Patent Application
20070223553
The present invention concerns amplified laser systems having a single optical pump. In particular, these amplified laser systems may use a single optical pump to pump a laser oscillator and one or more laser amplifiers.
Many laser systems use an oscillator-amplifier architecture. For example, a short-pulse regenerative amplifier laser has a laser oscillator that generates a short pulse train by mode-locking. The pulse train typically has a pulse frequency (repetition rate) in tens to hundreds of megahertz, and the pulse energy is typically in the picojoule to nanojoule range. For many applications it is desirable to increase the pulse energy to microjoule to millijoule levels. The regenerative amplifier selects one pulse from the pulse train and injects the selected pulse into another laser cavity that traps the pulse for amplification. When the pulse energy of the pulse reaches a desired level, or saturation, the pulse is dumped out of the regenerative amplifier. This process is repeated at a lower frequency, typically on the order of one kilohertz to tens of kilohertz. The result is a laser output with much higher pulse energy at lower pulse frequency than the output signal of the oscillator.
Presently, many laser oscillator-amplifier systems are pumped by laser diodes. Furthermore, many systems use fiber-coupled laser diodes as optical pumps. Lasers pumped by fiber-coupled laser diodes may offer many advantages over those pumped by direct laser diodes, such as circular pump beams for better mode matching and ease of optical pump replacement.
The laser oscillator-amplifier systems that are pumped by fiber-coupled laser diodes use separate laser diodes to pump the laser oscillator and the laser amplifier. This is done because the desired pump power and pump beam profile in the gain material are typically different for the laser oscillator and the laser amplifier. For example, a laser oscillator may require 1 W of pump power and a beam size of 200 microns in the laser gain medium, while a laser amplifier used in conjunction with this laser oscillator may require 10 W of pump power and a beam size of 800 microns in the gain medium. To achieve these power levels and beam sizes, two fiber-coupled laser diodes are used: one low-power laser diode with a fiber core diameter of 100 microns delivering 1 W of power; and another high-power laser diode with fiber core diameter of 400 microns delivering 10 W of power.
An exemplary embodiment of the present invention is an optically-pumped, amplified laser source including a single optical pump. The laser source includes: an optical pump to generate pump light; a laser oscillator adapted to generate laser light when irradiated with light having the pump wavelength; a laser oscillator adapted to generate laser light when irradiated with light having the pump wavelength; a laser amplifier optically coupled to the laser oscillator to receive the laser light generated by the laser oscillator; and beam splitting optics optically coupled to the optical pump, the laser oscillator, and the laser amplifier. The pump light generated by the optical pump includes a pump power level and a predetermined pump wavelength and the laser light generated by the laser oscillator has a laser wavelength. The laser amplifier is adapted to amplify light that has the laser wavelength when irradiated with light having the pump wavelength. The beam splitting optics couple a first portion of the pump light having a first fraction of the pump power level into the laser oscillator and a second portion of the pump light having a second fraction of the pump power level into the laser amplifier.
Another exemplary embodiment of the present invention is a method of optically-pumping an amplified laser source using a single optical pump. Pump light having a pump power level is generated using the single optical pump. The pump light is split into a first portion having a first fraction of the pump power level and a second portion having a second fraction of the pump power level. The first portion of the pump light is coupled into a laser oscillator to generate laser light. The second portion of the pump light and the laser light are coupled into a laser amplifier to amplify the laser light. The amplified laser light is emitted from the laser amplifier.
A further exemplary embodiment of the present invention is an optically-pumped, amplified laser source including a single optical pump. The laser source includes: an optical pump to generate pump light; a laser oscillator adapted to generate laser light when irradiated with light having the pump wavelength; a laser oscillator adapted to generate laser light when irradiated with light having the pump wavelength; a laser amplifier optically coupled to the laser oscillator to receive the laser light generated by the laser oscillator; and fiber optics optically coupled to the optical pump, the laser oscillator, and the laser amplifier. The pump light generated by the optical pump includes a pump power level and a predetermined pump wavelength and the laser light generated by the laser oscillator has a laser wavelength. The laser amplifier is adapted to amplify light that has the laser wavelength when irradiated with light having the pump wavelength. The fiber optics include: an input fiber section optically coupled to the optical pump; a first output fiber section optically coupled to the laser oscillator; a second output fiber section optically coupled to the laser amplifier; and a fiber splitter. The fiber splitter couples a first portion of the pump light having a first fraction of the pump power level from the input fiber section into the first output fiber section, and a second portion of the pump light having a second fraction of the pump power level from the input fiber section into the second output fiber section.
The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:
The present invention involves a laser oscillator-amplifier system pumped by a single optical pump, such as a single fiber-coupled high-power laser diode. Compared to conventional laser systems that use separate laser diodes for oscillator and amplifier, the present invention reduces the cost and complexity of the laser system and simplifies its operation significantly.
