Deep-ultraviolet Coherent Light Research Articles

DUV coherent light emission from ultracompact microcavity wavelength conversion device.

A unique design of our ultracompact microcavity wavelength conversion device exploits the simple principle that the wavelength conversion efficiency is proportional to the square of the electric field amplitude of enhanced pump light in the microcavity, and expands the range of suitable device materials to include crystals that do not exhibit birefringence or ferroelectricity. Here, as a first step toward practical applications of all-solid-state ultracompact deep-ultraviolet coherent light sources, we adopted a low-birefringence paraelectric SrB4O7 crystal with great potential for wavelength conversion and high transparency down to 130 nm as our device material, and demonstrated 234 nm deep-ultraviolet coherent light generation, whose wavelength band is expected to be used for on-demand disinfection tools that can irradiate the human body.

Gigahertz-repetition-rate, narrowband-deep-ultraviolet light source for minimization of acquisition time in high-resolution angle-resolved photoemission spectroscopy.

Ultrahigh-repetition-rate (1.1 GHz), deep-ultraviolet coherent light at 208.8 nm is generated by applying an external Fabry-Pérot cavity for repetition-rate multiplication to the fourth harmonics of a 10-ps, mode-locked Ti:sapphire laser. Its small pulse energy minimizes the unwanted space charge effect, while its high repetition rate drastically reduces the acquisition time in high-energy resolution angle-resolved photoemission spectroscopy using hemispherical electron analyzers. The absence of the space charge effect in the photoemission spectrum near the Fermi edge of polycrystalline Au at 8 K demonstrates this idea.

Targeting the Next Generation of Deep-Ultraviolet Nonlinear Optical Materials: Expanding from Borates to Borate Fluorides to Fluorooxoborates.

Coherent light radiation down to the deep-ultraviolet spectral range (λ < 200 nm) produced by common laser sources is extensively used in diverse fields ranging from ultrahigh-resolution photolithography to photochemical synthesis to high-precision microprocessing. Actually, it is hard to immediately obtain certain wavelengths, deep-ultraviolet coherent light in particular, from commercial laser sources. However, the direct second harmonic generation process governed in part by nonlinear optical crystals is a feasible and effective approach to generate deep-ultraviolet coherent light, which motivates chemists and materials scientists to find potential deep-ultraviolet nonlinear optical materials that can practically meet the scientific requirements. The research progress required to go from a new single-crystal structure to final device applications involves many pivotal steps and is highly time-consuming and challenging, and therefore, it is necessary to commence systematic studies aimed at shortening the research cycle and accelerating the rational design of deep-ultraviolet nonlinear optical materials. In this Account, we choose borates as raw materials because they have ever-greater possibilities to form desired noncentrosymmetric structures, wide optical transparency windows, rich structural chemistry, and also large polarizabilities to guarantee the coexistence of large second-order nonlinear optical coefficients and suitable birefringence. Besides, the effects of fluorine atoms on the structural chemistry and optical properties of borates have been summarized and analyzed. On the basis of these favorable influences, three specific rational design strategies, including experimental and theoretical methods, have been proposed in order to shorten the investigational cycle of discovering the new expected compounds with high physicochemical performances required for practical applications. In this way, the progress of searching for candidates for the next generation of deep-ultraviolet nonlinear optical materials was accelerated from borates to borate fluorides to fluorooxoborates with three effective strategies: (1) expansion of the frontier from borates to borate fluorides with the introduction of fluorine to achieve enhanced optical performance; (2) computer-assisted design of new deep-ultraviolet nonlinear optical materials with a newly introduced systematic global structure optimization method; and (3) expansion of the frontier from borate fluorides to fluorooxoborates by proposed functionalizedoxyfluoride [BO xF4- x]( x+1)- ( x = 1, 2, 3) chromophores to balance multiple criteria. The preliminary development of fluorooxoborates exhibiting high performance as a new fertile field to search for deep-ultraviolet nonlinear optical materials is highly encouraging and inspiring and can guide chemists and materials scientists with new directions and thoughts aimed at finding the next generation of practical deep-ultraviolet nonlinear optical materials.

Finding the Next Deep-Ultraviolet Nonlinear Optical Material: NH4B4O6F.

Nonlinear optical materials are essential for the development of solid-state lasers. KBe2BO3F2 (KBBF) is a unique nonlinear optical material for generation of deep-ultraviolet coherent light; however, its industrial application is limited. Here, we report a new material NH4B4O6F, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm. NH4B4O6F possesses large nonlinear coefficients about 2.5 times that of KBBF. In addition, it is easy to grow bulk crystals and does not contain toxic elements.

Beryllium-free Li4Sr(BO3)2 for deep-ultraviolet nonlinear optical applications.

Nonlinear optical (NLO) materials are of great importance in laser science and technology, as they can expand the wavelength range provided by common laser sources. Few NLO materials, except KBe2BO3F2 (KBBF), can practically generate deep-ultraviolet coherent light by direct second-harmonic generation process, limited by the fundamental requirements on the structure-directing optical properties. However, KBBF suffers a strong layering tendency and high toxicity of the containing beryllium, which hinder the commercial availability of KBBF. Here we report a new beryllium-free borate, Li4Sr(BO3)2, which preserves the structural merits of KBBF, resulting in the desirable optical properties. Furthermore, Li4Sr(BO3)2 mitigates the layering tendency greatly and enhances the efficiency of second-harmonic generation by more than half that of KBBF. These results suggest that Li4Sr(BO3)2 is an attractive candidate for the next generation of deep-ultraviolet NLO materials. This beryllium-free borate represents a new research direction in the development of deep-ultraviolet NLO materials.

Single-frequency nanosecond-pulsed deep-ultraviolet coherent light source at 252 nm for manipulating silicon atoms resonantly

A frequency-tripled deep-ultraviolet single-frequency nanosecond-pulsed Ti:Sapphire laser injection-locked with a cw single-frequency Ti:Sapphire laser was developed for the laser manipulation of silicon atoms with 252 nm resonant light. The cavity frequency of the slave-laser was controlled dynamically with a piezotransducer mounted on an output mirror to match the optical frequency of the seed laser, so as to minimize the build-up time of the slave-laser. Stable mode matching was achieved and resulted in high stability of the wavelength, making it sufficient for use in silicon atom optics.

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.

Fine Frequency Tuning in Sum-Frequency Generation of Continuous-Wave Single-Frequency Deep Ultraviolet Coherent Light with Dual-Wavelength Enhancement

Novel fine frequency tuning of the deep-ultraviolet single-mode coherent light at 252 nm was investigated by changing the temperature of the β-BaB2O4 (BBO) in doubly resonant external cavity for the sum-frequency mixing of 373-nm light and 780-nm light. The temperature-dependant frequency tuning rate is 19.3 MHz/°C, which is fine enough to realize the laser cooling of neutral silicon atoms.

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

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

Injection Effects of Nanosecond Pulsed Deep-Ultraviolet Coherent Light Source for Manipulating Atomic Wave of Silicon Atom

Injection Effects of Nanosecond Pulsed Deep-Ultraviolet Coherent Light Source for Manipulating Atomic Wave of Silicon Atom