Chirped laser mirrors

R. Szipocz, A. Kobazi-Kis Theory and designs of chirped dielectric laser mirrors. Appl. Phys. B 65, 115 (1997)... 

C. Spielmann, M. Lenzer, F. Krausz, R. Szipocs, and K. Ferencz, Chirped Dielectric Mirrors Improve Ti Sapphire Lasers , Focus World 12, 55 (1995). 

FIGURE 6.2 Generation of ultrafast laser pulses using a filamentation technique. Tube 1 and Tube 2 are filled with Ar gas at approximately 1-atm pressure in order to obtain spectral broadening. CDMl and CDM2 are sets of chirped dielectric mirrors that are used to achieve temporal compression. Ml-6 are high-reflectivity mirrors. Al-3 are apertures. The temporal characterization of the output beam is by spectral phase interferometry for direct electric-field reconstruction (SPIDER). 

Figure 5. (A) Scheme of two-photon laser scanning microscope (1) Ti Sa laser, 100 fs, 80 MHz, 750-980 nm, 1.6W 800 nm (TSUNAMI, Spectra Physics), (2) pre-chirp, (3) beam multiplexer, (4) scanning mirrors, (5) microscope (Olympus IX 71, XLUMPLFL20XW, WD = 2 mm, NA = 0.95), (6) fluorescent foci in sample, (7) filter wheel/spectrograph (SpectraPro 2300i, Acton Research Corporation)/spectrometer (home built), (8) back illuminated EMCCD camera (IXON BV887ECS-UVB, Andor Technology), (9) dichroic mirror (2P-Beamsplitter 680 DCSPXR, Chroma). (B) Experimental setup of two-photon laser scanning microscope.

The maximum incident pump power was 3.97 W. The folding mirrors, i.e., Ml and M2, had a 100 mm radius of curvature (ROC) and AR-coated below 1000 nm and HR-coated above 1020 nm. The laser beam was focused onto a semiconductor saturable absorption mirror (SESAM) by a concave mirror M3 with ROC = 50 mm. The chirped mirror pair, i.e., CMl and CM2, had a group-delay dispersion of -2000 fs per one round trip. The OC had a 1 % transmittance. 

The development of broadband saturable semiconductor absorber mirrors and of dispersion-engineered chirped multilayer dielectric mirrors has allowed the realization of self-starting ultrashort laser pulses, which routinely reach sub-10 fs pulsewidths and peak powers above the megawatt level. 

These mirrors may be regarded as one-dimensional holograms that are generated when a chirped and an unchirped laser pulse from opposite directions are superimposed in a medium where they generate a refractive index pattern proportional to their total intensity [693]. When a chirped pulse is reflected by such a hologram, it becomes compressed, similar to the situation with phase-conjugated mirrors. 

Another alternative for the generation of ultrafast pulses is the passive mode locking by fast semiconductor saturable absorbers in front of chirped mirrors (Fig. 6.35) in combination with Kerr lens mode locking [694]. The recovery time of the saturable absorber must be generally faster then the laser pulse width. This is provided by KLM, which may be regarded as artificial saturable absorber that is as fast as the Kerr nonlinearity following the laser intensity. Since the recovery time in a semi-... 

Fig. 6.36 Setup of the double-Z cavity for an ultrashort pulse Ti sapphire laser. The two prisms Pi and 2 and eight bounces on double-chirped mirrors M2-M6 provide flat dispersion. A second focus in a BK7-plate (P) leads to enhanced SPM, and the laser generates significantly wider spectra [695]...

There are several ways of generating short pulses. One is based on mode-locking lasers which have gain media with a broad special range. While the first experiments relied on dye lasers or Nd YAG-lasers, the Ti Sapphire laser has now become the most attractive choice. Some of the most commonly used materials are listed in Table 6.1 and [756]. Laser pulses down to 4 fs have been demonstrated using Ken-lens mode-locking and chirped mirrors. 

Fig. 2.2 Optical scheme of a typical laser system. Here we report an ultra-fast laser system based on Ti sapphire solid state active medium and on the Kerr lens mode-locking principle. The main oscillator uses the chirped mirrors technique and the regenerative amplifier is based on a chirped pulse amplification scheme...

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