Optical synchronously pumped

More recently Ghiggino and co-workers(32) have applied laser scanning confocal fluorescence lifetime microscopy to the study of polyvinyl alcohol films containing rhodamine B (650 nm emission) and cresyl violet (632 nm emission). Synchronously pumped dye laser excitation and APD detection were used with optical fiber coupling. A schematic diagram of their apparatus is shown in Figure 12.5. 

Khaydarov, J. D., Andrews, J. H., and Singer, K. D. 1994. Pulse compression in a synchronously pumped optical parametric oscillator from group-velocity mismatch. Opt. Lett. 19 831-33. 

Picosecond pulses can be produced in a number of different types of laser systems. As an example, a brief description is first given of a synchronously pumped c.w. dye laser such as can be readily assembled from commercially available units. Generation of repetitive subnanosecond pulses in a c.w. laser by mode-locked synchronous pumping was first described by Harris et al. [12]. The essential features of such a system are shown in Fig. 3. In this system, an acousto-optically mode-locked ion laser is used to pump the dye laser. In order to achieve synchronous pumping, the length of the dye cavity must be adjusted so that the dye laser intermode spacing is an integral multiple of the pump mode-locker frequency. 

The apparatus used to perform vibrational relaxation experiments in supercritical fluids consists of a picosecond mid-infrared laser system and a variable-temperature, high-pressure optical cell (68,73). Because the vibrational absorption lines under study are quite narrow (<10 cm-1), a source of IR pulses is required that produces narrow bandwidths. To this end, an output-coupled, acousto-optically Q-switched and mode-locked Nd YAG laser is used to synchronously pump a Rhodamine 610 dye laser. The Nd YAG laser is also cavity-dumped, and the resulting 1.06 pm pulse is doubled to give an 600 u.l pulse at 532 nm with a pulse duration of "-75 ps. The output pulse from the amplified dye laser ("-35 uJ at 595 nm, 40 ps FWHM) and the cavity-dumped, frequency-doubled pulse at 532 nm... 

The basis of the experimental femtosecond CARS apparatus developed by Okamoto and Yoshihara (1990) which is reproduced in Fig. 3.6-10 is essentially the same as that of Leonhardt et al. (1987) and Zinth et al. (1988) with the addition of the possibility to change the polarization of the laser radiation. The main parts of the system are two dye lasers with short pulses and high repetition rates, pumped by a cw mode-locked Nd YAG laser (1064 nm, repetition rate 81 MHz). The beam of the first dye-laser which produces light pulses with 75-100 fsec duration is divided into two parts of equal intensities and used as the pump and the probe beam. After fixed (for the pump beam) and variable (for the probe beam) optical delay lines, the radiation is focused onto the sample together with the Stokes radiation produced by the second laser (DL2), which is a standard synchronously pumped dye laser. The anti-Stokes signal generated in the sample is separated from the three input laser beams by an aperture, an interference filter, and a monochromator, and detected by a photomultiplier. For further details we refer to Okamoto and Yoshihara (1990). 

It is worth noting that the four-fold symmetry of hexadecapole moment is revealed only at the synchronous pumping and, what is important, at time moments when the hexadecapole moment is precisely aligned with one of its symmetry axis along the linear polarization of the field and the atomic coherence p 2, 2 in the M-system has its maximal value. The periodic change of the optical properties of atomic medium modulates the angle of tight polarization that leads to the FM NMOR resonances. If the time-dependent optical rotation is measured at the first harmonic of (.lm, a resonance is seen when Qm = k Ql which allows one to separate the NFS produced by different atomic PM. Indeed, in the experiment the in-phase and quadrature amplitudes of optical rotation,... 

The accumulated 3-pulse stimulated photon-echo method " was used in order to monitor vibrational relaxation times of the first excited electronic state of pentacene. Two amplified dye lasers were used to perform ps photon-echo measurements on pentacene and naphthalene samples, which established that pseudo-local photon scattering was responsible for optical dephasing in vibronic transitions. A mode-locked cavity-dumped synchronously pumped dye laser system was used to demonstrate long coherence times for the delocalized optical excitation of dimer states, by ps photon-echo spectroscopy. ... 

