Microscopy > Components > Laser Launchers & Components > Intensity Control of Ti:Sapphire Laser

Intensity Control of Ti:Sapphire Laser

The Intensity Control of Ti:Sapphire laser is designed for continuously controlling the laser power intensity of polarized lasers emitting in the wavelength range from 640 nm to 1050 nm and average power up to 100 W. The laser attenuator basic working principle makes use of a half wave-plate and a polarizer. The wave-plate is rotated through a stepper motor. The unit is controlled through the USB port of the computer.

The beam from the laser, which is vertically-polarized, first impinges onto a wave-plate that rotates its plane of polarization prior to entering into the polarizer: The wave-plate is mounted on a computer-controlled rotating stage. The achromatic zero-order wave-plate consists of two different birefringent crystals: crystalline quartz and magnesium fluoride (MgF2), in an air-spaced design for high power; achromatic quartz MgF2 wave-plates offer excellent retardation accuracy over broad wavelength. It is a zero-order wave-plate; the thickness of this plate is such that the difference in phase between the ordinary and extraordinary axis of the light beam passing through it is exactly half a wavelength. The zero order assures that the property is maintained over a broader range of wavelengths. When rotating the wave-plate by φ degrees, the polarization of the output beam is rotated by 2φ degrees. That is, full control of the intensity is achieved by rotating the wave-plate in the range 0 - 45°. When the wave-plate is rotated, the intensity at the output of the polarizer is regulated according to the Malus' law:

where I0 is the intensity of the light beam prior to impinging onto the polarizer and θ is the angle between the polarization of the incoming beam (direction of the electrical field) and the axis of the polarizer. The intensity is at its maximum when the polarization of the beam is aligned with the axis of the polarizer; it is null for θ = π / 2 when the polarizer axis is perpendicular to the polarization of the incoming beam. With respect to the angle of rotation of the wave-plate, the intensity at the output is:

The P component passes through with minimal loss; the S component is dumped outside the optical axis.

Unit

Dimensions 254 x 292 mm
Height Adjustability 105 - 140 mm
Power 110 - 240 V
Control USB Port

Polarizer

Diameter 25.4 mm
Material Calcite
Wavelength Range 650 - 1000 nm
Extinction Ratio Tp/Ts > 100,000:1, 400 - 1064 nm, unpolarized input
Transmission Tp > 92%, polarized input, with broadband AR coating; Tp > 95%, polarized input
Damage Threshold 500 W/cm2 CW, 4 J/cm2 with 10 ns pulses, typical
Wavefront Distortion ≤ λ/4 at 632.8 nm over full aperture
Acceptance Angle Wavelength dependent, from 4° full angle at 441.6 nm to 1° full angle at 1064 nm

Waveplate

Diameter 25.4 mm
Material Crystalline quartz and magnesium fluoride (MgF2), in air-spaced design
Wavelength Range 650 - 1000 nm
Retardation λ/2
Retardation Accuracy From ±λ/50 to ±λ/100

Maximum allowed laser power versus beam diameter

Beam Diameter (mm) 5 4 3 2 1
Laser Power (W) 100 64 36 16 4