Optical parametric amplifier

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. 

Figure B2.1.1 Femtosecond light source based on an amplified titanium-sapphire laser and an optical parametric amplifier. Symbols used P, Brewster dispersing prism X, titanium-sapphire crystal OC, output coupler B, acousto-optic pulse selector (Bragg cell) FR, Faraday rotator and polarizer assembly DG, diffraction grating BBO, p-barium borate nonlinear crystal.

Cerullo G, Nisoli M, Stagira S and De Silvestri S 1998 Sub-8 fs pulses from an ultrabroadband optical parametric amplifier in the visible Opt. Lett. 23 1283-5... 

Reed M K, Steiner-Shepard M K and Negus D K 1994 Widely tunable femtosecond optical parametric amplifier at 250 kHz with a Ti sapphire regenerative amplifier Opt. Lett. 19 1855-7... 

Figure C3.5.3. Schematic diagram of apparatus used for (a) IR pump-probe or vibrational echo spectroscopy by Payer and co-workers [50] and (b) IR-Raman spectroscopy by Dlott and co-workers [39]. Key OPA = optical parametric amplifier PEL = free-electron laser MOD = high speed optical modulator PMT = photomultiplier OMA = optical multichannel analyser.

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

Optical nanoimprinting, 15 193—195 Optical nonimaging techniques, spray-related, 23 193—194 Optical nonlinearity, in crystals, 11 94 Optical parametric amplifiers (OPAs), 17 452... 

The femtosecond (fs) laser system consists of a TiiSapphire laser and a regenerative amplifier pumping two independent optical parametric amplifiers that provide laser pulses of around 100 fs duration over a very broad range of wavelengths (250-2000 nm). The signal is detected in the transmitted phase-matching direction lc = k3 + k2 — ki and recorded by a spectrometer with spectral resolution = 2 nm. The spectra are measured by scanning over the... 

We performed transient absorption measurements on BP(OH>2 with a spectrometer based on two noncollinearly phase matched optical parametric amplifiers (NOPAs) pumped by an homebuilt regenerative Ti Sapphire laser system or a CPA 2001 (Clark-MXR) [1,7]. The tunable UV pump pulses are generated by frequency doubling the output of one of the NOPAs. The other NOPA provides the visible probe pulses. The cross correlation between pump and probe pulses has a typical width (FWHM) of 40 fs. The sample is a cyclohexane solution of BP(OH)2 pumped through a flow cell with a 120 pm thick channel. 

The double-beam transient absorption spectrometer utilized in this work is described in detail elsewhere [3]. Briefly, the output from a 1 kHz Ti Sapphire laser is frequency quadrupled to generate the 200 nm photolysis pulses. The probe pulses are generated by frequency doubling the output of an optical parametric amplifier (OPA) pumped at 400 nm or by sum-frequency mixing of the OPA output with 400 nm and 800 nm pulses. The sample consisted of a 0.1 mm jet of aqueous KNO3 solution. The acidity of the solutions was adjusted by addition of HN03(aq). 

Transient spectra of solvated indole are measured in a 120 Jim liquid jet with a crosscorrelation of 80 fs by means of a white light continuum (450 - 740 nm) generated in a sapphire disc. The molecules are excited at 270 nm with pump pulses generated by frequency doubling the output of a noncollinearly phase matched optical parametric amplifier [2], Due to the short pump pulses there is a small yet finite probability for two-photon ionization in pure solvents. This allows us to study the spectral properties of the generated solvated electrons by measurements in pure solvents. The transient spectra of the indole solution are corrected for these solvent contributions. 

The laser system consisted of a home-built Ti sapphire fs laser oscillator and regenerative amplifier (RGA). The pulse duration was 50 fs at 800 nm and 1 kHz repetition rate. The output of the RGA was split into two parts. One part was used as pump pulse. The other part served as a source for the generation of probe pulses with the help of a non-collinear optical parametric amplifier (NOPA, Clark). The sample preparation was explained elsewhere [7]. Briefly, sodium (Alfa Aesar) was used as received and sodium bromide (Alfa Aesar) was dried and re-crystallized under vacuum. The preparation of the samples was carried out in a glovebox under argon atmosphere. Localized electrons were generated by heating the metal-salt mixture to 800 °C, i.e. well above the melting point of the salt. 

The experimental configuration of the pump-probe experiment is similar to Ref. [5]. A home built non-collinear optical parametric amplifier (nc-OPA) was used as a pump, providing Fourier-transform-limited 30 fs pulses, which could be spectrally tuned between 480-560 nm. In all experiments white-light generated in a sapphire crystal using part of the fundamental laser (800 nm), was used as probe light. In the pump-probe experiments the pump was tuned to the S2 0-0 band for carotenoids with n>l 1. In the case of M9, it was not possible to tune the nc-OPA to its 0-0 transition, and hence another nc-OPA tuned to 900 nm was frequency doubled and used for excitation. In addition to conventional transient absorption pump-probe measurements, we introduce pump-deplete-probe spectroscopy, which is sensitive to the function of an absorbing state within the deactivation network. In this technique, we... 

Sub-5-fs pulse generation from a noncollinear optical parametric amplifier and its application to ultrafast dynamics in polymers... 

Transform-limited (TL) visible pulses with as short as sub-5-fs duration have been generated from a noncollinear optical parametric amplifier and applied to the study of polyacetylene, polydiacetylene, azobenzene, and J-aggregates of porphyrin for optical -devices. 

Transform-limited (TL) visible pulses with as short as 3.9 and 4.7-fs duration have been generated from noncollinear optical parametric amplifiers (NOPA)[l-7], and they were applied to the study of various systems [8-14], We reported several new phenomena the direct observation of transition state during photochemical reaction by probing the change in the electronic transition probability induced by nuclear motion. In this paper four subjects are discussed. They are (1) NOPA, (2) polyacetylene, (3) polydiacetylene and (4) bacteriorhodopsin. 

Time-resolved fluorescence was used to detect rhodamine 6G (R6G), sulfor-hodamine 101 (SR101), and rhodamine B (RB). A Ti-sapphire laser (800 nm, 50 fs) was used, but the excitation wavelength has been converted to 400 nm (for R6G) or 532 nm (for SR 101 or RB) by an optical parametric amplifier or by second harmonic generation [676], In another report, fluorescence burst detection was used for detection of single chromophore molecules [677]. 

Recent Experimental Approaches Our most recent attempt to investigate the problem of ground-state heterogeneity experimentally uses tunable pump laser pulses derived from a home-made optical parametric amplifier (Fig. 1.9). A white light continuum is used to seed a two-stage optical parametric amplifier pumped by the second harmonic of a regeneratively amplified Ti-sapphire laser... 

Figure 1.9. The optical parametric amplifier (OPA). BS, beam splitter TFP, thin-film polarizer HWP, half-wave plate IMP, dichroic beam splitter or long wave pass filter F,...

Our laser system was a typical one it consists of a Tiisapphire femtosecond laser (Alpha 100/XS, Thales Laser) and an optical parametric amplifier (TOPAS femtosecond version, Quantronix). The laser system delivers a pulse... 

Experiments were performed using a visible optical parametric amplifier based on noncollinear phase-matching in /3-barium borate, followed by a pulse compressor using chirped dielectric mirrors. This optical source provides ultrabroadband pulses, with bandwidth extending from 500 to 720 nm, compressed to an almost transform-limited duration of 5-6 fs. The pump-... 

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