, there is no need with the present invention to shape the excitation laser light, and it becomes possible to provide a laser output of high beam quality, without inviting increase of size of the solid-state laser apparatus.

In a second aspect, the present invention provides an optical scanning apparatus scanning a surface by an optical beam, wherein the optical scanning apparatus comprises at least one laser-diode pumped solid-state laser apparatus of the present invention for producing the optical beam.

According to the present invention, in which the optical scanning apparatus comprises at least one laser-diode pumped solid-state laser apparatus as set forth above, it becomes possible to scan the surface with the optical beam with high precision as a result.

In a third aspect, the present invention provides an image forming apparatus forming an image on an object by using a laser light, wherein the image forming apparatus comprises at least one laser-diode pumped solid-state laser apparatus as set forth above for producing the laser light.

According to the present invention, in which the image forming apparatus comprises at least one laser-diode pumped solid-state laser apparatus as set forth above, it becomes possible to form high-quality images as a result.

In a fourth aspect, the present invention provides a display apparatus displaying information by using laser light, wherein the display apparatus comprises at least one laser-diode pumped solid-state laser apparatus as set forth above for producing the laser light.

According to the present invention, in which the display apparatus comprises at least one laser-diode pumped solid-state laser apparatus as set forth above, it becomes possible to attain high-quality display of information as a result.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Hereinafter, a laser-diode pumped solid-state laser apparatus according to a first embodiment of the present invention will be described.

FIGS. 1A and 1Bshow the schematic construction of a laser-diode pumped solid-state laser apparatus100according to a first embodiment of the present invention. In the present invention, explanation will be made based on the coordinate system in which Z-axis is chosen in the laser oscillation direction and X and Y-axes are chosen in a plane perpendicular to the Z-axis with mutually perpendicular relationship.

Referring toFIGS. 1A and 1B, the laser-diode pumped solid-state laser apparatus100of the present embodiment is an apparatus of so-called side-pumped type and includes two laser diode array elements LDa and LDb for the purpose of pumping, a solid-state laser crystal10, an output mirror40, and a heat sink30.

The two laser diode array elements LDa and LDb are disposed on the +Z-side of the heat sink30in a manner so as to face each other in the Y-axis direction, wherein each of the laser diode array elements LDa and LDb produces a pumping laser light of the wavelength of 808 nm with the output power of 40 W. In the illustrated example, the laser diode array LDa emits the pumping laser light in the +Y direction while the laser diode array LDb produces the pumping laser light in the −Y direction.

Further, there are provided two optical systems20aand20brespectively in correspondence to the laser diodes LDa and LDb, wherein each of the optical systems20aand20bis formed by a combination of plural lenses and is disposed on the +Z side of the heat sink30. Thereby, it becomes possible to form an optical spot on the incident surface of the solid-state laser crystal100with a size of 100 μm (in the thickness direction of the solid-state laser crystal10: Z-axis direction)×1000 μm (X-axis direction). Here, the optical system20ais deposed at the +Y side of the laser diode array LDa and focuses the pumping laser light therefrom. Further, the optical system20bis deposed at the −Y side of the laser diode array LDb and focuses the pumping laser light therefrom.

The solid-state laser crystal10is disposed on the +Z side of the heat sink30at the +Y side of the optical system20aand at the −Y side of the optical system20b.

As shown inFIGS. 2A and 2B, the solid-state laser crystal10may be a uniaxial monocrystal of gadolinium vanadate (GdVO4) having a disk shape (or chip shape), wherein it should be noted that the solid-state laser crystal10is doped with neodymium (Nd) as the dopant element (emission center) excited by the pumping laser light from the laser-diode array elements.

As represented in the example ofFIG. 2A, the concentration profile of Nd has a sloped shape in which the Nd concentration increases gradually from near zero concentration in the direction perpendicular to the direction of laser oscillation (Z-axis direction in the present case). Hereinafter, the part contributing to laser oscillation will be designated as “core part10a” and the part scarcely contributing to laser oscillation will be designated as “cladding part10b”. Thus, the solid-state laser crystal10is integrally formed of the core part10aand the cladding part10b.

In the present example, the core part10ais a circular part of a diameter Da located at a central part of the solid-state laser crystal10, while the cladding part10bis a donuts shape part surrounding the core part10a.

As shown in the example ofFIG. 2A, the concentration of Nd in the core part10abecomes maximum near the center of the core part10aand decreases gradually toward the cladding part10b. In one example, the Nd concentration near the center of the core part10ais about 0.5 at %. Thereby, the Nd concentration profile has a shape resembling a Gauss distribution profile.

In one example, the solid-state laser crystal10is formed by slicing a rod-shaped monocrystal (columnar crystal) ingot manufactured by the dual-die EFG process explained before or by a μPD process and may have a thickness t of 0.5 mm, a diameter Db of 5 mm and a diameter Da of 1 mm. It should be noted that the solid-state laser crystal10is a crystal that is designed to emit a laser light of linear polarization upon excitation by optical pumping.

