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Laser Safety

Topics:
Laser Beam Divergence
Laser Intensity
Max. Permissible Radiation
Min. Safety Distance
Damaging Effects
Laser Classification
Safety Goggles
Pulsed Laser

In this experiment the students are required to convert the essential theoretical contents regarding „Laser Safety“ into practice. The application and use of the basics in calculation defined within the standards is submitted and trained by means of practical examples. The experiment is composed of seven segments. Aspects such as the following ones have been considered:
1. Determination of the maximum permissible radiation (MPR) for skin and eyes.
2. Minimum safety distance from a radiation source for direct and indirect irradiation of the skin and the eyes (MSD).
3. Demonstration of the damaging effect of laser radiation.
4. Characterisation of pulsed laser systems.
5. In addition the experiment is supposed to generate a sensitivity for the dangers of laser use.
The fundamentals of VBG, EN 60825 or corresponding literature of laser safety must be known. The danger of lasers are understood by the characteristic properties of laser radiation. In comparison with other light sources, a high energy and power density can be obtained, because of the generally small beam divergence the radiation density can be very high even at large distances from the laser (potential danger of lasers used in metrology).
Not only direct radiation but also reflected and scattered radiation can cause damage at a large distance from the radiation source. Laser radiation can be generated within a broad spectral range. It extends from a few nanometers up to some hundred micrometers and is, in many cases, outside of the visible spectrum.
The damage of biological tissue (skin, eyes) depends strongly on the wavelength and on the duration of the exposure. This is of great importance under safety aspects when classifying lasers and fixing radiation limits which is also the subject of this workshop.
By means of five different laser sources, all parameters are measured in order to classify each laser and to determine the limits for which the laser can be considered as save. This also includes the characterisation of laser safety goggles.

Principle of Operation

A bank of five lasers (L1 to L5) is arranged in such a way, that the moveable beam bending mirror (S1) selects the beam to be measured. In front (P2) of each laser different modules can be placed to manipulate the beam properties as divergence or beam diameter. Other target modules as the simulator for human eye, attenuator etc. can be placed into the path P1. For the measurement of angular dependant parameters of scattering surfaces the rotatable holder S2 is used. The power meter head (PM) can be placed at various positions of interest

