Deep-ultraviolet Light Source Research Articles

Novel Optogalvanic Spectroscopy of Semiconductor Atoms with a Frequency-tripled ns Ti:sapphire Laser Injection-seeded by a cw Frequency-scanning Ti:sapphire Laser

Novel optogalvanic spectroscopy of silicon atoms was conducted with the narrow-linewidth nanosecond pulsed deep-ultraviolet coherent light source which was comprised of the frequency-tripled nanosecond pulsed Ti:sapphire laser injection-seeded by another frequency-scanning cw Ti:sapphire laser. Only when the laser frequency of the seed laser matched with the cavity frequency of the slave laser, signals increased remarkably. The individual spectral widths derived from the injection-seeding effect should be the tolerance for successful injection-seeding in the axial mode of the slave laser, and indicated the linewidth of the injection-seeded ns pulsed deep-ultraviolet laser. So the cavity performances of the slave laser can be seen from the spectrum. The envelope of these peaks indicated the absorption spectrum of silicon atoms. This spectral width had the FWHM of 4.8 GHz in the Gaussian fitting and was equivalent to nearly the pure Doppler width, which could not be measured with the system without the injection seeding.

Development of a single-frequency deep-ultraviolet coherent light source

Development of a single-frequency deep-ultraviolet coherent light source

Controlling the Motion of Silicon Isotopes with Atomic Mirror

Controlling the motion of silicon isotopes with an atomic mirror which is comprised of dielectric dual layers is numerically demonstrated under the realistic condition. The performance of the atomic mirror depends on the power and the effective detune frequency of the deep-ultraviolet light source which is enhanced in the dielectric waveguide layer. Taking advantage of these features and the frequency separation in isotopes, we can control silicon isotopes, furthermore, nuclear spin with the atomic mirror.

Research on nitride semiconductors for deep-ultraviolet light sources

Research on nitride semiconductors for deep-ultraviolet light sources

High-Power CW Deep-UV Coherent Light Sources Around 200 nm Based on External Resonant Sum-Frequency Mixing

We report pure continuous-wave (CW) high-power (>100 mW) deep-ultraviolet (DUV) light sources emitting around 200-nm spectral region based on singly resonant sum-frequency mixing (SRSFM). Efficient DUV generation is made possible by use of a Brewster-cut CsLiB/sub 6/O/sub 10/ (CLBO) crystal near noncritically phase-matched (NCPM) condition for the SFM of 1-/spl mu/m output of neodymium lasers. The CW radiation of fifth-harmonic wavelength of a neodymium laser at 213 nm was generated by the SFM of enhanced 1064-nm radiation with single-passing 266-nm radiation produced by external-resonant frequency doubling of a 532-nm green laser. With 1.8 W of 266-nm radiation incident upon a CLBO crystal, as much as 180 mW of CW 213-nm power has been produced. The sub-200-nm CW radiation with 140-mW power has also been achieved by SFM of 1064 nm with 244-nm radiation from a frequency-doubled Argon-ion laser in the CLBO crystal operated near the NCPM condition.

Development of a Continuous-Wave, Deep-Ultraviolet, and Single-Frequency Coherent Light Source—Challenges Toward Laser Cooling of Silicon

Laser cooling techniques of silicon may be a powerful tool to create a new silicon road map. In the first step, to realize the laser cooling of neutral silicon atoms highly efficient frequency conversions are conducted to obtain a deep-ultraviolet single-mode coherent light using two-stage external cavities. The 154-mW power at around 252 nm is obtained with a conversion efficiency of more than 8% by doubly resonant sum-frequency mixing of 373-nm light from the first-stage conversion and 780-nm light from a single-mode Ti:sapphire laser. This paper reviews a series of challenges for taking possession of the spatial design of nuclear spins of the family of stable isotopes with laser cooling of silicon.

Deep ultraviolet scanning near-field optical microscopy for the structural analysis of organic and biological materials

Scanning near-field optical microscopy (SNOM) using a deep ultraviolet (DUV) light source was developed for in situ imaging of a variety of chemical species without staining. Numerous kinds of chemical species have a carbon–carbon double bond or aromatic group in their chemical structure, which can be excited at the wavelength below 300 nm. In this study, the wavelength range available for SNOM imaging was extended to the DUV region. DUV–SNOM allowed the direct imaging of polymer thin films with high detection sensitivity and spatial resolution of several tens of nanometers. In addition to the polymer materials, we demonstrated the near-field imaging of a cell without using a fluorescence label.

Efficient sum-frequency generation of continuous-wave single-frequency coherent light at 252 nm with dual wavelength enhancement

Highly efficient frequency conversions were conducted to obtain deep-ultraviolet single-mode coherent light by use of two-stage external cavities. A power of 154 mW at approximately 252 nm was obtained with a conversion efficiency of more than 8% by doubly resonant sum-frequency mixing of 373-nm light from the first-stage conversion and 780-nm light from a single-mode Ti:sapphire laser. The output performance of the deep-ultraviolet light source is sufficient for use in the laser cooling of neutral silicon atoms.

New product developments

The recent development of group III nitrides allows researchers world-wide to consider AlGaN based light emitting diodes as a possible new alternative deep ultra–violet light source for surface decontamination and water purification. In this paper we will describe our recent results on plasma-assisted molecular beam epitaxy (PA-MBE) growth of free-standing wurtzite AlxGa1−xN bulk crystals using the latest model of Riber's highly efficient nitrogen RF plasma source. We have achieved AlGaN growth rates up to 3 µm/h. Wurtzite AlxGa1−xN layers with thicknesses up to 100 μm were successfully grown by PA-MBE on 2-inch and 3-inch GaAs (111)B substrates. After growth the GaAs was subsequently removed using a chemical etch to achieve free-standing AlxGa1−xN wafers. Free-standing bulk AlxGa1−xN wafers with thicknesses in the range 30–100 μm may be used as substrates for further growth of AlxGa1−xN-based structures and devices. High Resolution Scanning Transmission Electron Microscopy (HR-STEM) and Convergent Beam Electron Diffraction (CBED) were employed for detailed structural analysis of AlGaN/GaAs (111)B interface and allowed us to determine the N-polarity of AlGaN layers grown on GaAs (111)B substrates. The novel, high efficiency RF plasma source allowed us to achieve free-standing AlxGa1−xN layers in a single day's growth, making this a commercially viable process.

Optical Nanolithography Using Evanescent Fields

ABSTRACTIn the optical near field region the well understood resolution limits for projection optical lithography can be overcome. This offers the possibility of performing optical nanolithography without the need to use expensive, deep ultraviolet light sources. For exposures that utilise evanescent fields close to metallic amplitude masks sub-diffraction-limited resolution has been achieved experimentally, and the theoretical resolution limits have been explored using vector electromagnetic near field simulations. Resolution down to 20nm using exposure wavelengths greater than 400nm is predicted. It is also found that the exposure wavelength is of secondary importance in this regime, and that the properties of the mask are much more significant. Scaling to smaller feature sizes requires better resolution and control during mask manufacture, rather than the conventional (and costly) approach of driving the exposure wavelength deeper and deeper into the ultraviolet. Near field interference effects have also been explored, and the characteristics of spatial frequency doubling using Evanescent Interferometric Lithography (EIL) have been determined by simulation. Sub-diffraction-limited resolution can be achieved with increased exposure intensity compared with conventional interferometric lithography. The tradeoff is against the depth of field in the resultant interference pattern. Finally, the use of negative refraction and surface plasmons have been investigated to improve further the resolution in the evanescent near field, and to produce novel, three dimensional near field patterns.