Session K3: Laser Science

Tunable Mid-Infrared Source based on Difference-Frequency Mixing of Soliton-Shifted Pulses

We present a compact, fiber-based mid-infrared comb source tunable across the 9.5 to 15 $\mu $m region. The system begins with a single erbium fiber laser (1550nm) coupled into a 25 m length of polarization maintaining telecommunication fiber. The incident intensity is sufficient to launch a soliton within the first meter of fiber, which is then coherently red-shifted as it co-propagates with the residual laser pulse. The two pulses are then mixed in a nonlinear crystal to create mid infrared light by difference frequency generation (DFG). As the soliton red-shift is proportional to both input power and fiber length, the soliton center wavelength, and thus the DFG center wavelength, can be continuously tuned. The mid infrared power is linearly proportional to the 1550nm pump power, allowing power scaling using standard telecom amplifiers. Design parameters and experimental results will be discussed.   

Demonstration of an all-diode-pumped soft x-ray laser

We have demonstrated an 18.9 nm, Ni-like molybdenum, transient collisional soft x-ray laser, pumped by a compact, all-diode pumped chirped pulse amplification system. The solid state pump laser is based on cryo-cooled Yb:YAG and produces 8.5 ps pulses with up to 1 J energy at 10 Hz repetition rate. This diode-pumped laser has the potential to greatly increase the repetition rate and average power of soft x-ray lasers on a significantly smaller footprint.   

Soft x-ray interferometry study of radiation cooling and jet collimation in dense laboratory plasmas

Collimated jets were observed in Al, Cu and Mo laboratory plasmas with peak densities of 10$^{20}$ cm$^{-3}$. Short laser pulses of 10$^{12}$ W cm$^{-2}$, 120 ps duration and ~0.5-1.0 J at 800 nm were used to create dense plasmas from solid targets. Expansion of the plasmas from 90$^\circ$ triangular-grooved targets was probed using soft x-ray interferometry. Results were compared to simulations from the hydrodynamic code HYDRA. Radiation cooling was found to significantly increase the collimation of the jets. The collimation was furthermore observed to increase with higher Z materials. Preliminary results are also reported on similar studies of 90$^\circ$ concave conical targets at laser intensities of $3\times 10^{13}$ W cm$^{-2}$ with peak densities of $>10^{21}$ cm$^{-3}$.   

Talbot nano-patterning with a table-top soft X-ray laser

We demonstrate a novel high resolution soft X-ray (SXR) patterning approach based on the generalization of the Talbot effect. This effect was used to print periodic structures of arbitrary patterns with nanometer resolution over a large area. The coherent illumination of a tiled mask produced self images of arbitrary motifs allowing for a non-contact replication technique that opens a new avenue for nanofabrication. Compact soft X-ray laser sources recently developed enable this new nanopatterning technique demonstrated with a table-top SXR laser at $\lambda$ = 46.9 nm. Shorter wavelength SXR lasers emitting in the 13 nm region would allow printing of millimeter square areas with sub-10 nm resolution.   

Cavity ring-down spectroscopy in the ultraviolet region using calcium fluoride prism retroreflectors

Cavity ring-down spectroscopy (CRDS) is a highly sensitive laser absorption technique that is useful for trace species detection of atoms and molecules in a range of applications. High sensitivity CRDS detection requires highly reflective mirrors, typically multilayer dielectrics. Such mirrors are available in many spectral regions, though not in the ultraviolet (UV) where optical absorption in the mirror layers tends to limit reflectivities. In our electric propulsion research, detection of boron nitride (BN) via ground state boron atoms near 250 nm is of particular interest. In order to improve the sensitivity of UV CRDS for BN detection, we are developing the use of prism retroreflectors made from calcium fluoride (CaF2). In addition to higher cavity finesse at 250 nm, total internal reflection allows for broadband CRDS with a single experimental setup. We have obtained super-polished UV grade CaF2 samples in order to make transmission measurements. The measurements are obtained by placing the CaF2 samples as loss elements within a CRDS cavity. In this contribution, we present the measurement setup and results of initial CaF2 material characterizations.   

Precise Characterization of a Laser Current Driver

I will be presenting a characterization of our unique low-noise laser current driver. Our current driver improves on the typical model used in laboratories, giving extra current stability and lower noise. I will discuss our techniques for measuring the noise and drift and the results we obtained. The current driver has a lower noise and drift than any other current driver with a published value, so it has value in making precision measurements. Many other labs have expressed interest in our design as there is a need for this type of current driver in many applications. The current driver demonstrates some interesting applications of electronics principles and uses of electric components, as well as practical considerations in designing circuitry.