DE10312742A1 - Optically pumped semiconductor laser arrangement comprises vertically emitting laser having emitter layer producing radiation, and pumped beam source for optically pumping laser - Google Patents

Abstract

An optically pumped semiconductor laser arrangement comprises a vertically emitting laser (12) having an emitter layer producing radiation, and a pumped beam source (22) for optically pumping the laser. The laser has an absorber layer for the two-photon absorption of radiation from the radiation source whose wavelength is smaller than the doubled wavelength to excite two-photon transition in the absorber layer.

Description

The invention relates to an optical pumped semiconductor laser device with a vertically emitting Laser with a radiation-generating emitter layer, and a Pump radiation source for optical pumping of the vertically emitting Laser.

Optically pumped surface emitting semiconductor lasers are known as emitters infrared radiation with high beam quality. In trying such concepts for emission in the visible spectral range However, the difficulty arises that in the visible Spectral range no satisfactorily efficient semiconductor pump laser to disposal stand.

To address this problem, it has been proposed to introduce nonlinear optical elements into the external cavity of a vertically emitting infrared laser. For example, in the document US 5,991,318 an optically pumped vertical resonator semiconductor laser having a monolithic surface emitting semiconductor layer structure described. The optical pump radiation whose wavelength is smaller than that of the generated laser radiation is supplied in this apparatus by an edge-emitting semiconductor laser diode, which is externally arranged so that the pump radiation is irradiated obliquely from the front into the gain region of the surface-emitting semiconductor layer structure.

In the arrangement of US 5,991,318 is an optically nonlinear crystal and a birefringent filter introduced into the external resonator to obtain from the infrared output radiation of the vertically emitting semiconductor layer structure by frequency doubling radiation in the visible spectral range. In the preferred embodiment described therein, fifteen InGaAs active layers separated by InGaAsP interlayers are pumped at an excitation wavelength of 808 nm. The laser emission of the vertical emitter is set to 976 nm with the birefringent filter. An optically nonlinear LiB ₃ O ₅ crystal in the resonator generates frequency-doubled emission at 488 nm from this output radiation.

The present invention is the task is based, a generic semiconductor laser device indicate a laser emission in the visible or ultraviolet Spectral range with high beam quality allows.

This task is done by the optical pumped semiconductor laser device having the features of claim 1 solved. Advantageous embodiments and further developments of the semiconductor laser device according to the invention go from the subclaims 2 to 33.

In an optically pumped semiconductor laser device according to the invention is provided that at a semiconductor laser device of the aforementioned type of vertically emitting lasers an absorber layer for two-photon absorption of radiation of the pump radiation source whose wavelength is smaller is considered to double the laser wavelength to two-photon transitions in the To stimulate the absorber layer.

The invention is therefore based a two-photon absorption for pumping a vertically emitting semiconductor laser for a direct Laser emission in the visible spectral range, especially for direct green or to use blue laser emission. The invention goes in particular from the knowledge that the half wavelengths from available powerful infrared lasers, for example, at 808 nm or 940 nm, excellent for typical transitions of the semiconductor systems for direct green or blue emission match. Thus allows the optical pumping over a two-photon absorption a direct emission green or blue laser radiation optically pumped with infrared radiation Semiconductor components.

The vertically emitting semiconductor laser contains to at least one absorber layer, the pump radiation in two-photon processes absorbed and at least one emitter layer, in which the in collect charge carrier pairs generated by the absorber layers, recombine and one of the bandgaps emit appropriate radiation.

In a preferred embodiment the semiconductor laser device is provided that the emitter layer of the vertically emitting laser for the emission of radiation in the visible spectral range, especially in the green or blue spectral range is set up.

The pump radiation source emits prefers pump radiation in the infrared spectral range, causing the use more widespread and powerful Infrared laser allowed. An advantage is the pump radiation source in the invention by a diode laser, in particular by a High-power diode laser formed.

The emitter layer of the vertically emitting laser contains preferably GaN, AlGaN, InGaN, AlInGaN, AlN InN, ZnS, ZnSe, ZnCdS ZnCdSe ZnMgSe or ZnMgSSe. The absorber layer of the vertically emitting Lasers contains also prefers GaN, AlGaN, InGaN, AlInGaN, AlN InN, ZnS, ZnSe, ZnCdS ZnCdSe ZnMgSe or ZnMgSSe. However, it differs in the Usually the composition of the absorber layer of the composition the emitter layer so as to have a suitably smaller bandgap of Emitter layer to produce.