Further, as shown inFIG. 3, the surface of the solid-state laser crystal10at the side where the heat sink30is provided (the surface at −Z side, designated as “A surface” for the sake of convenience) is provided with a coating providing a reflectance of 99.9% for the light of a wavelength of 1063 nm. Further, as shown inFIG. 3, the surface of the solid-state laser crystal10at the side opposite to the side where the heat sink30is provided (the surface at +Z side, designated as “B surface” for the sake of convenience) is provided with a coating providing a transmittance of 99.9% for the light of the wavelength of 1063 nm.

On the surface of the coating at the A surface, there is formed a metal layer32of Cr/Ni/Au laminated structure, wherein the metal layer32is jointed to an Au—Sn alloy layer31formed on the heat sink30.

Further, there is disposed an output mirror40at the +Z side of the solid-state laser crystal10. This output mirror40has a radius of curvature of 5000 mm at the −Z side surface and has a transmittance of 5% to the light of the wavelength of 1063 nm.

Thereby, there is formed a cavity35by the A surface of the solid-state laser crystal10and the output mirror40as shown inFIG. 3.

In the illustrated example, the distance between the A surface of the solid-state laser crystal10and surface of the output mirror40at the −Z side is set to 100 mm. Further, the laser light forms a beam of the beam diameter of 0.5 mm inside the solid-state laser crystal10.

It should be noted that the output mirror40may have a so-called microchip construction integrated with the solid-state laser crystal10.

Next, the operation of the laser-diode pumped solid-state laser apparatus100of the foregoing construction will be explained briefly.

Referring toFIG. 1, the laser diode array LDa emits a pumping laser light with the wavelength of 808 nm, wherein the emitted pumping laser light is injected into the solid-state laser crystal10at a side surface thereof after passing through the optical system20a. Similarly, the laser diode array LDb emits a pumping laser light with the wavelength of 808 nm, wherein the emitted pumping laser light is injected into the solid-state laser crystal10at a side surface thereof after passing through the optical system20b.

Thereby, the Nd dopant in the solid-state laser crystal10undergoes excitation by the pumping laser light and there is caused laser oscillation by the cavity35formed by the A surface of the solid-state laser crystal10and the output mirror40(seeFIG. 3) with the wavelength of 1063 nm. That laser light of the wavelength of 1063 nm is then emitted after passing through the output mirror40.

As explained above, the laser-diode pumped solid-state laser apparatus100of the first embodiment is thus provided with the solid-state laser crystal10that includes a uniaxial monocrystal of gadolinium vanadate (GdVO4) doped with Nd, which undergoes excitation by the pumping laser lights from the two pumping laser diode array elements LDa and LDb, wherein Nd is doped with such a concentration profile that the concentration of Nd increases gradually in the sloped shape from near zero concentration in the direction perpendicular to the laser oscillation direction (Z-axis direction in the present example). As a result, it is easily attained the absorption profile such as those shown inFIGS. 4 and 5, in which there appears a peak of absorption at the central part of the solid-state laser crystal10. With this, a lateral mode of excellent Gaussian distribution is attained for the laser light output therefrom (designated hereinafter as “output laser light” for the sake of convenience).

Meanwhile, in the case a solid state laser crystal having a uniform Nd concentration profile for the core part, and thus having a sharp increase of Nd concentration from near zero concentration, is used for the laser-diode pumped solid-state laser apparatus of side pumping construction, there occurs strong and sharp absorption for the pumping laser light injected from the side surface as shown inFIGS. 6 and 7, and it becomes difficult to attain an output laser light of excellent beam quality. Thus, in this case, it is advisable to provide a correction mechanism for correcting the beam quality, while such correction mechanism invites increase of size and cost of the laser apparatus. In addition, such a construction requires adjustment of the correction mechanism.

Further, according to the laser-diode pumped solid-state laser apparatus100of the first embodiment, the heat generated in the solid-state laser crystal10, originating from the energy difference between the pumping laser light and the output laser light, is radiated directly via the A surface, and it becomes possible to suppress the temperature rise of the solid-state laser crystal10. As a result, it becomes possible to achieve high power operation of the laser-diode pumped solid-state laser apparatus100.

It should be noted that, in the event there is a uniform Nd concentration in the core part, it should be noted that there arises a heat distribution profile similar to that of the absorption profile in the solid-state laser crystal, while such heat distribution profile induces a change of refractive index (thermal lens effect), leading to further deterioration of the beam quality.

With the laser-diode pumped solid-state laser apparatus100of the first embodiment, it is possible to optimize the heat distribution profile by adjusting the concentration profile of Nd in the solid-state laser crystal10. Thus, with the laser-diode pumped solid-state laser apparatus100of the first embodiment of the present invention, it becomes possible to provide an output laser light of excellent beam quality without providing a correction mechanism for the change of refractive index (thermal lens effect).

Thus, according to the laser-diode pumped solid-state laser apparatus100of the first embodiment, it becomes possible to output a laser light of the wavelength of 1063 nm with excellent beam quality and with high output power.

While the first embodiment has been explained for the case of the output laser light has the wavelength of 1063 nm, the present invention is not limited to such a particular construction. For example, by appropriately choosing the specification of coating of the solid-state laser crystal10and the optical properties of the output mirror40, it is also possible to obtain an output laser light of the wavelength of 912 nm or 1340 nm.

Second Embodiment

Hereinafter, a laser-diode pumped solid-state laser apparatus according to a second embodiment of the present invention will be described with reference toFIGS. 8A and 8B.

