Momoko Maruyama

Contact grating device with Fabry-Perot resonator for effective terahertz light generation.

A novel design for a contact grating device with an incorporated Fabry-Perot resonator is proposed for high-power terahertz (THz) light generation. We deposited a multilayer consisting of Ta(2)O(5) and Al(2)O(3) on a magnesium-doped stoichiometric LiNbO(3) substrate and fabricated grating grooves on the outermost layer. The multilayer was designed such that conditions for a Fabry-Perot resonator were satisfied for light diffracted by the grating. Consequently, the fraction of light transmitted into the LiNbO(3) substrate, i.e., the diffraction efficiency, was enhanced by the resonator. The diffraction efficiency of the fabricated device was 71%, which is close to the calculated value of 78% from the optimized design. THz light generation was also demonstrated with the contact grating device. The THz output of 0.41 μJ was obtained using near-infrared pump light of 2.7 mJ.

Yb:YAG thin-disk chirped pulse amplification laser system for intense terahertz pulse generation.

We have developed a 1 kHz repetition picosecond laser system dedicated for intense terahertz (THz) pulse generation. The system comprises a chirped pulse amplification laser equipped with a Yb:YAG thin-disk amplifier. At room temperature, the Yb:YAG thin-disk regenerative amplifier provides pulses having energy of over 10 mJ and spectral bandwidth of 1.2 nm. The pulse duration achieved after passage through a diffraction grating pair compressor was 1.3 ps. By employing this picosecond laser as a pump source, THz pulses having a peak frequency of 0.3 THz and 4 µJ of energy were generated by means of optical rectification in an Mg-doped LiNbO3 crystal.

High-efficiency contact grating fabricated on the basis of a Fabry–Perot type resonator for terahertz wave generation

We have designed and fabricated a contact grating device to increase diffraction efficiency on the basis of the principle of the Fabry–Perot resonator. The grating structure and layer thicknesses were carefully determined by considering the electric field strength in the device and the fabrication accuracy of the grating. The prototype device had a peak diffraction efficiency of 71% at an incident angle of 42°; these values were slightly different from the design values of 78% and 44.5°, respectively. Numerical calculations revealed that this deviation was caused by the fabricated grating structure. A higher terahertz power will be expected with a device as per the design.

Sub-picosecond regenerative amplifier of Yb-doped Y 2 O 3 ceramic thin disk

We have developed a 1 kHz regenerative amplifier using an Yb:Y(2)O(3) ceramic thin disk as the gain medium. Furthermore, the thermal conductivity and heat generation property of Yb:Y(2)O(3) ceramic were investigated. In the developed regenerative amplifier, a laser beam is bounced off the thin disk six times in each round trip. The output energy is over 2 mJ, spectral bandwidth is 1.8 nm at FWHM, and pulse duration after pulse compression is 0.9 ps.

THz pulse generation using a contact grating device composed of TiO2/SiO2 thin films on LiNbO3 crystal

We developed a new contact grating device for terahertz (THz) pulse generation by optical rectification. The device was made from polycrystalline rutile TiO2 thin film in the grating region and an amorphous SiO2 layer deposited on a Mg-doped LiNbO3 crystal. Our calculations indicated that the TiO2 grating on the SiO2 layer would yield an increase in diffraction efficiency of up to 0.69. The prepared TiO2 thin film had a sufficient laser induced damage threshold (140 GW/cm2) to enable effective THz pulse generation. Using a prototype device, we demonstrated THz pulse generation and investigated the phase-matching conditions experimentally.

Improvement of contact grating device for efficient terahertz wave generation using bi-angular filter

We have proposed an improved contact grating device for generating terahertz waves efficiently and have succeeded in developing the device with a very high diffraction efficiency and a wide spectral width. This device has a bi-angular filter and a Fabry–Perot-type structure, which are composed of dielectric multilayers. The bi-angular filter is designed to reflect the 0th-order wave and transmit the–1st-order diffraction wave. Numerical calculations indicate that the new device has a maximum diffraction efficiency over 99% and a spectral width of approximately 20 nm. We measured a high efficiency of 90% over a broad spectral range using a fabricated device.

Yb:YAG thin-disk CPA laser system for intense THz pulse generation at 1 kHz repetition rate

We have developed a high average power picosecond laser system dedicated to intense terahertz (THz) pulse generation. The system is a chirped pulse amplification laser equipping with a Yb:YAG thin-disk amplifier. The Yb:YAG thin-disk regenerative amplifier at room temperature provides pulses with energy over 10 mJ and spectral bandwidth of 1.2 nm at a repetition rate of 1 kHz. In a pulse compressor, the laser pulse is compressed to be 1.3 ps. By employing this picosecond pulse as a pump source, THz pulses at the center frequency of 0.3 THz with energy over a few microjoules have been generated at 1 kHz repetition rate by the optical rectification in Mg-LiNbO3 crystal.