Exemplary embodiments of the present invention involve exemplary laser oscillator-amplifier systems pumped by single optical pumps. In one exemplary embodiment this may be realized by the use of a fiber splitter with the desired power ratio and fiber core sizes to couple the optical pump into the laser oscillator and the laser amplifier. In other exemplary embodiments, planar waveguide and free space optics may be used to split the pump light power and shape the pump beams coupled into the laser oscillator and the laser amplifier.
The exemplary embodiment of
Fiber splitter 210 has one input end to receive pump light from optical pump 204 and two output ends to couple first and second portions of the pump light into laser oscillator 110 and laser amplifier 124, respectively. Such a fiber splitter may be made by fusing two fibers, with one end of one fiber to the side of the other fiber. A fiber splitter may also be made by a special splitting/coupling joint. The fiber splitter is desirably designed such that the output power and cross sectional pump beam profile coupled into laser oscillator 110 from the first fiber output end are matched to the laser oscillator for efficient pumping of the laser oscillator and the output power and cross sectional pump beam profile coupled into laser amplifier 124 from the second fiber output end are matched to the laser amplifier for efficient pumping of the laser amplifier. As noted above, the fraction of the pump power level and the area of the cross sectional pump beam profile of the portion of the pump light coupled into the laser amplifier are typically larger than the fraction of the pump power level and the area of the cross sectional pump beam profile of the portion of the pump light coupled into the laser oscillator.
Laser oscillator 110 is adapted to generate laser light, having a predetermined laser wavelength, when its gain medium is irradiated with light that has the pump wavelength. The gain medium of the laser oscillator may be a solid state gain material, such as Nd:YAG or Ti:Sapphire, a laser dye, or a gaseous gain material. Laser oscillator 110 may be any sort of optically pumped laser oscillator. For example, the laser oscillator may a traveling wave ring laser oscillator, a standing wave ring laser oscillator, or a Fabry-Perot cavity laser oscillator. Also, the laser oscillator may operate as a single mode or a multimode laser oscillator. Additionally, the laser oscillator may be either a continuous wave laser oscillator or a pulsed laser oscillator.
Laser amplifier 124 is optically coupled to the laser oscillator via beam path 112 to receive the laser light generated by laser oscillator 110. It is noted that optical isolator 212 may be included in beam path 112 between the laser oscillator and the laser amplifier to reduce the amount of stray laser light that is coupled into the laser oscillator due to reflections off of, or leakage through, the laser light input port of laser amplifier 124. Laser amplifier 124 is adapted to amplify light having the laser wavelength when irradiated with light having the pump wavelength (i.e. when pumped). This laser amplifier may be a single pass laser amplifier or a multipass laser amplifier. Laser light is transmitted out of laser amplifier 124 through a laser light output port.
In the exemplary embodiment of
As with the gain medium of the laser oscillator described above, the gain medium of the laser amplifier may be a solid state gain material, laser dye, or a gaseous gain material. The gain media in the laser oscillator and the laser amplifier are the same.
The first portion of the pump light is coupled into the laser oscillator to generate laser light, step 404. The coupled pump light desirably has a predetermined cross sectional pump beam profile. The second portion of the pump light is coupled into the laser amplifier along with the laser light generated by the laser oscillator to amplify the laser light, step 406. This coupled pump light also desirably has a predetermined cross sectional pump beam profile. The desired power level and cross sectional area of pump beam profile of the pump light coupled into the laser amplifier are typically larger than the desired power level and cross sectional area of pump beam profile of the pump light coupled into the laser oscillator. The amplified laser light is then emitted from the laser amplifier, step 408.
To illustrate the present invention, an exemplary Nd:YLF laser source containing a laser oscillator and a regenerative laser amplifier may be described with reference to
It is desirable for at least one of the output fibers to have the same core diameter and numerical aperture as that of the input fiber to minimize loss in fiber splitting. However, this is not necessary. Additionally, it may be difficult to make a fiber splitter with the exact specified splitting ratio. Fortunately, laser oscillators may typically accept a range of pump power levels without significantly affecting their performance. For example, the Nd:YLF laser oscillator in this example may be designed to operate with 3-6 W of pump power. In this case, an exact splitting ratio is not critical for the design of the fiber splitter.
One advantage of exemplary embodiments of the present invention is reduced system complexity and simplified operation. With one optical pump, and the associated components used to operate that optical pump eliminated, the system becomes simpler and more compact. It may also be more reliable because the number of active optical and electronic components is reduced. Thus, there are fewer components to fail. Another advantage may be cost savings. Exemplary embodiments of the present invention eliminate one optical pump source of lower output power, which includes a fiber-coupled laser diode, a laser diode driver, a temperature control device such as a thermoelectric cooler (TEC) and controller.
The present invention includes a number of exemplary amplified laser sources and methods of operating these laser sources. Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.
