Ondrej Novak

On test time reduction using pattern overlapping, broadcasting and on-chip decompression

The paper deals with the problem of test data volume, test application time and on-chip test decompressor hardware overhead of scan based circuits. Broadcast-based test compression techniques can reduce both the test data volume and test application time. Pattern overlapping test compression techniques are proven to be highly effective in the test data volume reduction and low decompressor hardware requirements. This paper presents a new test compression and test application approach that combines both the test pattern overlapping technique and the test pattern broadcasting technique. This new technique significantly reduces test application time by utilizing a new on-chip test decompressor architecture presented in this paper.

High-power, picosecond pulse thin-disk lasers in the Hilase project

Development of high-power, picosecond laser sources is a desirable venture for both industry and research. Within the Hilase project, we are conducting research on both 500-mJ, 1-kHz and 5-mJ, 100-kHz picosecond laser sources based on the Yb:YAG thin-disk technology. We have developed a prototype thin-disk regenerative amplifier operating up to 10- kHz repetition rate pumped by the 940-nm fiber-coupled laser diodes. We achieved 5-mJ pulse energy at 10-kHz operation and 29.5-mJ at 1-kHz. Afterwards, we developed the high-energy regenerative amplifier operating at fixed repetition rate of 1-kHz and the pulse energy was achieved up to 40-mJ. Simultaneously, we elaborated the highrepetition rate regenerative amplifier operating at 100-kHz with pulse energy of 220-μJ. The amplified pulse was compressed with the efficiency of 88% using chirped volume Bragg grating.

Scan chain configuration method for broadcast decompressor architecture

The high test data volume and long test application time are two major concerns for testing scan based circuits. Broadcast-based test compression techniques can reduce both the test data volume and test application time. The broadcast rate is a major issue in these techniques. This paper describes a novel broadcast-based test decompressor architecture and a new method of configuration of the scan chain for this architecture based on the test set analysis. This paper presents and compares several similar heuristic algorithms that according to the test set analysis produce the scan chain configuration with the maximum broadcast rate for the given test set.

Test pattern compression based on pattern overlapping and broadcasting

The high test data volume and long test application time are two major concerns for testing scan based circuits. Broadcast-based test compression techniques can reduce both the test data volume and test application time. Pattern overlapping test compression techniques are proven to be highly effective in the test data volume reduction. This paper presents a new test compression and test application approach that combines both the test pattern overlapping technique and the test pattern broadcasting technique. This paper will illustrate that these new techniques are effective in both the test application time and the test data volume reduction.

50-mJ, 1-kHz Yb:YAG thin-disk regenerative amplifier with 969-nm pulsed pumping

We are developing a 100-mJ Yb:YAG thin-disk regenerative amplifier operating at 1-kHz repetition rate pumped at zero-phonon-line (968.825-nm1) and delivering 1-2 ps pulses for EUV plasma sources applicable in science and industry. Recently we achieved the output energy of nearly 50-mJ from a single laser-head cavity with good beam quality (M2<1.2) as well as stable beam-pointing (<4μrad). Applying pulsed pumping with the pulse duration shorter than the upper state lifetime of Yb:YAG helps to reduce the ASE and thermal loading of the thin-disk.

Picosesond pulses in deep ultraviolet produced by a 100 kHz solid-state thin disk laser

We report on the generation of 100 kHz 0.1mJ-level deep ultraviolet pulses based on frequency-quadrupled (257.5 nm) beam of a diode pumped Yb:YAG thin disk laser at the HiLASE Centre. The 100-kHz beamline used for the generation of the harmonic frequencies is operated at an average output power of 100 W level and 2 picosecond duration of pulses. The amplification of the oscillator beam is performed in a regenerative amplifier where the thin disk serves as an active mirror. The CPA technique is used for achieving high average output power of the whole system. The outcoming laser beam at 1030 nm wavelength is frequency-doubled in an LBO crystal and then frequency-quadrupled in BBO crystal, conversion efficiencies being 40% and 19%, resp. The basic characteristics of the harmonics generation in both crystals are given.

