Mode-locked Nd:YAG laser

The third order optical susceptibility was measured by degenerate four-wave mixing (DFWM). A single pulse at 1.064 pm with a full width at half maximum of 35 ps was selected from the output of a passively mode locked Nd/YAG laser and split into three... 

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... 

Optical pumped UV lasing spectrum of ZnO film was observed as shown in figure 5. The samples were optically pumped by a frequency-tripled mode-locked Nd YAG laser 355nm, lOHz repetition rate, 15ps pulse width. The pump beam was focused to a spot with diameter of about 20 pm on the surface of ZnO film. The threshold of lasing was as low as 0.24 pJ. From the lasing spectrum, we could find that much narrow lasing peak with line-width less than 0.6nm. This was due to self-formed resonator cavities [14]. 

Figure 3.6-10 Schematic diagram of a femtosecond time-resolved CARS apparatus. YAG, cw mode-locked Nd YAG laser ML, mode locker PL, polarizer A s, apertures LP, laser pot DM, dichroic mirror DLl, femtosecond dye laser SA, saturable absorber CLFB, cavity-length feedback system DL2, picosecond dye laser W, tuning wedge E, etalon FD, fixed delay VD, variable delay BS, beam splitter P s, half-wave plates (when necessary) F s, filters S, sample MC, monochromator PMT, cooled photomultiplier. (Okamoto and Yoshihara, 1990).

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). 

Fig. 11. Experimental setup for the in situ detection of chemisorbed CO during catalytic combustion of CO on Pt using optical infrared-visible sum frequency generation (SFG) and mass spectrometry. A mode-locked Nd YAG laser system is used to provide the visible laser beam (second harmonic 532 nm) and to pump an optical parametric system to generate infrared radiation (wir) tunable with a pulse duration of 25 ps. MC monochromator, PMT Photomultiplier, AES Auger Electron Spectrometer, LEED Low Energy Electron Diffraction Spectrometer, QMS Quadrupole Mass Spectrometers for CO Thermal Desorption (TD) and CO2 production rate measurements.

For the detection of chemisorbed CO, a 40 ps mode-locked Nd YAG laser system was used which has been described in detail elsewhere. A... 

The reactive intermediates leading to the (charge-transfer) photodecomposition of the 6w(arene)iron(II) acceptor are revealed by picosecond time-resolved spectroscopy. For example, photoexcitation of the CT absorption band of the ferro-cene-(HMB)2Fe complex (HMB = hexamethylbenzene) with the second harmonic output (at 532 nm) of a mode-locked Nd YAG laser (25-ps pulse width) generates a transient spectrum with an absorption maximum at 580 nm (see Figure 11 A). Careful deconvolution of this absorption spectrum reveals the superposition of the absorption bands of ferrocenium (Imax = 620 nm, e = 360 cm [162]) and (HMB)2Fe+ (2 ,ax = 580 nm, = 604 M" cm" [163]). 

All azocopolymer was employed by Hattori et to produce SRGs with pulsed lasers as well as with a cw laser. In the first experiment, s-polarized beams of a 532 nm line of the mode-locked Nd YAG laser were made to impinge on the polymer surface. The average beam power was 0.4W, with a pulse duration of 100 ps and repetition rate of 82 MHz. In the second experiment, an SRG with 25 nm modulation amplitude was formed by exposing the film to an interference pattern of two s-polarized lights with 2.8 W/ern intensity, for 40 minutes. Infrared (IR) absorption spectroscopy indicated... 

The first photochemical events in vision under physiological conditions have to be studied with picosecond spectroscopy because of the rapid formation 62,63,64>. Earlier observations have been made at low temperature. The formation lifetime of the first intermediate product (prelumirhodopsin) was measured to be less than 6 ps at room temperature 63). A double-beam picosecond spectrometer with a mode-locked Nd YAG laser was used 62). 

Selective action on nucleic acid components in solution by picosecond pulses and the production of irreversible photoproducts were reported by Angelov et al. 80,81). They used the fourth harmonic wavelength of a mode-locked Nd YAG laser at 266 nm near the maximum of the first electronic absorption band of nucleic acids the irradiation intensity amounted to about 1 GW/cm2. Figure 18 shows the dependence upon the photoproduct yield versus irradiation intensity. The photoproduct yield was determined by the relative change in optical density. The molecular character of action was found to be different for each type of bases 81 ... 

Figure 3.90. Dependence of the integrated absorption coefficient (%) on the angle between polarization vectors of light waves of a mode-locked Nd YAG laser generating 35-ps light pulses at the wavelength of 1.06 pm (dots correspond to experimental data and the solid line represents the result of computer simulation). (From Ref. [243] with permission of The Japan Society of Applied Physics.)...

