Laser Safety, ANP 5 nov Working with lasers

Homework: calculate what goggles are needed at your setup! Laser Safety, ANP 5 nov

3 The sun is the brightest source.

Laser Safety, ANP 5 nov Eye “reference” values: Sunlight: 1000 W/m 2 (= 1 mW/mm 2 ) Pupil range Ø: 3 – 7 mm (7 –38 mm 2 ) Optical power received by the eye: 7 – 38 mW Eye blink reflex: 0.25 sec. (only applicable in the visible area)

Laser Safety, ANP 5 nov The human eye (simplified).

Types of photoreceptors Laser Safety, ANP 5 nov

Distribution of rods and cones Laser Safety, ANP 5 nov

8 Wavelength (λ) and impact.

Laser Safety, ANP 5 nov Classification EN Class 1:always safe 1M:always safe without focusing Class 2:safe, due to the blink reflex, <1mW 2M:safe, without focusing Class 3R:low risk of injury, restricted beam viewing, <5mW 3B:direct exposure = eye hazard, <0.5W Class 4:ALL OTHER LASERS (reflection from a matted surface up to a few watts is allowed)

Laser class Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov (il)legal? purchases… Dutch legislation Source: Informatieblad 26 / 4 september 2006, Voedsel en Waren Autoriteit: Laserpointer: no selling of class 3R, 3B and 4. Lasergadget: no selling of class 2, 2M, 3R, 3B and 4.

Laser Safety, ANP 5 nov Not always a laser…..

Laser Safety, ANP 5 nov Maximum Permissible Exposure Typically set at 10% of the dose creating damage with a probability of 50%, worst case conditions. Basis for selecting laser goggles. Warning symbol class 2 and up.

Laser Safety, ANP 5 nov MPE in W/cm 2.

Laser Safety, ANP 5 nov MPE in J/cm 2.

Laser Safety, ANP 5 nov MPE in J/cm 2.

Laser Safety, ANP 5 nov Eye protection terminology. Example of EN 207 specifications

Laser Safety, ANP 5 nov EN 207 laser working modes. EN 207 specifies four laser working modes: Working modeLetterPulse length Continuous modeD> 0.25 s Pulsed modeI>1 μs–0.25 s Giant pulsed modeR1 ns–1 μs ModelockedM< 1 ns

Laser Safety, ANP 5 nov EN 207 scale numbers. Range: L1-L10, Ln means that OD > n; n=0: no protection.

Laser Safety, ANP 5 nov Example 1, Q A laser operates at 1064 nm and has a pulse duration of 10 ns, 10 3 J/m². You have goggles that are specified as DIR 1064 L5 Do these goggles offer suitable protection for this particular laser?

Laser Safety, ANP 5 nov Example 1, A The pulse duration indicates that we should look at the R specification, with scale number n=5, which gives an upper limit of 5×10 2 J/m², which means that these goggles do not offer suitable protection for this particular laser. 1064nm/10ns/ 10 3 J/m² DIR 1064 L5 ??

Laser Safety, ANP 5 nov Example 2, Q A laser operates at 780 nm, is continuous wave with a power density of P = 500 W/m². Does a D 780 L2 rated goggle offer suitable protection for this particular laser?

Laser Safety, ANP 5 nov Example 2, A You need a D protection level of log(500) − 1 = 1.69, which is rounded up to 2. In other words, the safety goggles should be at least D 780 L2. 780nm CW, P=500W/m 2 D 780 L2 ??

Case: pulsed diode laser Laser Safety, ANP 5 nov Peak power 70 W λ peak = 905 nm Duty cycle = 0.1 % Application: Range finding, … Type: SPL-LL90-3, price per 27 may 2015: € per piece, 2 pieces, RS-Components.

