1 Introduction

The line of demarcation between Ultra Violet [UV] and visible wavelengths is generally considered to be 400 nm. The relationship between wavelength and photon energy is given by E= (hc/λ) where h is Plank’s constant, c is the speed of light, and λ is the wavelength of light.

This equation shows that photon energy is solely dependent on the reciprocal of wavelength since both numbers in the numerator are constants. The smaller the wavelength the higher the energy carried by each photon. Therefore deep blue light, whose wavelengths are closer to the 400 nm boundary, carries more energy in each photon than light in other regions of the visible spectrum.

Examples of applications that benefit from higher photon energy are direct imaging lithography and some types of 3D printing. The former typically uses a photosensitive emulsion called a “photoresist” and the latter a photopolymerized resin. Typically photoresist and resin materials are more reactive to higher photon energy resulting in faster cure rates.

Remarkable design techniques are implemented in Digital Micromirror Devices [DMD] specified to operate down to 400 nm. Examples are the DLP7000BFLP, DLP9500BFLN, DLP6500BFLQ, DLP9000BFLS and DLP9000XBFLS. In particular 405 nm light can be used with this type of DMD. Light Emitting Diodes [LED] and laser diodes at this wavelength are now readily available at reasonable cost, making the use attractive in systems that use 405 nm optimized materials.

A TI DLP® DMD modulates light using reflective micromirrors that switch between two physical states. Since the primary modulation control of a DMD is reflection from aluminum micromirrors, these devices are significantly more tolerant of shorter wavelengths (higher energy photons) than other spatial light modulator [SLM] technologies that use organic molecules for modulation control since such molecules tend to degrade when exposed to these shorter wavelengths of light.^{Ref 1,2}

However the higher energy of shorter wavelength photons that are an excellent choice for lithography and 3D print systems requires greater attention to design considerations when used with a DMD, Important design considerations are explored in this application note.