Optical film, sputtering target, and method of producing optical film

A method of producing an optical film having transmissivity in a visible wavelength band, having absorbance in a near-infrared wavelength band, and having radio wave transparency, the optical film comprising cesium, tungsten, and oxygen, in which a refractive index n and an extinction coefficient k of the optical film at each of wavelengths [300 nm, 350 nm, 400 nm, 450 nm, . . . , 1700 nm] specified at 50 nm intervals in a wavelength region from 300 nm to 1700 nm are set respectively within numerical ranges of a TABLE, as set forth below, characterized in that the method comprises:

• forming the optical film by a dual-sputtering method using a sputtering target of a cesium source and a sputtering target of a tungsten source and feedback-controlling an oxygen partial pressure of a dual-sputtering film formation atmosphere
• TABLE
• Wavelength
• Refractive
• Extinction
• (nm)
• Index
• Coefficient
• 300
• 2.2 to 3.2
• 0.6 to 1.6
• 350
• 2.1 to 3.1
• 0.0 to 0.8
• 400
• 1.8 to 2.8
• 0.0 to 0.6
• 450
• 1.6 to 2.6
• 0.0 to 0.6
• 500
• 1.4 to 2.4
• 0.0 to 0.6
• 550
• 1.1 to 2.1
• 0.0 to 0.6
• 600
• 0.8 to 1.8
• 0.0 to 0.7
• 650
• 0.6 to 1.6
• 0.1 to 1.1
• 700
• 0.7 to 1.7
• 0.5 to 1.5
• 750
• 0.9 to 1.9
• 0.6 to 1.6
• 800
• 1.1 to 2.1
• 0.5 to 1.5
• 850
• 1.0 to 2.0
• 0.4 to 1.4
• 900
• 0.8 to 1.8
• 0.4 to 1.4
• 950
• 0.6 to 1.6
• 0.4 to 1.4
• 1000
• 0.4 to 1.4
• 0.6 to 1.6
• 1050
• 0.3 to 1.3
• 0.8 to 1.8
• 1100
• 0.3 to 1.3
• 1.1 to 2.1
• 1150
• 0.2 to 1.2
• 1.3 to 2.3
• 1200
• 0.3 to 1.3
• 1.4 to 2.4
• 1250
• 0.3 to 1.3
• 1.6 to 2.6
• 1300
• 0.3 to 1.3
• 1.8 to 2.8
• 1350
• 0.3 to 1.3
• 1.9 to 2.9
• 1400
• 0.3 to 1.3
• 2.1 to 3.1
• 1450
• 0.3 to 1.3
• 2.2 to 3.2
• 1500
• 0.3 to 1.3
• 2.4 to 3.4
• 1550
• 0.4 to 1.4
• 2.5 to 3.5
• 1600
• 0.4 to 1.4
• 2.6 to 3.6
• 1650
• 0.4 to 1.4
• 2.8 to 3.8
• 1700
• 0.5 to 1.5
• 2.9 to 3.9.