FIG. 8Ashows the schematic construction of a laser-diode pumped solid-state laser apparatus200according to a second embodiment of the present invention.

Referring toFIG. 8A, the laser-diode pumped solid-state laser apparatus200has a construction similar to that of the laser-diode pumped solid-state laser apparatus100of the first embodiment, except that there is disposed a non-linear optic crystal50on the optical path of the laser light between the solid-state layer crystal10and the output mirror40and that the optical properties of the output mirror40is different and the specification of the coating of the solid-state laser crystal10is different. Otherwise, the construction of the present embodiment is the same as the first embodiment.

Hereinafter, explanation will be made mainly on the difference over the first embodiment. Thereby, it should be noted that the same reference numerals are used for the parts identical to or equivalent to the parts of the first embodiment and the description thereof will be simplified or omitted.

The non-linear optic crystal50converts the laser light of the wavelength of 1063 nm of the fundamental mode to a laser light of the wavelength of 531.5 nm forming a second harmonic mode. For this non-linear optic crystal50, a PPMgLN device (a device of LiNbO3having a periodically inversed polarization structure doped with MgO) may be used. This non-linear optic crystal50has a length of 5 mm (in the X-axis direction and Y-axis direction) and a thickness of 2 mm (in the Z-axis direction). Thereby, the non-linear optic crystal50is disposed with such an orientation that the crystal axis thereof points the direction in which there is attained a pseudo phase matching condition with the polarization direction of the laser light inside the cavity. On both end surfaces of the non-linear optic crystal50, there are provided a coating providing a transmittance of 99.5% or higher for both the fundamental mode light of the wavelength of 1063 nm and the second harmonics light of the wavelength of 531.5 nm. In the explanation below, the surface at the −Z side of the non-linear optic crystal50will be designated as C surface, while the surface at the +Z side will be designated as D surface.

On the surface (A surface) of the solid-state laser crystal10jointed to the heat sink30, there is provided a coating having a reflectance of 99.9% with regard to the light of the wavelength of 1063 nm as shown inFIG. 8B. Further, as shown inFIG. 8B, there is provided a coating on the surface (B surface) opposite to the A surface of the solid-state laser crystal10, such that the coating provides the transmittance of 99.9% for the light of the wavelength of 1063 nm and the reflectance of 99% for the light of the wavelength of 531.5 nm. With this, it is possible to suppress the incidence of the second harmonic wave generated inside the cavity to penetrate into the solid-state layer crystal10.

The output mirror40has a radius of curvature of 5000 mm at the −Z side surface and has a reflectance of 99.9% to the light of the wavelength of 1063 nm and the transmittance of 99% to the light of the wavelength of 531.5 nm.

Thereby, there is formed a cavity35A by the A surface of the solid-state laser crystal10and the output mirror40as shown inFIG. 8B.

Next, the operation of the laser-diode pumped solid-state laser apparatus200will be explained briefly.

Referring toFIG. 8A, the laser diode array LDa emits a pumping laser light with the wavelength of 808 nm, wherein the emitted pumping laser light is injected into the solid-state laser crystal10at a side surface thereof after passing through the optical system20a. Similarly, the laser diode array LDb emits a pumping laser light with the wavelength of 808 nm, wherein the emitted pumping laser light is injected into the solid-state laser crystal10at a side surface thereof after passing through the optical system20b.

Thereby, the Nd dopant element in the solid-state laser crystal10undergoes excitation by the pumping laser light and there is caused laser oscillation by the cavity35A formed by the A surface of the solid-state laser crystal10and the output mirror40(seeFIG. 8B) with the wavelength of 1063 nm. Thereby, the laser light of the wavelength of 1063 nm is confined inside the cavity35A and forms the fundamental mode. Thereby, because the non-linear optic element50is disposed inside the cavity35A, the confined fundamental mode wave undergoes wavelength transition, resulting in generation of the second order harmonics, and the laser light of the wavelength of 531.5 nm is formed as the second order harmonics, wherein this laser light of the wavelength of 531.5 nm is outputted through the output mirror40.

As explained above, the laser-diode pumped solid-state laser apparatus200of the second embodiment is thus provided with the solid-state laser crystal10that includes a uniaxial monocrystal of gadolinium vanadate (GdVO4) doped with Nd, which undergoes excitation by the pumping laser lights from the two pumping laser diode array elements LDa and LDb, wherein Nd is doped with such a concentration profile that the concentration of Nd increases gently in the sloped shape from near zero concentration in the direction perpendicular to the laser oscillation direction (Z-axis direction in the present example). As a result, it is easily attained the desired absorption profile in which there appears a peak of absorption at the central part of the solid-state laser crystal10. With this, a lateral mode of excellent Gaussian distribution is obtained for the laser light from the solid-state laser crystal10. Thus, the laser light of the wavelength of 1063 nm of high power and excellent beam quality is injected into the non-linear optic element50.

Meanwhile, it is known that, in non-linear optic elements, the output of the second harmonics is proportional to the square of the optical power of the incident light. This means that there occurs increase of output in proportion with the beam quality.

According to the laser-diode pumped solid-state laser apparatus200of the second embodiment, in which it is possible to inject a high power laser light of excellent beam quality into the non-linear optic element50, there is attained improvement of efficiency of conversion in the non-linear optic element50.

