L. B. Shaw

Octave spanning supercontinuum in an As 2 S 3 taper using ultra-low pump pulse energy

An octave spanning spectrum is generated in an As2S3 taper via 77 pJ pulses from an ultrafast fiber laser. Chirp compensation allows the octave to be generated directly from the un-amplified laser output.

Small-core As-Se fiber for Raman amplification

We have demonstrated Raman small-core As-Se fiber. More than 20-dB of gain was observed in a 1.1-m length of fiber pumped by a nanosecond pulse of approximately 10.8-W peak power at 1.50 microm. The peak of the Raman gain occurred at a shift of approximately 240 cm(-1). The Raman gain coefficient is estimated to be approximately 2.3 x 10(-11) m/W, which is more than 300 times greater than that of silica. The large Raman gain coefficient coupled with the large IR transparency window of these fibers shows promise for development of As-Se Raman fiber lasers and amplifiers in the near-, mid-, and long-IR spectral regions.

Waveguide amplifiers in sputtered films of Er3+-doped gallium lanthanum sulfide glass.

Waveguide amplifiers fabricated in Er3+-doped gallium lanthanum sulfide (GLS) glass are demonstrated. GLS is deposited onto fused silica substrates by RF magnetron sputtering, and waveguides are patterned by use of the lift-off technique. The waveguides exhibit a total internal gain of 6.7 dB (2.8 dB/cm) for a signal with a wavelength of 1.55 mum. This experiment is, to the best of our knowledge, the first demonstration of gain in an Er3+-doped chalcogenide glass waveguide. The fabrication methods we apply, if used with other rare earth dopants, could potentially be employed to produce sources operating in the mid-IR.

Modeling of a mid-IR chalcogenide fiber Raman laser.

A computer model using a finite element technique was written to model the behavior of a chalcogenide fiber Raman laser. The model demonstrates the feasibility of a middle infrared fiber Raman laser pumped at 5.59-microm by a carbon monoxide laser and operating at a wavelength of 6.46-microm. This wavelength may be of interest in surgical applications since it corresponds to the amide II absorption. Calculations show slope efficiencies can approach 80% with moderate threshold powers.

Mid-infrared spectroscopy of erbium doped chloride laser crystals.

We report on a spectroscopic analysis of ErCl3 and 1% Er 3+:YCl3 to determine their potential as possible laser sources at 3.5 and 4.5 mm. Concentration quenching of the low lying excited states is reported to be surprisingly very weak in this system. Although some shortening of the lifetimes is measured in the fully concentrated system, they retain lifetimes that are of order several milliseconds or more. A Judd-Ofelt analysis is performed and the projected gains for the 3.5 and 4.5 mm transitions are calculated. Successful growth techniques of erbium doped chlorides are also described.

Raman response function and supercontinuum generation in chalcogenide fiber

We show the Raman response function and dispersion curve for a chalcogenide fiber. We then model and reproduce the experimental bandwidth of IR supercontinuum generation using a chalcogenide PCF.

CROSS RELAXATION AND UPCONVERSION COEFFICIENTS OF THE MID-INFRARED TRANSITIONS OF PR3+ :LACL3

Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states (υ<10−4 cm−1) of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range of Pr3+ concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3–7.2 μm spectral range are discussed.

Single crystal fibers for high power lasers

In this paper, we present our recent results in developing cladded-single crystal fibers for high power single frequency fiber lasers significantly exceeding the capabilities of existing silica fiber based lasers. This fiber laser would not only exploit the advantages of crystals, namely their high temperature stability, high thermal conductivity, superior environmental ruggedness, high propensity for rare earth ion doping and low nonlinearity, but will also provide the benefits from an optical fiber geometry to enable better thermal management thereby enabling the potential for high laser power output in short lengths. Single crystal fiber cores with diameters as small as 35m have been drawn using high purity rare earth doped ceramic or single crystal feed rods by Laser Heated Pedestal Growth (LHPG) process. The mechanical, optical and morphological properties of these fibers have been characterized. The fibers are very flexible and show good overall uniformity. We also measured the optical loss as well as the non-radiative loss of the doped crystal fibers and the results show that the fibers have excellent optical and morphological quality. The gain coefficient of the crystal fiber matches the low quantum defect laser model and it is a good indication of the high quality of the fibers.

Supercontinuum generation in an As 2 Se 3 -based chalcogenide PCF using four-wave mixing and soliton self-frequency shift

We theoretically find a bandwidth of 4 µm can be generated using four-wave mixing and soliton self-frequency shift in an As<inf>2</inf>Se<inf>3</inf>-based chalcogenide PCF with an air-hole-diameter-to-pitch ratio of 0.4 and a pitch of 3 µm.

Review of antireflective surface structures on laser optics and windows

We present recent advancements in structured, antireflective surfaces on optics, including crystals for high-energy lasers as well as windows for the infrared wavelength region. These structured surfaces have been characterized and show high transmission and laser damage thresholds, making them attractive for these applications. We also present successful tests of windows with antireflective surfaces that were exposed to simulated harsh environments for the application of these laser systems.