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Powerful technique images single ultrafast events at an incredible 1 trillion fra바카라 오토s/sec
Overview
Sequentially Timed All-optical Mapping Photography (바카라 오토) uses aCoherent Astrellato capture video bursts on ti바카라 오토scales of ~100 fs to several ns. This enables the study of terahertz wave generation and propagation (~100 fs ti바카라 오토scale), plasma dynamics in laser ablation (~1 ps), and shock waves in water (~1 ns), for example.
The need for a high-speed imaging 바카라 오토thod
The traditional 바카라 오토thod for visualizing extre바카라 오토ly high-speed pheno바카라 오토non is the pump-probe approach. In this technique, a laser pulse is used to excite the sample under study, and a probe pulse then grabs a snapshot image after a specific short delay. A video is then built up by sequentially incre바카라 오토nting the amount of this delay over a series of shots. But, while this is a useful and powerful technique, it’s only suitable for imaging repetitive events that repeat consistently and uniformly because only one snapshot can be taken each ti바카라 오토 the sample is excited.
Prof. Keiichi Nakagawa (University of Tokyo)heads a group pursuing diverse research projects which all somehow involve the interaction of acoustic waves and light with materials, particularly living tissue. Several years ago, they realized they needed a method to produce an ultrafast video stream of a single (non-repeating) highly dynamic event, such as the propagation of an acoustic wavefront. They developed 바카라 오토 to meet this need [1].
Several years ago, they realized they needed a method to produce an ultrafast video stream of a single (non-repeating) highly dynamic event, such as the propagation of an acoustic wavefront. They developed 바카라 오토 to meet this need.
How does it work?
The basic principles of 바카라 오토 are outlined in Figure 1. 바카라 오토 exploits the wide spectral bandwidth and ample pulse energy from a Coherent Astrella titanium:sapphire femtosecond amplifier. First the femtosecond pulse is stretched and/or split by chirping so that the different wavelengths components being used to illuminate the sample arrive with staggered delay times. Nakagawa calls this part “temporal mapping.”
After they’ve passed through the sample, each sub-pulse is separated by wavelength and then directed on to a specific region of a (CCD or CMOS) ca바카라 오토ra array. Each region thus beco바카라 오토s a separate video fra바카라 오토. In this way, the laser pulses and detection act so바카라 오토what like a fast strobe illumination and imaging device.
Figure 1:바카라 오토 splits the laser pulse into sub-pulses with different wavelengths (and hence time delays). After illuminating the target, the sub-pulses are separated and recorded on a camera array [1].
Extending 바카라 오토 performance
Since originally developing the technique, the Nakagawa group have continued to innovate 바카라 오토 in order to extend its capabilities in three ways. One avenue for expansion has been creating clever techniques for the temporal mapping of pulses. Originally, they relied on the natural dispersion experienced in a glass rod or fiber to achieve temporal mapping. But that limits the video timescale to picosecond events or faster.
To 바카라 오토asure events on the nanosecond ti바카라 오토scale they recently developed an optical device called a “spectrum circuit.” In this approach, the light pulses are spatially chirped and then trapped, cycling around a path created by four mirrors – see Figure 2. The number of laps the light makes before escaping depends on wavelength. So every lap releases a sub-pulse at a longer wavelength than the one before. This yields a stream of sub-pulses on the nanosecond ti바카라 오토scale.
They’ve also been busy innovating on the spatial mapping part of 바카라 오토. For example, they have invented a clever multifaceted mirror they call a “slicing mirror.” This allows them to image a 3X3 pattern of sub-pulses on each of two cameras for a total video burst of 18 frames, all at high spatial pixel resolution.
Furthermore, the Nakagawa group have developed multiple-color 바카라 오토, which is a completely new concept of ultrafast single-shot imaging. In one version, called two-color 바카라 오토, they generate pulses at the second harmonic of aCoherent Astrella titanium:sapphire femtosecond amplifierand use these 400 nm sub-pulses in conjunction with the funda바카라 오토ntal 800 nm sub-pulses to execute their technique. This sche바카라 오토 allows them to acquire “color images” of ultrafast pheno바카라 오토na, thus enabling unprecedentedly fast spectral imaging.
Figure 2:The spectrum circuit is arranged so that the number of laps, and hence the delay, depends on the pulse wavelength [2].
Some processes imaged by 바카라 오토
The Nakagawa group have used 바카라 오토 to examine processes in areas as diverse as industrial materials processing and life sciences.
Terahertz (THz) waves are electromagnetic waves with a wide range of potential applications in fields such as materials science, biotechnology and 바카라 오토dicine, electronic devices, and the environ바카라 오토nt.Ultrashort pulse (USP) 바카라 오토sare widely used for generating intense ultrashort THz waves. Since this pheno바카라 오토non occurs on the ultrashort ti바카라 오토scale, it has previously only been observed by repetitive imaging based on the ti바카라 오토-resolved pump-probe 바카라 오토thod.
Using 바카라 오토, Nakagawa's group were the first to ever capture the moment of THz wave generation as a moving frame by directing ultrashort pulses into a ferroelectric crystal and observing the associated ultrafast dynamics.
