Brendan A. Reagan

Demonstration of a 100 Hz repetition rate gain-saturated diode-pumped table-top soft x-ray laser

We demonstrate the operation of a gain-saturated table-top soft x-ray laser at 100 Hz repetition rate. The laser generates an average power of 0.15 mW at λ=18.9  nm, the highest laser power reported to date from a sub-20-nm wavelength compact source. Picosecond laser pulses of 1.5 μJ energy were produced at λ=18.9  nm by amplification in a Mo plasma created by tailoring the temporal intensity profile of single pump pulses with 1 J energy produced by a diode-pumped chirped pulse amplification Yb:YAG laser. Lasing was also obtained in the 13.9 nm line of Ni-like Ag. These results increase by an order of magnitude the repetition rate of plasma-based soft x-ray lasers opening the path to milliwatt average power table-top lasers at sub-20 nm wavelengths.

Demonstration of a compact 100 Hz, 0.1 J, diode-pumped picosecond laser

We have demonstrated an all-diode-pumped Yb:YAG chirped pulse amplification laser that produces 100 mJ pulses of 5 ps duration at 100 Hz repetition rate. The compact laser system combines a room-temperature Yb:YAG regenerative amplifier for increased bandwidth and a cryogenically cooled Yb:YAG four-pass amplifier for improved heat dissipation and increased efficiency. The optical efficiency of this amplifier is higher than that of other diode-pumped systems of comparable energy.

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

We have demonstrated an 18.9 nm Ni-like molybdenum soft x-ray laser, pumped by a compact all-diode-pumped Yb:YAG laser. The solid-state pump laser 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 the average power of soft x-ray lasers on a significantly smaller footprint.

1 J, 05 kHz repetition rate picosecond laser

We report the demonstration of a diode-pumped chirped pulse amplification Yb:YAG laser that produces λ=1.03  μm pulses of up to 1.5 J energy compressible to sub-5 ps duration at a repetition rate of 500 Hz (750 W average power). Amplification to high energy takes place in cryogenically cooled Yb:YAG active mirrors designed for kilowatt average power laser operation. This compact laser system will enable new advances in high-average-power ultrashort-pulse lasers and high-repetition-rate tabletop soft x-ray lasers. As a first application, the laser was used to pump a 400 Hz λ=18.9  nm laser.

Development of High Energy Diode-Pumped Thick-Disk Yb:YAG Chirped-Pulse-Amplification Lasers

We discuss the results of work directed toward the development of high energy (>;1 J), high average power, diode-pumped picosecond lasers. The design and operation of diode-pumped chirped-pulse-amplification Yb:YAG lasers that combine either room temperature or cryogenically-cooled regenerative amplifiers with cryo-cooled power amplifiers for superior thermal performance and efficient energy extraction are discussed. Results obtained using thick-disk amplifiers include the generation of 100 mJ, 5-ps duration laser pulses at 100-Hz repetition rate, and 1-J pulses of 8.5-ps duration at 10-Hz repetition rate. The performance of the amplifiers in terms of pulse energy and bandwidth under a variety of pump condition is presented.

Point defects in Sc 2 O 3 thin films by ion beam sputtering

We show that the concentration of oxygen interstitials trapped in Sc2O3 films by ion beam sputtering from metal targets can be controlled by modifying deposition conditions. We have identified point defects in the form of oxygen interstitials that are present in Sc2O3 films, in significantly high concentrations, i.e., ∼10(18)  cm(-3). These results show a correlation between the increase of oxygen interstitials and the increase in stress and optical absorption in the films. Sc2O3 films with the lowest stress and optical absorption loss at 1 μm wavelength were obtained when using a low oxygen partial pressure and low beam voltage.

Hour-long continuous operation of a tabletop soft x-ray laser at 50-100 Hz repetition rate.

We report the uninterrupted operation of an 18.9 nm wavelength tabletop soft x-ray laser at 100 Hz repetition rate for extended periods of time. An average power of about 0.1 mW was obtained by irradiating a Mo target with pulses from a compact diode-pumped chirped pulse amplification Yb:YAG laser. Series of up to 1.8 x 10(5) consecutive laser pulses of ~1 µJ energy were generated by displacing the surface of a high shot-capacity rotating molybdenum target by ~2 µm between laser shots. As a proof-of-principle demonstration of the use of this compact ultrashort wavelength laser in applications requiring a high average power coherent beam, we lithographically printed an array of nanometer-scale features using coherent Talbot self-imaging.

1 Joule, 100 Hz Repetition Rate, Picosecond CPA Laser for Driving High Average Power Soft X-Ray Lasers

A diode-pumped cryogenic Yb:YAG CPA laser that produces 1J, 5ps pulses allowed for the first time the uninterrupted generation of 1.8×105 sub-20nm wavelength laser pulses with microjoule energy at 100Hz repetition rate on a table-top.

What role do defects play in the laser damage behavior of metal oxides

We have investigated the role of native point defects in the laser damage behavior of amorphous thin films of Sc2O3 deposited by ion beam sputtering. Through systematic characterization and detailed modeling we show that native defects influence the 1-on-1 laser induced damage threshold fluence of the Sc2O3. This effect, as shown by the model and confirmed by experiments, is pulse duration dependent.

SiO2/HfO2 multilayers: impact of process parameters and stack geometry on the optical and structural properties

We present a complete systematic study on the effect of assist beam energy on SiO2/HfO2 quarter wave stacks deposited by dual ion beam sputter (DIBS) deposition. Increasing assist beam energy results in lower surface roughness and reduced micro-crystallinity. The coatings also show reduced mechanical stress. The improvements in the structural properties are accompanied by a reduction in the absorption loss and an increase in the laser resistance to damage at 1 μm.