Lasers Design and Laser Systems Tel: 04-8563674 Nir Dahan Tel: 04-8292151 nirdahan@tx.technion.ac.il Thank You 1
Measuring the width of a laser beam is like trying to measure the size of a cotton ball with a caliper. -- Tom Johnston Course Subjects Beam diagnostics and laser safety Material processing Medical applications Optical communication Other applications 2
Safety Effects of Laser Energy on the Eye 3
Effects of Laser Energy on the Eye Effects of Laser Energy on the Eye The site of damage depends on the wavelength of the incident or reflected laser beam: Laser light in the visible to near infrared spectrum (i.e., 400-1400 nm) can cause damage to the retina resulting in scotoma (blind spot in the fovea). This wave band is also know as the "retinal hazard region". Laser light in the ultraviolet (290-400 nm) or far infrared (1400-10,600 nm) spectrum can cause damage to the cornea and/or to the lens. ( skin hazard ). I 0 7mm 16 µm 2x10 5 I 0 4
Effects of Laser Energy on the Eye Laser Classification ANSI Z136.1 5
Laser Hazard Classification Class 1 A Class 1 laser is considered safe based upon current medical knowledge. This class includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any exposure conditions inherent in the design of the laser product. There may be a more hazardous laser embedded in the enclosure of a Class 1 product, but no harmful radiation can escape the enclosure. Class 2 A Class 2 laser or laser system must emit a visible laser beam. Because of its brightness, Class 2 laser light will be too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous since the upper radiant power limit on this type of device is less than the MPE (Maximum Permissible Exposure) for momentary exposure of 0.25 second or less. Intentional extended viewing, however, is considered hazardous. Laser Hazard Classification Class 3 A Class 3 laser or laser system can emit any wavelength, but it cannot produce a diffuse (not mirror-like) reflection hazard unless focused or viewed for extended periods at close range. It is also not considered a fire hazard or serious skin hazard. Any continuous wave (CW) laser that is not Class 1 or Class 2 is a Class 3 device if its output power is 0.5 W or less. Since the output beam of such a laser is definitely hazardous for intrabeam viewing, control measures center on eliminating this possibility. Class 4 A Class 4 laser or laser system is any that exceeds the output limits (Accessible Emission Limits, AEL's) of a Class 3 device. As would be expected, these lasers may be either a fire or skin hazard or a diffuse reflection hazard. Very stringent control measures are required for a Class 4 laser or laser system. 6
Laser Hazard Classification Types of safety eyeware Goggles: fit tightly on the face typically worn over vision-correcting prescription eye glasses usually constructed with frame vents to minimize lens fogging larger, heavier than spectacles or wraps Spectacles: a frame that usually has two separate lenses with side shields can be made with vision-correcting prescription eye glasses Wraps: a frame with a single lens that covers both eyes usually lighter than spectacles/goggles 7
Laser safety (Israel) Laser safety (Israel) 8
Laser safety (Israel) Laser Safety - NOHD NOHD Nominal Ocular Hazard Distance 9
Laser Safety - NOHD NOHD calculation via NOMOGRAM Draw the red line from ENERGY OUTPUT through BEAM DIVERGENCE Find the intersection with INTEGRATED RADIANT INTENSITY From that point draw the blue line to the Radiant Exposure (set @ MPE value) Find the intersection with RANGE THIS IS THE NOHD (without turbulence) Add the turbulence factor Safety Goals Priority 1: Eliminating or minimizing dangers through constructive measures Example: covering dangerous areas (danger of being crushed, struck, etc.) Priority 2: Implementing necessary safety measures for dangers which cannot be eliminated Example: optical sensors for securing moving machine parts Priority 3: Informing users about remaining dangers which cannot be avoided by constructional or safety measures Example: a note in the operating instructions about wearing gloves as a means of protection against sharp edges or hot workpieces 10
Commercial Examples Closed safety cabin Optical sensors Laser System Standards (EC) Safety of machinery - EN 292 Electrical equipment EN 60204 Emergency stop equipment EN 418 Laser processing machinery pr EN 31553 Electromagnetic interference Product standards (RF, HV, harmonics) Basic standards, testing and measuring Generic standards, emission and immunity 11
Beam Diagnostics Power Spectral analysis (wavelengths meters) Location Temporal features (pulse duration) Cross section intensity distribution 2D beam shape 3D beam analysis Quality (M 2 ) Power Meters Visual Fluorescing plates (mainly for IR) Laser burn Thermopile Photodiodes Pyroelectric detectors and arrays CCD cameras 12
Laser burn Laser burn paper Wood sticks Acrylic materials Thermopile Surface Absorbers (Ophir) Flat spectral response - 0.19-20 micron Damage threshold up to 20KW/cm 2 Wide dynamic range µw to KW Fast response time as short as 1 second Option for water cooling 13
Photodiode Detector Heads (Ophir) Spectral response - 200-1100nm High sensitivity Pico Watt Low power only damage at 10 Watts/cm 2 Option for background subtraction Very fast response time 0.1-0.2 second Option for wavelength calibration Higher powers with Neutral Density Filters Pyroelectricity Pyroelectricity is the electrical potential created in certain materials when they are heated. Pyroelectric charge develops on the opposite faces of asymmetric crystals. Pyroelectricity is a migration of positive and negative charge to opposite ends of a crystal's polar axis as a result of a change in temprature. All pyroelectric materials are also piezoelectric, the two properties being closely related. 14
Pyroelectric Detectors Pulsed energy measurement Spectral response - 0.15-400 micron Damage threshold up to 10KJ/cm 2 High sensitivity micro Joules High repetition rate up to few KHz Option for arrays and cameras (124x124 matrix, 100 micron resolution) Beam Diagnostics The application Laser cavity become misaligned Off axis delivery optics Alignment of devices to lenses Laser modes change with power setting Fiber optic critical coupling You can get more out of your laser 15
Beam Diagnostics - Why? Beam Diagnostics - Why? 16
Industrial Beam Profilers (Spiricon) Measurement of High Power Beam 17
Mechanical scanning Instruments Rotating drum with Knife edge Slit Pinhole Rotating needle Down to 1 micron spatial resolution Optional 3D scan Rotating Needle Scan System For very high power (industrial) lasers The needle is placed directly in the beam A small hole allows a very small portion of the beam to enter the needle A 45º mirror in the hollow needle reflects the light to the detector The needle rotates in the beam and axially move in and out the beam It samples the beam in a complete 2 dimensional manner The needle introduce a very small distortion in the beam It enables on-line operation Only for CW lasers 18
ICCL 1600 TEM 01* Mode Needle Scan 2D Beam Profile with Cross Section 19
3D Beam Profile Display The M 2 Characteristic 20
The M 2 Characteristic Beam propagation characteristic of a laser beam Especially important for applications that requires Gaussian beam ISO definition for beam propagation factor In Europe: The beam factor k=1/m 2 Only second moment measurement follows the beam propagation laws 3D Multiple Measurements Method 21
Device with Fixed Position Lens A Typical Readout of M2 Measurement 22
Device with Moving Lens 23