Recent advances of high power and narrow bandwidth laser diodes emitting at 1.9 μm open the path to direct diode
pumping of Ho3+:YAG lasers. The usual method to pump such laser is to use thulium fiber laser which has an excellent
beam quality with high power and narrow bandwidth emission. The draw back of this system is the low efficiency of this
fiber laser and the increased overall complexity. In this paper we present first results of resonantly diode pumping of a
Ho3+:YAG laser with fiberlike geometry. The fiber coupled diode modules used for pumping in this work (BrightLockTMUltra-500) produce each 25 W at 1.91 μm with 3 nm linewidth. The fiber has a core diameter of 600 μm with 0.22
numerical aperture. The Ho3+:YAG crystal has a diameter of 1.2 mm, a length of 60 mm, a doping concentration of 0.75
at.% and is symmetrically pumped by two diode modules from both ends. Total internal reflection on the polished rod
barrel allows a high pump intensity along the rod length. The Ho3+:YAG laser cavity is composed of a high reflective flat
mirror and a concave output coupler with a radius of curvature of 500 mm. With an output coupler of 50 % we measured
a threshold of 11 W. The maximum output power was 11.87 W with a wavelength of 2.09 μm. The incident power to
output power slope efficiency was 0.38 at currently 4 % of internal losses.
Diode lasers in the 1400 nm to 1600 nm regime are used in a variety of applications including pumping Er:YAG lasers,
range finding, materials processing, aesthetic medical treatments and surgery. In addition to the compact size, efficiency,
and low cost advantages of traditional diode lasers, high power semiconductor lasers in the eye-safe regime are
becoming widely used in an effort to minimize the unintended impact of potentially hazardous scattered optical radiation
from the laser source, the optical delivery system, or the target itself.
In this article we describe the performance of high efficiency high brightness InP laser bars at 1470nm and 1550nm
developed at QPC Lasers for applications ranging from surgery to rangefinding.
InP based diode lasers are required to realize the next generation of eyesafe applications, including direct rangefinding
and HEL weapons systems. We report on the progress of high power eyesafe single spatial and longitudinal mode
1550nm MOPA devices, where we have achieved peak powers in excess of 10W with 50ns pulse widths. A conceptual
model based on our recent MOPA results show the path towards scaling to high powers based on spatial beam
combination with operating conditions suitable for direct rangefinding applications. We also report on the progress
towards high power 14xx and 15xx nm pump lasers for eyesafe HEL systems.
KEYWORDS: Semiconductor lasers, Diodes, Laser applications, High power lasers, Defense and security, Crystals, Continuous wave operation, Laser marking, RGB color model, Laser development
Compact, efficient visible lasers are important for heads up displays, pointing and illumination, undersea
communications, and less than lethal threat detection. We report on high power red, green, and blue lasers with output
powers above 3 watts and efficiencies greater than 20%, 15%, and 5% respectively.
KEYWORDS: Diodes, Semiconductor lasers, Diode pumped solid state lasers, Solid state lasers, Fiber lasers, Absorption, High power lasers, Continuous wave operation, Laser systems engineering
The development of on-chip grating stabilized semiconductor lasers for diode pumped solid state lasers is discussed. The
diode lasers, specifically at wavelengths of 808nm, 976nm, and 1532nm are stabilized via internal gratings to yield a
typical center wavelength tolerance of ± 1nm, FWHM of < 1-2nm, and a temperature tuning coefficient of < 0.09 nm/°C.
We also report on the CW and QCW operation of conduction cooled bars, stacks, and fiber coupled modules.
Simulations show that on-chip stabilized pump sources yield performance improvements over standard pumping
schemes. A comparison in laser performance is shown for typical DPSS configuration.
We present recent advances in high power semiconductor laser bars and arrays at near infrared and eye-safe
wavelengths. We report on increased spectral brightness with internal gratings to narrow and stabilize the spectrum and
increased spatial brightness in multimode and single mode devices. These devices have the potential to dramatically
improve diode pumped systems and enable new direct diode applications.
We present recent advances in high power semiconductor laser bars and arrays at near infrared and eye-safe
wavelengths. We report on increased spectral brightness with internal gratings to narrow and stabilize the spectrum and
increased spatial brightness in multimode and single mode devices. These devices have the potential to dramatically
improve diode pumped systems and enable new direct diode applications.
We demonstrate a chirped-pulse amplification system generating 25 μJ compressed pulses at a center wavelength of
1552.5 nm. The seed module and the amplifier chain are all in-fiber (with a few small fiber-pigtailed free-space
components), followed by a free-space diffraction grating pulse compressor. The amplifier chain contains a pre-amplifier
and a booster whose gain fibers are 45/125 μm core/cladding-diameter, core-pumped Er-doped fibers. The pump lasers
for both amplifiers are single-mode 1480 nm Raman lasers capable of up to 8 W output. The seed module generates up
to 2 ns chirped pulses that are amplified and subsequently compressed to <800 fs duration. At a repetition rate of 50 kHz,
the 2 ns pulses from the seed module were amplified to 72 μJ, resulting in 25 μJ after pulse compression. The
corresponding peak power levels after the amplifier chain and compressor were 36 kW and 31 MW, respectively.
