Patent Application
20150117477
Embodiments relate to Q-switching, and, more particularly, to a laser apparatus and method for generating optical pulses based on Q-switching controllable with a two-dimensional (2-D) spatial light modulator.
Q-switching, sometimes referred to as giant pulse formation, is a technique by which a laser can be configured to generate a pulsed output beam. The technique allows generation of light pulses having relatively high peak power, much higher than would be produced by the same laser if it were operating in a continuous wave (constant output) mode. Some switches involve mechanical designs that inhibit laser action during the optical pumping cycle by blocking the light path, causing a mirror misalignment, or reducing the reflectivity of one of the resonator mirrors in the laser cavity. For example, at some point of a flashlamp pulse, when maximum energy has been stored in a laser rod, a high Q-condition may be established and a Q-switch pulse is emitted from the laser. Mechanical Q-switches are relatively slow and bulky. Moreover, mechanical wear generally requires burdensome and costly maintenance. Electro-optic or acousto-optic devices have been proposed for Q-switching. However, some of these devices may suffer from certain drawbacks for infrared applications, such as applications in the mid-wavelength infrared (MWIR) frequency range. Accordingly, there continues to be a need for improved laser apparatuses and/or techniques useful for generation of optical pulses based on Q-switching.
Embodiments relate to a laser apparatus and method for generating optical pulses. The laser apparatus may comprise a laser cavity and a spatial light modulator including a two dimensional array of pixels arranged to provide Q-switching at a pixel level in the laser cavity. A controller is connected to the spatial light modulator (SLM) to temporally and spatially modulate the two-dimensional array of pixels to selectively control the Q-switching provided by the spatial light modulator.
The method allows performing Q-switching at a pixel level in a laser cavity with a spatial light modulator comprising a two-dimensional array of pixels. Temporal and spatial modulation of the two-dimensional array of pixels with a controller allows selectively controlling the Q-switching performed by the spatial light modulator.
Embodiments may be explained in the following description in view of the drawings that show:
The present inventor has cleverly recognized certain limitations in connection with known laser apparatuses and techniques for generating optical pulses based on Q-switching. It is believed that fast and reliable Q-switches are presently not available for Q-switching applications in the mid-wavelength infrared (MWIR) frequency range. For example, such Q-switches are relatively slow or prone to unreliable operation. In view of such recognition, the present inventor proposes innovative laser apparatus and method for reliably and cost-effectively generating optical pulses based on Q-switching controllable with a fast and reliable two-dimensional (2-D) spatial light modulator. The apparatus and method may be optionally optimized with straightforward optical components to increase angular magnification of a beam incident on the spatial light modulator and thus effectively reduce the Q-switching time. For readers desirous of general background information in connection with Q-switching, reference is made to chapter 8 (Q-Switching) of textbook titled “Solid State Lasers: A Graduate Text” by Walter Koechner and Michael Bass, © 2003 Springer-Verlag New York, Inc., which is incorporated by reference herein.
In the following detailed description, various specific details are set forth in order to provide a thorough understanding of depicted embodiments. However, those skilled in the art will understand that such embodiments may be practiced without these specific details; that the depicted embodiments are non-limiting embodiments; and that alternative embodiments may be implemented. In other instances, methods, procedures, and components, which would be well-understood by one skilled in the art have not been described in detail to avoid unnecessary and burdensome explanation.
Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding the embodiments. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent unless otherwise do described. Moreover, repeated usage of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising”, “including”, “having”, and the like, as used in the present application, are intended to be synonymous unless otherwise so indicated.
Embodiments relate to a laser apparatus and method for generating optical pulses. The laser apparatus may comprise a laser cavity and a spatial light modulator including a two-dimensional array of pixels arranged to provide Q-switching at a pixel level in the laser cavity. A controller is connected to the spatial light modulator to temporally and spatially modulate the two-dimensional array of pixels to selectively control the Q-switching provided by the spatial light modulator.
As will be appreciated by one skilled in the art, one end of laser cavity 12 includes an output coupler (OC) 16, which may be a partially transmissive mirror. A spatial light modulator (SLM) 18 is disposed at an opposite end of laser cavity 12 to provide Q-switching by way of a two-dimensional (2-D) array (e.g., 1024×768) of individually-addressable, tiltable micro-mirror pixels. One non-limiting example of such a device is known in the art as a digital micro-mirror device (DMD) available front Texas Instruments Incorporated. For readers desirous of general background information in connection with DMD technology, reference is made to Application Report DLPA008, titled “introduction to Digital Micromirror Device (DMD) Technology”, © 2008 Texas Instrument incorporated, which is incorporated by reference herein.
A controller 22 is connected to spatial light modulator 18 to temporally and spatially modulate the two-dimensional array of pixels to selectively control the Q-switching provided by spatial light modulator 18. SLM 18 may be used as a switching device for controlling Q-switching at a pixel level in the laser cavity. Essentially, each pixel can function as an individualized Q-switch and the aggregate response may be selectively controlled based on the characteristics of the temporal and spatial modulation applied to the two-dimensional array of pixels.
In operation, each micro-mirror (in the array of individually controllable, tiltable mirror-pixels SLM 18) comprises an opto-mechanical element that can have at least two resting tilt states. For example, these states could be located at ±6° relative to the normal of the micro-mirror. When a given micro-mirror transitions from one resting position to the other resting position, such micro-mirror can pass through a singular angle with respect to the normal of the micro-mirror that is arranged to reflect the laser light in a direction back toward the lasing medium 14 and effect a lasing condition. Conversely, at angles other than such singular angle, the micro-mirror may be set to reflect the laser light away from lasing medium 14. That is, the laser light is not returned to the lasing medium. Accordingly, cavity loss of the laser can be temporally and spatially modulated based on the tilt state transitions of the micro-mirrors. Presently, a standard DMD may tilt though an arch of 12° in approximately 16 μsec, which is equivalent to approximately 125,000 RPM.
In one non-limiting application, the disclosed laser apparatus may be a medical laser apparatus configured to operate in a mid-wavelength infrared (MWIR) frequency range, capable of generating nanosecond-width pulses (e.g. a few nanoseconds, such as 10 nsec or less) in the MWIR. The temporally and spatially modulating of the two-dimensional array of pixels may be selected to: shape a profile of the generated optical pulses (e.g., forming pulses comprising a flat-top profile 40, a super-Gaussian profile 42 (a practical approximation to a flat-top profile) or a Gaussian profile 44, as shown in
While various embodiments have been described, it will be understood by those skilled in the an that various changes, omissions and/or additions may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the embodiments. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the embodiments without departing from the scope thereof. Therefore, it is intended that the embodiments not be limited to the particular embodiments being disclosed, but that all possible embodiments within the scope of the appended claims are considered. Moreover, unless specifically stated, any use of the terms first, second, etc., does not denote any order or importance, but rather the terms first, second, etc., are used to distinguish one element from another.
