In this paper we present a novel sub-system for synchronizing motion of the galvanometer-based scanner and the XY stage system using a compact single controller that is independent of XY stage type or manufacturer. This integration directly utilizes the stage’s encoder output to compensate its motion in real time. Better than 10μm accuracy is demonstrated with various application patterns.
A galvanometer laser beam scanning system is an essential element in many laser additive manufacturing (LAM) technologies including Stereolithography (SLA), Selective Laser Sintering (SLS) and Selective Laser Melting (SLM). Understanding the laser beam scanning techniques and recent innovations in this field will greatly benefit the 3D laser printing system integration and technology advance. One of the challenges to achieve high quality 3D printed parts is due to the non-uniform laser power density delivered on the materials caused by the acceleration and deceleration movements of the galvanometer at ends of the hatching and outlining patterns. One way to solve this problem is to modulate the laser power as the function of the scanning speed during the acceleration or deceleration periods. Another strategy is to maintain the constant scanning speed while accurately coordinating the laser on and off operation throughout the job. In this paper, we demonstrate the high speed, high accuracy and low drift digital scanning technology that incorporates both techniques to achieve uniform laser density with minimal additional process development. With the constant scanning speed method, the scanner not only delivers high quality and uniform results, but also a throughput increase of 23% on a typical LAM job, compared to that of the conventional control method that requires galvanometer acceleration and deceleration movements.
The wavelength tunable 1060-nm distributed Bragg reflector (DBR) laser chip consists of three sections: a gain section
for lasing, and phase and DBR sections for wavelength control. A micro-heater is lithographically integrated on the top
of the DBR section to tune the emission wavelength. The phase section is designed with either a top heater or by current
injection to provide fine tuning of the wavelength. The wavelength tuning efficiency of our DBR laser is approximately
9 nm/W at the laser heat sink temperature of 25°C. Single-mode output powers of 686 mW and 605 mW were obtained
at a CW gain drive current of 1.25 A and heat sink temperatures of 25°C and 60°C, respectively. Gain-switching by
applying 1.1 GHz sinusoidal signal mixed with 600 mA DC injection current produced approximately 58 ps long optical
pulses with 3.1 W peak power and 228 mW average power. The average power increased to 267 mW and pulse width
broadened to 70 ps with DC bias of 700 mA. In CW operation, one of the applications for high-power single-mode DBR
lasers is for non-linear frequency conversion. The light emitted from the 1060-nm DBR laser chip was coupled into a
single-mode periodically poled lithium niobate (PPLN) crystal waveguide. Up to 350 mW optical power at 530 nm with
the wall-plug efficiency of up to 15% was demonstrated.
Coherent terahertz radar systems, using CO2 laser-pumped molecular lasers have been used during the past decade for
radar scale modeling applications, as well as proof-of-principle demonstrations of remote detection of concealed
weapons. The presentation will consider the potential for replacement of molecular laser sources by quantum cascade
lasers. While the temporal and spatial characteristics of current THz QCLs limit their applicability, rapid progress is
being made in resolving these issues. Specifications for satisfying the requirements of coherent short-range THz radars
will be reviewed and the feasibility of incorporating existing QCL devices into such systems will be described.
The fabrication of thick orientation-patterned GaAs (OP-GaAs) films is reported using a two-step process where an OP-GaAs template with the desired crystal domain pattern was prepared by wafer fusion bonding and then a thick film was grown over the template by low pressure hydride vapor phase epitaxy (HVPE). The OP template was fabricated using molecular beam epitaxy (MBE) followed by thermocompression wafer fusion, substrate removal, and lithographic patterning. On-axis (100) GaAs substrates were utilized for fabricating the template. An approximately 350 μm thick OP-GaAs film was grown on the template at an average rate of ~70 μm/hr by HVPE. The antiphase domain boundaries were observed to propagate vertically and with no defects visible by Nomarski microscopy in stain-etched cross sections. The optical loss at ~2 μm wavelength over an 8 mm long OP-GaAs grating was measured to be no more than that of the semi-insulating GaAs substrate. This template fabrication process can provide more flexibility in arranging the orientation of the crystal domains compared to the Ge growth process and is scalable to quasi-phase-matching (QPM) devices operating from the IR to terahertz frequencies utilizing existing industrial foundries.
This paper reviews recent progress of high-power 14xx-nm pump lasers using AlGaInAs/InP material. This material has superior temperature characteristics to conventional InGaAsP/InP. As a result, it is more suitable for high current and high efficiency operations as well as uncooled applications for the high power 14xx-nm lasers, which are required for advanced optical amplifications. The laser module consists of a laser chip coupled to a fiber lens and mounted on a thermoelectric cooler in a standard butterfly package. The wavelength of the laser can be stabilized with an external fiber Bragg grating (FBG). We have demonstrated a maximum module fiber output power of 550mW at 1.75A and characteristic temperatures of T0 = 99K and T1 = 348K over a range of chip heat-sink temperatures from 15°C to 50°C. To the best of our knowledge, these are the highest efficiency and temperature characteristics from a single-mode 14xx-nm semiconductor laser module capable of over 0.5W fiber output power. At a chip heat-sink temperature of 70°C, a power of 360mW was obtained for a laser module with FBG, which is the highest reported to date for any wavelengths from 1300nm to 1600nm and would enable uncooled applications of the 14xx-nm lasers in the future.
We investigate the recognition of fingerprints from the Fourier spectrum. The inherent properties of fingerprints allow a feature extraction and data reduction in the spatial frequency domain. The Fourier representation allows fingerprints to be distinguished from a small and spatially well-defined area. This suggests various schemes to detect the significant information in order to optimize the trade-off between sensitivity and robustness. We show illustrative results which confirm the usefulness of this approach. In addition, the classification of fingerprints from their plane wave spectra allows the design of compact systems, where the Fourier transformation is performed optically, while detection and post-processing is done by electronics. This provides the advantage that both optics and electronics are used in an optimum way to minimize the physical size of the system, as well as the computational load to interpret the detected signal.