Thus, according to the laser-diode pumped solid-state laser apparatus200of the second embodiment, it becomes possible to output a laser light of the wavelength of 531.5 nm with excellent beam quality and with high output power, without inviting increase of size of the apparatus.

In the laser-diode pumped solid-state laser apparatus200according to the second embodiment explained above, the non-linear optic element50may have a length of 5 mm and a thickness of 2 nm, while the present invention is by no means limited to such a specific example. Thus, other construction may be used as long as the laser light of the fundamental mode having the wavelength of 1063 nm is converted to the laser light of the second harmonics of the wavelength of 531.5 nm with desired conversion efficiency.

Third Embodiment

Hereinafter, a laser-diode pumped solid-state laser apparatus according to a third embodiment of the present invention will be described with reference toFIGS. 9A and 9B.

FIG. 9Ashows the schematic construction of a laser-diode pumped solid-state laser apparatus300according to a third embodiment of the present invention.

Referring toFIG. 9A, the laser-diode pumped solid-state laser apparatus300has a construction similar to that of the laser-diode pumped solid-state laser apparatus200of the second embodiment, except that the non-linear optic crystal50is disposed a the +Z side of the output mirror40. Otherwise, the construction of the present embodiment is same to that of the second embodiment. Hereinafter, explanation will be made mainly on the difference over the second embodiment. Thereby, it should be noted that the same reference numerals are used for the parts identical to or equivalent to the parts of the second embodiment and the description thereof will be simplified or omitted.

Referring toFIG. 9A, the non-linear optic element50is disposed on the optical path of the laser light passed through the output mirror40. This non-linear optic crystal50may have a thickness (length in the Z-axis direction) of 10 mm, for example. It should be noted that, in the case the non-linear optic crystal50is disposed inside the optical cavity as in the case of the second embodiment, the non-linear optic crystal50may have a small thickness in view of large optical intensity, while in the case of the third embodiment in which the non-linear optic element50is disposed outside the optical cavity, it is necessary to achieve the wavelength conversion with one pass of the laser light through the non-linear optic crystal50, and thus, there is a need of increasing the thickness of the non-linear optic crystal50for attain the conversion efficiency comparable to that of the second embodiment.

According t the laser-diode pumped solid-state laser apparatus300of the third embodiment, in which the laser light of the wavelength of 1063 nm of high power and excellent beam quality is injected into the non-linear optic element50, it becomes possible to emit a laser light of the wavelength of 531.5 nm with high beam quality and high output without inviting increase of size of the apparatus, similarly to the laser-diode pumped solid-state laser apparatus200according to the second embodiment of the present invention.

In the laser-diode pumped solid-state laser apparatus300according to the third embodiment explained above, the non-linear optic element50may have a length of 5 mm and a thickness of 10 nm, while the present invention is by no means limited to such a specific example. Thus, other construction may be used as long as the laser light of the fundamental mode having the wavelength of 1063 nm is converted to the laser light of the second harmonics of the wavelength of 531.5 nm with desired conversion efficiency.

Further, with the laser-diode pumped solid-state laser apparatus300of the third embodiment, it is also possible to dispose a lens between the output mirror40and the non-linear optic crystal50. With this, it becomes possible to focus the fundamental mode wave incident to the non-linear optic element50, resulting in improvement of beam strength of the fundamental wave, and the conversion efficiency in the non-linear optic crystal50is improved further as a result.

Fourth Embodiment

Hereinafter, a laser-diode pumped solid-state laser apparatus according to a fourth embodiment of the present invention will be described with reference toFIGS. 10A and 10B.

FIG. 10Ashows the schematic construction of a laser-diode pumped solid-state laser apparatus400according to a fourth embodiment of the present invention.

Referring toFIG. 10A, the laser-diode pumped solid-state laser apparatus400has a construction similar to that of the laser-diode pumped solid-state laser apparatus200of the second embodiment, except that the specification is changed for the coating on the D surface of the non-linear optic crystal50and that the output mirror40is eliminated. Otherwise, the construction of the present embodiment is same to that of the second embodiment. Hereinafter, explanation will be made mainly on the difference over the second embodiment. Thereby, it should be noted that the same reference numerals are used for the parts identical to or equivalent to the parts of the second embodiment and the description thereof will be simplified or omitted.

As shown inFIG. 10B, there is provided a coating on the D surface of the non-linear optic crystal50, wherein the coating thus provided has a reflectance of 99.9% for fundamental mode light of the wavelength of 1063 nm and the transmittance of 99.5% for the second harmonics light of the wavelength of 531.5 nm. Further, on the C surface of the non-linear optic crystal50, there is provided a coating providing a transmittance of 99.5% or higher for both the fundamental mode light of the wavelength of 1063 nm and the second harmonics light of the wavelength of 531.5 nm.

Thereby, there is formed a cavity35A by the A surface of the solid-state laser crystal10and the D surface of the non-linear optic crystal50as shown inFIG. 10B.

Thereby, the solid-state laser crystal10and the non-linear optic element50are fixed with each other with simple contact or with a photo-resistive adhesive. Thereby, the solid-state laser crystal10and the non-linear optic crystal50may make an optical contact free from coating.