Required Equipment

Cat. No.	Qty.	Description	Illustration
02.2126 02.2132	2 3	Mounting plate OCM 650 for click 25 Mounting plate OCM 650 for click 30 Mounting plates are used to hold optical mounts. A characteristic feature of the mounting plates is the “click” mechanism of the inserts based on spring loaded spheres. Snapping in the groove of the inserted click mount, the optical element is kept in an exact position. On the other hand, the system allows a quick and easy change of the mounted inserts. The mounting plates are made out of special anodized aluminum. Mounted onto the carrier 20 mm, the mounting plates can be placed onto an optical rail.
02.2202	1	Filter plate holder FH 650 for 3 filters 50 x 50 x 3 mm including carrier 30 mm The holder can support a total of three filter plates with the dimension of 50x50 mm. The maximum thickness can be 5 mm. Lateral springs fix the filters within the holder. Round filters can be used by means of filter adapter.
04.0124	1	BG 39 Coloured glass filter In order to separate visible radiation (400 - 750 nm) from the above following wavelength (NIR), this filter is used. Commonly such a BG39 filter is used to remove residual pump power at 810 nm and fundamental laser radiation at 1064 nm from the second harmonic generated radiation at 532 nm. It has a size of 50x50 mm and a thickness of 3 mm fitting into the filter plate holder (02.2202).
04.0308	1	Iris aperture mounted in click 25 mount, max. opening 14 mm This variable iris aperture is mounted into a click 25 holder. Such an iris is commonly used to decrease the intensity in front of a photo detector, or to force a laser to operate in a single transverse mode when applied inside the optical resonator.
05.0240	1	Nd:YAG Laser, Q-switched 473 nm (blue) mounted on OCM 650 carrier platform This laser emits repetitive short pulses generated with a frequency doubled and q - switched Nd:YAG Laser with an emission wavelength of 473 nm. For the operation, the power supply 07.0232 is required.
05.0244	1	DIMO L3 Laser 543 nm (green) with mounting plate and carrier As laser source a solid state laser with an output power of 1 mW at a wavelength of 532 nm is used. The laser is mounted in a mounting plate centred to the optical axes of the rail system. The power supply of the laser is provided with a blanking input.
05.0246	1	L5 Nd:YAG Laser 1064 nm (near infrared) The laser module emits 100 mW laser radiation at a wavelength of 1064 nm generated from a diode pumped Nd:YAG Laser. The module comes with the required power supply and is fixed via two mounting plates to a carrier platform.
05.0302	1	HeNe-Pilot laser OCM 650-30 The laser consists of a well to its housing centrally aligned HeNe laser. The HeNe laser is a two-mode laser with a frequency difference of 900 MHz between both orthogonal modes, which are randomly polarised. This means that, although both modes are linearly polarised, the polarisation depends on the tube geometry. The beam diameter is 0.5 mm at the exit and the divergence is 1.5 mrad. The output power is 2.5 mW and belongs to the laser safety class 3b. The diameter of the housing is 30 mm and provides grooves to make use of the click facilities of the mounting plates with click mounts. The laser comes with its power supply HVPS-01, however, the shown mounting plates ( 2 x 02.0030) must be ordered separately.
05.0306	1	L4 HeNe laser 594 nm (yellow) including 2 mounting plates and carrier This Helium Neon Laser is designed to emit only the “yellow” line at 594 nm. The tube is accommodated to two mounting plates with carrier to be used within the optical rail system OCM650.
07.0102	1	PIN Si Photo detector BPX 61 complete with housing In a housing a PIN Si photo detector is mounted. Via a BNC connection the signal is fed to the respective pre-amplifier or oscilloscope. The module is clicked into the mounting plate, where it is fixed by means of three separate spring loaded balls which snap into the groove of the detector housing.
07.0232	1	TECC-01 Thermoelectrical cooler controller For the operation of the “blue” laser (05.0240), this controller has been designed. Besides the power supply, a temperature controller is integrated to stabilize the temperature of the laser head which is attached to a Peltier cooler. The optimum temperature is internally set with respect to the individual attached laser for the highest output power.
09.0201	1	OB Bread board incl. 7 mounted optical rails OCM650 This so called bread board provides all optical rails required for the performance of the experiment “Laser Safety”.
09.0202	1	MC Simulator for the human eye This module simulates the human eye and contains a convex lens for the eye lens and black paper for the retina. Inflammation of the paper illustrates the danger of laser radiation.
09.0203	1	MB Beam expander To reduce the diameter of a laser beam a combination of mounted concave / convex lens systems is used. With this module the up-conversion of a laser Class 2 to 3 is demonstrated.
09.0204	1	AO1 and AO2 Beam expander AO1 consists of a mounted achromat with focal length of 20 mm and AO2 of a mounted convex lens with f=60 mm forming a beam expander with a magnification of 3.
09.0205	1	S2 Rotatable mount for mirror and reflector# S2 is mounted on the moveable part of the hinged joined angle connector and serves as a mirror or scattering surface.
09.0206	1	S1 Moveable beam bending mirror The moveable beam bending mirror (S1) selects the laser beam to be measured. To cover the wavelength range from 473 nm up to 1064 nm, a protective coated aluminium mirror is used.
09.0207	1	ABS Set of attenuation filters incl. holder To reduce the peak power of the q - switch pulses of (L1) a set of two mounted round VG9 filters are used.
10.0200	1	EXP 20 manual	No illustration
Required Options
19.0160	1	Digital Dual Channel Storage Scope 150MHz Bandwidth With Monochrome LCD Display 125 k Long Memory and 12 Division Horizontal Display 25 GS/s Sampling Rate for Repetitive Waveforms Advanced Trigger: Pulse Width, TV Line, Event Delay and Time Delay
Options
19.0310	1	LM10 laser power meter including head 10W and console Features: Accuracy: ±2 LSD meter only. Net accuracy with any head is head accuracy plus instrument accuracy. Display: Three digit liquid crystal display (LCD) and conventional moving coil meter. Contrast can be adjusted via push buttons. Power Requirements: AC Operation: 230 VAC 50/60 Hz 7.5 VA Maximum 1.5 VA Typical DC Operation: Uses 2 standard 9 V transistor radio batteries. Unit is fully functional with one battery. Memory: Retains configuration information when turned off (wavelength correction values, display contrast etc.) Power Meter Head 10 W Power Max (W) 10.0 Power Min (W) 0.01 Resolution (W) 0.001 Aperture (mm) 26.0 Spectral Range (µm) 0.26 - 10.6
19.0312	1	LM2 laser power meter 50mW Features: Power Max (W) 0.050 Power Min (µW) 0.01 Resolution (µW) 0.001 Aperture (mm) 7.9 Spectral Range (µm) 0.4 - 1.0
09.0209	1	Set of Spare parts	No illustration