Vertical cavity surface emitting laser (VCSEL) arrays pumped solid-state lasers

• US 20060245460A1
• Filed: 04/28/2006
• Published: 11/02/2006
• Est. Priority Date: 04/29/2005
• Status: Active Grant

• Current Assignee: Pavilion Integration Corporation
• Original Assignee: Pavilion Integration Corporation
• Inventors: Luo, Ningyi, Zhu, Sheng-Bai
• Granted Patent: US 7,430,231 B2
• Time in Patent Office: Days
• US Class Current: 372/70
• CPC Class Codes: H01S 3/025 of solid state lasers, e.g. housings or mountings
• CPC Class Codes: H01S 3/08054 Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation quarter-wave plates in a Q-switch laser H01S3/1124, H01S3/115
• CPC Class Codes: H01S 3/094084 with pump light recycling, i.e. with reinjection of the unused pump light, e.g. by reflectors or circulators
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/1083 using parametric generation
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 3/1312 by controlling the optical pumping
• CPC Class Codes: H01S 3/161 holmium
• CPC Class Codes: H01S 3/1611 neodymium
• CPC Class Codes: H01S 3/1618 ytterbium
• CPC Class Codes: H01S 3/1653 YLiF4(YLF, LYF)
• CPC Class Codes: H01S 3/1673 YVO4 [YVO]

Abstract

Solid-state lasers pumped by incoherent or partially coherent, monochromatic light sources such as high power VCSEL arrays. Efficient and uniform injection of pumping energy into gain medium is achieved through spectral match of the pump source with the gain medium absorption and multi-bounce reflections of unabsorbed pump light in a diffusing pump chamber. One preferred embodiment of the diffusing pump chamber is a hollow cylinder coaxially surrounding the gain medium. One or more transparent windows, slit-shaped or otherwise, for transmission of pump light are evenly distributed around the perimeter of the chamber and are parallel to the axis. Another preferred embodiment of the diffusing pump chamber is a highly reflecting compound parabolic concentrator. A 2-D VCSEL array is employed as the pump source and the gain medium is located at the focusing point of the chamber. This invention demonstrates solid-state lasers that are compact, robust, low-cost, and able to produce high power output in CW or pulse modes for practical applications. An important application of the present invention is high-power solid-state lasers featuring wavelength conversion such as optical parametric oscillation and second-harmonic generation. Another important application of the present invention is injection seeding, especially for pulse mode with high repetition rates.

Claims

1. A laser device comprising:

a lasing element having an active gain medium that generates laser light in response to incoherent or partially coherent, monochromatic excitation light;

a pump assembly for generation and efficient injection of incoherent or partially coherent, monochromatic excitation light into said lasing element; and

a housing assembly, containing the lasing element and the pump assembly;

said housing assembly physically protects the laser system and effectively dissipates the heat generated during laser operation;

said pump assembly further comprising;

an excitation element having at least one array of vertical cavity surface emitting lasers (VCSEL) for generating incoherent or partially coherent, monochromatic excitation light;

a diffusing pump chamber, which is interposed between the excitation element and the lasing element, to enhance the effect of the excitation light on the lasing element;

a set of optical elements for effective delivery of the excitation light into the diffusing pump chamber.

2. The laser device according to claim 1 further comprising:

an optical resonator, composed of at least two mirrors, for producing a laser beam from the stimulated emission generated by the lasing element;

such that when the excitation element outputs at least 1 W/cm² excitation light, a sufficient portion of that excitation light is absorbed by the lasing element, resulting in a laser light being generated by the lasing element wherein it is resonated through the effect of the optical resonator.

3. The laser device according to claim 1 further comprising:

a power supply, electrically connected to the excitation element, for energizing the excitation element to produce the excitation light.

4. The laser device according to claim 3 further comprising:

a pulse controller for producing pulses of excitation light from the excitation element such that pulses of laser light are produced from the lasing element.

5. The laser device according to claim 1, wherein

the diffusing pump chamber is interposed between the excitation element and the lasing element, has one or more transmitting window(s), slit-shaped or otherwise for effective delivery of the excitation light;

said transmitting window(s) are coated anti-reflectively to the pump wavelength; and

the rest part of the inner surface of the diffusing pump chamber is coated with highly diffuse reflective materials.