As explained heretofore, according t the laser-diode pumped solid-state laser apparatus400of the fourth embodiment, in which the laser light of the wavelength of 1063 nm of high power and excellent beam quality is injected into the non-linear optic element50, it becomes possible to emit a laser light of the wavelength of 531.5 nm with high beam quality and high output without inviting increase of size of the apparatus, similarly to the laser-diode pumped solid-state laser apparatus200according to the second embodiment of the present invention.

Further, according to the laser-diode pumped solid-state laser apparatus400according to the fourth embodiment of the present invention, there is no need of providing the output mirror40used with the laser-diode pumped solid-state laser apparatus200, and it becomes possible to facilitate size reduction further.

Fifth Embodiment

Hereinafter, a laser-diode pumped solid-state laser apparatus excited according to a fifth embodiment of the present invention will be described with reference toFIGS. 11A and 11B.

FIG. 11Ashows the schematic construction of a laser-diode pumped solid-state laser apparatus500according to a fifth embodiment of the present invention.

Referring toFIG. 11A, the laser-diode pumped solid-state laser apparatus500has a construction similar to that of the laser-diode pumped solid-state laser apparatus300of the second embodiment, except that the specification is changed for the solid-state laser crystal10and the non-linear optic crystal50and that the output mirror40is eliminated. Otherwise, the construction of the present embodiment is same to that of the third embodiment. Hereinafter, explanation will be made mainly on the difference over the third embodiment. Thereby, it should be noted that the same reference numerals are used for the parts identical to or equivalent to the parts of the third embodiment and the description thereof will be simplified or omitted.

On the A surface of the solid-state laser crystal10, there is provided a coating having a reflectance of 99.9% with regard to the light of the wavelength of 1063 nm as shown inFIG. 11B. Further, as shown inFIG. 11B, there is provided a coating having a transmittance of 5% with regard to the light of the wavelength of 1063 nm on the B surface of the solid-state laser crystal10.

Thus, there is formed a cavity35A by the A surface and the B surface of the solid-state laser crystal10as shown inFIG. 11B.

Further, on both edge surfaces of the non-linear optic crystal50, there are provided a coating having a transmittance of 99.5% or more for the second harmonics light of the wavelength of 531.5 nm.

Thereby, the solid-state laser crystal10and the non-linear optic element50are fixed with each other with simple contact or with a photo-resistive adhesive. Thereby, the solid-state laser crystal10and the non-linear optic crystal50may make an optical contact free from coating.

As explained heretofore, according t the laser-diode pumped solid-state laser apparatus500of the fifth embodiment, in which the laser light of the wavelength of 1063 nm of high power and excellent beam quality is injected into the non-linear optic element50, it becomes possible to emit a laser light of the wavelength of 531.5 nm with high beam quality and high output without inviting increase of size of the apparatus, similarly to the laser-diode pumped solid-state laser apparatus300according to the third embodiment of the present invention.

Further, according to the laser-diode pumped solid-state laser apparatus500according to the fifth embodiment of the present invention, there is no need of providing the output mirror40used with the laser-diode pumped solid-state laser apparatus300, and it becomes possible to facilitate size reduction further.

While the second through fifth embodiments have been explained for the case of the output laser light has the wavelength of 131.5 nm, the present invention is not limited to such a particular construction. Thus, by choosing the pitch of polarization reversal or coating specification of the non-linear optic crystal50appropriately, it is also possible to obtain an output laser light of the wavelength of 670 nm or 456 nm.

Sixth Embodiment

Hereinafter, a solid-state laser apparatus excited by laser diode according to a sixth embodiment of the present invention will be described with reference toFIG. 12andFIGS. 13A and 13B,14A and14B and15A and15B.

FIG. 12shows the schematic construction of a laser-diode pumped solid-state laser apparatus600according to a sixth embodiment of the present invention.

The laser-diode pumped solid-state laser apparatus600includes: a first solid-state laser apparatus600R emitting an output laser light of red color with the wavelength of 670 nm; a second solid-state laser apparatus600B emitting an output laser light of blue color with the wavelength of 456 nm; and a third solid-state laser apparatus600G emitting an output laser light of green color with the wavelength of 531.5 nm.

As shown inFIG. 13A, the first solid-state laser apparatus600R has a construction similar to the laser-diode pumped solid-state laser apparatus500according to the fifth embodiment explained before. In one example, there is provided a coating having a reflectance of 99.9% with regard to the light of the wavelength of 1063 nm as shown inFIG. 11Bon the A surface of the solid-state laser crystal10. Further, as shown inFIG. 13B, there is provided a coating having a transmittance of 5% with regard to the light of the wavelength of 1340 nm and the transmittance of 99.9% with regard to the light of the wavelength of 1063 nm on the B surface of the solid-state laser crystal10. With regard to the material of the solid-state laser crystal10, the same material as in the case of the laser-diode pumped solid-state laser apparatus500of the fifth embodiment may be used. The non-linear optic crystal50is a PPMgLN device having a different pitch for the polarization reversal and carries a coating on the respective end surfaces thereof such that a transmittance of 99.5% or more is attained for the light of the wavelength of 1340 nm and the light of the wavelength of 670 nm.