Case: pulsed diode laser, precautions 25 “Depending on the mode of operation, these devices emit highly concentrated non visible infrared light which can be hazardous to the human eye. Products which incorporate these devices have to follow the safety precautions given in IEC "Safety of laser products". “ So lets calculate ourselves what laser goggles we need From the datasheet: Laser Safety, ANP 5 nov

Case: pulsed diode laser, safety 26 Rep. rate = 30 kHz Pulse duration = 30 ns Peak power = 70 W Wavelength = 905 nm For modulated lasers there are two ways to go : First, calculation assuming the thermal correction factor: Energy of one pulse = 30e -9 s x 70 W = 2.1e -6 J Assume all power enters the eye, the energy density = 2.1e -6 / 0.39 cm 2 = 5.4e -6 J/cm 2 = 5.4e -2 J/m 2 (= E) Thermal correction factor C p in 0.25 sec. = (30000 x 0.25) 0.25 = 9.3 Attenuation needed = log(C p x E/5) +3 = log(9.3 x 5.4e -2 / 5) + 3 = = 2.0 Laser Safety, ANP 5 nov

Case: pulsed diode laser, safety 27 Rep. rate = 30 kHz Pulse duration = 30 ns Peak power = 70 W Wavelength = 905 nm Second calculation method: assume (quasi) DC. For DC calculation, average power = Peak power x duty cycle = 70 W x 30 ns x pulses/second = 63 mW. Assume all power enters the eye, power density = 0.063/0.39 cm 2 = 0.16 W/cm 2 = 1600 W/m 2. Attenuation needed = log(P) -1 = log(1600) -1 = 3.2 – 1 = 2.2. The DC calculation gives the worst result(!), and OD 2 is just not good enough. OD3 however is on the safe side, considering the far from perfect beam profile. Laser Safety, ANP 5 nov

28 Goggles, summary. Consult the laser manufacturer Consider the Visible Light Transmittance Consider comfort Keep the goggles in good shape

Laser Safety, ANP 5 nov

Enclosure, black cloth curtain Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov Good practice in beampath design.

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov

Top 14 of laser related injuries, Rockwell Laser Industries Unanticipated eye exposure during alignment. Misaligned optics and upwardly directed beams. Available laser eye protection was not used. Equipment malfunction. Improper method of handling high voltage. Intentional exposure of unprotected persons. Operators unfamiliar with laser equipment. No protection provided for associated hazards. Improper restoration of equipment following servicing. Incorrect eyewear selection and/or eyewear failure. Accidental eye/skin exposure during normal use. Inhalation of laser-generated fume or viewing of secondary radiation (UV, blue light). Laser ignition of fires. Photochemical eye or skin exposure. Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov Laser accidents are: - High impact - Low probability

Laser Safety, ANP 5 nov To err is human Key to safety: Protocol, multiple lines of defense.

Laser Safety, ANP 5 nov Thank you!

Laser Safety, ANP 5 nov

Laser Safety, ANP 5 nov Luminosity function of the eye. Wavelength [nm]

Laser Safety, ANP 5 nov Good practice in beampath design.

Enclosure, black plastic curtain Laser Safety, ANP 5 nov

Case: Fianium SC400-4 What goggles to buy ???? Laser Safety, ANP 5 nov

Case: Fianium SC400-4 Pulse width: 6 ps Total power: > 4 W Rep. Rate: 40 MHz Beam diameter at 633 nm: 1.5 mm Laser Safety, ANP 5 nov Peak power = 17 kW Peak Energy = 100 nJ

Case: Fianium SC400-4 MPE curve not directly applicable (λ dependancy) Calculate energy density for open pupil area: E = 100e -9 / 0.39 = 25e -8 J/cm 2 = 25e -4 J/m 2. In 0.25 s, 10 e6 (=N) pulses occur, thermal correction factor N 1/4 applies (EN 60825). Cp=(10 e6 ) 0.25 = 56. Attenuation needed = log(E/1.5)+4= log(56*25e-4/1.5) +4 = 3.0. DC calculation: log(P)-1 = log(4/0.39*1 e4 )-1 = = 4.0 (!) Laser Safety, ANP 5 nov

Case: Fianium SC400-4 Laser Safety, ANP 5 nov Transmitted: ~7 mW, still not safe.

Case: Fianium SC LaserVision T1L01, VLT = 30 %, € Laser Safety, ANP 5 nov Transmitted: 60 mW, OD needed = 2.2 Conclusion: still not safe. From 1400 nm to 2400 nm: ~OD4.

Case: Fianium SC Thorlabs LG2, VLT = 19 %, € Laser Safety, ANP 5 nov Transmitted (vis): 105 mW, OD needed 2.4 Conclusion: still not safe.

Case: Fianium SC % protection Laser Safety, ANP 5 nov