Ⅲ-1. Atomic & Solid State Physics (Ion)

RIKEN Accel. Prog. Rep. 52 (2019)

Development of UV microbeam irradiation system by glass capillary optics
S. Kawamura,∗1,∗2 T. Ikeda,∗1,∗2 M. Mori,∗1,∗2 M. Ikekame,∗1,∗2 Y. Hikima,∗1,∗2 T. Minowa,∗1 and W. G. Jin∗1
The tapered glass capillary is known to be a powerfultool for producing ion microbeams. Many studies on ion
microbeam produced by the glass capillaries as well as
its application of irradiation to a living cell have beenreported.1) Several years ago, a group from Toho university and RIKEN started studies on the visible-light microbeams by glass capillaries.2) Recently, we have developed an ion microbeam irradiation system with a visiblelaser microbeam.3–5) Another irradiation setup based on
UV-laser microbeams will be newly introduced to a beamline of RIKEN Pelletron accelerator so that the ion andUV-laser microbeam irradiations can be switched quickly
without any changing around the sample stage. Thistime, we will report the details on the UV-laser microbeam proﬁles and the estimation of the beam energy
byglasscapillaryperthepulse([J])
by the optics.
glass capillary optics.
The glass capillary was fabricated from a straight glass
tube made of borosilicate, whose inner and outer diameters are 1.8 mm and 3.0 mm, respectively. The glass
capillaries were made using a puller (Narishige PE-22) byheating a straight glass tube and pulling both ends witha constant force. The outlet diameter a of the capillary
was determined using a microforge (Narishige MF-900).
Figure 1 shows the experimental setup for beam proﬁle measurement. In this measurement, we used a diodelaser with wavelength (λ) of 375 nm. A ﬂuorescentscreen was used to obtain the spot shape at the distanceL, called irradiation distance, from the capillary outlet.
The spot pictures were taken by a digital camera thatis installed behind a ﬂuorescent screen. Generally, thespot shapes for L > 1 mm and L < 100 µm are likea Fraunhofer diﬀraction pattern and a Fresnel pattern,
respectively,
which areare known
knownasasringspotpatterns
images for a parrespectively, whichallel beam entered a small circular aperture. In previousstudy, the spot pictures with Ar+ laser with λ = 488 nm
were analyzed for L > 1 mm and L < 100 µm.4) We
will support the pin-point irradiation to the nucleus in aliving cell. Therefore, we deﬁned the irradiation distance(L = 17 µm) and obtained spot diameters D(FWHM)
for the microbeam. Figure 2 shows the results of D asMirror
Diode laser (375 nm)
Fluorescent screen
Glass capillary
Objective lensL∗2Toho University
RIKEN Nishina CenterFig. 3. Density enhancement of the extracted laser beam for
λ = 375 nm with diﬀerent outlet diameters a.

a function of a at L = 17 µm. In this experiment, weobtained smaller spots for smaller outlet capillaries without high-order rings like a Fraunhofer diﬀraction pattern.
The spot shapes are good for irradiating a small target
like the nucleus in a living cell.
Using a power sensor (Ophir PD-300) and photodiode(HAMAMATSU S2281), we measured the beam powerfor diﬀerent glass capillaries, and estimated the focusingability. To estimate the focusing ability of the capillaries,
we introduced density enhancement, which is the ratio
between the output beam density at the outlet and theinput beam density at the inlet.
Figure 3 shows the density enhancement for glass capillaries that have diﬀerent outlet diameters. This resultmeans that the tapered glass capillary has a strong focusing ability even for UV-laser beam (λ = 375 nm). In thenear future, we will install this system to the beam lineof the Pelletron accelerator and for biological irradiation.
References

MirrorFig. 1. Experimental setup for beam proﬁle measurement.
∗1Fig. 2. Spot diameters D(FWHM) for glass capillaries with
diﬀerent outlet diameters a. The input laser wavelength
was 375 nm. L is the irradiation distance.

1) T. Ikeda et al., Appl. Phys. Lett. 89, 163502 (2016).
2) W. G. Jin et al., J. Phys. Soc. Jpn. 84, 114301 (2015).
3) M. Koushima et al., J. Phys. Conf. Ser. 875, 112004 (2017).
4) K. Sato et al., RIKEN Accel. Prog. Rep. 51, 21 (2018).
5) K. Hirose et al., RIKEN Accel. Prog. Rep. 51, 193 (2018).

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