As shown inFIG. 14A, the second solid-state laser apparatus600B has a construction similar to the laser-diode pumped solid-state laser apparatus500according to the fifth embodiment explained before. Thus, in one example, there is provided a coating having a reflectance of 99.9% with regard to the light of the wavelength of 912 nm on the A surface of the solid-state laser crystal10as shown inFIG. 14B. Further, as shown inFIG. 14B, there is provided a coating having a transmittance of 3% with regard to the light of the wavelength of 912 nm and the transmittance of 99.9% with regard to the light of the wavelength of 1063 nm on the B surface of the solid-state laser crystal10. With regard to the material of the solid-state laser crystal10, the same material as in the case of the laser-diode pumped solid-state laser apparatus500of the fifth embodiment may be used. The non-linear optic crystal50is a PPMgLN device having a different pitch for the polarization reversal and carries a coating on the respective end surfaces thereof such that a transmittance of 99.5% or more is attained for the light of the wavelength of 912 nm and the light of the wavelength of 456 nm.

As shown inFIGS. 15A and 15B, the third solid-state laser apparatus600G has a construction similar to the laser-diode pumped solid-state laser apparatus500according to the fifth embodiment explained before.

As explained heretofore, it becomes possible, with the laser-diode pumped solid-state laser apparatus600of the sixth embodiment including therein a plurality of solid-state laser apparatuses each having a solid-state laser crystal10, to provide a plurality of laser output lights of high output power with excellent beam quality, without inviting increase of size of the laser apparatus600.

In the sixth embodiment, it is possible that each of the solid-state laser apparatuses emits the laser light with the same wavelength.

Further, while explanation has been made for the case of the laser apparatus includes three solid-state laser apparatuses, the present invention is by no means limited to such a construction. Thus, the laser-diode pumped solid-state laser apparatus600may include two solid-state laser apparatuses or four or more solid-state laser apparatuses.

While the second through sixth embodiment has been explained for the case of using the PPMgLN device, it should be noted that the present invention is not limited to such a specific construction. Thus, any non-linear optic crystal having a function equivalent to the PPMgLN device may be used.

Seventh Embodiment

Hereinafter, a laser-diode pumped solid-state laser apparatus according to a seventh embodiment of the present invention will be described with reference toFIGS. 16A and 16B.

FIG. 16Ashows the schematic construction of a laser-diode pumped solid-state laser apparatus700according to a seventh embodiment of the present invention.

Referring toFIG. 16A, the laser-diode pumped solid-state laser apparatus700is an apparatus of the edge pumping structure and includes a laser diode LD for pumping, a lens20, the solid-state laser crystal10and the output mirror40.

The laser-diode LD is a device of single-stripe structure and can produce a laser light of the wavelength of 808 nm with an output power of 2 W. In the illustrated example, the laser diode LD emits a laser light in the +Z direction.

The lens20is disposed at the +Z side of the laser diode LD and focuses the pumping laser light from the laser diode LD upon the solid-state laser crystal10. For example, the lens20may be the element capable of focusing the pumping laser light to form a beam with a beam diameter of about 1 mm.

The solid-state laser crystal10is disposed at the +Z side of the lens20. Further, as shown inFIG. 16B, the surface of the solid-state laser crystal10at the side where the lens20is provided (the surface at −Z side, designated as “E surface” for the sake of convenience) is provided with a coating providing a reflectance of 99.9% for the light of the wavelength of 808 nm and a transmittance of 0.1% for the light of the wavelength of 1063 nm. Further, as shown inFIG. 16B, the surface of the solid-state laser crystal10at the side opposite to the E surface (the surface at +Z side, designated as “F surface” for the sake of convenience) is provided with a coating providing a transmittance of 99.9% for the light of the wavelength of 1063 nm.

Further, there is disposed an output mirror40at the +Z side of the solid-state laser crystal10. This output mirror40has a radius of curvature of 5000 mm at the −Z side surface and has a transmittance of 5% to the light of the wavelength of 1063 nm.

Thereby, there is formed a cavity35C by the E surface of the solid-state laser crystal10and the output mirror40as shown inFIG. 16B.

In the illustrated example, the distance between the E surface of the solid-state laser crystal10and surface of the output mirror40at the −Z surface is set to 100 mm. Further, the laser light forms a beam of the beam diameter of 0.5 mm inside the solid-state laser crystal10.

It should be noted that the output mirror40may have a so-called microchip construction integrated with the solid-state laser crystal10.

Next, the operation of the laser-diode pumped solid-state laser apparatus700of the foregoing construction will be explained briefly.

The laser light (pumping laser light) of the wavelength of 808 nm emitted from the laser diode LD passes through the lens20and enters into the solid-state crystal10. Thereby, the Nd dopant element in the solid-state laser crystal10undergoes excitation by the pumping laser light and there is caused laser oscillation by the cavity35C formed by the E surface of the solid-state laser crystal10and the output mirror40with the wavelength of 1063 nm. That laser light of the wavelength of 1063 nm is then emitted after passing through the output mirror40.

Meanwhile, with a laser-diode pumped solid-state laser apparatus of the edge pumping structure, it is generally known that the beam shape (spot shape) of the focused pumping laser light provides a profound influence on the beam quality of the laser light (output laser light) emitted from the laser-diode pumped solid-state laser apparatus.

