Elliott Helium-Neon Laser

In 2008 I had found an interest laser on ebay, I had not seen any other. This tube is of a hot-cathode variety with a filament located in the larger glass chamber. The glass bore is of similar design to modern Helium-Neon tubes.

One interesting design of the resonator is the use of external mirrors and an intra-cavity adjustable aperture (akin to a camera lens aperture).

One experiment I had performed was an Aerotech laser tube, this had an internal Brewster window with an external mirror. I was able to separate the mirror from the tube and allow for alignment within the Elliott resonator.

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Elliott Helium-Neon Laser

One of the most important factors when working with lasers are the safety considerations and minimisation of risks of injury.

Lasers pose the most risk to our eyesight, even small powered (low energy density) lasers in the milliwatt output range can produce enough laser light to cause permanent damage to the retina.

Lasers produce optical energies from ultra-violet, visible and infrared parts of the electromagnetic spectrum, and either as a pulsed or continuous wave (CW) output.

The effects lasers have on biological tissue, through various mechanisms, is influenced by their wavelengths and their output (optical power, CW vs Pulsed).

The following list summarises the pathological effect to the eye caused by lasers operating at different wavelengths.

• Ultra-violet lasers (180nm-400nm) pose risks to the cornea and lens (photokeratitis and cataract).

• Visible lasers (400nm-780nm) pose risks to the retina and cause retinal burns.

• Infrared lasers (780nm-1mm) capable of affecting most of the eye.

High-power lasers also present a risk to the skin via photochemical or thermal burns. Depending on the wavelength, the beam may penetrate both the epidermis and the dermis. Ultra-violet lasers present a risk to the epidermis with similar effects as a "sunburn".

The topic on Laser safety is a considerable subject area, and furthermore, the important criteria of calculating the Maximum Permissible Exposure (MPE); the highest power or energy density (in W/cm² or J/cm²) of a light source that is considered safe, can be rather complex.

For futher reading on laser safety: Laser Safety, Wikipedia.

Coherent System 900 Photocoagulator

Over the years I have been fortunate to have been give some old / ex medical lasers. Some of the major system included the Coherent system 900 series photocoagulator, 920 Dye and the 930

Most recently I also acquired two Coherent Ultima 2000 On-demand argon laser units which are still operational.

I also have a number of ND-YAG cavities from the Coherent 7900 series YAG lasers.

Norseld Copper Bromide II Laser

Not very common to come across as a surplus unit, however I was fortunate enough to be able to acquire a Copper Bromide II laser that was being sold off and then later another unit was saved from being thrown away.

The lasers are an Australian manufactured unit by Norseld in South Australia for cosmetic and medical industry.

The laser tube is also made in Australia by a glass blower, Jess Fisher whom meticulously makes them from quartz glass.

The power supply for this laser is of the older variety using a hydrogen thyratron to switch the high voltage at high frequency.

The laser tube features three vertical extensions in which hold the Copper Bromide II material and are held inside a heated pot.

The tube is filled with neon buffer gas, when powered, the heaters are activated to begin the heating process. After around 10-min, the high-voltage will fire, causing the tube to discharge in the typical neon glow. The discharge will continue to heat the tube, as the copper vapour pressure continues to rise, the tube begins to lase.

The laser outputs two distinct wavelengths at 578.2nm (Yellow) and 510.6nm (Green).

Power output is around 8 Watts, with a power distribution of 2.5W yellow and 5.5W green and is a pulsed output at around 16kHz with a pulse width of 30ns.

The output windows are quartz, with a slight angle to prevent reflection back which would affect lasing due to the operational physics of a Copper Vapour system.

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Copper Bromide Laser