We demonstrate the location and identification of delaminations and water intrusion in advanced composite materials used in ground based radome panels, shelters and towers using time domain terahertz imaging. Water has a very high absorption in the THz spectral region in comparison to polymer foam and fiberglass, so the method is very sensitive to water intrusion. The sub-picosecond near single cycle electromagnetic images enabled identification of delaminations of the fiberglass shell and foam. We report a novel time domain terahertz non-destructive evaluation control system, which is suitably portable for applications such as field examination of radome composites.
As applications demanding microJoule level pulses at "real-time" rates of delivery increase, and the expectations in terms of long-term, reliable, high quality performance become greater, fiber lasers are becoming increasingly attractive sources. When a combination of excellent beam quality, flexibility in design for repetition rate over 100 kHz - 5 MHz, and robust design for operation in a variety of environments, in a plug-and-play, non-water cooled package are necessary, IMRA’s fiber chirped-pulse amplifier (FCPA) system delivers in a compact, single-box solution. This type of laser has particular promise in precision material processing applications, enabling the use of technology that was previously considered too unstable or difficult to use. The basis for this advanced technology is a novel Yb:fiber oscillator/amplifier combination. The modular design architecture ensures a very robust construction that is well-suited to integration into commercial systems. To show the utility of such a laser in commercial applications, results of ablation thresholds and processing tests of various materials including metals and dielectrics are presented using IMRA’s FCPA μJewel femtosecond fiber laser.
The development of ultrashort pulse laser technology will have a strong impact on the advancement of laser machining. Ultrashort laser pulses can reduce the heat-affected zone and the shock-affected zone, resulting in much cleaner cuts, and therefore higher precision. Also, ultrashort laser pulses have shown remarkable opportunity for processing transparent materials such as glass, fused silica, and sapphire. However, acceptance of ultrafast technology is hindered by the size, cost, and complexity of ultrafast lasers. In this paper, we describe recent progress in fiber- based ultrafast laser technology which promises to be sufficiently compact, rugged, and potentially low-cost.
The development of ultrashort pulse laser technology will have a strong impact on the advancement of laser machining. Ultrashort laser pulses can reduce the heat-affected zone and the shock-affected zone, resulting in much cleaner cuts, and therefore higher precision. However, acceptance of ultrafast technology is hindered by the cost and complexity of ultrafast lasers. In this paper, we describe recent progress in fiber-based ultrafast laser technology which promises to be sufficiently rugged and low-cost to enter the industrial arena. We also discuss results of micromachining using a sub-nanosecond laser pulses from a new Yb:fiber- based laser system.
The current status of ultrafast fiber lasers is discussed. Recent advances in optical fiber designs as well as improved saturable absorbers have greatly improved the performance and the reliability of ultrafast fiber oscillators. Equally significant have been improvements in ultrafast fiber amplifier designs and compact chirped pulse amplification systems in conjunction with chirped periodically-poled LiNbO3, which now allow the manufacture of compact ultrafast fiber laser systems that can exceed the performance of conventional ultrafast lasers based on bulk optics. The unique size advantage of fiber lasers opens up the field of ultrafast optics to novel OEM-type applications. For example ultrafast fiber lasers have been successfully employed as subsystems in all-optical time delay scanning, for two-photon microscopy as well as for THz pulse generation.
Industrial applications of THz techniques require compact and reliable systems. We have designed and constructed two portable THz systems integrated with femtosecond, erbium- doped fiber lasers. Terahertz emitters based on photoelectron-transport and optically-rectification were tested in the system. With the use of a 10-mW laser pump beam, the signal-to-noise ratio of the system is greater than 5,000. We studied THz beam generation and detection with two different laser wavelengths. Under the consideration of group velocity matching, the frequency response of the THz system is calibrated. Our portable systems have been applied for the coherent measurement of the refractive index and dielectric constant of polymer thin films, which will play an important role in the ongoing quest for higher speeds in integrated circuits. The measurement is based on a comparison of THz phases with and without the film. The refractive index of thin film can be derived according to the phase difference. The system has sufficient sensitivity to perform these measurements on films as thin as 10 microns. We have also used one of these systems for THz measurements of molecular rotation spectra in air/vapor mixtures.