Patrick Leisching

All fiber-coupled THz-TDS system with kHz measurement rate based on electronically controlled optical sampling.

We demonstrate a completely fiber-coupled terahertz (THz) time-domain spectrometer (TDS) system based on electronically controlled optical sampling with two erbium-doped femtosecond fiber lasers at a central wavelength of 1560 nm. The system employs optimized InGaAs/InAlAs photoconductive antennas for THz generation and detection. With this system, we achieve measurement rates of up to 8 kHz and up to 180 ps scan range. We further achieve 2 THz spectral bandwidth and a dynamic range of 76 dB at only 500 ms measurement time.

A bright continuous-wave laser source at 193 nm

This Letter reports on the realization of a highly coherent light source at 193 nm. By frequency-quadrupling an amplified diode laser, over 15 mW of laser emission could be generated using the nonlinear crystal potassium fluoro-beryllo-borate. The high stability of the setup was proven in an 80 h-measurement, and the impact of the crystal transmission on the output power was thoroughly studied. This laser source is an ideal tool for photoemission spectroscopy and reaches the power level to replace excimer lasers in metrological applications.

1.3-mW tunable and narrow-band continuous-wave light source at 191 nm

We report on the realization of a continuous-wave light source based on nonlinear interaction in KBBF at a wavelength of 191 nm. More than 1.3 mW of deep-ultraviolet power was generated in a mechanically robust setup pumped by an amplified grating stabilized diode laser. Mode hop-free tuning over 40 GHz at 191 nm could be demonstrated.

Series production of next-generation guide-star lasers at TOPTICA and MPBC

Large telescopes equipped with adaptive optics require high power 589-nm continuous-wave sources with emission linewidths of ~5 MHz. These guide-star lasers should be highly reliable and simple to operate and maintain for many years at the top of a mountain facility. After delivery of the first 20-W systems to our lead customer ESO, TOPTICA and MPBC have begun series production of next-generation sodium guide-star lasers. The chosen approach is based on ESO’s patented narrow-band Raman fiber amplifier (RFA) technology [1]. A master oscillator signal from a TOPTICA 50-mW, 1178-nm diode laser, with stabilized emission frequency and linewidth of ~ 1 MHz, is amplified in an MPBC polarization-maintaining (PM) RFA pumped by a high-power 1120-nm PM fiber laser. With efficient stimulated Brillouin scattering suppression, an unprecedented 40 W of narrow-band RFA output has been obtained. This is spatially mode-matched into a patented resonant-cavity frequency doubler providing also the repumper light [2]. With a diffraction-limited output beam and doubling efficiencies < 80%, all ESO design goals have been easily fulfilled. Together with a wall-plug efficiency of < 3%, including all system controls, and a cooling liquid flow of only 5 l/min, the modular, turn-key, maintenance-free and compact system design allows a direct integration with a launch telescope. With these fiber-based guide star lasers, TOPTICA for the first time offers a fully engineered, off-the-shelf guide star laser system for ground-based optical telescopes. Here we present a comparison of test results of the first batch of laser systems, demonstrating the reproducibility of excellent optical characteristics.

Difference-frequency combs in cold atom physics

Abstract Optical frequency combs provide the clockwork to relate optical frequencies to radio frequencies. Hence, combs allow optical frequencies to be measured with respect to a radio frequency where the accuracy is limited only by the reference signal. In order to provide a stable link between the radio and optical frequencies, the two parameters of the frequency comb must be fixed: the carrier envelope offset frequency, fceo, and the pulse repetition-rate, frep. We have developed the first optical frequency comb based on difference frequency generation (DFG) that eliminates fceo by design — specifically tailored for applications in cold atom physics. An fceo-free spectrum at 1550 nm is generated from a super continuum spanning more than an optical octave. Established amplification and frequency conversion techniques based on reliable telecom fibre technology allow the generation of multiple wavelength outputs. The DFG comb is a convenient tool to both stabilise laser sources and accurately measure optical frequencies in Rydberg experiments and more generally in quantum optics. In this paper we discuss the frequency comb design, characterization, and optical frequency measurement of Strontium Rydberg states. The DFG technique allows for a compact and robust, passively fceo stable frequency comb significantly improving reliability in practical applications.

15 mW of CW emission at 193 nm using the crystal KBBF

We report on a narrow-band continuous-wave laser source in the deep-ultraviolet with an output power of > 15 mW at 193 nm. We see applications of this laser source in semiconductor metrology and high-resolution spectroscopy.

A narrow-band continuous-wave laser source at 191 nm

A continuous-wave deep-ultraviolet light source is demonstrated based on a grating-stabilized diode laser pump system and two consecutive nonlinear conversion stages. Using the crystal Potassium Fluoroberylloborate (KBBF), direct second-harmonic generation to 191 nm could be realized with an output power of up to 1.3 mW. The linewidth at this wavelength is estimated to be around 100 kHz. The emission can be tuned mode hop-free over 40 GHz. Our scheme can be easily extended to 193 nm or – given the availability of suitable fundamental sources – to wavelengths as small as 165 nm. These parameters make our light source an ideal tool for applications in deep-ultraviolet metrology and photoemission spectroscopy.

Semiconductor-based narrow-line and high-brilliance 193-nm laser system for industrial applications

We present a novel industrial-grade prototype version of a continuous-wave 193 nm laser system entirely based on solid state pump laser technology. Deep-ultraviolet emission is realized by frequency-quadrupling an amplified diode laser and up to 20 mW of optical power were generated using the nonlinear crystal KBBF. We demonstrate the lifetime of the laser system for different output power levels and environmental conditions. The high stability of our setup was proven in > 500 h measurements on a single spot, a crystal shifter multiplies the lifetime to match industrial requirements. This laser improves the relative intensity noise, brilliance, wall-plug efficiency and maintenance cost significantly. We discuss first lithographic experiments making use of this improvement in photon efficiency.

Frequency locking of compact laser-diode modules at 633 nm

This work reports on a compact diode-laser module emitting at 633 nm. The emission frequency can be tuned with temperature and current, while optical feedback of an internal DBR grating ensures single-mode operation. The laser diode is integrated into a micro-fabricated package, which includes optics for beam shaping, a miniaturized optical isolator, and a vapor cell as frequency reference. The achieved absolute frequency stability is below 10−8 , while the output power can be more than 10 mW. This compact absolute frequency-stabilized laser system can replace gas lasers and may be integrated in future quantum technology devices.

Mask-aligner lithography using a continuous-wave diode laser frequency-quadrupled to 193 nm

We present a mask-aligner lithographic system operated with a frequency-quadrupled continuous-wave diode laser emitting at 193 nm. For this purpose, a 772 nm diode laser is amplified by a tapered amplifier in the master-oscillator power-amplifier configuration. The emission wavelength is upconverted twice, using LBO and KBBF nonlinear crystals in second-harmonic generation enhancement cavities. An optical output power of 10 mW is achieved. As uniform exposure field illumination is crucial in mask-aligner lithography, beam shaping is realized with optical elements made from fused silica and CaF2 featuring a diffractive non-imaging homogenizer. A tandem setup of shaped random diffusers, one static and one rotating, is used to control speckle formation. We demonstrate first experimental soft contact and proximity prints for a field size of 1 cm2 with a standard binary photomask and proximity prints with a two-level phase mask, both printed into 120 nm layers of photoresist on unstructured silicon substrates.