Lasercom system architecture with reduced complexity

Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention, a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides the means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost

Automated Laser Ultrasonic Inspection of Hybrid Laser Arc Welding for Pipeline Construction

Hybrid laser arc welding (HLAW) is a technology that promises to increase the efficiency of welded fabrication. By incorporating automation, and integrating an automated inspection system, HLAW can produce high quality welds at higher production rates and lower costs compared to even the most advanced pipeline welding system that is in use today. As the HLAW technique is developed and implemented for pipeline construction, it is important to develop an associated automated technique for weld inspection. We have applied automated laser ultrasonic testing (ALUT) to the important requirement of the in-line monitoring of new HLAW welds in the field. Laser ultrasonic testing (LUT) offers the advantage of true in-process measurement, providing immediate information on weld integrity. In this paper, we will describe our efforts to apply LUT to pipeline girth weld inspection. The technology development process and the integration into an HLAW system will be described.</jats:p

Sizing Stress Corrosion Cracks Using Laser Ultrasonics

Integrity management decisions related to operating energy transmission pipelines affected by Stress Corrosion Cracking (SCC) represent a formidable challenge to the pipeline industry. Effective management of SCC damage requires the development of tools and technology to identify the occurrence of SCC and to assess the impact of the SCC on pipeline integrity. Development of practical non-destructive evaluation (NDE) solutions for the measurement and evaluation of SCC, including crack depths, is difficult due to the complexity of crack shapes and their inter-relationship and distribution within crack colonies. Laser ultrasonics is an inspection technology using laser beams to generate and detect ultrasonic waves in the pipeline wall to be inspected. Unlike conventional ultrasound, it has a large bandwidth and the beams have a very small (∼0.5mm) footprint. These characteristics make it ideally suited for application as a depth sizing tool for SCC in pipelines. Through a collaborative research project jointly funded by the US Department of Transportation, Pipeline and Hazardous Materials Safety Administration (PHMSA) and PRCI, Applus RTD and its research partners have conclusively shown that laser ultrasonic inspection technology using the Time of Flight Diffraction (TOFD) technique reliably and accurately measures the depth of SCC. In addition, this technique may also be applicable to measuring the depth of other cracks such as seam weld anomalies. The project included the development of a prototype NDE inspection tool for measurement of SCC, and recently culminated with a series of full-scale demonstrations of the tool. This paper describes the detailed technical work conducted to support the development of the tool and validation of the TOFD technique for sizing the depth of SCC. In addition, this paper presents the preliminary results of work on a closely related project that builds on the technology described above to produce an integrated approach and tool for mapping, sizing, and evaluating SCC that filters significant (i.e., deep) cracks from more benign cracks within an SCC colony.</jats:p

Coherent optical link demonstrations for space communication

Development of a coherent optical communication system using frequency stabilized solid state lasers for eventual deployment in space is being actively pursued at the Jet Propulsion Laboratory. A demonstration system transmitting at 1.06 μm with low to moderate data rates has been implemented. Both the transmitter and the local oscillator (LO) employ frequency stabilized (Δv ~ 5 kHz), diode pumped Nd:YAG monolithic ring lasers. Frequency tuning and phase locking are accomplished piezoelectrically with a response time &lt;1 μs.1 Pulse position modulation of the transmitted beam is accomplished by an external GaAs acoustooptic modulator. At the receiver, the signal is mixed with the LO, detected, and processed to retrieve the data stream as well as the error signal for frequency tuning and phase locking of the LO laser. At low data rates, the small received signal energy (per laser coherence time) makes receiver phase and frequency tracking the limiting factor in system performance.</jats:p