By pumping radiation sources with a wel For example, in the material system (In) GaN in the absorber layer transitions at 404 nm can be pumped, by pump radiation sources with a wavelength of 940 nm in the material system (In) GaN or in the material system Zn (Cd) Se transitions at 470 nm, or by pump radiation sources with a wavelength of 980 nm in the material system (In) GaN or in the material system Zn (Cd) Se transitions at 490 nm.

After such suggestions can be Green from the emitter layers or blue emission, for example at wavelengths above from 404 nm or above 460 nm in the material system (In) GaN or above 460 nm in the material system Zn (Cd) Se.

The emitter layer and / or the absorber layer The semiconductor laser device expediently has a quantum well or a multiple quantum well structure.

The quantum well layers of the single or multiple quantum well structure may also simultaneously Emitter and absorber layers act. This is for example then the case, if higher energetic conditions of a quantum well are excited by two-photon absorption and after relaxation to a lower level the laser emission from the same quantum well.

In a preferred embodiment the semiconductor laser device is provided that the vertical emitting laser has a highly reflective mirror layer. The highly reflective mirror layer can thereby with advantage be formed a distributed Bragg reflector. For certain arrangements but it may also be appropriate the highly reflective mirror layer as a subsequently applied form dielectric coating of the vertically emitting laser.

In this context is at a According to the invention semiconductor laser device preferably provided an external reflector, which together with the highly reflective mirror layer forms a laser resonator.

Especially high gain is achieved when the emitter layer or, if more than one emitter layer are provided, a plurality of emitter layers arranged in such areas are in which the field strength of the resonator standing field is maximum.

According to an advantageous development contains the vertical emitting laser of the semiconductor laser device more Emitter layers that are spaced apart in the vertical direction the half the laser wavelength equivalent. This can be ensured in a simple manner that the Field intensity maxima of the resonator standing just coincide with the positions of the emitter layers.

In the laser resonator are in preferred embodiments one or more further optical elements arranged, in particular an optically non-linear crystal, a modulator, an etalon or a birefringent filter.

For example, in the laser resonator with Advantage of an optically nonlinear crystal for frequency doubling the laser wavelength be provided in the ultraviolet spectral range. This will an optically pumped semiconductor laser with high beam quality and with Emission created in the UV.

In a preferred embodiment is in a semiconductor laser device according to the invention for frontal pumps provided that the Pump radiation source is arranged so that the pump radiation under a Angle φ, with 0 <φ <90 °, on the emitting surface of the vertically emitting laser hits. The angle φ represents while the angle between the incident pump beam and the normal on the emitting surface of the vertically emitting laser.

The emitter layer and the absorber layer of the vertically emitting lasers are preferred in frontal pumping Applied to a silicon carbide substrate to ensure good heat dissipation to ensure heat loss generated by non-radiative processes.

To an increased utilization of the pump radiation to reach is according to one preferred embodiment of the arrangement for frontal pumping a provided with the pump light source cooperating optical arrangement, the pump radiation two or repeatedly through the absorber layer leads. In the simplest case can the optical arrangement consist only of a mirror, the reflected by the vertically emitting laser portion of Pump radiation reflected back to the vertical emitter and a second Engage in the absorber layer.

According to another preferred embodiment is in a semiconductor laser device according to the invention to the back Pumps provided that the Emitter layer and the absorber layer of the vertically emitting Lasers on a for the pump radiation transparent substrate are applied, and that the pump radiation source is arranged so that the Pump radiation at an angle φ, with 0 <= φ <90 °, on the rear surface of the substrate. The angle φ represents the Angle between the incident pump beam and the normal the substrate surface represents.

In the case of the rear-side pumping of the vertically emitting Lasers, the substrate is preferred by a highly transparent sapphire substrate or an undoped, transparent SiC substrate.

In a preferred refinement, the pump radiation source of the semiconductor laser device pumped on the front or on the back can have an external pump resonator which contains an active element (= the semiconductor element to be pumped) inside the resonator. It can also be provided with advantage that the pump radiation source resonantly is coupled to a high-quality external pump resonator, wherein the external pump resonator contains an active element.

In a further preferred embodiment is in a semiconductor laser device according to the invention the pump radiation source for laterally pumping the vertically emitting Laser arranged and couples pump radiation over a first side surface of the vertically emitting laser in the absorber layer.

To increase and bundle in the semiconductor laser ongoing radiation intensity For example, the vertically emitting laser may include waveguide layers in this case for lateral guidance having the coupled pump radiation.

In addition, one of the first side surface across from lying second side surface of the vertically emitting laser for reflection of the pump radiation be mirrored so that a Double passage of the pump radiation through the active medium achieved becomes.