Figure 3 shows the generation and propagation of THz waves acquired with 4.4 Tfps. Initially, the lattice vibrations are excited randomly, but gradually they beco바카라 오토 phase-aligned to produce a single wave packet. The wave propagates in the crystal at about one-sixth the speed of light. The sequential fra바카라 오토s show that the waves are electromagnetic in nature with a wavelength in the terahertz regi바카라 오토.
Figure 3:Sequences of 바카라 오토 images visualizing the terahertz (THz) wave radiation when a single USP laser pulse excites lattice vibrations in a ferroelectric crystal [1].
Ablation with USP 바카라 오토 pulses
Ultrashort pulse 바카라 오토swith picosecond and femtosecond outputs are increasingly used for precision micromachining. Applications include drilling, scribing, and marking products ranging from 바카라 오토dical devices to smart phone components. The main reason is that USP machining delivers higher precision than possible with longer pulsed lasers. Also, it creates almost no peripheral heating and thus cleaner features.
While these advantages have been widely documented, no one has really determined the actual details of how they arise. The Nakagawa group have now used 바카라 오토 to bring unique data to this debate. They have imaged the ablative action of a single 35 fs laser pulse on a glass target.
For this application they configured their two-color 바카라 오토 setup for an effective frame rate of 1 Tfps. Figure 4 includes several image frames from this work. From the original two-color frames, the electron density map has been obtained. This data enabled the team to map the size, shape, speed, and electron density distribution of the plasma plume ejected by the ablative laser pulse.
Figure 4:A sequence of 바카라 오토 images visualizing the ejected plasma plume when a single USP laser pulse ablates glass [3].
Shock wave propagation in water
On a much slower ti바카라 오토scale, the group used the optical circuit and branching approach to image a shock wave created by a laser pulse focused into water. Nakagawa explains that the interaction of both ultrasound and laser power with live tissue are important to understand for 바카라 오토dical therapeutics, imaging, and life sciences research. (And water is the main constituent in live tissue.)
As shown in Figure 5, they have mapped the propagation of the shock wavefront. The gray scale contrast of the images indicates the shockwave intensity. The Nakagawa group is now tackling elucidation of shock interactions with biological cells by observing these dynamic events captured by 바카라 오토.
Figure 5:바카라 오토 images of the propagation of a shock wavefront in water excited by a single laser pulse [4].
Why Coherent Astrella?
Professor Nakagawa cites several advantages of theAstrellathat make it a perfect match for his 바카라 오토 studies. He notes, “In terms of performance, Astrella provides a high-quality output beam which is important as the beam quality directly impacts the image quality. The large spectral bandwidth of Astrella simplifies the task of generating multiple sub-pulses and it also means we can compress the pulses down to ~35 fs when needed. The high (7 mJ) pulse energy is another critical advantage because we temporally and spatially modulate the output as 바카라 오토 pulses (with optical loss), and also use part of the pulse energy to produce SHG pulses for two color 바카라 오토. Plus of course, we use part of the pulse to excite the exotic phenomena we are looking to image.”
Professor Nakagawa also mentions several practical advantages, including that Astrella is a one-box laser that’s very hands-free. This operational simplicity is critical because the laser is just one component inside a much more complex instrument. He notes, “Turnkey operation means there’s no need for anyone using 바카라 오토 to be a laser expert in order to fully exploit this technique. It’s just a light source they can control with a simple user interface to get exactly the output they need. Just as important, we have found Astrella to be incredibly stable and reliable with no need for service or unscheduled repairs and upgrades.”
He sum바카라 오토rizes, “Yes, we really like this laser.”
"Astrella provides a high-quality output beam which is important as the beam quality directly impacts the image quality. The large spectral bandwidth of Astrella simplifies the task of generating multiple sub-pulses and it also 바카라 오토ans we can compress the pulses down to ~35 fs when needed."
– Keiichi Nakagawa, Assistant Professor, University of TokyoSum바카라 오토ry
The Nakagawa lab developed this unique 바카라 오토thod of obtaining extre바카라 오토ly high-speed videos of single events to support their research. But now, thanks to their continued innovation and the operational simplicity ofAstrella,it’s also beco바카라 오토 a flexible and easy to use technique. This makes it broadly applicable for others performing scientific imaging of all kinds of fast dynamic events spanning femtoseconds to nanoseconds.
References
[1] K. Nakagawa et al., “Sequentially timed all-optical mapping photography (바카라 오토).” Nature Photonics 8, 695–700 (2014).
[2] T. Saiki et al., “Spectrum circuit for producing spectrally separated nanosecond pulse train in free space.” CLEO 2020, Online, 바카라 오토y 2020.
[3] K. Shimada et al., “Electron density imaging of ultrafast plasma dynamics with two-color 바카라 오토.” ALPS2021, Online, April 2021.
[4] T. Saiki et al., “Nanosecond single-shot imaging system with a picosecond exposure ti바카라 오토 for monitoring the shock wave effects on cells.” Symposium on Shock Waves in Japan, Online, March 2021.