According to the laser-diode pumped solid-state laser apparatus700of the seventh embodiment thus provided with the solid-state laser crystal10that includes a uniaxial monocrystal of gadolinium vanadate (GdVO4) doped with Nd, which undergoes excitation by the pumping laser lights from the pumping laser diode LD, wherein Nd is doped with such a concentration profile that the concentration of Nd increases gently in the sloped shape from near zero concentration in the direction perpendicular to the laser oscillation direction (X-axis direction in the present example). As a result, it becomes possible to obtain a high-quality laser output without shaping the spot shape or optical intensity distribution for the pumping laser light. Thus, it becomes possible to provide a laser light output of high beam quality, without inviting increase of size of the solid-state laser apparatus.

While explanation has been made in the foregoing embodiments with regard to the case of using a disc-shaped (or chip-shaped) crystal for the solid-state laser crystal10, the present invention is by no means limited to such a specific example, and thus, the solid-state laser crystal10may also be the one having a rectangular plate shape as shown inFIGS. 17A and 17B, wherein the solid-state laser crystal10ofFIGS. 17A and 17Bmay be manufactured by cutting a periphery of a rod-shaped crystal ingot produced by a dual-die EFG process or μPD process, followed by a slicing process. Further, the solid-state laser crystal10may also have a polygonal shape.

While explanation has been made in the embodiments heretofore with regard to the case of using GdVO4for the material of the solid-state laser crystal10, the present invention is not limited to such a specific example and it is also possible to use a crystal of yttrium vanadate (YVO4) or other crystal.

Further, while explanation has been made in the embodiments heretofore with regard to the case of using Nd for the dopant element of the solid-state laser crystal10, the present invention is not limited to such a specific example and it is also possible to use other rare earth element or metal ions. Further, the concentration of the dopant element is not limited to 0.5 at %.

Further, while explanation has been made in each of the foregoing embodiments of using a uniaxial monocrystal for the solid-state laser crystal10, the present invention is not limited to such a specific construction and it is also possible to use a biaxial monocrystal.

Further, while explanation has been made in the foregoing embodiments for the ease of the solid-state laser crystal10has a thickness t of 0.5 mm, the diameter Da of 5 mm and the diameter db of 1 mm, the present invention is not limited to such a specific construction. The dimensions of the solid-state laser crystal10may be changed as needed according to the beam quality demanded for the output laser light.

FIG. 18shows a schematic construction of a laser printer1000as an image forming apparatus according to an embodiment of the present invention.

Referring toFIG. 18, the laser printer1000comprises an optical scanning apparatus900, a photosensitive drum901, an electrostatic charger902, a developing roller903, a toner cartridge904, a cleaning blade905, a sheet feed tray906, a sheet feed roller907, resist roller pairs908, a transfer charger911, discharging unit914, a fixing roller909, a sheet discharging roller912, a sheet discharging tray910, and the like.

The electrostatic charger902, the developing roller903, the transfer charger911, the discharging unit914and the cleaning blade905are disposed in the vicinity of the photosensitive drum901. Thereby, the electrostatic charger902, the developing roller903, the transfer charger911, the discharging unit914and the cleaning blade905are disposed in the order of: electrostatic charger902→developing roller903→transfer charger911→discharging unit914→cleaning blade905, along the rotating direction of the photosensitive drum901.

The photosensitive drum901carries thereon a photosensitive layer. In the present example, the photosensitive drum901rotates in the clockwise direction (arrow direction) within the plane ofFIG. 18.

The electrostatic charger902charges the surface of the photosensitive drum901uniformly.

The optical scanning apparatus900irradiates a modulated light upon the surface of the photosensitive drum901charged with the electric charger902with modulation based upon the image information from upper hierarchy apparatus such as personal computer. With this, there is formed a latent image corresponding to the image information on the surface of the photosensitive drum901. The latent image thus formed is moved in the direction of the developing roller903with rotation of the photosensitive drum905. It should be noted that the elongating direction of the photosensitive drum901(direction along the rotational axis) is called “main scanning direction” and the rotational direction of the photosensitive drum901is called “sub-scanning direction”. This construction of this optical scanning apparatus900will be explained later.

The toner cartridge904holds toners, and the toners are supplied therefrom to the developing roller903.

Thus, the developing roller903causes the toners supplied from the toner cartridge904to adhere to the latent image formed on the surface of the photosensitive drum901, and with this, development of the image information is attained. The latent image thus formed is moved in the direction of the transfer charger911with rotation of the photosensitive drum901.

The sheet feed tray906accommodates therein recording sheets913. Further, there is disposed a sheet feed roller907in the vicinity of the sheet feed tray906, and the sheet feed roller907picks up the recording sheet913one by one from the sheet feed tray906and supplies the same to the resist roller pair908. The resist roller pair908is disposed in the vicinity of the transfer roller911and holds the recording sheet913picked up by the sheet feed roller907temporarily and supplies the recording sheet to the gap between the photosensitive drum901and the transfer charger911in synchronization with the rotation of the photosensitive drum901.

Thereby, the transfer charger911is applied with a voltage of reverse polarity to the toners for attracting the toners on the surface of the photosensitive drum901to the recording sheet913electrically. With this voltage, the toner image on the surface of the photosensitive drum901is transferred to the recording sheet913. The recording sheet913thus transferred with the toner image is then forwarded to the fixing roller909.