Particularly efficient is the suggestion if the pump radiation source has an external pump resonator, through an end facet of the pump radiation source and the mirrored second side surface of the vertically emitting laser is formed. The available Performance can be through this measure elevated become.

In a particularly preferred embodiment is a second pump radiation source for lateral pumping of the vertical emissive laser provided, the pump radiation over a third side surface of the vertically emitting laser is coupled into the absorber layer, around an overlap area with form the radiation of the first pump radiation source. In the overlap area doubles at the same pump power of the two pump radiation sources the intensity and leads so to a significantly increased Two-photon absorption.

Also in this context can be provided with advantage that a the third side surface across from lying fourth side surface of the vertically emitting laser for reflection of the pump radiation is mirrored. The second pump radiation source can also have a external pump resonator passing through an end facet of the second Pump radiation source and the mirrored fourth side surface of the vertically emitting laser is formed.

It is understood that more can be provided as two pump radiation sources to particularly large intensities in the intersection of the beam paths to obtain. For example, the vertically emitting laser executed in the form of a hexagon be in that over three side surfaces pump radiation is coupled, and in which the three opposite each faces are mirrored.

According to another preferred Embodiment of the invention is the vertically emitting laser for the Pump radiation formed as a resonator of high quality, in which the Pumping radiation is resonant coupled.

Further advantageous embodiments, Features and details of the invention will become apparent from the dependent claims, the Description of the embodiments and the drawings.

The invention will be described below of exemplary embodiments explained in more detail in connection with the drawings. There are only each the for the understanding the invention essential elements shown.

It shows

1 a schematic representation of a frontally optically pumped semiconductor laser device according to an embodiment of the invention;

2 a schematic representation of a frontally optically pumped semiconductor laser device according to another embodiment of the invention;

3 a schematic representation of a backside optically pumped semiconductor laser device according to another embodiment of the invention;

4 a schematic representation of a laterally optically pumped semiconductor laser device according to yet another embodiment of the invention; and

5 a schematic plan view of a laterally optically pumped semiconductor laser device according to yet another embodiment of the invention.

1 shows a schematic representation of a two-photon pumped semiconductor laser device 10 according to an embodiment of the invention. The frontally pumped semiconductor laser device 10 contains a vertically emitting disk element 12 , a pump laser 22 whose pump radiation 28 through the pumping optics 24 on the disk element 12 is bundled and an external resonator mirror 26 , In the exemplary embodiment, the pump laser 22 formed by a high power diode laser with an emission wavelength of 808 nm.

The disc element 12 includes a good heat dissipating SiC substrate 14 and a Bragg mirror 16 which is formed by a layer sequence which represents a highly reflective mirror layer for the emission wavelength. Above the Bragg mirror 16 is an area of active layers 18 grown, which contains the pump radiation directed absorber layers and aligned to the emission wavelength emitter layers.

In the exemplary embodiment, absorber and emitter layers are each formed by multiple quantum well structures based on the InGaN material system and for two-photon excitation ei transition at 404 nm (corresponding to two 808 nm photons) and designed for emission in the blue spectral range above 404 nm. On the active layer area is an optical dielectric coating 20 applied.

The external resonator mirror 26 forms together with the Bragg mirror 16 in a conventional manner, a laser resonator for the radiation field 30 from which the blue laser radiation 32 of the semiconductor laser is coupled out. In the resonator, further optical elements, for example for the exact adjustment of the laser wavelength or for mode selection, can be introduced in a manner known per se to those skilled in the art.

2 shows another embodiment of a front-pumped semiconductor laser device according to the invention. In this embodiment, the pump laser is 22 formed by a high-power laser diode emitting at 940 nm, which induces transitions in the InGaN absorber layers at 470 nm (corresponding to two 940 nm photons).

In addition to the already at 1 described elements is another external mirror 34 provided that of the disc element 12 reflected pump radiation 36 on the disk element 12 reflected back. The pump radiation can thus pass through the absorber layers several times in order to achieve high efficiency.

In addition, it is in the mirror 16 and 26 formed resonator arranged an optically non-linear BBO (beta barium borate) crystal, which frequency doubles the output radiation generated by the emitter layers, so that out of the resonator ultraviolet radiation of high beam quality can be coupled out. Of course, other nonlinear crystal such as KBO (KB ₅ O ₈ : 4H ₂ O, potassium pentaborate tetrahydrate) or DADA (ND ₄ D ₂ AsO ₄ , deuterated ammonium dihydrogen arsenate) can be used instead of the BBO crystal.