Despite the growing number of biomedical and micromachining applications enabled by ultra-short pulse lasers in
laboratory environments, realworld applications remain scarce due to the lack of robust, affordable and flexible laser
sources with meaningful energy and average power specifications. In this presentation, we will describe a laser source
developed at the eye-safe wavelength of 1552.5 nm around a software architecture that enables complete autonomous
control of the system, fast warm-up and flexible operation. Our current desktop ultra-short pulse laser system offers
specifications (1-5 microJ at 500 kHz, 800 fs-3 ps pulse width, variable repetition rate from 1 Hz to 500 kHz) that are
meaningful for many applications ranging from medical to micromachining. We will also present an overview of
applications that benefit from the range of parameters provided by our desktop platform. Finally, we will present a novel
scalable approach for fiber delivery of high peak power pulses using a hollow core Bragg fiber recently developed for
the first time by Raydiance and the Massachusetts Institute of Technology for operation around 1550 nm. We will
demonstrate that this fiber supports single mode operation for core sizes up to 100 micron, low dispersion and low
nonlinearities with acceptable losses. This fiber is a good candidate for flexible delivery of ultra-short laser pulses in
applications such as minimally accessible surgery or remote detection.
A hybridly modelocked grating-coupled surface-emitting laser (GCSEL) with pulse duration 2.8psec at 980nm is demonstrated. The unpumped grating section of the GCSEL is used as a saturable absorber to generate pulses with a 535MHz repetition rate. The peak power of 0.31W and a spectral bandwidth of 1.1nm are obtained.
We report on the design and fabrication of diffractive optical elements on high power broad area semiconductor lasers. Several issues related to the integrated diffractive elements fabrication by electron beam lithography and focused ion beam are discussed. We illustrate the flexibility of electron beam lithography by presenting results for beam focusing, splitting and tapering functions. An additional technique based on focused ion beam milling is presented for fabricating refractive lens elements onto the laser diode.
KEYWORDS: Polishing, Optical fibers, Beam propagation method, Multimode fibers, Single mode fibers, Index matching antireflective coatings, Digital micromirror devices, Cladding, Local area networks, Optical simulations
Micro-Optics have begun to play a key role in micro-photonic systems and devices. This is largely due to the fact that semiconductor processing has enabled one to incorporate complex optical functions and integration features into the actual optical substrates. In this paper, key application areas of micro-optics are demonstrated for mode matching, gain equalization, and spectral filtering.
This paper investigates methods to launch high modes propagating along helix paths into a graded index fiber. These techniques may be particularly useful to avoid the central dip problem due to defects located in the center of the index profile of multimode fibers. Light was coupled into a graded index multimode fiber using the flat surface of side-polished or D-shaped fiber. The fibers were polished down to a few microns close to the core on a distance of about 3mm. The first method, active, is based on coupling the light from a D-shaped single mode fiber to a D-shaped graded index fiber. The two fibers are in contact through a film of index matching fluid and the coupling may be thought as the leakage from a fiber to a slab waveguide. The launching angle of the skew rays in the multimode fiber is controlled by the tilt between the fibers. Simulations using beam propagation method are presented. Analytical equations for the path of the skew rays in graded index fiber are also used for a parabolic index profile. The second method, passive, consists of etching a tilted grating on a side polished multimode fiber by means of focused-ion beam (FIB) technology. We discuss the fabrication of such a grating and the possibility of using FIB technology to etch diffractive elements on fused silica waveguides.
Photonic band gap structures and their applications have gained a great deal of interest in recent years, with the primary focus on designing structures that have specific optical characteristics. However, little attention has been given to solving the inverse problem of determining the optimum photonic lattice given a desired output. In this paper, we address this need using optimization techniques to design two-dimensional photonic crystals to arbitrarily guide light in two dimensions. By switching the rods of this lattice on and off (rod or no rod), the optimization algorithm arrives at a solution (distribution of the rod in this lattice) that minimizes the cost function. The performance of the optimization is driven by the proper selection of both the cost function and optimization algorithm.
Eyetracking is typically not available in head-mounted displays, and eye motions are thus simply ignored when 2D virtual images are displayed, giving rise to rendered depth errors in generating stereoscopic image pairs in head- mounted displays. We present an investigation and quantification of rendered depth errors linked to natural eye movements in binocular head-mounted displays, or Albertian errors, for three possible eyepoint locations: the center of the entrance pupil, the nodal point, and the center of rotation. Theoretical computations based on the intersection of chief rays concluded that, while the center of rotation yields minimal depth errors if no eyetracking is used, rendered angular errors may in some cases be significant (i.e. up to six degrees). Based on the analysis presented in this paper, we suggest that the center of entrance pupil be chosen for far field applications. The center of rotation of the eye should be chosen for near field applications under the assumption that they emphasize position accuracy versus angular accuracy. Preventing or minimizing rendered depth errors may be required for some high accuracy tasks related, for example, to medical or military visualization.
Accuracy of rendered depth in virtual environments includes the correct specification of the eyepoints from which a stereoscopic pair of images is rendered. Rendered depth errors should be minimized for any virtual environment. It is however critical if perception is the object of study in such environments, or augmented reality environments are created where virtual objects must be registered with their real counterparts. Based on fundamental optical principles, the center of the entrance pupil is the eyepoint location that minimizes rendered depth errors over the entire field of view if eyetracking is enable. Because binocular head mounted displays (HMDs) have typically no eyetracking capability, the change in eyepoints location associate with eye vergence in HMDs is not accounted for. To predict the types and the magnitude of rendered depth errors that thus result, we conducted a theoretical investigation of rendered depth errors linked to natural eye movements in virtual environments for three possible eyepoints locations: the center of the entrance pupil, the nodal point, and the center of rotation of the eye. Results show that, while the center of rotation yields minimal rendered depth errors at the gaze point, it also yields rendered angular errors around the gaze point, not previously reported.
While computer graphics play a significant component in the development of virtual environments, optics and its interface to the computer graphics software play an essential role as well because they are both required for the effective visualization of virtual environments. Moreover, optical technology is often a component in satisfying stringent tracking requirements. We shall focus in this paper on aspects of virtual environments where optics play a part, describe the development of the VRDA tool for visualization of anatomy, and summarize recent investigations of visual optics for improved head-mounted displays.
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