An image forming apparatus has an electrostatic latent image bearing member capable of bearing an electrostatic latent image thereon, and a developer apparatus having a developer material for visualizing the electrostatic latent image into a visualized image. The packaged electronic chip includes a MEMS device, an integrated circuit and a wire bond electrically coupling the MEMS device and the integrated circuit. The sheath includes a circumferential wall that strains and circles around the sidewall of the probe, and an infrared window fitted on an opening at the front end of the probe.