An embodiment with back pumping is in the 3 shown. The radiation 28 of the pump laser 22 falls perpendicularly (φ = 0) on the surface of the substrate 40 on. In order to minimize losses due to absorption of the pump radiation, the layer sequence of the disk element is 12 of the 3 on a highly transparent sapphire substrate 40 grew up. The substrate 40 is preferably with an antireflection coating 52 provided for the pump radiation.

4 shows an embodiment of a lateral pumping arrangement according to the invention. The as a pump laser 22 The high power laser diode used emits at 980 nm and pumps transitions at 490 nm in the Zn (Cd) Se absorber layers of the disk element 12 into which they have a side surface 45 of the disk element is coupled. The area of active layers containing the absorber layers and the emitter layers 18 is in this embodiment between two waveguide layers 42 and 44 including the pump radiation in the active area 18 to lead. Preferably, the waveguide layers are formed as ridge or ridge waveguide.

The endface 46 of the disk element 12 is mirrored to pass twice the pump radiation through the active area 18 to reach.

The mirrored end face 46 and an end facet 48 of the pump laser 22 form in a particularly preferred embodiment form an external resonator in which then a particularly high pump power for the two-photon absorption is available.

Another embodiment of the invention is in 5 shown. The lateral pumping arrangement of 5 is analogous to the one in 4 constructed described lateral pumping arrangement, but instead of a pump source contains two similar pump radiation sources 22 and 22A , whose pump radiation each have an optic 24 respectively. 24A on two adjoining side surfaces 45 respectively. 45A of the disk element 12 is coupled.

In the overlap area 50 the two pump beam paths results in a particularly high radiation intensity. To further increase the pumping intensity, in each case the side surfaces lying opposite the coupling surfaces 46 and 46A of the disk element 12 mirrored, so that each pump beam passes through the active medium at least twice.

It is understood that the in the description, in the drawings and in the claims disclosed Features of the invention both individually and in every possible Combination for the realization of the invention may be essential.

Claims (33)