Broadband OPCPA pumped by ultra-narrowband gaseous iodine laser

Amplification of femtosecond pulses using an ultra-narrowband gaseous pulse laser was demonstrated for the first time. A single-shot sub-nanosecond iodine photodissociation laser with a bandwidth of 20 pm was used as a driver in an allstage OPCPA. An externally triggerable OPO tuned to laser line of 1315.24 nm was used in the front end of the iodine laser. Frequency tripled beam at 438 nm was used to pump parametric amplifiers, LBO and KDP crystals. The signal pulses from a Ti:sapphire laser at the central wavelength of 800 nm with a bandwidth of 70 nm (FWHM) were stretched from 12.5 fs to 250 ps and amplified by a factor of 2×108. The amplified pulses of typical bandwidth of 50 nm were compressed down to 27 fs. The output power of 0.5 TW was achieved. An optimized amplifier chain and addition of a third nonlinear crystal would enable to generate femtosecond pulses of several terawatts. The broadband pulses at 800 nm central wavelength were amplified in the KDP crystal for the first time, due to the suitable wavelength of the pump pulses. Availability of large aperture KDP crystals promises the generation of petawatt beam at kJ iodine laser facilities.

Ten-watt level picosecond parametric mid-IR source broadly tunable in wavelength

Mid-IR wavelength range (between 2 and 8 μm) offers perspective applications, such as minimally-invasive neurosurgery, gas sensing, or plastic and polymer processing. Maturity of high average power near-IR lasers is beneficial for powerful mid-IR generation by optical parametric conversion. We utilize in-house developed Yb:YAG thin-disk laser of 100 W average power at 77 kHz repetition rate, wavelength of 1030 nm, and about 2 ps pulse width for pumping of a ten-watt level picosecond mid-IR source. Seed beam is obtained by optical parametric generation in a double-pass 10 mm long PPLN crystal pumped by a part of the fundamental near-IR beam. Tunability of the signal wavelength between 1.46 μm and 1.95 μm was achieved with power of several tens of miliwatts. Main part of the fundamental beam pumps an optical parametric amplification stage, which includes a walk-off compensating pair of 10 mm long KTP crystals. We already demonstrated the OPA output signal and idler beam tunability between 1.70-1.95 μm and 2.18-2.62 μm, respectively. The signal and idler beams were amplified up to 8.5 W and 5 W, respectively, at 42 W pump without evidence of strong saturation. Thus, increase in signal and idler output power is expected for pump power increase.

High-power mid-IR picosecond pulses tunable between 2.2 and 2.4 μm

Mid-infrared (mid-IR) wavelength range is utilized in applications such as gas sensing, medicine, defence, and material processing. When using picosecond pulses high peak power is reached at moderate pulse energy and the heat affected zone is low. A wavelength tunable mid-IR source would enable optimization of the laser-matter interaction in dependence on wavelength. Increase in processing speed requires sources of higher average power. Parametric devices offer both broad wavelength tunability and power scalability [1]. We are developing a ten watt level wavelength tunable picosecond mid-IR source based on an optical parametric generator (OPG) followed by an optical parametric amplifier (OPA).

A CEP-stable, femtosecond 8.5 μm source based on intrapulse DFG of 2.1 μm pulses

Few-cycle carrier-envelope phase (CEP) stable laser pulses enable the precise control of strong-field electron dynamics, such as high-harmonic generation in gases and solids or electron emission in nano-structures [1]. The intrapulse difference-frequency generation (DFG) pumped by a broadband pulse is a reliable method of producing passively CEP-stable pulses. Mid-infrared (mid-IR) pulse generation via intrapulse DFG has been demonstrated with near-IR pump pulses. For example, the intrapulse DFG of Ti:sapphire laser pulses can generate ∼2 μm [2] or ∼5 μm pulses [3], while spectrally broadened and compressed pulses of Yb:YAG laser were used to cover the region from 6.8 to 16.4 μm [4]. Since the efficiency and output pulse energy is rather low for intrapulse DFG, these pulses typically seed further optical parametric amplifiers. If the pump wavelength is shifted to ∼2 μm region, the mid-IR intrapulse DFG at >5 μm becomes more efficient due to a lower quantum defect and the excellent phase matching characteristics of mid-IR nonlinear crystals based on non-oxide materials.