- Innovations and Services
The first picture of a moving body was made in order to analyze the movement of objects too fast for the human eye to be clearly identified. In the famous article by J.D.B Stillman and E. Muybridge a running horse was the object. An example much closer to nowadays' realities would be pump-probe spectroscopy, which was introduced in the 19th century for exploring shock waves. So, in order to analyze short processes which change rapidly in time, we need as short as possible light pulses, as they define time the resolution of our experiments or setups. Laser sources exceeding long pulses were a breakthrough [1, 2]. Only several decades had passed until the first ultrashort pulses were demonstrated using passive-mode synchronization in dye lasers . Since then, ultrashort pulse systems became a universal tool to make not only scientific research but were also used in industrial, medical and other applications. Pulses exceeding several optical cycles were used to monitor molecular dynamics, to make the micromachining of various materials .
One of the main characteristics of the short pulse is a broad spectral range. All these spectral components in the pulse have to be in a specific manner or, as it is called, "in phase" to form a transform limited pulse . This means that the pulse is then travelling in a dispersive medium, and phase changes have to be compensated to maintain it short. Several different methods have been proposed over the years. Most of them are based on diffraction gratings , prism pairs , dispersive mirror [8-11) or a combination of these methods [5, 12]. Each of the aforementioned methods has its benefits and drawbacks. The grating and prism systems can create large amounts of negative dispersion, but they are sensible to alignment errors, have a low efficiency and cannot compensate a higher-order dispersion in a wide spectral range. Meanwhile, dispersive mirrors can efficiently compensate a higher-order dispersion, are easy to align, but can create a limited amount of dispersion . However, today dispersive mirrors are most widely used when it comes to pulse compression, mostly because of the alignment advantage and flexibility to have a varying dispersion in a wide spectral range [14-16]. Since the first demonstration of a chirped mirror in 1994 , a lot of different designs have been proposed to modify the classical one: At present, it is possible to distinguish at least five most popular lypes of these mirrors: double ehirped [17-19], Brewster [20, 21 ], complementary pair [16, 22, 23], high dispersion (HDM) [II, 14, 24], BASIC  mirrors. Each type has its own benefits, but in general they all are ttying to solve several problems related to chirped mirrors: 1) GVD dispersion oscillations caused by interference at the interface between the air and the mirror surface; 2) a large GVD characteristic sensitivity to deposition errors; 3) the amount ofGVD introduced in one bounce from such a mirror.