Shinichiro Aoshima

Femtosecond time-resolved optical polarigraphy:?imaging of the propagation dynamics of intense light in a medium

A time-resolved imaging technique for visualizing ultrafast propagation dynamics of intense light pulses in a medium has been demonstrated. The method probes the instantaneous birefringence induced by a pulse in the medium. Through consecutive femtosecond snapshot images of intense femtosecond laser pulses propagating in air, ultrafast temporal changes in the two-dimensional spatial distribution of the optical pulse intensity were clearly seen.

Multiframe observation of an intense femtosecond optical pulse propagating in air.

We have demonstrated femtosecond time-resolved and picosecond time-interval successive observations of a single femtosecond optical pulse propagating in air with ultrafast self-modulation such as filamentation. A quadruple femtosecond probe pulse crossing an intense propagating pulse at picosecond intervals was able to capture directly four successive images of the propagating pulse as in a movie but with femtosecond time resolution. From this observation, we can directly analyze and recognize the propagation process, which is significantly affected by pulse-energy fluctuation, and (or) atmospheric turbulence from shot to shot.

Non-Contact Picosecond Electro-Optic Sampling Utilizing Semiconductor Laser Pulses

Non-contact picosecond electro-optic sampling utilizing semiconductor laser pulses, which is compact, easy to use and inexpensive, is described focusing on the recent improvements such as reduction of system noise, adoption of a longitudinal E-0 probe and its advantages, monitoring system of the measurement point, and improvement of the space dependent sensitivity. We demonstrate the equivalent input noise of 125mV/IHz with a temporal resolution of 45ps at a distance of 20gm between the probe tip and the device under test, with a 4.5s measuring time. We also discuss the possibility of absolute voltage measurement.

How the electro-optic probing system can contribute to LSI testing?

The electro-optic (E-O) probing system using laser diode (LD) for measuring the voltage waveform at internal nodes of high speed LSI is described comparing performance to other electric instruments. The voltage sensitivity was improved by using an external ZnTe E-O probe and a low noise LD. Two kinds of E-O probing systems have been developed; a sampling system using a pulsed LD has the frequency bandwidth of 10 GHz and the minimum detectable voltage of 430 /spl mu/V/spl radic/Hz, and a real time system using a CW LD and a high speed photo detector has 480 MHz and 23 mV with 700 accumulations. Each system is based on mechanical prober and a microscope. Approach of the E-O probe to the electrode is computer-controlled. The advantages of high temporal resolution, noncontact and noninvasive method have realized measurements for microwave devices and passivated electrodes. Dependency of the output signal on the space between E-O probe and electrode is discussed as well as that on the electrode width.<<ETX>>

Laser Pulse Tomography Using A Streak Camera

Non-destructive tomographic images for a semi-transparent bottle and fingers of man have been obtained in real time by using HAMAMATSU C1587 synchroscan streak camera and a colliding pulse mode locked ring dye laser which emits 615nm laser pulses with 100 femtosecond duration, as a probe. This new technique, Laser pulse tomography, has been invented by adopting the streak camera to analyze time delays of reflected and transmitted light from/through the object. Experimentally, spatial resolutions of approx. 1 mm for the tomographic direction and approx. 0.4 mm for the spatial direction on the objects have been achieved for the first time.

A multichannel time-of-flight system for observation of energetic ions of multispecies generated from relativistic laser plasma

A multichannel time-of-flight (TOF) system was constructed to observe the ions generated from relativistic laser plasma, where the ions have polychromatic energies and multiple species. The TOF system is composed of a ten-channel scintillation detector array and an electromagnet that generates a magnetic field of 0-1.24 T. The magnet field enables us to analyze protons, deuterons, and full-stripped carbon ions to 50, 25, and 150 MeV, respectively. The system experimentally identified protons of 0.27-1.6 MeV energy and ions of a half specific charge (deuterons of 0.3-0.8 MeV and full-stripped carbons of 1.8-4.8 MeV). The measured TOF values agree well with the calculated values within the designed accuracy; +/-2.5 ns for protons and +/-5 ns for the others (d or C(6+)) on each detector channel. Comparison of ion numbers detected by a track detector (CR-39) and the TOF system enabled us to obtain the number of ions detected on each scintillation counter with less than 16% error.

Tunable picosecond all solid-state Cr:LiSAF laser

Many kinds of experiments about all solid-state Cr:LiSAF laser have been made for the purpose of generating tunable femtosecond pulses. For the first time, a tunable all solid-state cw laser having tunability over more than 100 nm was developed by using new spectrum selection self-injection locking (SSSIL) method in 1992. We report that we have realized tunable picosecond radiation from an all solid-state laser with 146/spl sim/200 ps pulses in a 88 nm range. Also, 70 fs pulse generation was achieved using a Kerr-lens mode-locking pumped with an Ar/sup +/ laser.<<ETX>>

Sampling Optical Oscilloscope Using A Traveling-Wave Semiconductor Laser Amplifier

Optical sampling with a traveling-wave semiconductor laser amplifier driven by short electrical current pulses is experimentally investigated for the purpose of designing a simple, compact and sensitive solid-state sampling optical oscilloscope.The temporal resolution of about 350 ps with the chip gain of 10 dB is demonstrated. The minimum detectable power is about 45 nw, which corresponds to input optical energy less than 0.01 fRpuise. The larger chip gain of 23 dB with aperture time of 110 ps for optical sampling is obtained if the laser amplifier is driven near the dynamic threshold level, however unexpected output signals where the intensity variation is inverted are observed.

Optical Oscilloscope Capable Of Measuring Picosecond Electrical Waveforms

We have developed a new system for measuring picosecond electrical waveforms, where the advantages of electro-optic sampling are maintained, but the need for a complex short-pulse-laser is eliminated. The system utilizes two advanced technologies; an optical oscilloscope which is a conceptually new optical waveform analyzer with picosecond time resolution, and an electro-optic modulator for electric to optical signal convertor. Using this system, the waveform of the driving current and optical pulses from a laser diode have been simultaneously measured with the temporal resolution of < 25 ps.

Femtosecond Laser Flashed Frame Imaging Utilizing A Femtosecond Streak Camera

An excellent and simple multi-framing technique has been demonstrated as femtosecond laser flashed frame imaging utilizing a femtosecond laser and a femtosecond streak camera. A framing speed of approx. 2x1011frames/s has been achieved at the first time by illuminating a transmission pattern with successive 100 femtosecond laser pulses with interval time of 5 ps. The ultrashort light pulses can be obtained from a colliding pulse mode-locked ring dye laser.