6. The laser device according to claim 5, wherein

the diffusing pump chamber is a glass tube, its outer surface, except for transmitting windows, is coated with highly diffuse reflective materials;

water or other index-matching coolant transparent to the pump wavelength is circulated within the diffusing pump chamber surrounding the lasing element for removing excessive heat;

Alternatively, the space between the gain medium and the inner surface of the glass tube may be filled with transparent solid-state materials with high thermal conductivity;

Still alternatively, the solid-state filler may contain micro-channels for enhancing heat dissipation.

7. The laser device according to claim 5, further comprising one or more lens system(s) interposed between the vertical cavity surface emitting laser array(s) and the transmitting window(s) of the diffusing pump chamber for directing the pump beam into said diffusing pump chamber;

said lens system(s) can be separate elements or integrated microlenses;

the transmitting windows can be part or whole of the lens system(s).

8. The laser device according to claim 1, wherein

the diffusing pump chamber is a highly reflecting compound parabolic concentrator with one or more parabolic section(s);

wherein

the lasing element is located at the focus point of the diffusing pump chamber; and

the pump source is a two-dimensional VCSEL array.

9. The laser device according to claim 1, wherein

the lasing element has a host lattice selected from the group consisting of:

oxides, garnets, aluminates, oxysulfides, phosphates, silicates, tungstates, molybdates, vanadates, beryllates, fluorides, sapphire, forsterite, chrysoberyl, glasses, and ceramics.

10. The laser device according to claim 9 wherein

the lasing element host material is doped with active ions selected from the group consisting of:

Ti, Cu, Co, Ni, Cr, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Yb, and actinide ions.

15. A high-power solid-state laser system comprising:

an active gain medium surrounded by the pump assembly according to claim 1 for side-pump;

an optical resonator for establishing laser oscillation at selected wavelength and polarization;

one or more additional components for achievement of desired laser operation.

16. The high-power solid-state laser system according to claim 15 wherein:

said additional components include a seed laser, which injects signal into the active gain medium for spectral and temporal mode control, and a mechanism for optical coupling, which extracts laser output generated from the active gain medium and isolates the seed laser from fed-back light.

17. The high-power solid-state laser system according to claim 15 wherein:

said additional components include at least one nonlinear optical crystal, which is situated in the laser path for intracavity wavelength conversion, and a mechanism for selection of desired laser polarization and/or wavelength and suppression of undesired lasing;

selection of laser polarization and/or wavelength is achieved by natural birefringence of the active gain medium and/or nonlinear optical crystal or otherwise by a birefringent crystal sandwiched in between the active gain medium and nonlinear optical crystal;

suppression of undesired lasing is realized through walk-off of extraordinary beam in birefringent crystal.

18. The high-power solid-state laser according to claim 17, wherein

said nonlinear optical crystal is for optical parametric oscillation;

said birefringent crystal is for eliminating interference between the signal and the idler to realize singly-resonant optical parametric oscillation.

19. The high-power solid-state laser according to claim 17 wherein:

said nonlinear optical crystal is for harmonic generation.

20. The high-power solid-state laser according to claim 15 further comprising a Q-switch element for producing high-power laser pulses.

11. A method of generating pump light comprising the steps of:

generating incoherent or partially coherent, monochromatic excitation light through the action of an excitation element having at least one vertical cavity surface emitting laser array providing excitation light of at least 1 W/cm²; and

directing the excitation light to a lasing element having an active medium.

12. The method according to claim 11 further comprising the step(s) of:

enhancing effects of the incoherent or partially coherent, monochromatic excitation light on the active medium, through the action of a diffusing pump chamber and beam-shaping elements.

13. The method according to claim 11 further comprising a mechanism of:

enhancing delivery of the incoherent or partially coherent, monochromatic excitation light;

the light delivery enhancing mechanism includes integrated microlens systems;

the light delivery enhancing mechanism includes lens-type transmitting windows;

the light delivery enhancing mechanism includes external coupling lenses.

14. The method according to claim 11 wherein the generated incoherent or partially coherent, monochromatic excitation light has a pulse duration effectively matching an upper-state lifetime of the active medium, said method further comprising the steps of:

generating pulses of excitation light from the excitation element such that pulses of laser light are produced in the optical resonator;

enhancing pumping power at a given average value; and

generating laser pulses having a repetition rate inversely proportional to the upper state lifetime.