HCAL Laser Upgrade Study

German MartinezFlorida International University

Vasken HagopianFlorida State University

Present Laser• Nitrogen; pulsed; 337 nm and 300 µJ when new. Long time delay between pulse and laser light. Time jitter can be as high as 20 nsec Lifetime (30% drop in intensity) in 20 million pulses.

• Uses.1.Pulses to HPD’s and PMT’s for time and gain calibration. 2.Pulses to scintillator Megatiles (HB and HE Radiation

damage studies)3.HF RADDAM (an after thought)4.ZDC (another after thought).5.Not yet Castor …

Present Laser• Distribution and conversion.– Filters wheels and a moving stage control the light level

output and the detector to which the light is sent. – Light splitters at the laser room and on the detector side

distribute the light to the different components – Laser UV light is converted to an appropriate wavelength

in each case • Green light for HPD’s• Blue light for PMT’s and HF RADDDAM• Direct UV for Megatiles

– Wide range of light levels required.• i.e HPDs need 103 less light than Megatiles, HFRADAM.

– Note: The conversion is done in the Calibration Boxes for HPD’s and the HF PMT’s through appropriate scintillators. Changing the laser wavelength may require to modify all the Calibration Boxes if the scintillators are not excited by a new wavelength.

Problems with present laser system

• Three laser units (+2 lower power) in stock but:– the manufacturer no more in nitrogen laser business

• Time jitter is significant and changes from laser to laser and with aging.

• Occasional firing without external signal prevent its use during abort gap.

• High intensity needed for HF RADDAM bleaches the wavelength shifter scintillator.

Laser upgrade options1. Replacement of the current laser by a similar laser

of another manufacturer– Moderate costs, even for more powerful lasers i.e. 1mJ

pulse laser: 15,000 U$D (Not sealed unit)– Would require minimal changes (mechanics) – Could use a dye in a dedicated laser instead of

wavelength shifter to solve the HF RADDAM bleaching problem

– Jitter and misfiring will probably still be a problem .

Laser upgrade options

2) Q-switched Solid lasers Wide range of options (wavelength, power, pulsing length) in the

market.– Minimal jitter– Relatively expensive (i.e. 50uJ/pulse Blue laser 35,000 U$D) – Will need at least two types (blue and UV).– May need to redesign the laser table optics.– May need to redesign HF calibration boxes.

Laser upgrade options3) Laser Diodes• Low cost high power diode lasers are now on market.

– i.e. 1 watt CW blue laser cost ~ $ 00. 3̄ 3̄�

• 1 Watt blue laser (~450 nm) would have enough power in 10 nsec for RADDAM (no wavelength shifter needed).

• Low cost of laser diodes could allow the use different diodes for different detectors.

• Lower power UV diode lasers exist. Not yet powerful enough for Megatiles.

• Do not yet know if we can pulse it with 10 nsec signal.• Can they be easily focused to a 250 μm fiber?• Engineering costs (pulsers, optics, calibration boxes) may be

significant.

One (1) watt blue laser

Q Switched UV Laser 355 nm100 micro joule per pulse

What have we done so far

• Survey market. Several of the diode lasers came to the market during the past several months.

• Ordered three 100 mW continuous wave lasers at FNAL (about $32 each).

• Sergey Los at FNAL will try to pulse these lasers.

PLANS and costs• Provide two separate laser systems.• There are Q-switched lasers on the market but cost

about $ 35,000 (would need at least 2).• New diode lasers that can be pulsed (Nichia) cost

about $ 3,500 each.• New Q switched laser (from China) may be possible (?)• Put RADDAM diode lasers in HF (2 units; one each HF).• In each case pulser have to be (re)built. (Engineering

and manufacturing).• Developments are too new and will have better

knowledge in three months!