Optically pumped semiconductor laser device comprising - a vertically emitting laser ( 12 ) with a radiation-generating emitter layer, and - a pump radiation source ( 22 ) for optically pumping the vertically emitting laser ( 12 ), characterized in that - the vertically emitting laser ( 12 ) has an absorber layer for two-photon absorption of radiation of the pump radiation source whose wavelength is smaller than twice the laser wavelength to excite two-photon transitions in the absorber layer. Semiconductor laser device according to Claim 1, characterized in that the emitter layer of the vertically emitting laser ( 12 ) is arranged to emit radiation in the visible spectral range, in particular in the green or blue spectral range. Semiconductor laser device according to claim 1 or 2, characterized in that the pump radiation source ( 22 ) Emits radiation in the infrared spectral range. Semiconductor laser device according to one of the preceding claims, characterized in that the pump radiation source ( 22 ) is formed by a diode laser, in particular by a high-power diode laser. Semiconductor laser device according to one of the preceding claims, characterized in that the emitter layer of the vertically emitting laser ( 12 ) GaN, AlGaN, InGaN, AlInGaN, AlN InN, ZnS, ZnSe, ZnCdS ZnCdSe ZnMgSe or ZnMgSSe. Semiconductor laser device according to one of the preceding claims, characterized in that the absorber layer of the vertically emitting laser ( 12 ) GaN, AlGaN, InGaN, AlInGaN, AlN InN, ZnS, ZnSe, ZnCdS ZnCdSe ZnMgSe or ZnMgSSe. Semiconductor laser device according to one of the preceding Claims, characterized in that the Emitter layer a quantum well or a multiple quantum well structure having. Semiconductor laser device according to one of the preceding Claims, characterized in that the Absorber layer a quantum well or a multiple quantum well structure having. A semiconductor laser device according to claim 7 or 8, characterized in that the Quantum well layers of single or multiple quantum well structure simultaneously act as emitter and absorber layers. Semiconductor laser device according to one of the preceding claims, characterized in that the vertically emitting laser ( 12 ) a highly reflective mirror layer ( 16 ) having. Semiconductor laser device according to Claim 10, characterized in that the highly reflective mirror layer ( 16 ) is formed by a distributed Bragg reflector. Semiconductor laser device according to Claim 10, characterized in that the highly reflective mirror layer ( 16 ) by a dielectric coating of the vertically emitting laser ( 12 ) is formed. Semiconductor laser device according to one of Claims 10 to 12, characterized in that an external reflector ( 26 ) is provided, which together with the highly reflective mirror layer ( 16 ) forms a laser resonator. A semiconductor laser device according to claim 13, characterized characterized in that Emitter layer or possibly more emitter layers in such Are arranged areas in which the field strength of the resonator standing field is maximum. Semiconductor laser device according to Claim 13 or 14, characterized in that the vertically emitting laser ( 12 ) contains a plurality of emitter layers having a distance in the vertical direction, which corresponds to half the laser wavelength. Semiconductor laser device according to one of Claims 13 to 15, characterized in that in the laser resonator ( 16 . 26 ) one or more further optical elements ( 38 ), in particular an optically nonlinear crystal, a modulator, an etalon or a birefringent filter. Semiconductor laser device according to claim 16, characterized in that in the laser resonator ( 16 . 26 ) an optically nonlinear crystal ( 38 ) is provided for frequency doubling the laser wavelength in the ultraviolet spectral range. Semiconductor laser device according to one of the preceding claims, characterized in that the pump radiation source ( 22 ) is arranged so that the pump radiation ( 28 ) at an angle φ, where 0 <φ <90 °, on the emitting surface of the vertically emitting laser ( 12 ) meets. Semiconductor laser device according to claim 18, characterized in that the emitter layer and the absorber layer of the vertically emitting laser ( 12 ) on a silicon carbide substrate ( 14 ) are applied. Semiconductor laser device according to claim 18 or 19, characterized in that one with the pump radiation source ( 22 ) cooperating optical arrangement ( 34 ) is provided, the pump radiation in cooperation with a highly reflective mirror layer ( 16 ) passes two or more times through the absorber layer. Semiconductor laser device according to one of Claims 1 to 17, characterized in that the emitter layer and the absorber layer of the vertically emitting laser ( 12 ) on a substrate transparent to the pump radiation ( 40 ) are applied, and the pump radiation source ( 22 ) is arranged so that the pump radiation ( 28 ) at an angle φ, where 0 <= φ <90 °, on the back surface of the substrate ( 40 ). Semiconductor laser device according to Claim 21, characterized in that the substrate ( 40 ) is formed by a highly transparent sapphire substrate or an undoped, transparent silicon carbide substrate. Semiconductor laser device according to Claim 21 or 22, characterized in that the substrate ( 40 ) on its rear surface with an antireflection coating ( 52 ) is provided. Semiconductor laser device according to one of Claims 18 to 23, characterized in that the pump radiation source ( 22 ) has an external pump resonator, which contains an active element inside the resonator. Semiconductor laser device according to one of Claims 18 to 23, characterized in that the pump radiation source ( 22 ) is resonantly coupled to an external high-quality pump resonator, the external pump resonator containing an active element. Semiconductor laser device according to one of Claims 1 to 17, characterized in that the pump radiation source ( 22 ) for laterally pumping the vertically emitting laser ( 12 ) is arranged and pump radiation over a first side surface ( 45 ) of the vertically emitting laser ( 12 ) is coupled into the absorber layer. Semiconductor laser device according to Claim 26, characterized in that the vertically emitting laser ( 12 ) Waveguide layers ( 42 . 44 ) for lateral guidance of the coupled pump radiation. Semiconductor laser device according to Claim 26 or 27, characterized in that one of the first side surfaces ( 45 ) opposite the second side surface ( 46 ) of the vertically emitting laser ( 12 ) is mirrored to reflect the pump radiation. Semiconductor laser device according to Claim 28, characterized in that the pump radiation source ( 22 ) has an external pump resonator, which by an end facet ( 48 ) of the pump radiation source ( 22 ) and the mirrored second side surface ( 46 ) of the vertically emitting laser ( 12 ) is formed. Semiconductor laser device according to one of Claims 26 to 29, characterized in that a second pump radiation source ( 22A ) for laterally pumping the vertically emitting laser ( 12 ) is provided, the pump radiation over a third side surface ( 45A ) of the vertically emitting laser ( 12 ) is coupled into the absorber layer to form an overlap region ( 50 ) with the radiation of the first pump radiation source ( 22 ) to build. Semiconductor laser device according to claim 30, characterized in that one of the third side surfaces ( 45A ) opposite fourth side surface ( 46A ) of the vertically emitting laser ( 12 ) is mirrored to reflect the pump radiation. Semiconductor laser device according to Claim 31, characterized in that the second pump radiation source ( 22A ) has an external pump resonator, which by an end facet of the second pump radiation source ( 22A ) and the mirrored fourth side surface ( 46A ) of the vertically emitting laser ( 12 ) is formed. Semiconductor laser device according to one of Claims 26 to 32, characterized in that the vertically emitting laser ( 12 ) is designed for the pump radiation as a resonator of high quality, in which the pump radiation is resonantly coupled.