A three-pulse technique using a synchronously pumped mode-locked dye laser together with a modified Michelson interferometer has been described. By this technique, ps fluorescence decay times may be evaluated without the disadvantages of up-conversion or Kerr cell methods. The suitability of the system for the analysis of low. optical quality samples was suggested. An injection mode-locked Nd-YAG ring laser was used as an excitation source for a zero-background fluorescence study of the time evolution of the emission from large hydrocarbons with 12 ps resolution. ... 

Until recently, the pulses used in those experiments were the shortest optical pulses characterized. The transition-state spectroscopy of Zewail and Bernstein [16,17,18,19, 20,21 and 22] exploited an amplified CPM laser after frequency doubling and/or continuum generation. The chemical systems that were most easily studied, however, were those that could be stimulated either by the 620 nm output of the CPM directly or after frequency doubling to 310 nm. In addition, the CPM laser and its contemporary, more tunable alternative, the pulse-compressed, synchronously pumped dye laser [H], were tools that could be effectively used only by researchers with extensive backgrounds in lasers and optics. 

This unsatisfactory situation motivated Hesselink and Wiersma to attempt to generate and detect picosecond photon echos. Using a picosecond synchronously pumped dye laser system for excitation, and optical mixing as an echo-detection scheme they succeeded in measuring directly photon-echo relaxation times in the picosecond time domain. In Fig. 20 we show the results of such a picosecond photon-echo measurement on the... 

An instrument for optical biopsy of bones based on a diode laser and a single TCSPC channel is described in [151, 152]. Other instruments use a tuneable synchronously pumped dye laser and a Ti Sapphire laser [414]. The lasers are switched into a single source fibre by a fibre switch. A single TCSPC channel records the diffusely reflected light and a reference signal split off from the source fibre. 

For synchronous pumping the mode-locked pump laser Li, which delivers short pulses with the time separation T = 2d /c, is employed to pump another laser L2 (for example, a cw dye laser or a color-center laser). This laser L2 then operates in a pulsed mode with the repetition frequency / = l/T. An example, illustrated by Fig. 6.14, is a cw dye laser pumped by an acousto-optically mode-locked argon laser. 

For many applications the pulse repetition rate / = cfid (which is / = 150 MHz iox d = m) is too high. In such cases the combination of synchronous pumping and cavity dumping (Sect. 6.1.2) is helpful, where only every A th pulse k > 10) is extracted due to Bragg reflection by an ultrasonic pulsed wave in the cavity dumper. The ultrasonic pulse now has to be synchronized with the mode-locked optical pulses in order to assure that the ultrasonic pulse is applied just at the time when the mode-locked pulse passes the cavity dumper (Fig. 6.16b). 

A KC1 T1° color-center laser with end mirrors MO and Ml is synchronously pumped by a mode-locked Nd YAG laser. The output pulses of the color-center laser at X = 1.5 nm pass the beam splitter S. A fraction of the intensity is reflected by S and is focused into an optical fiber where the pulses propagate as solitons, because the dispersion of the fiber at 1.5 pm is dn/dX > 0. The pulses are compressed, are reflected by M5, pass the fiber again, and are coupled back into the laser resonator. If the length of the fiber is adjusted properly, the transit time along the path M0-S-M5-S-M0 just equals the round-trip time T = 2d c through the laser resonator MO-Ml-MO. In this case compressed pulses are always injected into the laser resonator at the proper times t = - - qld / c q = 1,2,...) io superimpose the... 

Ryan, J. R, Goldberg, L. S., and Bradley, D. J. (1978). Comparison of synchronous pumping and passive mode-locking of CW dye lasers for the generation of picosecond and subpicosecond pulses, Optics Commun. 27,127—132. 

Scavennec, A. (1976). Mismatch effects in synchronous pumping ofthe continuously operated mode-locked dye laser, Optics Commun. 17, 14-17. 

The experimental set-up we used is shown in Fig. 2, A synchronously pumped mode-locked and cavity-dvunped dye laser, which can be timed to the D or Dj line of Cs, generates pulses of about 20 ps duration at a pulse rate of U MHz and peak powers of several hundred watt. They are split into linearly polarized pump pulses and stronger circularly polarized probe pulses, which pass an optical delay line. Both beams are focussed into a common interaction region where they act on the Cs vapor, which is contained in a cell at room temperature. The radiated wave propagating in pump pulse direction is detected by a photomultiplier, which measures the transmitted average intensity behind a crossed polarizer as a function of the delay time. 

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