J. Eur. Opt. Society-Rapid Publ. 22, 46( 2026) 455
ultrafast imaging [ 22 ], and temporal and spatial shaping of femtosecond beams [ 23 – 25 ]. Therefore, the employment of fs pulses requires careful consideration to ensure that the high peak power of the electric fields does not damage the DMD. Then, achieving a complete characterisation of their interaction with ultrashort pulses, particularly femtosecond( fs) pulses, has become a central objective in photonics research.
Although some studies have already investigated the laser-induced damage on DMDs, they were initially focused on continuous sources. For example, the first study of DMD damage was conducted using continuous light, where damage occurred at the intensity of 19 kW / cm 2 [ 26 ]. However, the phenomena associated with continuous light differ from those observed with pulses, where the electronic excitation and the electron-phonon coupling become more significant [ 27 ]. In this context, previous studies have investigated laser-induced damage thresholds for ns and ps pulse durations. For instance, one study used a 532 nm laser with a 10 ns pulse duration and reported a damage threshold fluence of 0.13 J / cm 2. The same study also examined picosecond pulses( 9.2 ps), for which a fluence of 1.5 J / cm 2 was determined [ 28 ]. In the femtosecond regime, a similar approach has been applied to the material from which the micromirrors are fabricated, aluminium. Although a universally accepted damage threshold for femtosecond pulses in aluminium has not been established, studies provide indicative values. Under a helium atmosphere, the threshold fluence for aluminium has been measured at around 0.4 J / cm 2 [ 29 ], and nanoscale damage has been observed at fluences of 0.06 J / cm 2 [ 30 ]. Thus, in depth investigation of employing ultrashort pulses on the DMD is necessary to address the literature gap. In addition to the evaluation of DMD damage by ultrashort pulses, a deeper understanding of how DMD affects the temporal duration and broadband spectrum of the pulse is also essential to include in the characterisation of DMD-laser interaction.
This study presents a comprehensive characterisation of the interaction between near-infrared fs laser pulses and a DMD. This includes an analysis of the device’ s fluence threshold within a multi-pulse framework, the measurement of the temporal dispersion introduced by DMD, a theoretical study of the behaviour under ultrafast pulsed lasers and an examination of how the DMD affects the laser’ sbroadband spectrum. To illustrate the capability of the DMD, we employed SPI techniques to retrieve the intensity profile of the ultrafast laser pulse.
2 Multishot laser-induced damage threshold material and methods
In this section, we characterise the multishot laser-induced damage threshold( LIDT) of the DMD under ultrafast laser irradiation. But before that, we will first briefly review the characteristics of the DMD and, explain the basic physical processes involved in the DMD-pulsed-laser interaction. Then, a detailed description of the experimental procedure used to determine the LIDT of the DMD is also provided.
Figure 1. The bulk mirror refers to the aluminium micromirror, the silicon part contains the yoke, the hinge, the torsion hinge and the micromirror address electrodes, the Metal-3 layer contains are the bias / reset bus, the yoke address electrodes and the via 2 contact to CMOS. The ceramic refers to the memory cell or CMOS SRAM.
The DMD is monolithically fabricated by complementary metal-oxide-semiconductor( CMOS) compatible processes over a single-crystal silicon CMOS static randomaccess memory( SRAM) cell, a detailed structure is given in ref [ 31 ]. Thus, it can be separated onto three layers, according to its thermal properties [ 32 ]: The bulk micromirror( a), the silicon( b) and the ceramic( c), shown in Figure 1.
The bulk mirror part refers to the aluminium micromirror. The silicon part starts at the yoke, contains the hinge, and the three connected layers, where metal-1 and metal-2 are the underlying interconnects for the third layer, the ceramic, which contains the CMOS memory. Among these layers, the aluminium and silicon-based layers are the sites of various physical processes, which are crucial to understanding the response of the DMD to laser irradiation. Particularly, the aluminium micromirrors have metallic surfaces in which the incident laser energy is primarily absorbed by free electrons. This absorption is then followed by rapid energy relaxation within the electronic subsystem, which subsequently transfers energy to the atomic lattice through electron-phonon coupling. Because the electronic heat capacity is much smaller than that of the lattice, the electron temperature can reach very high transient values while maintaining a minimum heat diffusion. Meanwhile, in dielectric materials such as silicon, heat transfer is strongly suppressed. Ultrafast laser ablation of both metals and dielectric materials generally proceeds through multiphoton ionisation and avalanche ionisation to form a neutral plasma, eventually leading to optical breakdown [ 27, 33 ]. In previous studies, the aluminium ablation threshold was measured for a 100 fs pulse at 800 nm in a multi-pulse configuration was measured to be 0.52 J / cm 2 [ 34 ]. In the case of the DMD, the system is more complex, so it is essential to conduct experiments to determine the damage threshold fluence and ensure its durability and long-term stability in ultrafast laser applications.