In which spectrum is laser generally invisible?

The infrared spectrum is where lasers are generally considered to be invisible. Most lasers emit light in wavelengths that extend beyond the visible spectrum, which ranges from approximately 400 to 700 nanometers. In the infrared spectrum, the wavelengths are typically longer than 700 nanometers, making them invisible to the naked eye. This characteristic is particularly relevant in various applications, such as in certain medical and industrial settings where infrared lasers are commonly used for cutting, welding, or therapeutic purposes.

In contrast, the ultraviolet spectrum (which ranges from about 10 to 400 nanometers) and the X-ray spectrum (below 10 nanometers) are also not visible, but the applications and settings for lasers in those ranges are less common in practical usage compared to infrared lasers. The visible spectrum contains light wavelengths that can be seen, so it does not apply to the question of invisibility.