Figure 1. Q-switched, mode-locked Nd YAG laser with two synchronously pumped dye lasers PC = Pockels cell POL = polarizer with escape window DLl, DL2 = cavity dumped dye lasers PMT = photomultiplier tube. (Reproduced from Ref. 7. Copyright 1986 American Chemical Society.)...

The apparatus employs a passively mode locked Nd/YAG laser oscillator, a Pockel cell pulse extractor, and Nd/YAG laser amplifier to produce laser pulses at 1064 nm. Non-linear crystals convert 30% of this light to 355 nm, which is used for excitation of the sample. The optical path length of the 355 nm light is varied by a computer-controlled time delay stage. 

Using a mode-locked Nd + YAG laser system to generate picosecond sample excitation pulses and picosecond probing continuum pulses in their double beam spectrometer, Spalink et. al. (30) were able to measure difference absorption spectra of irradiated samples of 11-cis-rhodopsin and 9-cis-rhodopsin at selected times after excitation by means of a PAR OMA-2 optical multichannel detection system. The difference absorption spectral data were obtained over the entire spectral range from 410 nm to 650 nm at one time with an OMCD as opposed to the... 

If the 3 u) pulse of mode-locked Nd YAG laser and the picosecond continuum are used as an excitation and a monitoring pulses, respectively, just as in the transmittance and diffuse reflectance laser photolyses, the time-resolution should be improved up to 10 ps. In this case the pulse width of the picosecond continuum is less than 20 ps, so that the multichannel diode array without gating function was used. A demonstration experiment was performed for poly(methyl methacrylate) film containing 15 wt% benzophenone. The transient absorption spectrum at about 650 ps obtained with 6 = 59° is... 

A ps absorption-emission spectrometer design which uses both pump-probe and streak camera measurement with a single-mode locked Nd-YAG laser has been described in detail.The theory of non-stationary time-dependent emission measurement and its application to ultrafast processes has been exemplified by analysis of data on the fs time-resolved emission from dye molecules in water.The power of this experimental technique is exemplified by the... 

Experimental Setup. The first example of a one-color pump-probe experiment on a picosecond time scale was given by Shank et al., where hemoglobin was studied, and dates back to the first mode-locked Ar" synchronously pumped dye laser systems developed by Shank and Ippen. Since then many different groups have made use of the one-color pump-probe technique. " A simplified scheme of such a setup is given in Fig. 3. A high repetition rate (76 MHz) frequency-doubled (532 nm) mode-locked Nd-YAG laser (or Ar ion laser) is used to pump a dye laser with 50-100 psec pulses. In the dye laser one dye jet functions as a lasing medium leading to pulses which can be shorter than 10 psec. An additional... 

Experimental Setup. In general, at the heart of a continuum pump-probe experiment is a high repetition rate laser. This can be a passively mode-locked CPM laser which is pumped by a cw Ar laser and which produces pulses typically shorter than 100 fsec around 620 nm with a pulse energy of approximately 0.1 nJ. Alternatively, a mode-locked Nd-YAG laser (532 nm) pumps a dye laser. In that case pulses at somewhat shorter wavelengths can be obtained, which are higher in energy when the same repetition rate is used (typically 0.5 nJ), but the pulses are usually longer, even after pulse compression (>100 fsec). 

Nanosecond timescale measurements were recorded on a mode locked Nd YAG laser system located in the CNRS Laboratoire de Chimie Physique A, Universite de Bordeaux... 

Pulse widths below 100 fs can be reached with this CPM technique [675, 676]. If the CPM ring dye laser is synchronously pumped by a mode-locked argon laser stable operation over many hours can be realized [677]. Using a novel combination of saturable absorber dyes and a frequency-doubled mode-locked Nd YAG laser as a pump, pulse widths down to 39 ps at A = 815 nm have been reported [678]. 

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... 

The single photon counting apparatus will be described elsewhere. For these experiments, we utilized the laser dye Styryl 9 in a cavity-dumped dye laser synchronously-pumped by a mode-lock Nd YAG laser. Using this instrument we were able to excite the sample between 800 and 890 nm at a repetition rate of 3.8 MHz. 

For excitation and detection of fine structure beats with a frequency of 517 GHz subpicosecond light pulses are necessary. For this purpose we used a synchronously pumped mode-locked dye laser with saturable absorber in the dye solution. The dye laser generates light pulses of about ItOO fs duration at a pulse rate of 8U MHz. It is pumped by a frequency doubled actively mode-locked Nd YAG laser and tuned to a wavelength of 589.3 nm for resonant excitation of the Na atoms into the 3p fine structure states. 

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