With this fixing roller909, heat and pressure is applied to the recording sheet913and the toner image is fixed upon the recording sheet913. The recording sheet913thus fixed with the toner image is forwarded to the sheet discharge tray901via the sheet discharging roller912and is stuck upon the sheet discharge tray910one by one.

The discharging unit914discharges the surface of the photosensitive drum901.

The cleaning blade905removes the toner (residual toner) remaining on the surface of the photosensitive drum901. The residual toners thus removed are used again. After removal of the residual toners, the photosensitive drum901returns to the position of the electrostatic charger902.

Next, the construction and function of the optical scanning apparatus900will be explained with reference toFIG. 19.

The optical scanning apparatus comprises an optical source11, a coupling lens12, a modulator17, a cylindrical lens13, a polygonal mirror14, a fθ lens15a toroidal lens and a main controller not illustrated but used for controlling the foregoing various parts, wherein the optical source11includes a laser apparatus equivalent to any of the laser-diode pumped solid-state laser apparatus100-500and700explained previously.

The coupling lens12shapes the optical beam emitted from the optical source11to form a generally parallel light.

The modulator17turns on and off the optical beam passed through the coupling lens12.

The cylindrical lens13focuses the optical beam passed through the modulator17upon a reflection surface of the polygonal mirror14.

The polygonal mirror14has a right hexagonal pillar member of low profile and carries six deflection surfaces on the lateral side thereof. Further, the polygonal mirror14is rotated at a constant angular velocity in the direction of arrow indicated inFIG. 19. Thus, the optical beam emitted from the optical source11and is focused upon the deflection surface of the polygonal mirror14by the cylindrical lens13undergoes deflection with a constant angular velocity with rotation of the polygonal mirror14.

The fθ lens15has an image height proportional to the incident angle of the optical beam from the polygonal mirror14and causes the image plane of the optical beam deflected by the polygonal mirror14with the constant angular velocity with an equal speed in the main scanning direction.

The toroidal lens16focuses the optical beam passed through the fθ lens15on the surface of the photosensitive drum901.

As explained heretofore, according to the optical scanning apparatus900of the present embodiment, it becomes possible to scan the surface of the photosensitive drum901with high precision in view of the fact that the optical scanning apparatus900includes, for the optical source11thereof, a laser apparatus equivalent to any of the laser-diode pumped solid-state laser apparatuses100-500and700.

Further, according to the laser printer1000of the present embodiment, it becomes possible to form high-quality images in view of the fact that the laser printer1000includes the optical scanning apparatus900, which in turn includes a laser-diode pumped solid laser apparatus equivalent to any of the laser-diode pumped solid laser apparatuses100-500or700noted before.

Further, in the optical scanning apparatus900of the foregoing embodiment, the optical source11may include the foregoing laser apparatus in plural numbers. In such a case, it becomes possible to carry out plural scanning simultaneously, and as a result, it becomes possible to form images with high speed with the laser printer1000.

Further, with the foregoing embodiment, it is possible to use a MEMS (micro elector mechanical systems) mirror in place of the polygonal mirror14. In this case, the deflection direction of the optical beam is controlled by controlling the deflection angle of the MEMS mirror.

Further, while the foregoing embodiment has been explained for the case in which the image forming apparatus in the laser printer1000, the present invention is by no means limited to this specific application. In summary, it becomes possible to form high-quality images with stability by using the laser apparatus equivalent to any of the laser-diode pumped solid-state laser apparatuses100-500or700for the image forming apparatus.

Further, the image forming apparatus may be the one that includes a laser apparatus equivalent to any of the laser-diode pumped solid-state laser apparatuses100-700and irradiates the laser beam directly to the medium such as a sheet that shows coloring with laser irradiation.

FIG. 20shows a schematic construction of a laser display apparatus2000as a display apparatus according to an embodiment of the present invention.

The laser display apparatus2000comprises an optical source101, an optical system103including a mirror and directing a laser light from the optical source101to a screen104, and a control apparatus105for controlling the optical source101and the optical system103, wherein the optical source101includes a laser apparatus equivalent to any of the laser-diode pumped solid-state laser apparatuses100-700.

Thus, with the laser display apparatus2000of the present embodiment, it becomes possible to draw pictures or characters on the screen104with high quality as a result of use of any of the laser-diode pumped solid-state laser apparatuses100-700for the optical source of the laser light.

Further, with the use of the present invention also for the optical source101, it is possible to improve the display effect with the laser display apparatus that performs image display by laser lights penetrating through the space.

INDUSTRIAL APPLICABILITY

As explained heretofore, the laser-diode pumped solid-state laser apparatus can provide the laser light of excellent beam quality without inviting increase of size of the laser apparatus. Further, according to the optical scanning apparatus of the present invention, it becomes possible to scan a surface with high precision. Further, according to the image forming apparatus of the present invention, it becomes possible to form high-quality images. Further, according to the display apparatus of the present invention, it becomes possible to display information with high display quality.

Further, the present invention is by no means limited to the embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention.

The present invention is based on Japanese priority application No. 2006-178884 filed on Jun. 29, 2006, the entirety of which are incorporated herein as reference.