. Method for structuring a substrate having an upper surface and a lower surface, said method being characterised by the following steps: a) providing a device comprising: - a light source for generating a structuring incoming light beam capable of machining said upper surface of said substrate, the pulses of the structuring incoming light beam having a duration between 10 -14 s and 10 -8 s; - an optical system for obtaining, from said incoming light beam, an outgoing light beam spatially offset in relation to said incoming light beam, said optical system being capable of modifying the spatial offset between said incoming light beam and said outgoing light beam; - focusing means for focusing said outgoing light beam, the outgoing light beam being spatially offset in relation to the incoming light beam while remaining parallel to the direction of the incoming light beam upstream of the focusing means; - a substrate holder; - a movement device for generating a relative movement between said outgoing light beam and said substrate holder; b) providing and placing said substrate on said substrate holder so as to have towards said focusing means its upper surface characterised by a normal; c) generating with the light source the incoming light beam; d) generating from the incoming light beam as it passes through the optical system, then through the focusing means, a focused outgoing light beam describing with said normal of said upper surface of said substrate at a focusing point of said outgoing light beam an angle of attack greater than 1°, preferably greater than 3°, for any spatial offset between outgoing light beam and incoming light beam imposed by said optical system; e) initiating a relative movement between said substrate holder supporting said substrate and said focused outgoing light beam for etching a pattern from the upper surface of said substrate, said formed pattern comprising a cavity in the substrate opening through an opening at the upper surface of the substrate; defining parameters of said light source according to said relative movement initiated in step e) for generating said incoming light beam such that the cavity of the formed pattern is non-through between said upper surface and said lower surface of said substrate, the cavity having a shape of a groove with a depth in the range of 10 to 200 μm. a) providing a device comprising: - a light source for generating a structuring incoming light beam capable of machining said upper surface of said substrate, the pulses of the structuring incoming light beam having a duration between 10 -14 s and 10 -8 s; - an optical system for obtaining, from said incoming light beam, an outgoing light beam spatially offset in relation to said incoming light beam, said optical system being capable of modifying the spatial offset between said incoming light beam and said outgoing light beam; - focusing means for focusing said outgoing light beam, the outgoing light beam being spatially offset in relation to the incoming light beam while remaining parallel to the direction of the incoming light beam upstream of the focusing means; - a substrate holder; - a movement device for generating a relative movement between said outgoing light beam and said substrate holder; - a light source for generating a structuring incoming light beam capable of machining said upper surface of said substrate, the pulses of the structuring incoming light beam having a duration between 10 -14 s and 10 -8 s; - an optical system for obtaining, from said incoming light beam, an outgoing light beam spatially offset in relation to said incoming light beam, - focusing means for focusing said outgoing light beam, the outgoing light beam being spatially offset in relation to the incoming light beam while remaining parallel to the direction of the incoming light beam upstream of the focusing means; - a substrate holder; - a movement device for generating a relative movement between said outgoing light beam and said substrate holder; b) providing and placing said substrate on said substrate holder so as to have towards said focusing means its upper surface characterised by a normal; c) generating with the light source the incoming light beam; d) generating from the incoming light beam as it passes through the optical system, then through the focusing means, a focused outgoing light beam describing with said normal of said upper surface of said substrate at a focusing point of said outgoing light beam an angle of attack greater than 1°, preferably greater than 3°, for any spatial offset between outgoing light beam and incoming light beam imposed by said optical system; e) initiating a relative movement between said substrate holder supporting said substrate and said focused outgoing light beam for etching a pattern from the upper surface of said substrate, said formed pattern comprising a cavity in the substrate opening through an opening at the upper surface of the substrate;