Ti:Sapphire

Infrared pulses of 200 fs duration with 150 of bandwidth centred at 2000 were used in this study. They were generated in a two-step procedure [46]. First, a p-BaB204 (BBO) OPO was used to convert the 800 mn photons from the Ti sapphire amplifier system into signal and idler beams at 1379 and 1905 mn, respectively. These two pulses were sent tlirough a difference frequency crystal (AgGaS2) to yield pulses... 

Ti sapphire laser excitation Chem. Phys. Lett. 233 519-24... 

In order to achieve a reasonable signal strength from the nonlinear response of approximately one atomic monolayer at an interface, a laser source with high peak power is generally required. Conuuon sources include Q-switched ( 10 ns pulsewidth) and mode-locked ( 100 ps) Nd YAG lasers, and mode-locked ( 10 fs-1 ps) Ti sapphire lasers. Broadly tunable sources have traditionally been based on dye lasers. More recently, optical parametric oscillator/amplifier (OPO/OPA) systems are coming into widespread use for tunable sources of both visible and infrared radiation. 

These limitations have recently been eliminated using solid-state sources of femtosecond pulses. Most of the femtosecond dye laser teclmology that was in wide use in the late 1980s [11] has been rendered obsolete by tliree teclmical developments the self-mode-locked Ti-sapphire oscillator [23, 24, 25, 26 and 27], the chirped-pulse, solid-state amplifier (CPA) [28, 29, 30 and 31], and the non-collinearly pumped optical parametric amplifier (OPA) [32, 33 and 34]- Moreover, although a number of investigators still construct home-built systems with narrowly chosen capabilities, it is now possible to obtain versatile, nearly state-of-the-art apparatus of the type described below Ifom commercial sources. Just as home-built NMR spectrometers capable of multidimensional or solid-state spectroscopies were still being home built in the late 1970s and now are almost exclusively based on commercially prepared apparatus, it is reasonable to expect that ultrafast spectroscopy in the next decade will be conducted almost exclusively with apparatus ifom conmiercial sources based around entirely solid-state systems. 

The most connnon commercially prepared amplifier systems are pumped by frequency-doubled Nd-YAG or Nd-YLF lasers at a 1-5 kHz repetition rate a continuously pumped amplifier that operates typically in the 250 kHz regime has been described and implemented connnercially [40]. The average power of all of the connnonly used types of Ti-sapphire amplifier systems approaches 1 W, so the energy per pulse required for an experiment effectively detennines the repetition rate. 

The OPA should not be confiised with an optical parametric oscillator (OPO), a resonant-cavity parametric device that is syncln-onously pumped by a femtosecond, mode-locked oscillator. 14 fs pulses, tunable over much of the visible regime, have been obtained by Hache and co-workers [49, with a BBO OPO pumped by a self-mode-locked Ti-sapphire oscillator. 

Spence D E, Kean P N and Sibbett W 1991 60 fs pulse generation from a self-mode-locked Ti sapphire laser Qpt. Lett. 16 42—4... 

Pshenichnikov M S, de Boeij W P and Wiersma D A 1994 Generation of 13 fs, 5 MW pulses from a cavity-dumped Ti sapphire laser Opt. Lett. 19 572-4... 

Norris T B 1992 Femtosecond pulse amplification at 250 kHz with a Ti sapphire regenerative amplifier and application to continuum generation Opt. Lett. 17 1009-11... 

Joo T, Jia Y and Fleming G R 1995 Ti sapphire regenerative amplifier for ultrashort high-power multikilohertz pulses without an external stretcher Opt. Lett. 20 389-91... 

Le Blanc C, Grillon G, Chambaret J P, Migus A and Antonetti A 1993 Compact and efficient multipass Ti sapphire system for femtosecond chirped-pulse amplification at the terawatt level Opt. Lett. 18 140-... 

Backus S, Peatross J, Huang C P, Murnane M M and Kapteyn H C 1995 Ti sapphire amplifier producing millijoule-level, 21 fs pulses at 1 kHz Opt. Lett. 20 2000-2... 

Tilsch M and Tschudi T 1997 Self-starting 6.5-fs pulses from a Ti sapphire laser Opt. Lett. 22 1009-11... 

Brakenhoff G J, Squier J, Norris T, Bliton A C, Wade M FI and Athey B 1996 Real-time two-photon confocal microscopy using a femtosecond, amplified Ti sapphire system J. Microscopy 181 253-9... 

Figure C3.1.13. Experimentai configuration for far-UV nanosecond CD measurements using a frequency-upconverted Ti sapphire iaser as a probe source. Pj and P2 are Mgp2 Rochon poiarizers at cross orientations. SP is a strained transparent piate with about i ° of iinear birefringence for quasi-nuii eiiipsometric CD detection. Prism PMj and the iris Ij seiect the far-UV fourth hannonic of the argon iaser-pumped Ti-sapphire iaser s near-IR fundamentai output to probe the eiiipticity of the sampie. A second iaser beam at 532 nm is used to pump CD...

The most powerful teclmique for studying VER in polyatomic molecules is the IR-Raman method. Initial IR-Raman studies of a few systems appeared more than 20 years ago [16], but recently the teclmique has taken on new life with newer ultrafast lasers such as Ti sapphire [39]. With more sensitive IR-Raman systems based on these lasers, it has become possible to monitor VER by probing virtually every vibration of a polyatomic molecule, as illustrated by recent studies of chlorofonn [40], acetonitrile [41, 42] (see example C3.5.6.6 below) and nitromethane [39, 43]. 

A further advantage, compared with the alexandrite laser, apart from a wider tuning range, is that it can operate in the CW as well as in the pulsed mode. In the CW mode the Ti -sapphire laser may be pumped by a CW argon ion laser (see Section 9.2.6) and is capable of producing an output power of 5 W. In the pulsed mode pumping is usually achieved by a pulsed Nd YAG laser (see Section 9.2.3) and a pulse energy of 100 mJ may be achieved. 

The layout of the experimental set-up is shown in Figure 8-3. The laser source was a Ti sapphire laser system with chirped pulse amplification, which provided 140 fs pulses at 780 nm and 700 pJ energy at a repetition rate of 1 kHz. The excitation pulses at 390 nm were generated by the second harmonic of the fundamental beam in a 1-nun-thick LiB305 crystal. The pump beam was focused to a spot size of 80 pm and the excitation energy density was between 0.3 and 12 ntJ/crn2 per pulse. Pump-... 

For near-field imaging based on nonlinear or ultrafast spectroscopy, light pulses from a femtosecond Ti sapphire laser (pulse width ca. 100 fs, repetition rate ca. 

Figure 4.6 shows an apparatus for the fluorescence depolarization measurement. The linearly polarized excitation pulse from a mode-locked Ti-Sapphire laser illuminated a polymer brush sample through a microscope objective. The fluorescence from a specimen was collected by the same objective and input to a polarizing beam splitter to detect 7 and I by photomultipliers (PMTs). The photon signal from the PMT was fed to a time-correlated single photon counting electronics to obtain the time profiles of 7 and I simultaneously. The experimental data of the fluorescence anisotropy was fitted to a double exponential function. 

Figure 6.2 A fourth-order coherent Raman spectrometer constructed with a Ti sapphire regenerative amplifier (Ti sapphire) and noncollinear optical parametric amplifier (NOPA).

In addition, combining the microscope with the use of a pulsed laser light source provides temporal information on these systems in a small domain. The dispersion of refractive index, however, strongly affects the temporal resolution in the measurements of dynamics under the microscope and typical resolution stays around 100 fs when a Ti Sapphire laser is used as an excitation source. 

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