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Laser Module

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Laser module is a device or system which generates refined beam size, line length or pattern beam
designed for an industrial and military customer.
Dot, line, cross line beam generators are main products of Lanics.
 
Monochromatism :
consisting of a single wavelength or color, and emitted in a narrow beam. This contrasts with common light sources, such as the incandescent light bulb or LED which emit incoherent photons in almost all directions, usually over a wide spectrum of wavelengths.
Coherence and Interference:
the property of wave-like states that enables them to exhibit interference. It is also the parameter that quantifies the quality of the interference (also known as the degree of coherence). It was originally introduced in connection with Young’s double-slit experiment in optics but is now used in any field that involves waves, such as acoustics, electrical engineering, neuroscience, and quantum physics. In interference, at least two wave-like entities are combined and depending on the relative phase between them, they can add constructively or subtract destructively. The degree of coherence is equal to the interference visibility, a measure of how perfectly the waves can cancel due to destructive interference. Because of coherence, the beam has good directivity.

High Energy Density and Brightness :
Due to the coherence and monochcomatism, the laser module has high energy density and brightness.
 
Collimator lens collects a diversied beam to collimate and line generator spread collimated beam to
make a sharp line beam.
Collimator lens to make a dot beam are as listed below.
Type Lens Remark
Collimator(for Dot) spherical, non-spherical Collimation or focusing beam
Line Generator Deflection lens 45 degree (short range)
Cylinder,Cylindrical lens 10,15,30,45,60,90,120 degree
Cross Line Generator Deflectioon lens 45degree (short range)
Diffraction lens 5degree (short range)
Cylinder,Cylindrical lens 10,15,30,45,60,90,120degree
* Cylinder, cylindrical lens locates after the collimator.
 
LD is an abbreviation of Laser Diode, and called semiconductor diode.
After conjunction of P-type and N-type semiconductor, positive bias at P-type and negative bias at
N-type make high energy gap which derives the combination of holes and electrons to radiate the light.
The light amplified by resonator is a Laser.
LD is a simple PN junction PN semiconductor and the light is amplified by the polished surface of
light source.LD is very sensitive with current and circuit must be designed to drive proper
current.
Two types of circuit are currently in common. APC is an abbreviation of Automatic Power Control.
LD generates laser when the proper current is supplied to the device in the specified temperature.
If the unstable current causes increase of junction temperature, the output power decreases, and
hight emperature even break the LD junction. To prevent and compensate this phenomena circuit
monitors the output power of LD and regulates the current.
ACC is an abbreviation of Automatic Current Control, APC circuit supplies only specified current
without output power monitoring. ACC is usually applied to the pulse laser drive.
 
Picture1 is structure of TO-18 and TO-5, picture2 shows laser generation of picture1
Type Size
TO-18 5.6파이
TO-5 Pie 9
TO-3 eclipse
HHL rectangular
 
Picture1 shows the window glass under cap and LD chip located on the substrate. To radiates the
heat, heat sink mounted under submount. Lasing on the chip is described in the picture2, biased
current generates laser on both side of active layer.
Diffraction casuesd by narrow active layer derives the beam shape of eclipse with different colunm
length and row length. Laser beam is monitored by internal photo diode to provide monitoring signal.
 
In LD spec sheet, LD is distinguished to P and N type. When the case of LD must be connected to
ground, it is a p-type, vise versa.
 
For a thin double convex lens, all parallel rays will be focused to a point referred to as the principal
focal point. The distance from the lens to that point is the principal focal length f of the lens. For a
double concave lens where the rays are diverged, the principal focal length is the distance at which
the back-projected rays would come together and it is given a negative sign
If LD is located at the BFL of lens, parallel lay can be transmitted. However, because of spherical
aberration, different beam divergence angle, and astigmatism collimation is not easy.
Focus theorem is as picture below
 
With assumption of parallel beam incident from collimator to cylinder lens, the beam transmits as
following trace.
Because cylinder lens is spherical at only one side, incident beam has curvature about only one
axis, which decide length of line beam.
About another axis beam transmit directly, which decide beam width, line beam can be generated.
Following picture shows the lens shape.

If the incident beam is controlled to focus at the first surface of the cylinder lens, beam size can
be varied.
Which is how to control the beam width and length